Analysis pass to access profile summary info

Differential Revision: http://reviews.llvm.org/D20648

llvm-svn: 271728

1 files changed, 161 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ProfileSummaryInfo.cpp b/llvm/lib/Analysis/ProfileSummaryInfo.cpp
new file mode 100644
index 00000000000..f3dc8b48732
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+++ b/llvm/lib/Analysis/ProfileSummaryInfo.cpp
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+//===- ProfileSummaryInfo.cpp - Global profile summary information --------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains a pass that provides access to the global profile summary
+// information.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/ProfileSummaryInfo.h"
+#include "llvm/IR/Metadata.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/ProfileSummary.h"
+using namespace llvm;
+
+// The following two parameters determine the threshold for a count to be
+// considered hot/cold. These two parameters are percentile values (multiplied
+// by 10000). If the counts are sorted in descending order, the minimum count to
+// reach ProfileSummaryCutoffHot gives the threshold to determine a hot count.
+// Similarly, the minimum count to reach ProfileSummaryCutoffCold gives the
+// threshold for determining cold count (everything <= this threshold is
+// considered cold).
+
+static cl::opt<int> ProfileSummaryCutoffHot(
+    "profile-summary-cutoff-hot", cl::Hidden, cl::init(999000), cl::ZeroOrMore,
+    cl::desc("A count is hot if it exceeds the minimum count to"
+             " reach this percentile of total counts."));
+
+static cl::opt<int> ProfileSummaryCutoffCold(
+    "profile-summary-cutoff-cold", cl::Hidden, cl::init(999999), cl::ZeroOrMore,
+    cl::desc("A count is cold if it is below the minimum count"
+             " to reach this percentile of total counts."));
+
+// Find the minimum count to reach a desired percentile of counts.
+static uint64_t getMinCountForPercentile(SummaryEntryVector &DS,
+                                         uint64_t Percentile) {
+  auto Compare = [](const ProfileSummaryEntry &Entry, uint64_t Percentile) {
+    return Entry.Cutoff < Percentile;
+  };
+  auto It = std::lower_bound(DS.begin(), DS.end(), Percentile, Compare);
+  // The required percentile has to be <= one of the percentiles in the
+  // detailed summary.
+  if (It == DS.end())
+    report_fatal_error("Desired percentile exceeds the maximum cutoff");
+  return It->MinCount;
+}
+
+// The profile summary metadata may be attached either by the frontend or by
+// any backend passes (IR level instrumentation, for example). This method
+// checks if the Summary is null and if so checks if the summary metadata is now
+// available in the module and parses it to get the Summary object.
+void ProfileSummaryInfo::computeSummary() {
+  if (Summary)
+    return;
+  auto *SummaryMD = M.getProfileSummary();
+  if (!SummaryMD)
+    return;
+  Summary.reset(ProfileSummary::getFromMD(SummaryMD));
+}
+
+// Returns true if the function is a hot function. If it returns false, it
+// either means it is not hot or it is unknown whether F is hot or not (for
+// example, no profile data is available).
+bool ProfileSummaryInfo::isHotFunction(const Function *F) {
+  computeSummary();
+  if (!F || !Summary)
+    return false;
+  auto FunctionCount = F->getEntryCount();
+  // FIXME: The heuristic used below for determining hotness is based on
+  // preliminary SPEC tuning for inliner. This will eventually be a
+  // convenience method that calls isHotCount.
+  return (FunctionCount &&
+          FunctionCount.getValue() >=
+              (uint64_t)(0.3 * (double)Summary->getMaxFunctionCount()));
+}
+
+// Returns true if the function is a cold function. If it returns false, it
+// either means it is not cold or it is unknown whether F is cold or not (for
+// example, no profile data is available).
+bool ProfileSummaryInfo::isColdFunction(const Function *F) {
+  computeSummary();
+  if (F->hasFnAttribute(Attribute::Cold)) {
+    return true;
+  }
+  auto FunctionCount = F->getEntryCount();
+  // FIXME: The heuristic used below for determining coldness is based on
+  // preliminary SPEC tuning for inliner. This will eventually be a
+  // convenience method that calls isHotCount.
+  return (FunctionCount &&
+          FunctionCount.getValue() <=
+              (uint64_t)(0.01 * (double)Summary->getMaxFunctionCount()));
+}
+
+// Compute the hot and cold thresholds.
+void ProfileSummaryInfo::computeThresholds() {
+  if (!Summary)
+    computeSummary();
+  if (!Summary)
+    return;
+  auto &DetailedSummary = Summary->getDetailedSummary();
+  HotCountThreshold =
+      getMinCountForPercentile(DetailedSummary, ProfileSummaryCutoffHot);
+  ColdCountThreshold =
+      getMinCountForPercentile(DetailedSummary, ProfileSummaryCutoffCold);
+}
+
+bool ProfileSummaryInfo::isHotCount(uint64_t C) {
+  if (!HotCountThreshold)
+    computeThresholds();
+  return HotCountThreshold && C >= HotCountThreshold.getValue();
+}
+
+bool ProfileSummaryInfo::isColdCount(uint64_t C) {
+  if (!ColdCountThreshold)
+    computeThresholds();
+  return ColdCountThreshold && C <= ColdCountThreshold.getValue();
+}
+
+ProfileSummaryInfo *ProfileSummaryInfoWrapperPass::getPSI(Module &M) {
+  if (!PSI)
+    PSI.reset(new ProfileSummaryInfo(M));
+  return PSI.get();
+}
+
+INITIALIZE_PASS(ProfileSummaryInfoWrapperPass, "profile-summary-info",
+                "Profile summary info", false, true)
+
+ProfileSummaryInfoWrapperPass::ProfileSummaryInfoWrapperPass()
+    : ImmutablePass(ID) {
+  initializeProfileSummaryInfoWrapperPassPass(*PassRegistry::getPassRegistry());
+}
+
+char ProfileSummaryAnalysis::PassID;
+ProfileSummaryInfo ProfileSummaryAnalysis::run(Module &M) {
+  return ProfileSummaryInfo(M);
+}
+
+// FIXME: This only tests isHotFunction and isColdFunction and not the
+// isHotCount and isColdCount calls.
+PreservedAnalyses ProfileSummaryPrinterPass::run(Module &M,
+                                                 AnalysisManager<Module> &AM) {
+  ProfileSummaryInfo &PSI = AM.getResult<ProfileSummaryAnalysis>(M);
+
+  OS << "Functions in " << M.getName() << " with hot/cold annotations: \n";
+  for (auto &F : M) {
+    OS << F.getName();
+    if (PSI.isHotFunction(&F))
+      OS << " :hot ";
+    else if (PSI.isColdFunction(&F))
+      OS << " :cold ";
+    OS << "\n";
+  }
+  return PreservedAnalyses::all();
+}
+
+char ProfileSummaryInfoWrapperPass::ID = 0;