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      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