StripGCRelocates.cpp revision 360784 
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/InitializePasses.h"
22#include "llvm/Pass.h"
23#include "llvm/Support/raw_ostream.h"
24
25using namespace llvm;
26
27namespace {
28struct StripGCRelocates : public FunctionPass {
29  static char ID; // Pass identification, replacement for typeid
30  StripGCRelocates() : FunctionPass(ID) {
31    initializeStripGCRelocatesPass(*PassRegistry::getPassRegistry());
32  }
33
34  void getAnalysisUsage(AnalysisUsage &Info) const override {}
35
36  bool runOnFunction(Function &F) override;
37
38};
39char StripGCRelocates::ID = 0;
40}
41
42bool StripGCRelocates::runOnFunction(Function &F) {
43  // Nothing to do for declarations.
44  if (F.isDeclaration())
45    return false;
46  SmallVector<GCRelocateInst *, 20> GCRelocates;
47  // TODO: We currently do not handle gc.relocates that are in landing pads,
48  // i.e. not bound to a single statepoint token.
49  for (Instruction &I : instructions(F)) {
50    if (auto *GCR = dyn_cast<GCRelocateInst>(&I))
51      if (isStatepoint(GCR->getOperand(0)))
52        GCRelocates.push_back(GCR);
53  }
54  // All gc.relocates are bound to a single statepoint token. The order of
55  // visiting gc.relocates for deletion does not matter.
56  for (GCRelocateInst *GCRel : GCRelocates) {
57    Value *OrigPtr = GCRel->getDerivedPtr();
58    Value *ReplaceGCRel = OrigPtr;
59
60    // All gc_relocates are i8 addrspace(1)* typed, we need a bitcast from i8
61    // addrspace(1)* to the type of the OrigPtr, if the are not the same.
62    if (GCRel->getType() != OrigPtr->getType())
63      ReplaceGCRel = new BitCastInst(OrigPtr, GCRel->getType(), "cast", GCRel);
64
65    // Replace all uses of gc.relocate and delete the gc.relocate
66    // There maybe unncessary bitcasts back to the OrigPtr type, an instcombine
67    // pass would clear this up.
68    GCRel->replaceAllUsesWith(ReplaceGCRel);
69    GCRel->eraseFromParent();
70  }
71  return !GCRelocates.empty();
72}
73
74INITIALIZE_PASS(StripGCRelocates, "strip-gc-relocates",
75                "Strip gc.relocates inserted through RewriteStatepointsForGC",
76                true, false)
77