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 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)