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/InstIterator.h" 37 #include "llvm/IR/Instructions.h" 38 #include "llvm/IR/Intrinsics.h" 39 #include "llvm/IR/Module.h" 40 #include "llvm/InitializePasses.h" 41 #include "llvm/Pass.h" 42 #include "llvm/Transforms/Utils/GuardUtils.h" 43 44 using namespace llvm; 45 turnToExplicitForm(CallInst * Guard,Function * DeoptIntrinsic)46 static void turnToExplicitForm(CallInst *Guard, Function *DeoptIntrinsic) { 47 // Replace the guard with an explicit branch (just like in GuardWidening). 48 BasicBlock *OriginalBB = Guard->getParent(); 49 (void)OriginalBB; 50 makeGuardControlFlowExplicit(DeoptIntrinsic, Guard, true); 51 assert(isWidenableBranch(OriginalBB->getTerminator()) && "should hold"); 52 53 Guard->eraseFromParent(); 54 } 55 explicifyGuards(Function & F)56 static bool explicifyGuards(Function &F) { 57 // Check if we can cheaply rule out the possibility of not having any work to 58 // do. 59 auto *GuardDecl = F.getParent()->getFunction( 60 Intrinsic::getName(Intrinsic::experimental_guard)); 61 if (!GuardDecl || GuardDecl->use_empty()) 62 return false; 63 64 SmallVector<CallInst *, 8> GuardIntrinsics; 65 for (auto &I : instructions(F)) 66 if (isGuard(&I)) 67 GuardIntrinsics.push_back(cast<CallInst>(&I)); 68 69 if (GuardIntrinsics.empty()) 70 return false; 71 72 auto *DeoptIntrinsic = Intrinsic::getDeclaration( 73 F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()}); 74 DeoptIntrinsic->setCallingConv(GuardDecl->getCallingConv()); 75 76 for (auto *Guard : GuardIntrinsics) 77 turnToExplicitForm(Guard, DeoptIntrinsic); 78 79 return true; 80 } 81 run(Function & F,FunctionAnalysisManager &)82 PreservedAnalyses MakeGuardsExplicitPass::run(Function &F, 83 FunctionAnalysisManager &) { 84 if (explicifyGuards(F)) 85 return PreservedAnalyses::none(); 86 return PreservedAnalyses::all(); 87 } 88