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
  22 using namespace llvm;
  23
  24 static bool stripGCRelocates(Function &F) {
  25   // Nothing to do for declarations.
  26   if (F.isDeclaration())
  27     return false;
  28   SmallVector<GCRelocateInst *, 20> GCRelocates;
  29   // TODO: We currently do not handle gc.relocates that are in landing pads,
  30   // i.e. not bound to a single statepoint token.
  31   for (Instruction &I : instructions(F)) {
  32     if (auto *GCR = dyn_cast<GCRelocateInst>(&I))
  33       if (isa<GCStatepointInst>(GCR->getOperand(0)))
  34         GCRelocates.push_back(GCR);
  35   }
  36   // All gc.relocates are bound to a single statepoint token. The order of
  37   // visiting gc.relocates for deletion does not matter.
  38   for (GCRelocateInst *GCRel : GCRelocates) {
  39     Value *OrigPtr = GCRel->getDerivedPtr();
  40     Value *ReplaceGCRel = OrigPtr;
  41
  42     // All gc_relocates are i8 addrspace(1)* typed, we need a bitcast from i8
  43     // addrspace(1)* to the type of the OrigPtr, if the are not the same.
  44     if (GCRel->getType() != OrigPtr->getType())
  45       ReplaceGCRel = new BitCastInst(OrigPtr, GCRel->getType(), "cast", GCRel);
  46
  47     // Replace all uses of gc.relocate and delete the gc.relocate
  48     // There maybe unncessary bitcasts back to the OrigPtr type, an instcombine
  49     // pass would clear this up.
  50     GCRel->replaceAllUsesWith(ReplaceGCRel);
  51     GCRel->eraseFromParent();
  52   }
  53   return !GCRelocates.empty();
  54 }
  55
  56 PreservedAnalyses StripGCRelocates::run(Function &F,
  57                                         FunctionAnalysisManager &AM) {
  58   if (!stripGCRelocates(F))
  59     return PreservedAnalyses::all();
  60
  61   // Removing gc.relocate preserves the CFG, but most other analysis probably
  62   // need to re-run.
  63   PreservedAnalyses PA;
  64   PA.preserveSet<CFGAnalyses>();
  65   return PA;
  66 }