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)
76