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//===- LowerGuardIntrinsic.cpp - Lower the guard intrinsic ---------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This pass lowers the llvm.experimental.guard intrinsic to a conditional call
// to @llvm.experimental.deoptimize. Once this happens, the guard can no longer
// be widened.
#include "llvm/Transforms/Scalar/LowerGuardIntrinsic.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/GuardUtils.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/GuardUtils.h"
using namespace llvm;
namespace {
struct LowerGuardIntrinsicLegacyPass : public FunctionPass {
static char ID;
LowerGuardIntrinsicLegacyPass() : FunctionPass(ID) {
bool runOnFunction(Function &F) override;
static bool lowerGuardIntrinsic(Function &F) {
// Check if we can cheaply rule out the possibility of not having any work to
// do.
auto *GuardDecl = F.getParent()->getFunction(
if (!GuardDecl || GuardDecl->use_empty())
return false;
SmallVector<CallInst *, 8> ToLower;
// Traverse through the users of GuardDecl.
// This is presumably cheaper than traversing all instructions in the
// function.
for (auto *U : GuardDecl->users())
if (auto *CI = dyn_cast<CallInst>(U))
if (CI->getFunction() == &F)
if (ToLower.empty())
return false;
auto *DeoptIntrinsic = Intrinsic::getDeclaration(
F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()});
for (auto *CI : ToLower) {
makeGuardControlFlowExplicit(DeoptIntrinsic, CI, false);
return true;
bool LowerGuardIntrinsicLegacyPass::runOnFunction(Function &F) {
return lowerGuardIntrinsic(F);
char LowerGuardIntrinsicLegacyPass::ID = 0;
INITIALIZE_PASS(LowerGuardIntrinsicLegacyPass, "lower-guard-intrinsic",
"Lower the guard intrinsic to normal control flow", false,
Pass *llvm::createLowerGuardIntrinsicPass() {
return new LowerGuardIntrinsicLegacyPass();
PreservedAnalyses LowerGuardIntrinsicPass::run(Function &F,
FunctionAnalysisManager &AM) {
if (lowerGuardIntrinsic(F))
return PreservedAnalyses::none();
return PreservedAnalyses::all();