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//===- ProfileEstimatorPass.cpp - LLVM Pass to estimate profile info ------===//
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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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// This file implements a concrete implementation of profiling information that
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// estimates the profiling information in a very crude and unimaginative way.
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "profile-estimator"
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#include "llvm/Pass.h"
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#include "llvm/Analysis/Passes.h"
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#include "llvm/Analysis/ProfileInfo.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Support/CommandLine.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/Support/Format.h"
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static cl::opt<double>
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"profile-estimator-loop-weight", cl::init(10),
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cl::value_desc("loop-weight"),
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cl::desc("Number of loop executions used for profile-estimator")
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class ProfileEstimatorPass : public FunctionPass, public ProfileInfo {
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std::set<BasicBlock*> BBToVisit;
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std::map<Loop*,double> LoopExitWeights;
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std::map<Edge,double> MinimalWeight;
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static char ID; // Class identification, replacement for typeinfo
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explicit ProfileEstimatorPass(const double execcount = 0)
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: FunctionPass(&ID), ExecCount(execcount) {
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if (execcount == 0) ExecCount = LoopWeight;
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<LoopInfo>();
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virtual const char *getPassName() const {
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return "Profiling information estimator";
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/// run - Estimate the profile information from the specified file.
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virtual bool runOnFunction(Function &F);
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/// getAdjustedAnalysisPointer - This method is used when a pass implements
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/// an analysis interface through multiple inheritance. If needed, it
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/// should override this to adjust the this pointer as needed for the
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/// specified pass info.
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virtual void *getAdjustedAnalysisPointer(const PassInfo *PI) {
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if (PI->isPassID(&ProfileInfo::ID))
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return (ProfileInfo*)this;
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virtual void recurseBasicBlock(BasicBlock *BB);
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void inline printEdgeWeight(Edge);
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} // End of anonymous namespace
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char ProfileEstimatorPass::ID = 0;
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static RegisterPass<ProfileEstimatorPass>
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X("profile-estimator", "Estimate profiling information", false, true);
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static RegisterAnalysisGroup<ProfileInfo> Y(X);
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const PassInfo *ProfileEstimatorPassID = &X;
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FunctionPass *createProfileEstimatorPass() {
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return new ProfileEstimatorPass();
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/// createProfileEstimatorPass - This function returns a Pass that estimates
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/// profiling information using the given loop execution count.
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Pass *createProfileEstimatorPass(const unsigned execcount) {
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return new ProfileEstimatorPass(execcount);
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static double ignoreMissing(double w) {
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if (w == ProfileInfo::MissingValue) return 0;
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static void inline printEdgeError(ProfileInfo::Edge e, const char *M) {
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DEBUG(dbgs() << "-- Edge " << e << " is not calculated, " << M << "\n");
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void inline ProfileEstimatorPass::printEdgeWeight(Edge E) {
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DEBUG(dbgs() << "-- Weight of Edge " << E << ":"
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<< format("%20.20g", getEdgeWeight(E)) << "\n");
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// recurseBasicBlock() - This calculates the ProfileInfo estimation for a
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// single block and then recurses into the successors.
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// The algorithm preserves the flow condition, meaning that the sum of the
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// weight of the incoming edges must be equal the block weight which must in
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// turn be equal to the sume of the weights of the outgoing edges.
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// Since the flow of an block is deterimined from the current state of the
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// flow, once an edge has a flow assigned this flow is never changed again,
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// otherwise it would be possible to violate the flow condition in another
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void ProfileEstimatorPass::recurseBasicBlock(BasicBlock *BB) {
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// Break the recursion if this BasicBlock was already visited.
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if (BBToVisit.find(BB) == BBToVisit.end()) return;
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// Read the LoopInfo for this block.
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bool BBisHeader = LI->isLoopHeader(BB);
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Loop* BBLoop = LI->getLoopFor(BB);
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// To get the block weight, read all incoming edges.
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std::set<BasicBlock*> ProcessedPreds;
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for ( pred_iterator bbi = pred_begin(BB), bbe = pred_end(BB);
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bbi != bbe; ++bbi ) {
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// If this block was not considered already, add weight.
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Edge edge = getEdge(*bbi,BB);
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double w = getEdgeWeight(edge);
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if (ProcessedPreds.insert(*bbi).second) {
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BBWeight += ignoreMissing(w);
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// If this block is a loop header and the predecessor is contained in this
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// loop, thus the edge is a backedge, continue and do not check if the
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if (BBisHeader && BBLoop->contains(*bbi)) {
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printEdgeError(edge, "but is backedge, continueing");
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// If the edges value is missing (and this is no loop header, and this is
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// no backedge) return, this block is currently non estimatable.
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if (w == MissingValue) {
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printEdgeError(edge, "returning");
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if (getExecutionCount(BB) != MissingValue) {
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BBWeight = getExecutionCount(BB);
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// Fetch all necessary information for current block.
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SmallVector<Edge, 8> ExitEdges;
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SmallVector<Edge, 8> Edges;
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BBLoop->getExitEdges(ExitEdges);
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// If this is a loop header, consider the following:
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// Exactly the flow that is entering this block, must exit this block too. So
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// *) get all the exit edges, read the flow that is already leaving this
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// loop, remember the edges that do not have any flow on them right now.
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// (The edges that have already flow on them are most likely exiting edges of
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// other loops, do not touch those flows because the previously caclulated
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// loopheaders would not be exact anymore.)
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// *) In case there is not a single exiting edge left, create one at the loop
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// latch to prevent the flow from building up in the loop.
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// *) Take the flow that is not leaving the loop already and distribute it on
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// the remaining exiting edges.
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// (This ensures that all flow that enters the loop also leaves it.)
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// *) Increase the flow into the loop by increasing the weight of this block.
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// There is at least one incoming backedge that will bring us this flow later
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// on. (So that the flow condition in this node is valid again.)
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double incoming = BBWeight;
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// Subtract the flow leaving the loop.
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std::set<Edge> ProcessedExits;
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for (SmallVector<Edge, 8>::iterator ei = ExitEdges.begin(),
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ee = ExitEdges.end(); ei != ee; ++ei) {
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if (ProcessedExits.insert(*ei).second) {
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double w = getEdgeWeight(*ei);
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if (w == MissingValue) {
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Edges.push_back(*ei);
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// Check if there is a necessary minimal weight, if yes, subtract it
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if (MinimalWeight.find(*ei) != MinimalWeight.end()) {
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incoming -= MinimalWeight[*ei];
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DEBUG(dbgs() << "Reserving " << format("%.20g",MinimalWeight[*ei]) << " at " << (*ei) << "\n");
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// If no exit edges, create one:
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if (Edges.size() == 0) {
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BasicBlock *Latch = BBLoop->getLoopLatch();
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Edge edge = getEdge(Latch,0);
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EdgeInformation[BB->getParent()][edge] = BBWeight;
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printEdgeWeight(edge);
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edge = getEdge(Latch, BB);
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EdgeInformation[BB->getParent()][edge] = BBWeight * ExecCount;
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printEdgeWeight(edge);
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// Distribute remaining weight to the exting edges. To prevent fractions
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// from building up and provoking precision problems the weight which is to
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// be distributed is split and the rounded, the last edge gets a somewhat
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// bigger value, but we are close enough for an estimation.
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double fraction = floor(incoming/Edges.size());
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for (SmallVector<Edge, 8>::iterator ei = Edges.begin(), ee = Edges.end();
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incoming -= fraction;
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EdgeInformation[BB->getParent()][*ei] += w;
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// Read necessary minimal weight.
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if (MinimalWeight.find(*ei) != MinimalWeight.end()) {
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EdgeInformation[BB->getParent()][*ei] += MinimalWeight[*ei];
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DEBUG(dbgs() << "Additionally " << format("%.20g",MinimalWeight[*ei]) << " at " << (*ei) << "\n");
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printEdgeWeight(*ei);
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// Add minimal weight to paths to all exit edges, this is used to ensure
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// that enough flow is reaching this edges.
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const BasicBlock *Dest = GetPath(BB, (*ei).first, p, GetPathToDest);
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const BasicBlock *Parent = p.find(Dest)->second;
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Edge e = getEdge(Parent, Dest);
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if (MinimalWeight.find(e) == MinimalWeight.end()) {
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MinimalWeight[e] = 0;
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MinimalWeight[e] += w;
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DEBUG(dbgs() << "Minimal Weight for " << e << ": " << format("%.20g",MinimalWeight[e]) << "\n");
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// Increase flow into the loop.
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BBWeight *= (ExecCount+1);
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BlockInformation[BB->getParent()][BB] = BBWeight;
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// Up until now we considered only the loop exiting edges, now we have a
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// definite block weight and must distribute this onto the outgoing edges.
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// Since there may be already flow attached to some of the edges, read this
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// flow first and remember the edges that have still now flow attached.
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std::set<BasicBlock*> ProcessedSuccs;
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succ_iterator bbi = succ_begin(BB), bbe = succ_end(BB);
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// Also check for (BB,0) edges that may already contain some flow. (But only
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// in case there are no successors.)
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Edge edge = getEdge(BB,0);
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EdgeInformation[BB->getParent()][edge] = BBWeight;
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printEdgeWeight(edge);
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for ( ; bbi != bbe; ++bbi ) {
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if (ProcessedSuccs.insert(*bbi).second) {
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Edge edge = getEdge(BB,*bbi);
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double w = getEdgeWeight(edge);
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if (w != MissingValue) {
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BBWeight -= getEdgeWeight(edge);
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Edges.push_back(edge);
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// If minimal weight is necessary, reserve weight by subtracting weight
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// from block weight, this is readded later on.
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if (MinimalWeight.find(edge) != MinimalWeight.end()) {
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BBWeight -= MinimalWeight[edge];
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DEBUG(dbgs() << "Reserving " << format("%.20g",MinimalWeight[edge]) << " at " << edge << "\n");
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double fraction = floor(BBWeight/Edges.size());
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// Finally we know what flow is still not leaving the block, distribute this
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// flow onto the empty edges.
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for (SmallVector<Edge, 8>::iterator ei = Edges.begin(), ee = Edges.end();
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EdgeInformation[BB->getParent()][*ei] += fraction;
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BBWeight -= fraction;
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EdgeInformation[BB->getParent()][*ei] += BBWeight;
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// Readd minial necessary weight.
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if (MinimalWeight.find(*ei) != MinimalWeight.end()) {
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EdgeInformation[BB->getParent()][*ei] += MinimalWeight[*ei];
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DEBUG(dbgs() << "Additionally " << format("%.20g",MinimalWeight[*ei]) << " at " << (*ei) << "\n");
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printEdgeWeight(*ei);
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// This block is visited, mark this before the recursion.
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// Recurse into successors.
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for (succ_iterator bbi = succ_begin(BB), bbe = succ_end(BB);
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recurseBasicBlock(*bbi);
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bool ProfileEstimatorPass::runOnFunction(Function &F) {
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if (F.isDeclaration()) return false;
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// Fetch LoopInfo and clear ProfileInfo for this function.
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LI = &getAnalysis<LoopInfo>();
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FunctionInformation.erase(&F);
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BlockInformation[&F].clear();
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EdgeInformation[&F].clear();
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// Mark all blocks as to visit.
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for (Function::iterator bi = F.begin(), be = F.end(); bi != be; ++bi)
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BBToVisit.insert(bi);
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// Clear Minimal Edges.
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MinimalWeight.clear();
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DEBUG(dbgs() << "Working on function " << F.getNameStr() << "\n");
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// Since the entry block is the first one and has no predecessors, the edge
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// (0,entry) is inserted with the starting weight of 1.
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BasicBlock *entry = &F.getEntryBlock();
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BlockInformation[&F][entry] = pow(2.0, 32.0);
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Edge edge = getEdge(0,entry);
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EdgeInformation[&F][edge] = BlockInformation[&F][entry];
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printEdgeWeight(edge);
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// Since recurseBasicBlock() maybe returns with a block which was not fully
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// estimated, use recurseBasicBlock() until everything is calculated.
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bool cleanup = false;
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recurseBasicBlock(entry);
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while (BBToVisit.size() > 0 && !cleanup) {
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// Remember number of open blocks, this is later used to check if progress
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unsigned size = BBToVisit.size();
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// Try to calculate all blocks in turn.
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for (std::set<BasicBlock*>::iterator bi = BBToVisit.begin(),
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be = BBToVisit.end(); bi != be; ++bi) {
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recurseBasicBlock(*bi);
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// If at least one block was finished, break because iterator may be
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if (BBToVisit.size() < size) break;
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// If there was not a single block resolved, make some assumptions.
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if (BBToVisit.size() == size) {
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for (std::set<BasicBlock*>::iterator BBI = BBToVisit.begin(), BBE = BBToVisit.end();
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(BBI != BBE) && (!found); ++BBI) {
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BasicBlock *BB = *BBI;
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// Try each predecessor if it can be assumend.
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for (pred_iterator bbi = pred_begin(BB), bbe = pred_end(BB);
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(bbi != bbe) && (!found); ++bbi) {
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Edge e = getEdge(*bbi,BB);
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double w = getEdgeWeight(e);
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// Check that edge from predecessor is still free.
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if (w == MissingValue) {
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// Check if there is a circle from this block to predecessor.
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const BasicBlock *Dest = GetPath(BB, *bbi, P, GetPathToDest);
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// If there is no circle, just set edge weight to 0
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EdgeInformation[&F][e] = 0;
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DEBUG(dbgs() << "Assuming edge weight: ");
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DEBUG(dbgs() << "No assumption possible in Fuction "<<F.getName()<<", setting all to zero\n");
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// In case there was no safe way to assume edges, set as a last measure,
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// set _everything_ to zero.
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FunctionInformation[&F] = 0;
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BlockInformation[&F].clear();
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EdgeInformation[&F].clear();
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for (Function::const_iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
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const BasicBlock *BB = &(*FI);
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BlockInformation[&F][BB] = 0;
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pred_const_iterator predi = pred_begin(BB), prede = pred_end(BB);
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if (predi == prede) {
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Edge e = getEdge(0,BB);
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for (;predi != prede; ++predi) {
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Edge e = getEdge(*predi,BB);
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succ_const_iterator succi = succ_begin(BB), succe = succ_end(BB);
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if (succi == succe) {
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Edge e = getEdge(BB,0);
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for (;succi != succe; ++succi) {
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Edge e = getEdge(*succi,BB);