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//===- PartialInlining.cpp - Inline parts of functions --------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass performs partial inlining, typically by inlining an if statement
// that surrounds the body of the function.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/IPO.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Transforms/Utils/CodeExtractor.h"
using namespace llvm;
#define DEBUG_TYPE "partialinlining"
STATISTIC(NumPartialInlined, "Number of functions partially inlined");
namespace {
struct PartialInliner : public ModulePass {
void getAnalysisUsage(AnalysisUsage &AU) const override { }
static char ID; // Pass identification, replacement for typeid
PartialInliner() : ModulePass(ID) {
initializePartialInlinerPass(*PassRegistry::getPassRegistry());
}
bool runOnModule(Module& M) override;
private:
Function* unswitchFunction(Function* F);
};
}
char PartialInliner::ID = 0;
INITIALIZE_PASS(PartialInliner, "partial-inliner",
"Partial Inliner", false, false)
ModulePass* llvm::createPartialInliningPass() { return new PartialInliner(); }
Function* PartialInliner::unswitchFunction(Function* F) {
// First, verify that this function is an unswitching candidate...
BasicBlock* entryBlock = F->begin();
BranchInst *BR = dyn_cast<BranchInst>(entryBlock->getTerminator());
if (!BR || BR->isUnconditional())
return nullptr;
BasicBlock* returnBlock = nullptr;
BasicBlock* nonReturnBlock = nullptr;
unsigned returnCount = 0;
for (BasicBlock *BB : successors(entryBlock)) {
if (isa<ReturnInst>(BB->getTerminator())) {
returnBlock = BB;
returnCount++;
} else
nonReturnBlock = BB;
}
if (returnCount != 1)
return nullptr;
// Clone the function, so that we can hack away on it.
ValueToValueMapTy VMap;
Function* duplicateFunction = CloneFunction(F, VMap,
/*ModuleLevelChanges=*/false);
duplicateFunction->setLinkage(GlobalValue::InternalLinkage);
F->getParent()->getFunctionList().push_back(duplicateFunction);
BasicBlock* newEntryBlock = cast<BasicBlock>(VMap[entryBlock]);
BasicBlock* newReturnBlock = cast<BasicBlock>(VMap[returnBlock]);
BasicBlock* newNonReturnBlock = cast<BasicBlock>(VMap[nonReturnBlock]);
// Go ahead and update all uses to the duplicate, so that we can just
// use the inliner functionality when we're done hacking.
F->replaceAllUsesWith(duplicateFunction);
// Special hackery is needed with PHI nodes that have inputs from more than
// one extracted block. For simplicity, just split the PHIs into a two-level
// sequence of PHIs, some of which will go in the extracted region, and some
// of which will go outside.
BasicBlock* preReturn = newReturnBlock;
newReturnBlock = newReturnBlock->splitBasicBlock(
newReturnBlock->getFirstNonPHI());
BasicBlock::iterator I = preReturn->begin();
BasicBlock::iterator Ins = newReturnBlock->begin();
while (I != preReturn->end()) {
PHINode* OldPhi = dyn_cast<PHINode>(I);
if (!OldPhi) break;
PHINode* retPhi = PHINode::Create(OldPhi->getType(), 2, "", Ins);
OldPhi->replaceAllUsesWith(retPhi);
Ins = newReturnBlock->getFirstNonPHI();
retPhi->addIncoming(I, preReturn);
retPhi->addIncoming(OldPhi->getIncomingValueForBlock(newEntryBlock),
newEntryBlock);
OldPhi->removeIncomingValue(newEntryBlock);
++I;
}
newEntryBlock->getTerminator()->replaceUsesOfWith(preReturn, newReturnBlock);
// Gather up the blocks that we're going to extract.
std::vector<BasicBlock*> toExtract;
toExtract.push_back(newNonReturnBlock);
for (Function::iterator FI = duplicateFunction->begin(),
FE = duplicateFunction->end(); FI != FE; ++FI)
if (&*FI != newEntryBlock && &*FI != newReturnBlock &&
&*FI != newNonReturnBlock)
toExtract.push_back(FI);
// The CodeExtractor needs a dominator tree.
DominatorTree DT;
DT.recalculate(*duplicateFunction);
// Extract the body of the if.
Function* extractedFunction
= CodeExtractor(toExtract, &DT).extractCodeRegion();
InlineFunctionInfo IFI;
// Inline the top-level if test into all callers.
std::vector<User *> Users(duplicateFunction->user_begin(),
duplicateFunction->user_end());
for (std::vector<User*>::iterator UI = Users.begin(), UE = Users.end();
UI != UE; ++UI)
if (CallInst *CI = dyn_cast<CallInst>(*UI))
InlineFunction(CI, IFI);
else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI))
InlineFunction(II, IFI);
// Ditch the duplicate, since we're done with it, and rewrite all remaining
// users (function pointers, etc.) back to the original function.
duplicateFunction->replaceAllUsesWith(F);
duplicateFunction->eraseFromParent();
++NumPartialInlined;
return extractedFunction;
}
bool PartialInliner::runOnModule(Module& M) {
std::vector<Function*> worklist;
worklist.reserve(M.size());
for (Module::iterator FI = M.begin(), FE = M.end(); FI != FE; ++FI)
if (!FI->use_empty() && !FI->isDeclaration())
worklist.push_back(&*FI);
bool changed = false;
while (!worklist.empty()) {
Function* currFunc = worklist.back();
worklist.pop_back();
if (currFunc->use_empty()) continue;
bool recursive = false;
for (User *U : currFunc->users())
if (Instruction* I = dyn_cast<Instruction>(U))
if (I->getParent()->getParent() == currFunc) {
recursive = true;
break;
}
if (recursive) continue;
if (Function* newFunc = unswitchFunction(currFunc)) {
worklist.push_back(newFunc);
changed = true;
}
}
return changed;
}
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