llvm/lib/CodeGen/StaticDataAnnotator.cpp

//===- StaticDataAnnotator - Annotate static data's section prefix --------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// To reason about module-wide data hotness in a module granularity, this file
// implements a module pass StaticDataAnnotator to work coordinately with the
// StaticDataSplitter pass.
//
// The StaticDataSplitter pass is a machine function pass. It analyzes data
// hotness based on code and adds counters in StaticDataProfileInfo via its
// wrapper pass StaticDataProfileInfoWrapper.
// The StaticDataProfileInfoWrapper sits in the middle between the
// StaticDataSplitter and StaticDataAnnotator passes.
// The StaticDataAnnotator pass is a module pass. It iterates global variables
// in the module, looks up counters from StaticDataProfileInfo and sets the
// section prefix based on profiles.
//
// The three-pass structure is implemented for practical reasons, to work around
// the limitation that a module pass based on legacy pass manager cannot make
// use of MachineBlockFrequencyInfo analysis. In the future, we can consider
// porting the StaticDataSplitter pass to a module-pass using the new pass
// manager framework. That way, analysis are lazily computed as opposed to
// eagerly scheduled, and a module pass can use MachineBlockFrequencyInfo.
//===----------------------------------------------------------------------===//

#include "llvm/CodeGen/StaticDataAnnotator.h"
#include "llvm/Analysis/ProfileSummaryInfo.h"
#include "llvm/Analysis/StaticDataProfileInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/IR/Analysis.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PassManager.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"

#define DEBUG_TYPE "static-data-annotator"

using namespace llvm;

/// A module pass which iterates global variables in the module and annotates
/// their section prefixes based on profile-driven analysis.
class StaticDataAnnotatorLegacy : public ModulePass {
public:
  static char ID;

  StaticDataAnnotatorLegacy() : ModulePass(ID) {}

  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.addRequired<StaticDataProfileInfoWrapperPass>();
    AU.addRequired<ProfileSummaryInfoWrapperPass>();
    AU.setPreservesAll();
    ModulePass::getAnalysisUsage(AU);
  }

  StringRef getPassName() const override { return "Static Data Annotator"; }

  bool runOnModule(Module &M) override;
};

static bool annotateModule(Module &M, StaticDataProfileInfo *SDPI,
                           ProfileSummaryInfo *PSI) {
  if (!PSI || !PSI->hasProfileSummary())
    return false;

  bool Changed = false;
  for (auto &GV : M.globals()) {
    if (!llvm::memprof::IsAnnotationOK(GV))
      continue;

    StringRef SectionPrefix = SDPI->getConstantSectionPrefix(&GV, PSI);
    // setSectionPrefix returns true if the section prefix is updated.
    Changed |= GV.setSectionPrefix(SectionPrefix);
  }

  return Changed;
}

bool StaticDataAnnotatorLegacy::runOnModule(Module &M) {
  StaticDataProfileInfo *SDPI = &getAnalysis<StaticDataProfileInfoWrapperPass>()
                                     .getStaticDataProfileInfo();
  ProfileSummaryInfo *PSI =
      &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
  return annotateModule(M, SDPI, PSI);
}

char StaticDataAnnotatorLegacy::ID = 0;

INITIALIZE_PASS(StaticDataAnnotatorLegacy, DEBUG_TYPE, "Static Data Annotator",
                false, false)

ModulePass *llvm::createStaticDataAnnotatorLegacyPass() {
  return new StaticDataAnnotatorLegacy();
}

PreservedAnalyses StaticDataAnnoatorPass::run(Module &M,
                                              ModuleAnalysisManager &MAM) {
  StaticDataProfileInfo *SDPI = &MAM.getResult<StaticDataProfileInfoAnalysis>(M)
                                     .getStaticDataProfileInfo();
  ProfileSummaryInfo *PSI = &MAM.getResult<ProfileSummaryAnalysis>(M);
  return annotateModule(M, SDPI, PSI)
             ? PreservedAnalyses::none().preserveSet<CFGAnalyses>()
             : PreservedAnalyses::all();
}