llvm/lib/Transforms/Utils/StripGCRelocates.cpp

   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 intrinsics 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/InitializePasses.h"
  22 #include "llvm/Pass.h"
  23
  24 using namespace llvm;
  25
  26 static bool stripGCRelocates(Function &F) {
  27   // Nothing to do for declarations.
  28   if (F.isDeclaration())
  29     return false;
  30   SmallVector<GCRelocateInst *, 20> GCRelocates;
  31   // TODO: We currently do not handle gc.relocates that are in landing pads,
  32   // i.e. not bound to a single statepoint token.
  33   for (Instruction &I : instructions(F)) {
  34     if (auto *GCR = dyn_cast<GCRelocateInst>(&I))
  35       if (isa<GCStatepointInst>(GCR->getOperand(0)))
  36         GCRelocates.push_back(GCR);
  37   }
  38   // All gc.relocates are bound to a single statepoint token. The order of
  39   // visiting gc.relocates for deletion does not matter.
  40   for (GCRelocateInst *GCRel : GCRelocates) {
  41     Value *OrigPtr = GCRel->getDerivedPtr();
  42     Value *ReplaceGCRel = OrigPtr;
  43
  44     // All gc_relocates are i8 addrspace(1)* typed, we need a bitcast from i8
  45     // addrspace(1)* to the type of the OrigPtr, if the are not the same.
  46     if (GCRel->getType() != OrigPtr->getType())
  47       ReplaceGCRel = new BitCastInst(OrigPtr, GCRel->getType(), "cast", GCRel);
  48
  49     // Replace all uses of gc.relocate and delete the gc.relocate
  50     // There maybe unncessary bitcasts back to the OrigPtr type, an instcombine
  51     // pass would clear this up.
  52     GCRel->replaceAllUsesWith(ReplaceGCRel);
  53     GCRel->eraseFromParent();
  54   }
  55   return !GCRelocates.empty();
  56 }
  57
  58 PreservedAnalyses StripGCRelocates::run(Function &F,
  59                                         FunctionAnalysisManager &AM) {
  60   if (!stripGCRelocates(F))
  61     return PreservedAnalyses::all();
  62
  63   // Removing gc.relocate preserves the CFG, but most other analysis probably
  64   // need to re-run.
  65   PreservedAnalyses PA;
  66   PA.preserveSet<CFGAnalyses>();
  67   return PA;
  68 }
  69
  70 namespace {
  71 struct StripGCRelocatesLegacy : public FunctionPass {
  72   static char ID; // Pass identification, replacement for typeid
  73   StripGCRelocatesLegacy() : FunctionPass(ID) {
  74     initializeStripGCRelocatesLegacyPass(*PassRegistry::getPassRegistry());
  75   }
  76
  77   void getAnalysisUsage(AnalysisUsage &Info) const override {}
  78
  79   bool runOnFunction(Function &F) override { return ::stripGCRelocates(F); }
  80 };
  81 char StripGCRelocatesLegacy::ID = 0;
  82 } // namespace
  83
  84 INITIALIZE_PASS(StripGCRelocatesLegacy, "strip-gc-relocates",
  85                 "Strip gc.relocates inserted through RewriteStatepointsForGC",
  86                 true, false)