llvm/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp

//===-- PPCMergeStringPool.cpp -------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This transformation tries to merge the strings in the module into one pool
// of strings. The idea is to reduce the number of TOC entries in the module so
// that instead of having one TOC entry for each string there is only one global
// TOC entry and all of the strings are referenced off of that one entry plus
// an offset.
//
//===----------------------------------------------------------------------===//

#include "PPC.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/DomTreeUpdater.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/LoopIterator.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/ValueSymbolTable.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"

#define DEBUG_TYPE …

STATISTIC(NumPooledStrings, "Number of Strings Pooled");

usingnamespacellvm;

static cl::opt<unsigned>
    MaxStringsPooled("ppc-max-strings-pooled", cl::Hidden, cl::init(-1),
                     cl::desc("Maximum Number of Strings to Pool."));

static cl::opt<unsigned>
    MinStringsBeforePool("ppc-min-strings-before-pool", cl::Hidden, cl::init(2),
                         cl::desc("Minimum number of string candidates before "
				  "pooling is considered."));

namespace {
struct { … } CompareConstants;

class PPCMergeStringPool : public ModulePass { … };


// In order for a constant to be pooled we need to be able to replace all of
// the uses for that constant. This function checks all of the uses to make
// sure that they can be replaced.
static bool hasReplaceableUsers(GlobalVariable &GV) { … }

// Run through all of the constants in the module and determine if they are
// valid candidates to be merged into the string pool. Valid candidates will
// be added to MergeableStrings.
void PPCMergeStringPool::collectCandidateConstants(Module &M) { … }

bool PPCMergeStringPool::mergeModuleStringPool(Module &M) { … }

// For pooled strings we need to add the offset into the pool for each string.
// This is done by adding a Get Element Pointer (GEP) before each user. This
// function adds the GEP.
void PPCMergeStringPool::replaceUsesWithGEP(GlobalVariable *GlobalToReplace,
                                            GlobalVariable *GPool,
                                            unsigned ElementIndex) { … }

} // namespace

char PPCMergeStringPool::ID = …;

INITIALIZE_PASS(…)

ModulePass *llvm::createPPCMergeStringPoolPass() { … }