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 *BB = Guard->getParent(); 61 makeGuardControlFlowExplicit(DeoptIntrinsic, Guard, true); 62 assert(isWidenableBranch(BB->getTerminator()) && "should hold"); 63 64 Guard->eraseFromParent(); 65 } 66 67 static bool explicifyGuards(Function &F) { 68 // Check if we can cheaply rule out the possibility of not having any work to 69 // do. 70 auto *GuardDecl = F.getParent()->getFunction( 71 Intrinsic::getName(Intrinsic::experimental_guard)); 72 if (!GuardDecl || GuardDecl->use_empty()) 73 return false; 74 75 SmallVector<CallInst *, 8> GuardIntrinsics; 76 for (auto &I : instructions(F)) 77 if (isGuard(&I)) 78 GuardIntrinsics.push_back(cast<CallInst>(&I)); 79 80 if (GuardIntrinsics.empty()) 81 return false; 82 83 auto *DeoptIntrinsic = Intrinsic::getDeclaration( 84 F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()}); 85 DeoptIntrinsic->setCallingConv(GuardDecl->getCallingConv()); 86 87 for (auto *Guard : GuardIntrinsics) 88 turnToExplicitForm(Guard, DeoptIntrinsic); 89 90 return true; 91 } 92 93 bool MakeGuardsExplicitLegacyPass::runOnFunction(Function &F) { 94 return explicifyGuards(F); 95 } 96 97 char MakeGuardsExplicitLegacyPass::ID = 0; 98 INITIALIZE_PASS(MakeGuardsExplicitLegacyPass, "make-guards-explicit", 99 "Lower the guard intrinsic to explicit control flow form", 100 false, false) 101 102 PreservedAnalyses MakeGuardsExplicitPass::run(Function &F, 103 FunctionAnalysisManager &) { 104 if (explicifyGuards(F)) 105 return PreservedAnalyses::none(); 106 return PreservedAnalyses::all(); 107 } 108