1 //===- StripGCRelocates.cpp - Remove gc.relocates inserted by RewriteStatePoints===// 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 is a little utility pass that removes the gc.relocates inserted by 10 // RewriteStatepointsForGC. Note that the generated IR is incorrect, 11 // but this is useful as a single pass in itself, for analysis of IR, without 12 // the GC.relocates. The statepoint and gc.result instrinsics would still be 13 // present. 14 //===----------------------------------------------------------------------===// 15 16 #include "llvm/Transforms/Utils/StripGCRelocates.h" 17 #include "llvm/IR/Function.h" 18 #include "llvm/IR/InstIterator.h" 19 #include "llvm/IR/Instructions.h" 20 #include "llvm/IR/Statepoint.h" 21 #include "llvm/IR/Type.h" 22 #include "llvm/InitializePasses.h" 23 #include "llvm/Pass.h" 24 #include "llvm/Support/raw_ostream.h" 25 26 using namespace llvm; 27 28 static bool stripGCRelocates(Function &F) { 29 // Nothing to do for declarations. 30 if (F.isDeclaration()) 31 return false; 32 SmallVector<GCRelocateInst *, 20> GCRelocates; 33 // TODO: We currently do not handle gc.relocates that are in landing pads, 34 // i.e. not bound to a single statepoint token. 35 for (Instruction &I : instructions(F)) { 36 if (auto *GCR = dyn_cast<GCRelocateInst>(&I)) 37 if (isa<GCStatepointInst>(GCR->getOperand(0))) 38 GCRelocates.push_back(GCR); 39 } 40 // All gc.relocates are bound to a single statepoint token. The order of 41 // visiting gc.relocates for deletion does not matter. 42 for (GCRelocateInst *GCRel : GCRelocates) { 43 Value *OrigPtr = GCRel->getDerivedPtr(); 44 Value *ReplaceGCRel = OrigPtr; 45 46 // All gc_relocates are i8 addrspace(1)* typed, we need a bitcast from i8 47 // addrspace(1)* to the type of the OrigPtr, if the are not the same. 48 if (GCRel->getType() != OrigPtr->getType()) 49 ReplaceGCRel = new BitCastInst(OrigPtr, GCRel->getType(), "cast", GCRel); 50 51 // Replace all uses of gc.relocate and delete the gc.relocate 52 // There maybe unncessary bitcasts back to the OrigPtr type, an instcombine 53 // pass would clear this up. 54 GCRel->replaceAllUsesWith(ReplaceGCRel); 55 GCRel->eraseFromParent(); 56 } 57 return !GCRelocates.empty(); 58 } 59 60 PreservedAnalyses StripGCRelocates::run(Function &F, 61 FunctionAnalysisManager &AM) { 62 if (!stripGCRelocates(F)) 63 return PreservedAnalyses::all(); 64 65 // Removing gc.relocate preserves the CFG, but most other analysis probably 66 // need to re-run. 67 PreservedAnalyses PA; 68 PA.preserveSet<CFGAnalyses>(); 69 return PA; 70 } 71 72 namespace { 73 struct StripGCRelocatesLegacy : public FunctionPass { 74 static char ID; // Pass identification, replacement for typeid 75 StripGCRelocatesLegacy() : FunctionPass(ID) { 76 initializeStripGCRelocatesLegacyPass(*PassRegistry::getPassRegistry()); 77 } 78 79 void getAnalysisUsage(AnalysisUsage &Info) const override {} 80 81 bool runOnFunction(Function &F) override { return ::stripGCRelocates(F); } 82 }; 83 char StripGCRelocatesLegacy::ID = 0; 84 } // namespace 85 86 INITIALIZE_PASS(StripGCRelocatesLegacy, "strip-gc-relocates", 87 "Strip gc.relocates inserted through RewriteStatepointsForGC", 88 true, false) 89