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//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
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// The LLVM Compiler Infrastructure
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//===----------------------------------------------------------------------===//
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// Peephole optimize the CFG.
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "simplifycfg"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/Type.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/GlobalVariable.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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STATISTIC(NumSpeculations, "Number of speculative executed instructions");
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class SimplifyCFGOpt {
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const TargetData *const TD;
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ConstantInt *GetConstantInt(Value *V);
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Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values);
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Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values);
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bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
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std::vector<ConstantInt*> &Values);
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Value *isValueEqualityComparison(TerminatorInst *TI);
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BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
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std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
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bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
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bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI);
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explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
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bool run(BasicBlock *BB);
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/// SafeToMergeTerminators - Return true if it is safe to merge these two
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/// terminator instructions together.
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static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
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if (SI1 == SI2) return false; // Can't merge with self!
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// It is not safe to merge these two switch instructions if they have a common
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// successor, and if that successor has a PHI node, and if *that* PHI node has
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// conflicting incoming values from the two switch blocks.
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BasicBlock *SI1BB = SI1->getParent();
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BasicBlock *SI2BB = SI2->getParent();
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SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
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for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
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if (SI1Succs.count(*I))
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for (BasicBlock::iterator BBI = (*I)->begin();
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isa<PHINode>(BBI); ++BBI) {
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PHINode *PN = cast<PHINode>(BBI);
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if (PN->getIncomingValueForBlock(SI1BB) !=
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PN->getIncomingValueForBlock(SI2BB))
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/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
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/// now be entries in it from the 'NewPred' block. The values that will be
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/// flowing into the PHI nodes will be the same as those coming in from
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/// ExistPred, an existing predecessor of Succ.
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static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
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BasicBlock *ExistPred) {
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assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
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succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
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if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
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for (BasicBlock::iterator I = Succ->begin();
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(PN = dyn_cast<PHINode>(I)); ++I)
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PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
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/// GetIfCondition - Given a basic block (BB) with two predecessors (and
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/// presumably PHI nodes in it), check to see if the merge at this block is due
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/// to an "if condition". If so, return the boolean condition that determines
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/// which entry into BB will be taken. Also, return by references the block
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/// that will be entered from if the condition is true, and the block that will
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/// be entered if the condition is false.
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static Value *GetIfCondition(BasicBlock *BB,
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BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
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assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
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"Function can only handle blocks with 2 predecessors!");
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BasicBlock *Pred1 = *pred_begin(BB);
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BasicBlock *Pred2 = *++pred_begin(BB);
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// We can only handle branches. Other control flow will be lowered to
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// branches if possible anyway.
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if (!isa<BranchInst>(Pred1->getTerminator()) ||
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!isa<BranchInst>(Pred2->getTerminator()))
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BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
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BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
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// Eliminate code duplication by ensuring that Pred1Br is conditional if
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if (Pred2Br->isConditional()) {
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// If both branches are conditional, we don't have an "if statement". In
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// reality, we could transform this case, but since the condition will be
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// required anyway, we stand no chance of eliminating it, so the xform is
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// probably not profitable.
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if (Pred1Br->isConditional())
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std::swap(Pred1, Pred2);
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std::swap(Pred1Br, Pred2Br);
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if (Pred1Br->isConditional()) {
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// If we found a conditional branch predecessor, make sure that it branches
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// to BB and Pred2Br. If it doesn't, this isn't an "if statement".
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if (Pred1Br->getSuccessor(0) == BB &&
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Pred1Br->getSuccessor(1) == Pred2) {
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} else if (Pred1Br->getSuccessor(0) == Pred2 &&
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Pred1Br->getSuccessor(1) == BB) {
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// We know that one arm of the conditional goes to BB, so the other must
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// go somewhere unrelated, and this must not be an "if statement".
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// The only thing we have to watch out for here is to make sure that Pred2
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// doesn't have incoming edges from other blocks. If it does, the condition
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// doesn't dominate BB.
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if (++pred_begin(Pred2) != pred_end(Pred2))
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return Pred1Br->getCondition();
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// Ok, if we got here, both predecessors end with an unconditional branch to
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// BB. Don't panic! If both blocks only have a single (identical)
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// predecessor, and THAT is a conditional branch, then we're all ok!
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if (pred_begin(Pred1) == pred_end(Pred1) ||
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++pred_begin(Pred1) != pred_end(Pred1) ||
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pred_begin(Pred2) == pred_end(Pred2) ||
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++pred_begin(Pred2) != pred_end(Pred2) ||
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*pred_begin(Pred1) != *pred_begin(Pred2))
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// Otherwise, if this is a conditional branch, then we can use it!
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BasicBlock *CommonPred = *pred_begin(Pred1);
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if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
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assert(BI->isConditional() && "Two successors but not conditional?");
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if (BI->getSuccessor(0) == Pred1) {
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return BI->getCondition();
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/// DominatesMergePoint - If we have a merge point of an "if condition" as
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/// accepted above, return true if the specified value dominates the block. We
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/// don't handle the true generality of domination here, just a special case
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/// which works well enough for us.
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/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
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/// see if V (which must be an instruction) is cheap to compute and is
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/// non-trapping. If both are true, the instruction is inserted into the set
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/// and true is returned.
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static bool DominatesMergePoint(Value *V, BasicBlock *BB,
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std::set<Instruction*> *AggressiveInsts) {
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Instruction *I = dyn_cast<Instruction>(V);
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// Non-instructions all dominate instructions, but not all constantexprs
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// can be executed unconditionally.
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if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
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BasicBlock *PBB = I->getParent();
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// We don't want to allow weird loops that might have the "if condition" in
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// the bottom of this block.
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if (PBB == BB) return false;
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// If this instruction is defined in a block that contains an unconditional
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// branch to BB, then it must be in the 'conditional' part of the "if
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if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
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if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
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if (!AggressiveInsts) return false;
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// Okay, it looks like the instruction IS in the "condition". Check to
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// see if its a cheap instruction to unconditionally compute, and if it
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// only uses stuff defined outside of the condition. If so, hoist it out.
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if (!I->isSafeToSpeculativelyExecute())
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switch (I->getOpcode()) {
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default: return false; // Cannot hoist this out safely.
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case Instruction::Load: {
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// We have to check to make sure there are no instructions before the
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// load in its basic block, as we are going to hoist the loop out to
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BasicBlock::iterator IP = PBB->begin();
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while (isa<DbgInfoIntrinsic>(IP))
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if (IP != BasicBlock::iterator(I))
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case Instruction::Add:
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case Instruction::Sub:
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case Instruction::And:
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case Instruction::Or:
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case Instruction::Xor:
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case Instruction::Shl:
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case Instruction::LShr:
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case Instruction::AShr:
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case Instruction::ICmp:
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break; // These are all cheap and non-trapping instructions.
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// Okay, we can only really hoist these out if their operands are not
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// defined in the conditional region.
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for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
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if (!DominatesMergePoint(*i, BB, 0))
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// Okay, it's safe to do this! Remember this instruction.
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AggressiveInsts->insert(I);
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/// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
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/// and PointerNullValue. Return NULL if value is not a constant int.
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ConstantInt *SimplifyCFGOpt::GetConstantInt(Value *V) {
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// Normal constant int.
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ConstantInt *CI = dyn_cast<ConstantInt>(V);
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if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
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// This is some kind of pointer constant. Turn it into a pointer-sized
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// ConstantInt if possible.
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const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
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// Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
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if (isa<ConstantPointerNull>(V))
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return ConstantInt::get(PtrTy, 0);
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// IntToPtr const int.
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if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
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if (CE->getOpcode() == Instruction::IntToPtr)
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if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
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// The constant is very likely to have the right type already.
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if (CI->getType() == PtrTy)
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return cast<ConstantInt>
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(ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
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/// GatherConstantSetEQs - Given a potentially 'or'd together collection of
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/// icmp_eq instructions that compare a value against a constant, return the
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/// value being compared, and stick the constant into the Values vector.
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Value *SimplifyCFGOpt::
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GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values) {
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if (Instruction *Inst = dyn_cast<Instruction>(V)) {
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if (Inst->getOpcode() == Instruction::ICmp &&
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cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
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if (ConstantInt *C = GetConstantInt(Inst->getOperand(1))) {
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return Inst->getOperand(0);
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} else if (ConstantInt *C = GetConstantInt(Inst->getOperand(0))) {
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return Inst->getOperand(1);
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} else if (Inst->getOpcode() == Instruction::Or) {
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if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
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if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
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/// GatherConstantSetNEs - Given a potentially 'and'd together collection of
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/// setne instructions that compare a value against a constant, return the value
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/// being compared, and stick the constant into the Values vector.
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Value *SimplifyCFGOpt::
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GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values) {
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if (Instruction *Inst = dyn_cast<Instruction>(V)) {
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if (Inst->getOpcode() == Instruction::ICmp &&
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cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
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if (ConstantInt *C = GetConstantInt(Inst->getOperand(1))) {
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return Inst->getOperand(0);
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} else if (ConstantInt *C = GetConstantInt(Inst->getOperand(0))) {
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return Inst->getOperand(1);
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} else if (Inst->getOpcode() == Instruction::And) {
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if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
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if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
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/// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
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/// bunch of comparisons of one value against constants, return the value and
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/// the constants being compared.
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bool SimplifyCFGOpt::GatherValueComparisons(Instruction *Cond, Value *&CompVal,
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std::vector<ConstantInt*> &Values) {
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if (Cond->getOpcode() == Instruction::Or) {
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CompVal = GatherConstantSetEQs(Cond, Values);
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// Return true to indicate that the condition is true if the CompVal is
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// equal to one of the constants.
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} else if (Cond->getOpcode() == Instruction::And) {
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CompVal = GatherConstantSetNEs(Cond, Values);
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// Return false to indicate that the condition is false if the CompVal is
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// equal to one of the constants.
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static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
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Instruction* Cond = 0;
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if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
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Cond = dyn_cast<Instruction>(SI->getCondition());
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} else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
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if (BI->isConditional())
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Cond = dyn_cast<Instruction>(BI->getCondition());
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TI->eraseFromParent();
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if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
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/// isValueEqualityComparison - Return true if the specified terminator checks
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/// to see if a value is equal to constant integer value.
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Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
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if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
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// Do not permit merging of large switch instructions into their
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// predecessors unless there is only one predecessor.
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if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
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pred_end(SI->getParent())) <= 128)
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CV = SI->getCondition();
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} else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
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if (BI->isConditional() && BI->getCondition()->hasOneUse())
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if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
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if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
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ICI->getPredicate() == ICmpInst::ICMP_NE) &&
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GetConstantInt(ICI->getOperand(1)))
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CV = ICI->getOperand(0);
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// Unwrap any lossless ptrtoint cast.
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if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
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if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
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CV = PTII->getOperand(0);
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/// GetValueEqualityComparisonCases - Given a value comparison instruction,
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/// decode all of the 'cases' that it represents and return the 'default' block.
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BasicBlock *SimplifyCFGOpt::
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GetValueEqualityComparisonCases(TerminatorInst *TI,
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std::vector<std::pair<ConstantInt*,
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BasicBlock*> > &Cases) {
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if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
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Cases.reserve(SI->getNumCases());
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for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
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Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
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return SI->getDefaultDest();
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BranchInst *BI = cast<BranchInst>(TI);
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ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
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Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1)),
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BI->getSuccessor(ICI->getPredicate() ==
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ICmpInst::ICMP_NE)));
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return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
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/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
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/// in the list that match the specified block.
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static void EliminateBlockCases(BasicBlock *BB,
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std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
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for (unsigned i = 0, e = Cases.size(); i != e; ++i)
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if (Cases[i].second == BB) {
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Cases.erase(Cases.begin()+i);
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/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
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ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
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std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
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std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
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// Make V1 be smaller than V2.
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if (V1->size() > V2->size())
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if (V1->size() == 0) return false;
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if (V1->size() == 1) {
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ConstantInt *TheVal = (*V1)[0].first;
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for (unsigned i = 0, e = V2->size(); i != e; ++i)
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if (TheVal == (*V2)[i].first)
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// Otherwise, just sort both lists and compare element by element.
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std::sort(V1->begin(), V1->end());
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std::sort(V2->begin(), V2->end());
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unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
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while (i1 != e1 && i2 != e2) {
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if ((*V1)[i1].first == (*V2)[i2].first)
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if ((*V1)[i1].first < (*V2)[i2].first)
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/// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
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/// terminator instruction and its block is known to only have a single
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/// predecessor block, check to see if that predecessor is also a value
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/// comparison with the same value, and if that comparison determines the
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/// outcome of this comparison. If so, simplify TI. This does a very limited
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/// form of jump threading.
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bool SimplifyCFGOpt::
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SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
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Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
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if (!PredVal) return false; // Not a value comparison in predecessor.
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Value *ThisVal = isValueEqualityComparison(TI);
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assert(ThisVal && "This isn't a value comparison!!");
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if (ThisVal != PredVal) return false; // Different predicates.
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// Find out information about when control will move from Pred to TI's block.
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std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
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BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
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EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
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// Find information about how control leaves this block.
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std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
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BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
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EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
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// If TI's block is the default block from Pred's comparison, potentially
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// simplify TI based on this knowledge.
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if (PredDef == TI->getParent()) {
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// If we are here, we know that the value is none of those cases listed in
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// PredCases. If there are any cases in ThisCases that are in PredCases, we
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if (ValuesOverlap(PredCases, ThisCases)) {
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if (isa<BranchInst>(TI)) {
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// Okay, one of the successors of this condbr is dead. Convert it to a
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assert(ThisCases.size() == 1 && "Branch can only have one case!");
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// Insert the new branch.
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Instruction *NI = BranchInst::Create(ThisDef, TI);
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// Remove PHI node entries for the dead edge.
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ThisCases[0].second->removePredecessor(TI->getParent());
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DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
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<< "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
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EraseTerminatorInstAndDCECond(TI);
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SwitchInst *SI = cast<SwitchInst>(TI);
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// Okay, TI has cases that are statically dead, prune them away.
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SmallPtrSet<Constant*, 16> DeadCases;
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for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
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DeadCases.insert(PredCases[i].first);
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DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
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<< "Through successor TI: " << *TI);
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for (unsigned i = SI->getNumCases()-1; i != 0; --i)
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if (DeadCases.count(SI->getCaseValue(i))) {
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SI->getSuccessor(i)->removePredecessor(TI->getParent());
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DEBUG(dbgs() << "Leaving: " << *TI << "\n");
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// Otherwise, TI's block must correspond to some matched value. Find out
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// which value (or set of values) this is.
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ConstantInt *TIV = 0;
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BasicBlock *TIBB = TI->getParent();
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for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
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if (PredCases[i].second == TIBB) {
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TIV = PredCases[i].first;
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return false; // Cannot handle multiple values coming to this block.
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assert(TIV && "No edge from pred to succ?");
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// Okay, we found the one constant that our value can be if we get into TI's
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// BB. Find out which successor will unconditionally be branched to.
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BasicBlock *TheRealDest = 0;
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for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
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if (ThisCases[i].first == TIV) {
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TheRealDest = ThisCases[i].second;
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// If not handled by any explicit cases, it is handled by the default case.
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if (TheRealDest == 0) TheRealDest = ThisDef;
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// Remove PHI node entries for dead edges.
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BasicBlock *CheckEdge = TheRealDest;
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for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
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if (*SI != CheckEdge)
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(*SI)->removePredecessor(TIBB);
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// Insert the new branch.
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Instruction *NI = BranchInst::Create(TheRealDest, TI);
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DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
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<< "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
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EraseTerminatorInstAndDCECond(TI);
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/// ConstantIntOrdering - This class implements a stable ordering of constant
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/// integers that does not depend on their address. This is important for
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/// applications that sort ConstantInt's to ensure uniqueness.
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struct ConstantIntOrdering {
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bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
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return LHS->getValue().ult(RHS->getValue());
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/// FoldValueComparisonIntoPredecessors - The specified terminator is a value
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/// equality comparison instruction (either a switch or a branch on "X == c").
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/// See if any of the predecessors of the terminator block are value comparisons
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/// on the same value. If so, and if safe to do so, fold them together.
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bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
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BasicBlock *BB = TI->getParent();
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Value *CV = isValueEqualityComparison(TI); // CondVal
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assert(CV && "Not a comparison?");
614
bool Changed = false;
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SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
617
while (!Preds.empty()) {
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BasicBlock *Pred = Preds.pop_back_val();
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// See if the predecessor is a comparison with the same value.
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TerminatorInst *PTI = Pred->getTerminator();
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Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
624
if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
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// Figure out which 'cases' to copy from SI to PSI.
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std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
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BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
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std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
630
BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
632
// Based on whether the default edge from PTI goes to BB or not, fill in
633
// PredCases and PredDefault with the new switch cases we would like to
635
SmallVector<BasicBlock*, 8> NewSuccessors;
637
if (PredDefault == BB) {
638
// If this is the default destination from PTI, only the edges in TI
639
// that don't occur in PTI, or that branch to BB will be activated.
640
std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
641
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
642
if (PredCases[i].second != BB)
643
PTIHandled.insert(PredCases[i].first);
645
// The default destination is BB, we don't need explicit targets.
646
std::swap(PredCases[i], PredCases.back());
647
PredCases.pop_back();
651
// Reconstruct the new switch statement we will be building.
652
if (PredDefault != BBDefault) {
653
PredDefault->removePredecessor(Pred);
654
PredDefault = BBDefault;
655
NewSuccessors.push_back(BBDefault);
657
for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
658
if (!PTIHandled.count(BBCases[i].first) &&
659
BBCases[i].second != BBDefault) {
660
PredCases.push_back(BBCases[i]);
661
NewSuccessors.push_back(BBCases[i].second);
665
// If this is not the default destination from PSI, only the edges
666
// in SI that occur in PSI with a destination of BB will be
668
std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
669
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
670
if (PredCases[i].second == BB) {
671
PTIHandled.insert(PredCases[i].first);
672
std::swap(PredCases[i], PredCases.back());
673
PredCases.pop_back();
677
// Okay, now we know which constants were sent to BB from the
678
// predecessor. Figure out where they will all go now.
679
for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
680
if (PTIHandled.count(BBCases[i].first)) {
681
// If this is one we are capable of getting...
682
PredCases.push_back(BBCases[i]);
683
NewSuccessors.push_back(BBCases[i].second);
684
PTIHandled.erase(BBCases[i].first);// This constant is taken care of
687
// If there are any constants vectored to BB that TI doesn't handle,
688
// they must go to the default destination of TI.
689
for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
691
E = PTIHandled.end(); I != E; ++I) {
692
PredCases.push_back(std::make_pair(*I, BBDefault));
693
NewSuccessors.push_back(BBDefault);
697
// Okay, at this point, we know which new successor Pred will get. Make
698
// sure we update the number of entries in the PHI nodes for these
700
for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
701
AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
703
// Convert pointer to int before we switch.
704
if (CV->getType()->isPointerTy()) {
705
assert(TD && "Cannot switch on pointer without TargetData");
706
CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()),
710
// Now that the successors are updated, create the new Switch instruction.
711
SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
712
PredCases.size(), PTI);
713
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
714
NewSI->addCase(PredCases[i].first, PredCases[i].second);
716
EraseTerminatorInstAndDCECond(PTI);
718
// Okay, last check. If BB is still a successor of PSI, then we must
719
// have an infinite loop case. If so, add an infinitely looping block
720
// to handle the case to preserve the behavior of the code.
721
BasicBlock *InfLoopBlock = 0;
722
for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
723
if (NewSI->getSuccessor(i) == BB) {
724
if (InfLoopBlock == 0) {
725
// Insert it at the end of the function, because it's either code,
726
// or it won't matter if it's hot. :)
727
InfLoopBlock = BasicBlock::Create(BB->getContext(),
728
"infloop", BB->getParent());
729
BranchInst::Create(InfLoopBlock, InfLoopBlock);
731
NewSI->setSuccessor(i, InfLoopBlock);
740
// isSafeToHoistInvoke - If we would need to insert a select that uses the
741
// value of this invoke (comments in HoistThenElseCodeToIf explain why we
742
// would need to do this), we can't hoist the invoke, as there is nowhere
743
// to put the select in this case.
744
static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
745
Instruction *I1, Instruction *I2) {
746
for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
748
for (BasicBlock::iterator BBI = SI->begin();
749
(PN = dyn_cast<PHINode>(BBI)); ++BBI) {
750
Value *BB1V = PN->getIncomingValueForBlock(BB1);
751
Value *BB2V = PN->getIncomingValueForBlock(BB2);
752
if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
760
/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
761
/// BB2, hoist any common code in the two blocks up into the branch block. The
762
/// caller of this function guarantees that BI's block dominates BB1 and BB2.
763
static bool HoistThenElseCodeToIf(BranchInst *BI) {
764
// This does very trivial matching, with limited scanning, to find identical
765
// instructions in the two blocks. In particular, we don't want to get into
766
// O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
767
// such, we currently just scan for obviously identical instructions in an
769
BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
770
BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
772
BasicBlock::iterator BB1_Itr = BB1->begin();
773
BasicBlock::iterator BB2_Itr = BB2->begin();
775
Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
776
while (isa<DbgInfoIntrinsic>(I1))
778
while (isa<DbgInfoIntrinsic>(I2))
780
if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
781
!I1->isIdenticalToWhenDefined(I2) ||
782
(isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
785
// If we get here, we can hoist at least one instruction.
786
BasicBlock *BIParent = BI->getParent();
789
// If we are hoisting the terminator instruction, don't move one (making a
790
// broken BB), instead clone it, and remove BI.
791
if (isa<TerminatorInst>(I1))
792
goto HoistTerminator;
794
// For a normal instruction, we just move one to right before the branch,
795
// then replace all uses of the other with the first. Finally, we remove
796
// the now redundant second instruction.
797
BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
798
if (!I2->use_empty())
799
I2->replaceAllUsesWith(I1);
800
I1->intersectOptionalDataWith(I2);
801
BB2->getInstList().erase(I2);
804
while (isa<DbgInfoIntrinsic>(I1))
807
while (isa<DbgInfoIntrinsic>(I2))
809
} while (I1->getOpcode() == I2->getOpcode() &&
810
I1->isIdenticalToWhenDefined(I2));
815
// It may not be possible to hoist an invoke.
816
if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
819
// Okay, it is safe to hoist the terminator.
820
Instruction *NT = I1->clone();
821
BIParent->getInstList().insert(BI, NT);
822
if (!NT->getType()->isVoidTy()) {
823
I1->replaceAllUsesWith(NT);
824
I2->replaceAllUsesWith(NT);
828
// Hoisting one of the terminators from our successor is a great thing.
829
// Unfortunately, the successors of the if/else blocks may have PHI nodes in
830
// them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
831
// nodes, so we insert select instruction to compute the final result.
832
std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
833
for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
835
for (BasicBlock::iterator BBI = SI->begin();
836
(PN = dyn_cast<PHINode>(BBI)); ++BBI) {
837
Value *BB1V = PN->getIncomingValueForBlock(BB1);
838
Value *BB2V = PN->getIncomingValueForBlock(BB2);
840
// These values do not agree. Insert a select instruction before NT
841
// that determines the right value.
842
SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
844
SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
845
BB1V->getName()+"."+BB2V->getName(), NT);
846
// Make the PHI node use the select for all incoming values for BB1/BB2
847
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
848
if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
849
PN->setIncomingValue(i, SI);
854
// Update any PHI nodes in our new successors.
855
for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
856
AddPredecessorToBlock(*SI, BIParent, BB1);
858
EraseTerminatorInstAndDCECond(BI);
862
/// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
863
/// and an BB2 and the only successor of BB1 is BB2, hoist simple code
864
/// (for now, restricted to a single instruction that's side effect free) from
865
/// the BB1 into the branch block to speculatively execute it.
866
static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
867
// Only speculatively execution a single instruction (not counting the
868
// terminator) for now.
869
Instruction *HInst = NULL;
870
Instruction *Term = BB1->getTerminator();
871
for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
873
Instruction *I = BBI;
875
if (isa<DbgInfoIntrinsic>(I)) continue;
876
if (I == Term) break;
886
// Be conservative for now. FP select instruction can often be expensive.
887
Value *BrCond = BI->getCondition();
888
if (isa<Instruction>(BrCond) &&
889
cast<Instruction>(BrCond)->getOpcode() == Instruction::FCmp)
892
// If BB1 is actually on the false edge of the conditional branch, remember
893
// to swap the select operands later.
895
if (BB1 != BI->getSuccessor(0)) {
896
assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
903
// br i1 %t1, label %BB1, label %BB2
912
// %t3 = select i1 %t1, %t2, %t3
913
switch (HInst->getOpcode()) {
914
default: return false; // Not safe / profitable to hoist.
915
case Instruction::Add:
916
case Instruction::Sub:
917
// Not worth doing for vector ops.
918
if (HInst->getType()->isVectorTy())
921
case Instruction::And:
922
case Instruction::Or:
923
case Instruction::Xor:
924
case Instruction::Shl:
925
case Instruction::LShr:
926
case Instruction::AShr:
927
// Don't mess with vector operations.
928
if (HInst->getType()->isVectorTy())
930
break; // These are all cheap and non-trapping instructions.
933
// If the instruction is obviously dead, don't try to predicate it.
934
if (HInst->use_empty()) {
935
HInst->eraseFromParent();
939
// Can we speculatively execute the instruction? And what is the value
940
// if the condition is false? Consider the phi uses, if the incoming value
941
// from the "if" block are all the same V, then V is the value of the
942
// select if the condition is false.
943
BasicBlock *BIParent = BI->getParent();
944
SmallVector<PHINode*, 4> PHIUses;
945
Value *FalseV = NULL;
947
BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
948
for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
950
// Ignore any user that is not a PHI node in BB2. These can only occur in
951
// unreachable blocks, because they would not be dominated by the instr.
952
PHINode *PN = dyn_cast<PHINode>(UI);
953
if (!PN || PN->getParent() != BB2)
955
PHIUses.push_back(PN);
957
Value *PHIV = PN->getIncomingValueForBlock(BIParent);
960
else if (FalseV != PHIV)
961
return false; // Inconsistent value when condition is false.
964
assert(FalseV && "Must have at least one user, and it must be a PHI");
966
// Do not hoist the instruction if any of its operands are defined but not
967
// used in this BB. The transformation will prevent the operand from
968
// being sunk into the use block.
969
for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
971
Instruction *OpI = dyn_cast<Instruction>(*i);
972
if (OpI && OpI->getParent() == BIParent &&
973
!OpI->isUsedInBasicBlock(BIParent))
977
// If we get here, we can hoist the instruction. Try to place it
978
// before the icmp instruction preceding the conditional branch.
979
BasicBlock::iterator InsertPos = BI;
980
if (InsertPos != BIParent->begin())
982
// Skip debug info between condition and branch.
983
while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
985
if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
986
SmallPtrSet<Instruction *, 4> BB1Insns;
987
for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
988
BB1I != BB1E; ++BB1I)
989
BB1Insns.insert(BB1I);
990
for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
992
Instruction *Use = cast<Instruction>(*UI);
993
if (BB1Insns.count(Use)) {
994
// If BrCond uses the instruction that place it just before
995
// branch instruction.
1002
BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
1004
// Create a select whose true value is the speculatively executed value and
1005
// false value is the previously determined FalseV.
1008
SI = SelectInst::Create(BrCond, FalseV, HInst,
1009
FalseV->getName() + "." + HInst->getName(), BI);
1011
SI = SelectInst::Create(BrCond, HInst, FalseV,
1012
HInst->getName() + "." + FalseV->getName(), BI);
1014
// Make the PHI node use the select for all incoming values for "then" and
1016
for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1017
PHINode *PN = PHIUses[i];
1018
for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
1019
if (PN->getIncomingBlock(j) == BB1 ||
1020
PN->getIncomingBlock(j) == BIParent)
1021
PN->setIncomingValue(j, SI);
1028
/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1029
/// across this block.
1030
static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1031
BranchInst *BI = cast<BranchInst>(BB->getTerminator());
1034
for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1035
if (isa<DbgInfoIntrinsic>(BBI))
1037
if (Size > 10) return false; // Don't clone large BB's.
1040
// We can only support instructions that do not define values that are
1041
// live outside of the current basic block.
1042
for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1044
Instruction *U = cast<Instruction>(*UI);
1045
if (U->getParent() != BB || isa<PHINode>(U)) return false;
1048
// Looks ok, continue checking.
1054
/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1055
/// that is defined in the same block as the branch and if any PHI entries are
1056
/// constants, thread edges corresponding to that entry to be branches to their
1057
/// ultimate destination.
1058
static bool FoldCondBranchOnPHI(BranchInst *BI) {
1059
BasicBlock *BB = BI->getParent();
1060
PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
1061
// NOTE: we currently cannot transform this case if the PHI node is used
1062
// outside of the block.
1063
if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1066
// Degenerate case of a single entry PHI.
1067
if (PN->getNumIncomingValues() == 1) {
1068
FoldSingleEntryPHINodes(PN->getParent());
1072
// Now we know that this block has multiple preds and two succs.
1073
if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
1075
// Okay, this is a simple enough basic block. See if any phi values are
1077
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
1079
if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
1080
CB->getType()->isIntegerTy(1)) {
1081
// Okay, we now know that all edges from PredBB should be revectored to
1082
// branch to RealDest.
1083
BasicBlock *PredBB = PN->getIncomingBlock(i);
1084
BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1086
if (RealDest == BB) continue; // Skip self loops.
1088
// The dest block might have PHI nodes, other predecessors and other
1089
// difficult cases. Instead of being smart about this, just insert a new
1090
// block that jumps to the destination block, effectively splitting
1091
// the edge we are about to create.
1092
BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1093
RealDest->getName()+".critedge",
1094
RealDest->getParent(), RealDest);
1095
BranchInst::Create(RealDest, EdgeBB);
1097
for (BasicBlock::iterator BBI = RealDest->begin();
1098
(PN = dyn_cast<PHINode>(BBI)); ++BBI) {
1099
Value *V = PN->getIncomingValueForBlock(BB);
1100
PN->addIncoming(V, EdgeBB);
1103
// BB may have instructions that are being threaded over. Clone these
1104
// instructions into EdgeBB. We know that there will be no uses of the
1105
// cloned instructions outside of EdgeBB.
1106
BasicBlock::iterator InsertPt = EdgeBB->begin();
1107
std::map<Value*, Value*> TranslateMap; // Track translated values.
1108
for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1109
if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1110
TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1112
// Clone the instruction.
1113
Instruction *N = BBI->clone();
1114
if (BBI->hasName()) N->setName(BBI->getName()+".c");
1116
// Update operands due to translation.
1117
for (User::op_iterator i = N->op_begin(), e = N->op_end();
1119
std::map<Value*, Value*>::iterator PI =
1120
TranslateMap.find(*i);
1121
if (PI != TranslateMap.end())
1125
// Check for trivial simplification.
1126
if (Constant *C = ConstantFoldInstruction(N)) {
1127
TranslateMap[BBI] = C;
1128
delete N; // Constant folded away, don't need actual inst
1130
// Insert the new instruction into its new home.
1131
EdgeBB->getInstList().insert(InsertPt, N);
1132
if (!BBI->use_empty())
1133
TranslateMap[BBI] = N;
1138
// Loop over all of the edges from PredBB to BB, changing them to branch
1139
// to EdgeBB instead.
1140
TerminatorInst *PredBBTI = PredBB->getTerminator();
1141
for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1142
if (PredBBTI->getSuccessor(i) == BB) {
1143
BB->removePredecessor(PredBB);
1144
PredBBTI->setSuccessor(i, EdgeBB);
1147
// Recurse, simplifying any other constants.
1148
return FoldCondBranchOnPHI(BI) | true;
1155
/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1156
/// PHI node, see if we can eliminate it.
1157
static bool FoldTwoEntryPHINode(PHINode *PN) {
1158
// Ok, this is a two entry PHI node. Check to see if this is a simple "if
1159
// statement", which has a very simple dominance structure. Basically, we
1160
// are trying to find the condition that is being branched on, which
1161
// subsequently causes this merge to happen. We really want control
1162
// dependence information for this check, but simplifycfg can't keep it up
1163
// to date, and this catches most of the cases we care about anyway.
1165
BasicBlock *BB = PN->getParent();
1166
BasicBlock *IfTrue, *IfFalse;
1167
Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
1168
if (!IfCond) return false;
1170
// Okay, we found that we can merge this two-entry phi node into a select.
1171
// Doing so would require us to fold *all* two entry phi nodes in this block.
1172
// At some point this becomes non-profitable (particularly if the target
1173
// doesn't support cmov's). Only do this transformation if there are two or
1174
// fewer PHI nodes in this block.
1175
unsigned NumPhis = 0;
1176
for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1180
DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
1181
<< IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
1183
// Loop over the PHI's seeing if we can promote them all to select
1184
// instructions. While we are at it, keep track of the instructions
1185
// that need to be moved to the dominating block.
1186
std::set<Instruction*> AggressiveInsts;
1188
BasicBlock::iterator AfterPHIIt = BB->begin();
1189
while (isa<PHINode>(AfterPHIIt)) {
1190
PHINode *PN = cast<PHINode>(AfterPHIIt++);
1191
if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
1192
if (PN->getIncomingValue(0) != PN)
1193
PN->replaceAllUsesWith(PN->getIncomingValue(0));
1195
PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
1196
} else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
1197
&AggressiveInsts) ||
1198
!DominatesMergePoint(PN->getIncomingValue(1), BB,
1199
&AggressiveInsts)) {
1204
// If we all PHI nodes are promotable, check to make sure that all
1205
// instructions in the predecessor blocks can be promoted as well. If
1206
// not, we won't be able to get rid of the control flow, so it's not
1207
// worth promoting to select instructions.
1208
BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
1209
PN = cast<PHINode>(BB->begin());
1210
BasicBlock *Pred = PN->getIncomingBlock(0);
1211
if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1213
DomBlock = *pred_begin(Pred);
1214
for (BasicBlock::iterator I = Pred->begin();
1215
!isa<TerminatorInst>(I); ++I)
1216
if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1217
// This is not an aggressive instruction that we can promote.
1218
// Because of this, we won't be able to get rid of the control
1219
// flow, so the xform is not worth it.
1224
Pred = PN->getIncomingBlock(1);
1225
if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
1227
DomBlock = *pred_begin(Pred);
1228
for (BasicBlock::iterator I = Pred->begin();
1229
!isa<TerminatorInst>(I); ++I)
1230
if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
1231
// This is not an aggressive instruction that we can promote.
1232
// Because of this, we won't be able to get rid of the control
1233
// flow, so the xform is not worth it.
1238
// If we can still promote the PHI nodes after this gauntlet of tests,
1239
// do all of the PHI's now.
1241
// Move all 'aggressive' instructions, which are defined in the
1242
// conditional parts of the if's up to the dominating block.
1244
DomBlock->getInstList().splice(DomBlock->getTerminator(),
1245
IfBlock1->getInstList(),
1247
IfBlock1->getTerminator());
1250
DomBlock->getInstList().splice(DomBlock->getTerminator(),
1251
IfBlock2->getInstList(),
1253
IfBlock2->getTerminator());
1256
while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1257
// Change the PHI node into a select instruction.
1259
PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1261
PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
1263
Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
1264
PN->replaceAllUsesWith(NV);
1267
BB->getInstList().erase(PN);
1272
/// isTerminatorFirstRelevantInsn - Return true if Term is very first
1273
/// instruction ignoring Phi nodes and dbg intrinsics.
1274
static bool isTerminatorFirstRelevantInsn(BasicBlock *BB, Instruction *Term) {
1275
BasicBlock::iterator BBI = Term;
1276
while (BBI != BB->begin()) {
1278
if (!isa<DbgInfoIntrinsic>(BBI))
1282
if (isa<PHINode>(BBI) || &*BBI == Term || isa<DbgInfoIntrinsic>(BBI))
1287
/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1288
/// to two returning blocks, try to merge them together into one return,
1289
/// introducing a select if the return values disagree.
1290
static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1291
assert(BI->isConditional() && "Must be a conditional branch");
1292
BasicBlock *TrueSucc = BI->getSuccessor(0);
1293
BasicBlock *FalseSucc = BI->getSuccessor(1);
1294
ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1295
ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1297
// Check to ensure both blocks are empty (just a return) or optionally empty
1298
// with PHI nodes. If there are other instructions, merging would cause extra
1299
// computation on one path or the other.
1300
if (!isTerminatorFirstRelevantInsn(TrueSucc, TrueRet))
1302
if (!isTerminatorFirstRelevantInsn(FalseSucc, FalseRet))
1305
// Okay, we found a branch that is going to two return nodes. If
1306
// there is no return value for this function, just change the
1307
// branch into a return.
1308
if (FalseRet->getNumOperands() == 0) {
1309
TrueSucc->removePredecessor(BI->getParent());
1310
FalseSucc->removePredecessor(BI->getParent());
1311
ReturnInst::Create(BI->getContext(), 0, BI);
1312
EraseTerminatorInstAndDCECond(BI);
1316
// Otherwise, figure out what the true and false return values are
1317
// so we can insert a new select instruction.
1318
Value *TrueValue = TrueRet->getReturnValue();
1319
Value *FalseValue = FalseRet->getReturnValue();
1321
// Unwrap any PHI nodes in the return blocks.
1322
if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1323
if (TVPN->getParent() == TrueSucc)
1324
TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1325
if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1326
if (FVPN->getParent() == FalseSucc)
1327
FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1329
// In order for this transformation to be safe, we must be able to
1330
// unconditionally execute both operands to the return. This is
1331
// normally the case, but we could have a potentially-trapping
1332
// constant expression that prevents this transformation from being
1334
if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1337
if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1341
// Okay, we collected all the mapped values and checked them for sanity, and
1342
// defined to really do this transformation. First, update the CFG.
1343
TrueSucc->removePredecessor(BI->getParent());
1344
FalseSucc->removePredecessor(BI->getParent());
1346
// Insert select instructions where needed.
1347
Value *BrCond = BI->getCondition();
1349
// Insert a select if the results differ.
1350
if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1351
} else if (isa<UndefValue>(TrueValue)) {
1352
TrueValue = FalseValue;
1354
TrueValue = SelectInst::Create(BrCond, TrueValue,
1355
FalseValue, "retval", BI);
1359
Value *RI = !TrueValue ?
1360
ReturnInst::Create(BI->getContext(), BI) :
1361
ReturnInst::Create(BI->getContext(), TrueValue, BI);
1364
DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
1365
<< "\n " << *BI << "NewRet = " << *RI
1366
<< "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
1368
EraseTerminatorInstAndDCECond(BI);
1373
/// FoldBranchToCommonDest - If this basic block is ONLY a setcc and a branch,
1374
/// and if a predecessor branches to us and one of our successors, fold the
1375
/// setcc into the predecessor and use logical operations to pick the right
1377
bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
1378
BasicBlock *BB = BI->getParent();
1379
Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
1380
if (Cond == 0) return false;
1383
// Only allow this if the condition is a simple instruction that can be
1384
// executed unconditionally. It must be in the same block as the branch, and
1385
// must be at the front of the block.
1386
BasicBlock::iterator FrontIt = BB->front();
1387
// Ignore dbg intrinsics.
1388
while(isa<DbgInfoIntrinsic>(FrontIt))
1390
if ((!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1391
Cond->getParent() != BB || &*FrontIt != Cond || !Cond->hasOneUse()) {
1395
// Make sure the instruction after the condition is the cond branch.
1396
BasicBlock::iterator CondIt = Cond; ++CondIt;
1397
// Ingore dbg intrinsics.
1398
while(isa<DbgInfoIntrinsic>(CondIt))
1400
if (&*CondIt != BI) {
1401
assert (!isa<DbgInfoIntrinsic>(CondIt) && "Hey do not forget debug info!");
1405
// Cond is known to be a compare or binary operator. Check to make sure that
1406
// neither operand is a potentially-trapping constant expression.
1407
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1410
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1415
// Finally, don't infinitely unroll conditional loops.
1416
BasicBlock *TrueDest = BI->getSuccessor(0);
1417
BasicBlock *FalseDest = BI->getSuccessor(1);
1418
if (TrueDest == BB || FalseDest == BB)
1421
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1422
BasicBlock *PredBlock = *PI;
1423
BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
1425
// Check that we have two conditional branches. If there is a PHI node in
1426
// the common successor, verify that the same value flows in from both
1428
if (PBI == 0 || PBI->isUnconditional() ||
1429
!SafeToMergeTerminators(BI, PBI))
1432
Instruction::BinaryOps Opc;
1433
bool InvertPredCond = false;
1435
if (PBI->getSuccessor(0) == TrueDest)
1436
Opc = Instruction::Or;
1437
else if (PBI->getSuccessor(1) == FalseDest)
1438
Opc = Instruction::And;
1439
else if (PBI->getSuccessor(0) == FalseDest)
1440
Opc = Instruction::And, InvertPredCond = true;
1441
else if (PBI->getSuccessor(1) == TrueDest)
1442
Opc = Instruction::Or, InvertPredCond = true;
1446
DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
1448
// If we need to invert the condition in the pred block to match, do so now.
1449
if (InvertPredCond) {
1451
BinaryOperator::CreateNot(PBI->getCondition(),
1452
PBI->getCondition()->getName()+".not", PBI);
1453
PBI->setCondition(NewCond);
1454
BasicBlock *OldTrue = PBI->getSuccessor(0);
1455
BasicBlock *OldFalse = PBI->getSuccessor(1);
1456
PBI->setSuccessor(0, OldFalse);
1457
PBI->setSuccessor(1, OldTrue);
1460
// Clone Cond into the predecessor basic block, and or/and the
1461
// two conditions together.
1462
Instruction *New = Cond->clone();
1463
PredBlock->getInstList().insert(PBI, New);
1464
New->takeName(Cond);
1465
Cond->setName(New->getName()+".old");
1467
Value *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1468
New, "or.cond", PBI);
1469
PBI->setCondition(NewCond);
1470
if (PBI->getSuccessor(0) == BB) {
1471
AddPredecessorToBlock(TrueDest, PredBlock, BB);
1472
PBI->setSuccessor(0, TrueDest);
1474
if (PBI->getSuccessor(1) == BB) {
1475
AddPredecessorToBlock(FalseDest, PredBlock, BB);
1476
PBI->setSuccessor(1, FalseDest);
1483
/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1484
/// predecessor of another block, this function tries to simplify it. We know
1485
/// that PBI and BI are both conditional branches, and BI is in one of the
1486
/// successor blocks of PBI - PBI branches to BI.
1487
static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1488
assert(PBI->isConditional() && BI->isConditional());
1489
BasicBlock *BB = BI->getParent();
1491
// If this block ends with a branch instruction, and if there is a
1492
// predecessor that ends on a branch of the same condition, make
1493
// this conditional branch redundant.
1494
if (PBI->getCondition() == BI->getCondition() &&
1495
PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1496
// Okay, the outcome of this conditional branch is statically
1497
// knowable. If this block had a single pred, handle specially.
1498
if (BB->getSinglePredecessor()) {
1499
// Turn this into a branch on constant.
1500
bool CondIsTrue = PBI->getSuccessor(0) == BB;
1501
BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1503
return true; // Nuke the branch on constant.
1506
// Otherwise, if there are multiple predecessors, insert a PHI that merges
1507
// in the constant and simplify the block result. Subsequent passes of
1508
// simplifycfg will thread the block.
1509
if (BlockIsSimpleEnoughToThreadThrough(BB)) {
1510
PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
1511
BI->getCondition()->getName() + ".pr",
1513
// Okay, we're going to insert the PHI node. Since PBI is not the only
1514
// predecessor, compute the PHI'd conditional value for all of the preds.
1515
// Any predecessor where the condition is not computable we keep symbolic.
1516
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1517
if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
1518
PBI != BI && PBI->isConditional() &&
1519
PBI->getCondition() == BI->getCondition() &&
1520
PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1521
bool CondIsTrue = PBI->getSuccessor(0) == BB;
1522
NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1525
NewPN->addIncoming(BI->getCondition(), *PI);
1528
BI->setCondition(NewPN);
1533
// If this is a conditional branch in an empty block, and if any
1534
// predecessors is a conditional branch to one of our destinations,
1535
// fold the conditions into logical ops and one cond br.
1536
BasicBlock::iterator BBI = BB->begin();
1537
// Ignore dbg intrinsics.
1538
while (isa<DbgInfoIntrinsic>(BBI))
1544
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1549
if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1551
else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1552
PBIOp = 0, BIOp = 1;
1553
else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1554
PBIOp = 1, BIOp = 0;
1555
else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1560
// Check to make sure that the other destination of this branch
1561
// isn't BB itself. If so, this is an infinite loop that will
1562
// keep getting unwound.
1563
if (PBI->getSuccessor(PBIOp) == BB)
1566
// Do not perform this transformation if it would require
1567
// insertion of a large number of select instructions. For targets
1568
// without predication/cmovs, this is a big pessimization.
1569
BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
1571
unsigned NumPhis = 0;
1572
for (BasicBlock::iterator II = CommonDest->begin();
1573
isa<PHINode>(II); ++II, ++NumPhis)
1574
if (NumPhis > 2) // Disable this xform.
1577
// Finally, if everything is ok, fold the branches to logical ops.
1578
BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1580
DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
1581
<< "AND: " << *BI->getParent());
1584
// If OtherDest *is* BB, then BB is a basic block with a single conditional
1585
// branch in it, where one edge (OtherDest) goes back to itself but the other
1586
// exits. We don't *know* that the program avoids the infinite loop
1587
// (even though that seems likely). If we do this xform naively, we'll end up
1588
// recursively unpeeling the loop. Since we know that (after the xform is
1589
// done) that the block *is* infinite if reached, we just make it an obviously
1590
// infinite loop with no cond branch.
1591
if (OtherDest == BB) {
1592
// Insert it at the end of the function, because it's either code,
1593
// or it won't matter if it's hot. :)
1594
BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1595
"infloop", BB->getParent());
1596
BranchInst::Create(InfLoopBlock, InfLoopBlock);
1597
OtherDest = InfLoopBlock;
1600
DEBUG(dbgs() << *PBI->getParent()->getParent());
1602
// BI may have other predecessors. Because of this, we leave
1603
// it alone, but modify PBI.
1605
// Make sure we get to CommonDest on True&True directions.
1606
Value *PBICond = PBI->getCondition();
1608
PBICond = BinaryOperator::CreateNot(PBICond,
1609
PBICond->getName()+".not",
1611
Value *BICond = BI->getCondition();
1613
BICond = BinaryOperator::CreateNot(BICond,
1614
BICond->getName()+".not",
1616
// Merge the conditions.
1617
Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1619
// Modify PBI to branch on the new condition to the new dests.
1620
PBI->setCondition(Cond);
1621
PBI->setSuccessor(0, CommonDest);
1622
PBI->setSuccessor(1, OtherDest);
1624
// OtherDest may have phi nodes. If so, add an entry from PBI's
1625
// block that are identical to the entries for BI's block.
1627
for (BasicBlock::iterator II = OtherDest->begin();
1628
(PN = dyn_cast<PHINode>(II)); ++II) {
1629
Value *V = PN->getIncomingValueForBlock(BB);
1630
PN->addIncoming(V, PBI->getParent());
1633
// We know that the CommonDest already had an edge from PBI to
1634
// it. If it has PHIs though, the PHIs may have different
1635
// entries for BB and PBI's BB. If so, insert a select to make
1637
for (BasicBlock::iterator II = CommonDest->begin();
1638
(PN = dyn_cast<PHINode>(II)); ++II) {
1639
Value *BIV = PN->getIncomingValueForBlock(BB);
1640
unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1641
Value *PBIV = PN->getIncomingValue(PBBIdx);
1643
// Insert a select in PBI to pick the right value.
1644
Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1645
PBIV->getName()+".mux", PBI);
1646
PN->setIncomingValue(PBBIdx, NV);
1650
DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1651
DEBUG(dbgs() << *PBI->getParent()->getParent());
1653
// This basic block is probably dead. We know it has at least
1654
// one fewer predecessor.
1658
bool SimplifyCFGOpt::run(BasicBlock *BB) {
1659
bool Changed = false;
1660
Function *M = BB->getParent();
1662
assert(BB && BB->getParent() && "Block not embedded in function!");
1663
assert(BB->getTerminator() && "Degenerate basic block encountered!");
1664
assert(&BB->getParent()->getEntryBlock() != BB &&
1665
"Can't Simplify entry block!");
1667
// Remove basic blocks that have no predecessors... or that just have themself
1668
// as a predecessor. These are unreachable.
1669
if (pred_begin(BB) == pred_end(BB) || BB->getSinglePredecessor() == BB) {
1670
DEBUG(dbgs() << "Removing BB: \n" << *BB);
1671
DeleteDeadBlock(BB);
1675
// Check to see if we can constant propagate this terminator instruction
1677
Changed |= ConstantFoldTerminator(BB);
1679
// Check for and eliminate duplicate PHI nodes in this block.
1680
Changed |= EliminateDuplicatePHINodes(BB);
1682
// If there is a trivial two-entry PHI node in this basic block, and we can
1683
// eliminate it, do so now.
1684
if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
1685
if (PN->getNumIncomingValues() == 2)
1686
Changed |= FoldTwoEntryPHINode(PN);
1688
// If this is a returning block with only PHI nodes in it, fold the return
1689
// instruction into any unconditional branch predecessors.
1691
// If any predecessor is a conditional branch that just selects among
1692
// different return values, fold the replace the branch/return with a select
1694
if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
1695
if (isTerminatorFirstRelevantInsn(BB, BB->getTerminator())) {
1696
// Find predecessors that end with branches.
1697
SmallVector<BasicBlock*, 8> UncondBranchPreds;
1698
SmallVector<BranchInst*, 8> CondBranchPreds;
1699
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1700
TerminatorInst *PTI = (*PI)->getTerminator();
1701
if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
1702
if (BI->isUnconditional())
1703
UncondBranchPreds.push_back(*PI);
1705
CondBranchPreds.push_back(BI);
1709
// If we found some, do the transformation!
1710
if (!UncondBranchPreds.empty()) {
1711
while (!UncondBranchPreds.empty()) {
1712
BasicBlock *Pred = UncondBranchPreds.pop_back_val();
1713
DEBUG(dbgs() << "FOLDING: " << *BB
1714
<< "INTO UNCOND BRANCH PRED: " << *Pred);
1715
Instruction *UncondBranch = Pred->getTerminator();
1716
// Clone the return and add it to the end of the predecessor.
1717
Instruction *NewRet = RI->clone();
1718
Pred->getInstList().push_back(NewRet);
1720
// If the return instruction returns a value, and if the value was a
1721
// PHI node in "BB", propagate the right value into the return.
1722
for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
1724
if (PHINode *PN = dyn_cast<PHINode>(*i))
1725
if (PN->getParent() == BB)
1726
*i = PN->getIncomingValueForBlock(Pred);
1728
// Update any PHI nodes in the returning block to realize that we no
1729
// longer branch to them.
1730
BB->removePredecessor(Pred);
1731
Pred->getInstList().erase(UncondBranch);
1734
// If we eliminated all predecessors of the block, delete the block now.
1735
if (pred_begin(BB) == pred_end(BB))
1736
// We know there are no successors, so just nuke the block.
1737
M->getBasicBlockList().erase(BB);
1742
// Check out all of the conditional branches going to this return
1743
// instruction. If any of them just select between returns, change the
1744
// branch itself into a select/return pair.
1745
while (!CondBranchPreds.empty()) {
1746
BranchInst *BI = CondBranchPreds.pop_back_val();
1748
// Check to see if the non-BB successor is also a return block.
1749
if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
1750
isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
1751
SimplifyCondBranchToTwoReturns(BI))
1755
} else if (isa<UnwindInst>(BB->begin())) {
1756
// Check to see if the first instruction in this block is just an unwind.
1757
// If so, replace any invoke instructions which use this as an exception
1758
// destination with call instructions.
1760
SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1761
while (!Preds.empty()) {
1762
BasicBlock *Pred = Preds.back();
1763
if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
1764
if (II->getUnwindDest() == BB) {
1765
// Insert a new branch instruction before the invoke, because this
1766
// is now a fall through.
1767
BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1768
Pred->getInstList().remove(II); // Take out of symbol table
1770
// Insert the call now.
1771
SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
1772
CallInst *CI = CallInst::Create(II->getCalledValue(),
1773
Args.begin(), Args.end(),
1775
CI->setCallingConv(II->getCallingConv());
1776
CI->setAttributes(II->getAttributes());
1777
// If the invoke produced a value, the Call now does instead.
1778
II->replaceAllUsesWith(CI);
1786
// If this block is now dead, remove it.
1787
if (pred_begin(BB) == pred_end(BB)) {
1788
// We know there are no successors, so just nuke the block.
1789
M->getBasicBlockList().erase(BB);
1793
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
1794
if (isValueEqualityComparison(SI)) {
1795
// If we only have one predecessor, and if it is a branch on this value,
1796
// see if that predecessor totally determines the outcome of this switch.
1797
if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1798
if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
1799
return SimplifyCFG(BB) || 1;
1801
// If the block only contains the switch, see if we can fold the block
1802
// away into any preds.
1803
BasicBlock::iterator BBI = BB->begin();
1804
// Ignore dbg intrinsics.
1805
while (isa<DbgInfoIntrinsic>(BBI))
1808
if (FoldValueComparisonIntoPredecessors(SI))
1809
return SimplifyCFG(BB) || 1;
1811
} else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
1812
if (BI->isUnconditional()) {
1813
BasicBlock::iterator BBI = BB->getFirstNonPHI();
1815
// Ignore dbg intrinsics.
1816
while (isa<DbgInfoIntrinsic>(BBI))
1818
if (BBI->isTerminator()) // Terminator is the only non-phi instruction!
1819
if (TryToSimplifyUncondBranchFromEmptyBlock(BB))
1822
} else { // Conditional branch
1823
if (isValueEqualityComparison(BI)) {
1824
// If we only have one predecessor, and if it is a branch on this value,
1825
// see if that predecessor totally determines the outcome of this
1827
if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
1828
if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
1829
return SimplifyCFG(BB) || 1;
1831
// This block must be empty, except for the setcond inst, if it exists.
1832
// Ignore dbg intrinsics.
1833
BasicBlock::iterator I = BB->begin();
1834
// Ignore dbg intrinsics.
1835
while (isa<DbgInfoIntrinsic>(I))
1838
if (FoldValueComparisonIntoPredecessors(BI))
1839
return SimplifyCFG(BB) | true;
1840
} else if (&*I == cast<Instruction>(BI->getCondition())){
1842
// Ignore dbg intrinsics.
1843
while (isa<DbgInfoIntrinsic>(I))
1846
if (FoldValueComparisonIntoPredecessors(BI))
1847
return SimplifyCFG(BB) | true;
1852
// If this is a branch on a phi node in the current block, thread control
1853
// through this block if any PHI node entries are constants.
1854
if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
1855
if (PN->getParent() == BI->getParent())
1856
if (FoldCondBranchOnPHI(BI))
1857
return SimplifyCFG(BB) | true;
1859
// If this basic block is ONLY a setcc and a branch, and if a predecessor
1860
// branches to us and one of our successors, fold the setcc into the
1861
// predecessor and use logical operations to pick the right destination.
1862
if (FoldBranchToCommonDest(BI))
1863
return SimplifyCFG(BB) | 1;
1866
// Scan predecessor blocks for conditional branches.
1867
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
1868
if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
1869
if (PBI != BI && PBI->isConditional())
1870
if (SimplifyCondBranchToCondBranch(PBI, BI))
1871
return SimplifyCFG(BB) | true;
1873
} else if (isa<UnreachableInst>(BB->getTerminator())) {
1874
// If there are any instructions immediately before the unreachable that can
1875
// be removed, do so.
1876
Instruction *Unreachable = BB->getTerminator();
1877
while (Unreachable != BB->begin()) {
1878
BasicBlock::iterator BBI = Unreachable;
1880
// Do not delete instructions that can have side effects, like calls
1881
// (which may never return) and volatile loads and stores.
1882
if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
1884
if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
1885
if (SI->isVolatile())
1888
if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
1889
if (LI->isVolatile())
1892
// Delete this instruction
1893
BB->getInstList().erase(BBI);
1897
// If the unreachable instruction is the first in the block, take a gander
1898
// at all of the predecessors of this instruction, and simplify them.
1899
if (&BB->front() == Unreachable) {
1900
SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
1901
for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
1902
TerminatorInst *TI = Preds[i]->getTerminator();
1904
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
1905
if (BI->isUnconditional()) {
1906
if (BI->getSuccessor(0) == BB) {
1907
new UnreachableInst(TI->getContext(), TI);
1908
TI->eraseFromParent();
1912
if (BI->getSuccessor(0) == BB) {
1913
BranchInst::Create(BI->getSuccessor(1), BI);
1914
EraseTerminatorInstAndDCECond(BI);
1915
} else if (BI->getSuccessor(1) == BB) {
1916
BranchInst::Create(BI->getSuccessor(0), BI);
1917
EraseTerminatorInstAndDCECond(BI);
1921
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
1922
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1923
if (SI->getSuccessor(i) == BB) {
1924
BB->removePredecessor(SI->getParent());
1929
// If the default value is unreachable, figure out the most popular
1930
// destination and make it the default.
1931
if (SI->getSuccessor(0) == BB) {
1932
std::map<BasicBlock*, unsigned> Popularity;
1933
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1934
Popularity[SI->getSuccessor(i)]++;
1936
// Find the most popular block.
1937
unsigned MaxPop = 0;
1938
BasicBlock *MaxBlock = 0;
1939
for (std::map<BasicBlock*, unsigned>::iterator
1940
I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
1941
if (I->second > MaxPop) {
1943
MaxBlock = I->first;
1947
// Make this the new default, allowing us to delete any explicit
1949
SI->setSuccessor(0, MaxBlock);
1952
// If MaxBlock has phinodes in it, remove MaxPop-1 entries from
1954
if (isa<PHINode>(MaxBlock->begin()))
1955
for (unsigned i = 0; i != MaxPop-1; ++i)
1956
MaxBlock->removePredecessor(SI->getParent());
1958
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
1959
if (SI->getSuccessor(i) == MaxBlock) {
1965
} else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
1966
if (II->getUnwindDest() == BB) {
1967
// Convert the invoke to a call instruction. This would be a good
1968
// place to note that the call does not throw though.
1969
BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
1970
II->removeFromParent(); // Take out of symbol table
1972
// Insert the call now...
1973
SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
1974
CallInst *CI = CallInst::Create(II->getCalledValue(),
1975
Args.begin(), Args.end(),
1977
CI->setCallingConv(II->getCallingConv());
1978
CI->setAttributes(II->getAttributes());
1979
// If the invoke produced a value, the Call does now instead.
1980
II->replaceAllUsesWith(CI);
1987
// If this block is now dead, remove it.
1988
if (pred_begin(BB) == pred_end(BB)) {
1989
// We know there are no successors, so just nuke the block.
1990
M->getBasicBlockList().erase(BB);
1996
// Merge basic blocks into their predecessor if there is only one distinct
1997
// pred, and if there is only one distinct successor of the predecessor, and
1998
// if there are no PHI nodes.
2000
if (MergeBlockIntoPredecessor(BB))
2003
// Otherwise, if this block only has a single predecessor, and if that block
2004
// is a conditional branch, see if we can hoist any code from this block up
2005
// into our predecessor.
2006
pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
2007
BasicBlock *OnlyPred = *PI++;
2008
for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
2009
if (*PI != OnlyPred) {
2010
OnlyPred = 0; // There are multiple different predecessors...
2015
if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
2016
if (BI->isConditional()) {
2017
// Get the other block.
2018
BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
2019
PI = pred_begin(OtherBB);
2022
if (PI == pred_end(OtherBB)) {
2023
// We have a conditional branch to two blocks that are only reachable
2024
// from the condbr. We know that the condbr dominates the two blocks,
2025
// so see if there is any identical code in the "then" and "else"
2026
// blocks. If so, we can hoist it up to the branching block.
2027
Changed |= HoistThenElseCodeToIf(BI);
2029
BasicBlock* OnlySucc = NULL;
2030
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
2034
else if (*SI != OnlySucc) {
2035
OnlySucc = 0; // There are multiple distinct successors!
2040
if (OnlySucc == OtherBB) {
2041
// If BB's only successor is the other successor of the predecessor,
2042
// i.e. a triangle, see if we can hoist any code from this block up
2043
// to the "if" block.
2044
Changed |= SpeculativelyExecuteBB(BI, BB);
2049
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2050
if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2051
// Change br (X == 0 | X == 1), T, F into a switch instruction.
2052
if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
2053
Instruction *Cond = cast<Instruction>(BI->getCondition());
2054
// If this is a bunch of seteq's or'd together, or if it's a bunch of
2055
// 'setne's and'ed together, collect them.
2057
std::vector<ConstantInt*> Values;
2058
bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
2060
// There might be duplicate constants in the list, which the switch
2061
// instruction can't handle, remove them now.
2062
std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
2063
Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2065
// Figure out which block is which destination.
2066
BasicBlock *DefaultBB = BI->getSuccessor(1);
2067
BasicBlock *EdgeBB = BI->getSuccessor(0);
2068
if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2070
// Convert pointer to int before we switch.
2071
if (CompVal->getType()->isPointerTy()) {
2072
assert(TD && "Cannot switch on pointer without TargetData");
2073
CompVal = new PtrToIntInst(CompVal,
2074
TD->getIntPtrType(CompVal->getContext()),
2078
// Create the new switch instruction now.
2079
SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,
2082
// Add all of the 'cases' to the switch instruction.
2083
for (unsigned i = 0, e = Values.size(); i != e; ++i)
2084
New->addCase(Values[i], EdgeBB);
2086
// We added edges from PI to the EdgeBB. As such, if there were any
2087
// PHI nodes in EdgeBB, they need entries to be added corresponding to
2088
// the number of edges added.
2089
for (BasicBlock::iterator BBI = EdgeBB->begin();
2090
isa<PHINode>(BBI); ++BBI) {
2091
PHINode *PN = cast<PHINode>(BBI);
2092
Value *InVal = PN->getIncomingValueForBlock(*PI);
2093
for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2094
PN->addIncoming(InVal, *PI);
2097
// Erase the old branch instruction.
2098
EraseTerminatorInstAndDCECond(BI);
2106
/// SimplifyCFG - This function is used to do simplification of a CFG. For
2107
/// example, it adjusts branches to branches to eliminate the extra hop, it
2108
/// eliminates unreachable basic blocks, and does other "peephole" optimization
2109
/// of the CFG. It returns true if a modification was made.
2111
/// WARNING: The entry node of a function may not be simplified.
2113
bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2114
return SimplifyCFGOpt(TD).run(BB);
added
removed
libclamav/c++/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
