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-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This pass lowers the @llvm.experimental.guard intrinsic to the new form of 10 // guard represented as widenable explicit branch to the deopt block. The 11 // difference between this pass and LowerGuardIntrinsic is that after this pass 12 // 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 %deopt 20 // 21 // Here: 22 // - The semantics of @llvm.experimental.widenable.condition allows to replace 23 // %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 by 26 // the intrinsic call; 27 // - %deopt is a block containing a sole call to @llvm.experimental.deoptimize 28 // 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/IRBuilder.h" 37 #include "llvm/IR/InstIterator.h" 38 #include "llvm/IR/IntrinsicInst.h" 39 #include "llvm/IR/Intrinsics.h" 40 #include "llvm/InitializePasses.h" 41 #include "llvm/Pass.h" 42 #include "llvm/Transforms/Scalar.h" 43 #include "llvm/Transforms/Utils/GuardUtils.h" 44 45 using namespace llvm; 46 47 namespace { 48 struct MakeGuardsExplicitLegacyPass : public FunctionPass { 49 static char ID; 50 MakeGuardsExplicitLegacyPass() : FunctionPass(ID) { 51 initializeMakeGuardsExplicitLegacyPassPass(*PassRegistry::getPassRegistry()); 52 } 53 54 bool runOnFunction(Function &F) override; 55 }; 56 } 57 58 static void turnToExplicitForm(CallInst *Guard, Function *DeoptIntrinsic) { 59 // Replace the guard with an explicit branch (just like in GuardWidening). 60 BasicBlock *OriginalBB = Guard->getParent(); 61 (void)OriginalBB; 62 makeGuardControlFlowExplicit(DeoptIntrinsic, Guard, true); 63 assert(isWidenableBranch(OriginalBB->getTerminator()) && "should hold"); 64 65 Guard->eraseFromParent(); 66 } 67 68 static bool explicifyGuards(Function &F) { 69 // Check if we can cheaply rule out the possibility of not having any work to 70 // do. 71 auto *GuardDecl = F.getParent()->getFunction( 72 Intrinsic::getName(Intrinsic::experimental_guard)); 73 if (!GuardDecl || GuardDecl->use_empty()) 74 return false; 75 76 SmallVector<CallInst *, 8> GuardIntrinsics; 77 for (auto &I : instructions(F)) 78 if (isGuard(&I)) 79 GuardIntrinsics.push_back(cast<CallInst>(&I)); 80 81 if (GuardIntrinsics.empty()) 82 return false; 83 84 auto *DeoptIntrinsic = Intrinsic::getDeclaration( 85 F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()}); 86 DeoptIntrinsic->setCallingConv(GuardDecl->getCallingConv()); 87 88 for (auto *Guard : GuardIntrinsics) 89 turnToExplicitForm(Guard, DeoptIntrinsic); 90 91 return true; 92 } 93 94 bool MakeGuardsExplicitLegacyPass::runOnFunction(Function &F) { 95 return explicifyGuards(F); 96 } 97 98 char MakeGuardsExplicitLegacyPass::ID = 0; 99 INITIALIZE_PASS(MakeGuardsExplicitLegacyPass, "make-guards-explicit", 100 "Lower the guard intrinsic to explicit control flow form", 101 false, false) 102 103 PreservedAnalyses MakeGuardsExplicitPass::run(Function &F, 104 FunctionAnalysisManager &) { 105 if (explicifyGuards(F)) 106 return PreservedAnalyses::none(); 107 return PreservedAnalyses::all(); 108 } 109