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 
25 using namespace llvm;
26 
27 namespace {
28 struct 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 };
39 char StripGCRelocates::ID = 0;
40 }
41 
42 bool 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 (isa<GCStatepointInst>(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 
74 INITIALIZE_PASS(StripGCRelocates, "strip-gc-relocates",
75                 "Strip gc.relocates inserted through RewriteStatepointsForGC",
76                 true, false)
77