86 lines · cpp
1//===- MakeGuardsExplicit.cpp - Turn guard intrinsics into guard branches -===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8//9// This pass lowers the @llvm.experimental.guard intrinsic to the new form of10// guard represented as widenable explicit branch to the deopt block. The11// difference between this pass and LowerGuardIntrinsic is that after this pass12// the guard represented as intrinsic:13//14// call void(i1, ...) @llvm.experimental.guard(i1 %old_cond) [ "deopt"() ]15//16// transforms to a guard represented as widenable explicit branch:17//18// %widenable_cond = call i1 @llvm.experimental.widenable.condition()19// br i1 (%old_cond & %widenable_cond), label %guarded, label %deopt20//21// Here:22// - The semantics of @llvm.experimental.widenable.condition allows to replace23// %widenable_cond with the construction (%widenable_cond & %any_other_cond)24// without loss of correctness;25// - %guarded is the lower part of old guard intrinsic's parent block split by26// the intrinsic call;27// - %deopt is a block containing a sole call to @llvm.experimental.deoptimize28// intrinsic.29//30// Therefore, this branch preserves the property of widenability.31//32//===----------------------------------------------------------------------===//33 34#include "llvm/Transforms/Scalar/MakeGuardsExplicit.h"35#include "llvm/Analysis/GuardUtils.h"36#include "llvm/IR/InstIterator.h"37#include "llvm/IR/Instructions.h"38#include "llvm/IR/Intrinsics.h"39#include "llvm/Pass.h"40#include "llvm/Transforms/Utils/GuardUtils.h"41 42using namespace llvm;43 44static void turnToExplicitForm(CallInst *Guard, Function *DeoptIntrinsic) {45 // Replace the guard with an explicit branch (just like in GuardWidening).46 BasicBlock *OriginalBB = Guard->getParent();47 (void)OriginalBB;48 makeGuardControlFlowExplicit(DeoptIntrinsic, Guard, true);49 assert(isWidenableBranch(OriginalBB->getTerminator()) && "should hold");50 51 Guard->eraseFromParent();52}53 54static bool explicifyGuards(Function &F) {55 // Check if we can cheaply rule out the possibility of not having any work to56 // do.57 auto *GuardDecl = Intrinsic::getDeclarationIfExists(58 F.getParent(), Intrinsic::experimental_guard);59 if (!GuardDecl || GuardDecl->use_empty())60 return false;61 62 SmallVector<CallInst *, 8> GuardIntrinsics;63 for (auto &I : instructions(F))64 if (isGuard(&I))65 GuardIntrinsics.push_back(cast<CallInst>(&I));66 67 if (GuardIntrinsics.empty())68 return false;69 70 auto *DeoptIntrinsic = Intrinsic::getOrInsertDeclaration(71 F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()});72 DeoptIntrinsic->setCallingConv(GuardDecl->getCallingConv());73 74 for (auto *Guard : GuardIntrinsics)75 turnToExplicitForm(Guard, DeoptIntrinsic);76 77 return true;78}79 80PreservedAnalyses MakeGuardsExplicitPass::run(Function &F,81 FunctionAnalysisManager &) {82 if (explicifyGuards(F))83 return PreservedAnalyses::none();84 return PreservedAnalyses::all();85}86