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