Profile: set branch weight metadata with data generated from profiling.

This patch implements ProfileDataLoader which loads profile data generated by
-insert-edge-profiling and updates branch weight metadata accordingly.

Patch by Alastair Murray.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162799 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ProfileDataLoaderPass.cpp

@@ -0,0 +1,188 @@
+//===- ProfileDataLoaderPass.cpp - Set branch weight metadata from prof ---===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass loads profiling data from a dump file and sets branch weight
+// metadata.
+//
+// TODO: Replace all "profile-metadata-loader" strings with "profile-loader"
+// once ProfileInfo etc. has been removed.
+//
+//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "profile-metadata-loader"
+#include "llvm/BasicBlock.h"
+#include "llvm/InstrTypes.h"
+#include "llvm/Module.h"
+#include "llvm/LLVMContext.h"
+#include "llvm/MDBuilder.h"
+#include "llvm/Metadata.h"
+#include "llvm/Pass.h"
+#include "llvm/Analysis/Passes.h"
+#include "llvm/Analysis/ProfileDataLoader.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/Format.h"
+#include "llvm/ADT/Statistic.h"
+#include <vector>
+using namespace llvm;
+
+STATISTIC(NumEdgesRead, "The # of edges read.");
+STATISTIC(NumTermsAnnotated, "The # of terminator instructions annotated.");
+
+static cl::opt<std::string>
+ProfileMetadataFilename("profile-file", cl::init("llvmprof.out"),
+                  cl::value_desc("filename"),
+                  cl::desc("Profile file loaded by -profile-metadata-loader"));
+
+namespace {
+  /// This pass loads profiling data from a dump file and sets branch weight
+  /// metadata.
+  class ProfileMetadataLoaderPass : public ModulePass {
+    std::string Filename;
+  public:
+    static char ID; // Class identification, replacement for typeinfo
+    explicit ProfileMetadataLoaderPass(const std::string &filename = "")
+        : ModulePass(ID), Filename(filename) {
+      initializeProfileMetadataLoaderPassPass(*PassRegistry::getPassRegistry());
+      if (filename.empty()) Filename = ProfileMetadataFilename;
+    }
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesAll();
+    }
+
+    virtual const char *getPassName() const {
+      return "Profile loader";
+    }
+
+    virtual void readEdge(unsigned, ProfileData&, ProfileData::Edge,
+                          std::vector<unsigned>&);
+    virtual unsigned matchEdges(Module&, ProfileData&, std::vector<unsigned>&);
+    virtual void setBranchWeightMetadata(Module&, ProfileData&);
+
+    virtual bool runOnModule(Module &M);
+  };
+}  // End of anonymous namespace
+
+char ProfileMetadataLoaderPass::ID = 0;
+INITIALIZE_PASS_BEGIN(ProfileMetadataLoaderPass, "profile-metadata-loader",
+              "Load profile information from llvmprof.out", false, true)
+INITIALIZE_PASS_END(ProfileMetadataLoaderPass, "profile-metadata-loader",
+              "Load profile information from llvmprof.out", false, true)
+
+char &llvm::ProfileMetadataLoaderPassID = ProfileMetadataLoaderPass::ID;
+
+/// createProfileMetadataLoaderPass - This function returns a Pass that loads
+/// the profiling information for the module from the specified filename,
+/// making it available to the optimizers.
+ModulePass *llvm::createProfileMetadataLoaderPass() { 
+    return new ProfileMetadataLoaderPass();
+}
+ModulePass *llvm::createProfileMetadataLoaderPass(const std::string &Filename) {
+  return new ProfileMetadataLoaderPass(Filename);
+}
+
+/// readEdge - Take the value from a profile counter and assign it to an edge.
+void ProfileMetadataLoaderPass::readEdge(unsigned ReadCount,
+                                         ProfileData &PB, ProfileData::Edge e,
+                                         std::vector<unsigned> &Counters) {
+  if (ReadCount < Counters.size()) {
+    unsigned weight = Counters[ReadCount];
+    assert(weight != ProfileDataLoader::Uncounted);
+    PB.addEdgeWeight(e, weight);
+
+    DEBUG(dbgs() << "-- Read Edge Counter for " << e
+                 << " (# "<< (ReadCount) << "): "
+                 << PB.getEdgeWeight(e) << "\n");
+  }
+}
+
+/// matchEdges - Link every profile counter with an edge.
+unsigned ProfileMetadataLoaderPass::matchEdges(Module &M, ProfileData &PB,
+                                             std::vector<unsigned> &Counters) {
+  if (Counters.size() == 0) return 0;
+
+  unsigned ReadCount = 0;
+
+  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
+    if (F->isDeclaration()) continue;
+    DEBUG(dbgs() << "Loading edges in '" << F->getName() << "'\n");
+    readEdge(ReadCount++, PB, PB.getEdge(0, &F->getEntryBlock()), Counters);
+    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
+      TerminatorInst *TI = BB->getTerminator();
+      for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) {
+        readEdge(ReadCount++, PB, PB.getEdge(BB,TI->getSuccessor(s)),
+                 Counters);
+      }
+    }
+  }
+
+  return ReadCount;
+}
+
+/// setBranchWeightMetadata - Translate the counter values associated with each
+/// edge into branch weights for each conditional branch (a branch with 2 or
+/// more desinations).
+void ProfileMetadataLoaderPass::setBranchWeightMetadata(Module &M,
+                                                        ProfileData &PB) {
+  for (Module::iterator F = M.begin(), E = M.end(); F != E; ++F) {
+    if (F->isDeclaration()) continue;
+    DEBUG(dbgs() << "Setting branch metadata in '" << F->getName() << "'\n");
+
+    for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
+      TerminatorInst *TI = BB->getTerminator();
+      unsigned NumSuccessors = TI->getNumSuccessors();
+
+      // If there is only one successor then we can not set a branch
+      // probability as the target is certain.
+      if (NumSuccessors < 2) continue;
+
+      // Load the weights of all edges leading from this terminator.
+      DEBUG(dbgs() << "-- Terminator with " << NumSuccessors
+                   << " successors:\n");
+      std::vector<uint32_t> Weights(NumSuccessors);
+      for (unsigned s = 0 ; s < NumSuccessors ; ++s) {
+          ProfileData::Edge edge = PB.getEdge(BB, TI->getSuccessor(s));
+          Weights[s] = (uint32_t)PB.getEdgeWeight(edge);
+          DEBUG(dbgs() << "---- Edge '" << edge << "' has weight "
+                       << Weights[s] << "\n");
+      }
+
+      // Set branch weight metadata.  This will set branch probabilities of
+      // 100%/0% if that is true of the dynamic execution.
+      // BranchProbabilityInfo can account for this when it loads this metadata
+      // (it gives the unexectuted branch a weight of 1 for the purposes of
+      // probability calculations).
+      MDBuilder MDB(TI->getContext());
+      MDNode *Node = MDB.createBranchWeights(Weights);
+      TI->setMetadata(LLVMContext::MD_prof, Node);
+      NumTermsAnnotated++;
+    }
+  }
+}
+
+bool ProfileMetadataLoaderPass::runOnModule(Module &M) {
+  ProfileDataLoader PDL("profile-data-loader", Filename);
+  ProfileData PB;
+
+  std::vector<unsigned> Counters = PDL.getRawEdgeCounts();
+
+  unsigned ReadCount = matchEdges(M, PB, Counters);
+
+  if (ReadCount != Counters.size()) {
+    errs() << "WARNING: profile information is inconsistent with "
+           << "the current program!\n";
+  }
+  NumEdgesRead = ReadCount;
+
+  setBranchWeightMetadata(M, PB);
+
+  return ReadCount > 0;
+}