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//===--- PartiallyInlineLibCalls.cpp - Partially inline libcalls ----------===//
//
// 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 pass tries to partially inline the fast path of well-known library
// functions, such as using square-root instructions for cases where sqrt()
// does not need to set errno.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar/PartiallyInlineLibCalls.h"
#include "llvm/Analysis/DomTreeUpdater.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/DebugCounter.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include <optional>
using namespace llvm;
#define DEBUG_TYPE "partially-inline-libcalls"
DEBUG_COUNTER(PILCounter, "partially-inline-libcalls-transform",
"Controls transformations in partially-inline-libcalls");
static bool optimizeSQRT(CallInst *Call, Function *CalledFunc,
BasicBlock &CurrBB, Function::iterator &BB,
const TargetTransformInfo *TTI, DomTreeUpdater *DTU) {
// There is no need to change the IR, since backend will emit sqrt
// instruction if the call has already been marked read-only.
if (Call->onlyReadsMemory())
return false;
if (!DebugCounter::shouldExecute(PILCounter))
return false;
// Do the following transformation:
//
// (before)
// dst = sqrt(src)
//
// (after)
// v0 = sqrt_noreadmem(src) # native sqrt instruction.
// [if (v0 is a NaN) || if (src < 0)]
// v1 = sqrt(src) # library call.
// dst = phi(v0, v1)
//
Type *Ty = Call->getType();
IRBuilder<> Builder(Call->getNextNode());
// Split CurrBB right after the call, create a 'then' block (that branches
// back to split-off tail of CurrBB) into which we'll insert a libcall.
Instruction *LibCallTerm = SplitBlockAndInsertIfThen(
Builder.getTrue(), Call->getNextNode(), /*Unreachable=*/false,
/*BranchWeights*/ nullptr, DTU);
auto *CurrBBTerm = cast<BranchInst>(CurrBB.getTerminator());
// We want an 'else' block though, not a 'then' block.
cast<BranchInst>(CurrBBTerm)->swapSuccessors();
// Create phi that will merge results of either sqrt and replace all uses.
BasicBlock *JoinBB = LibCallTerm->getSuccessor(0);
JoinBB->setName(CurrBB.getName() + ".split");
Builder.SetInsertPoint(JoinBB, JoinBB->begin());
PHINode *Phi = Builder.CreatePHI(Ty, 2);
Call->replaceAllUsesWith(Phi);
// Finally, insert the libcall into 'else' block.
BasicBlock *LibCallBB = LibCallTerm->getParent();
LibCallBB->setName("call.sqrt");
Builder.SetInsertPoint(LibCallTerm);
Instruction *LibCall = Call->clone();
Builder.Insert(LibCall);
// Add memory(none) attribute, so that the backend can use a native sqrt
// instruction for this call.
Call->setDoesNotAccessMemory();
// Insert a FP compare instruction and use it as the CurrBB branch condition.
Builder.SetInsertPoint(CurrBBTerm);
Value *FCmp = TTI->isFCmpOrdCheaperThanFCmpZero(Ty)
? Builder.CreateFCmpORD(Call, Call)
: Builder.CreateFCmpOGE(Call->getOperand(0),
ConstantFP::get(Ty, 0.0));
CurrBBTerm->setCondition(FCmp);
// Add phi operands.
Phi->addIncoming(Call, &CurrBB);
Phi->addIncoming(LibCall, LibCallBB);
BB = JoinBB->getIterator();
return true;
}
static bool runPartiallyInlineLibCalls(Function &F, TargetLibraryInfo *TLI,
const TargetTransformInfo *TTI,
DominatorTree *DT) {
std::optional<DomTreeUpdater> DTU;
if (DT)
DTU.emplace(DT, DomTreeUpdater::UpdateStrategy::Lazy);
bool Changed = false;
Function::iterator CurrBB;
for (Function::iterator BB = F.begin(), BE = F.end(); BB != BE;) {
CurrBB = BB++;
for (BasicBlock::iterator II = CurrBB->begin(), IE = CurrBB->end();
II != IE; ++II) {
CallInst *Call = dyn_cast<CallInst>(&*II);
Function *CalledFunc;
if (!Call || !(CalledFunc = Call->getCalledFunction()))
continue;
if (Call->isNoBuiltin() || Call->isStrictFP())
continue;
if (Call->isMustTailCall())
continue;
// Skip if function either has local linkage or is not a known library
// function.
LibFunc LF;
if (CalledFunc->hasLocalLinkage() ||
!TLI->getLibFunc(*CalledFunc, LF) || !TLI->has(LF))
continue;
switch (LF) {
case LibFunc_sqrtf:
case LibFunc_sqrt:
if (TTI->haveFastSqrt(Call->getType()) &&
optimizeSQRT(Call, CalledFunc, *CurrBB, BB, TTI,
DTU ? &*DTU : nullptr))
break;
continue;
default:
continue;
}
Changed = true;
break;
}
}
return Changed;
}
PreservedAnalyses
PartiallyInlineLibCallsPass::run(Function &F, FunctionAnalysisManager &AM) {
auto &TLI = AM.getResult<TargetLibraryAnalysis>(F);
auto &TTI = AM.getResult<TargetIRAnalysis>(F);
auto *DT = AM.getCachedResult<DominatorTreeAnalysis>(F);
if (!runPartiallyInlineLibCalls(F, &TLI, &TTI, DT))
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserve<DominatorTreeAnalysis>();
return PA;
}
namespace {
class PartiallyInlineLibCallsLegacyPass : public FunctionPass {
public:
static char ID;
PartiallyInlineLibCallsLegacyPass() : FunctionPass(ID) {
initializePartiallyInlineLibCallsLegacyPassPass(
*PassRegistry::getPassRegistry());
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<TargetLibraryInfoWrapperPass>();
AU.addRequired<TargetTransformInfoWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
FunctionPass::getAnalysisUsage(AU);
}
bool runOnFunction(Function &F) override {
if (skipFunction(F))
return false;
TargetLibraryInfo *TLI =
&getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
const TargetTransformInfo *TTI =
&getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
DominatorTree *DT = nullptr;
if (auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>())
DT = &DTWP->getDomTree();
return runPartiallyInlineLibCalls(F, TLI, TTI, DT);
}
};
}
char PartiallyInlineLibCallsLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(PartiallyInlineLibCallsLegacyPass,
"partially-inline-libcalls",
"Partially inline calls to library functions", false,
false)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_END(PartiallyInlineLibCallsLegacyPass,
"partially-inline-libcalls",
"Partially inline calls to library functions", false, false)
FunctionPass *llvm::createPartiallyInlineLibCallsPass() {
return new PartiallyInlineLibCallsLegacyPass();
}
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