//===- StripGCRelocates.cpp - Remove gc.relocates inserted by RewriteStatePoints===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// This is a little utility pass that removes the gc.relocates inserted by

// RewriteStatepointsForGC. Note that the generated IR is incorrect,

// but this is useful as a single pass in itself, for analysis of IR, without

// the GC.relocates. The statepoint and gc.result intrinsics would still be

// present.

//===----------------------------------------------------------------------===//

#include "llvm/Transforms/Utils/StripGCRelocates.h"

#include "llvm/IR/Function.h"

#include "llvm/IR/InstIterator.h"

#include "llvm/IR/Instructions.h"

#include "llvm/IR/Statepoint.h"

using namespace llvm;

static bool stripGCRelocates(Function &F) {

  // Nothing to do for declarations.

  if (F.isDeclaration())

    return false;

  SmallVector<GCRelocateInst *, 20> GCRelocates;

  // TODO: We currently do not handle gc.relocates that are in landing pads,

  // i.e. not bound to a single statepoint token.

  for (Instruction &I : instructions(F)) {

    if (auto *GCR = dyn_cast<GCRelocateInst>(&I))

      if (isa<GCStatepointInst>(GCR->getOperand(0)))

        GCRelocates.push_back(GCR);

  }

  // All gc.relocates are bound to a single statepoint token. The order of

  // visiting gc.relocates for deletion does not matter.

  for (GCRelocateInst *GCRel : GCRelocates) {

    Value *OrigPtr = GCRel->getDerivedPtr();

    Value *ReplaceGCRel = OrigPtr;

    // All gc_relocates are i8 addrspace(1)* typed, we need a bitcast from i8

    // addrspace(1)* to the type of the OrigPtr, if the are not the same.

    if (GCRel->getType() != OrigPtr->getType())

      ReplaceGCRel = new BitCastInst(OrigPtr, GCRel->getType(), "cast", GCRel);

    // Replace all uses of gc.relocate and delete the gc.relocate

    // There maybe unncessary bitcasts back to the OrigPtr type, an instcombine

    // pass would clear this up.

    GCRel->replaceAllUsesWith(ReplaceGCRel);

    GCRel->eraseFromParent();

  }

  return !GCRelocates.empty();

}

PreservedAnalyses StripGCRelocates::run(Function &F,

                                        FunctionAnalysisManager &AM) {

  if (!stripGCRelocates(F))

    return PreservedAnalyses::all();

  // Removing gc.relocate preserves the CFG, but most other analysis probably

  // need to re-run.

  PreservedAnalyses PA;

  PA.preserveSet<CFGAnalyses>();

  return PA;

}