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//===- MakeGuardsExplicit.cpp - Turn guard intrinsics into guard branches -===//
// 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 the new form of
// guard represented as widenable explicit branch to the deopt block. The
// difference between this pass and LowerGuardIntrinsic is that after this pass
// the guard represented as intrinsic:
// call void(i1, ...) @llvm.experimental.guard(i1 %old_cond) [ "deopt"() ]
// transforms to a guard represented as widenable explicit branch:
// %widenable_cond = call i1 @llvm.experimental.widenable.condition()
// br i1 (%old_cond & %widenable_cond), label %guarded, label %deopt
// Here:
// - The semantics of @llvm.experimental.widenable.condition allows to replace
// %widenable_cond with the construction (%widenable_cond & %any_other_cond)
// without loss of correctness;
// - %guarded is the lower part of old guard intrinsic's parent block split by
// the intrinsic call;
// - %deopt is a block containing a sole call to @llvm.experimental.deoptimize
// intrinsic.
// Therefore, this branch preserves the property of widenability.
#include "llvm/Transforms/Scalar/MakeGuardsExplicit.h"
#include "llvm/Analysis/GuardUtils.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.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 MakeGuardsExplicitLegacyPass : public FunctionPass {
static char ID;
MakeGuardsExplicitLegacyPass() : FunctionPass(ID) {
bool runOnFunction(Function &F) override;
static void turnToExplicitForm(CallInst *Guard, Function *DeoptIntrinsic) {
// Replace the guard with an explicit branch (just like in GuardWidening).
BasicBlock *OriginalBB = Guard->getParent();
makeGuardControlFlowExplicit(DeoptIntrinsic, Guard, true);
assert(isWidenableBranch(OriginalBB->getTerminator()) && "should hold");
static bool explicifyGuards(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> GuardIntrinsics;
for (auto &I : instructions(F))
if (isGuard(&I))
if (GuardIntrinsics.empty())
return false;
auto *DeoptIntrinsic = Intrinsic::getDeclaration(
F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()});
for (auto *Guard : GuardIntrinsics)
turnToExplicitForm(Guard, DeoptIntrinsic);
return true;
bool MakeGuardsExplicitLegacyPass::runOnFunction(Function &F) {
return explicifyGuards(F);
char MakeGuardsExplicitLegacyPass::ID = 0;
INITIALIZE_PASS(MakeGuardsExplicitLegacyPass, "make-guards-explicit",
"Lower the guard intrinsic to explicit control flow form",
false, false)
PreservedAnalyses MakeGuardsExplicitPass::run(Function &F,
FunctionAnalysisManager &) {
if (explicifyGuards(F))
return PreservedAnalyses::none();
return PreservedAnalyses::all();