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 #include "llvm/InitializePasses.h"
22 #include "llvm/Pass.h"
23 
24 using namespace llvm;
25 
26 static bool stripGCRelocates(Function &F) {
27   // Nothing to do for declarations.
28   if (F.isDeclaration())
29     return false;
30   SmallVector<GCRelocateInst *, 20> GCRelocates;
31   // TODO: We currently do not handle gc.relocates that are in landing pads,
32   // i.e. not bound to a single statepoint token.
33   for (Instruction &I : instructions(F)) {
34     if (auto *GCR = dyn_cast<GCRelocateInst>(&I))
35       if (isa<GCStatepointInst>(GCR->getOperand(0)))
36         GCRelocates.push_back(GCR);
37   }
38   // All gc.relocates are bound to a single statepoint token. The order of
39   // visiting gc.relocates for deletion does not matter.
40   for (GCRelocateInst *GCRel : GCRelocates) {
41     Value *OrigPtr = GCRel->getDerivedPtr();
42     Value *ReplaceGCRel = OrigPtr;
43 
44     // All gc_relocates are i8 addrspace(1)* typed, we need a bitcast from i8
45     // addrspace(1)* to the type of the OrigPtr, if the are not the same.
46     if (GCRel->getType() != OrigPtr->getType())
47       ReplaceGCRel = new BitCastInst(OrigPtr, GCRel->getType(), "cast", GCRel);
48 
49     // Replace all uses of gc.relocate and delete the gc.relocate
50     // There maybe unncessary bitcasts back to the OrigPtr type, an instcombine
51     // pass would clear this up.
52     GCRel->replaceAllUsesWith(ReplaceGCRel);
53     GCRel->eraseFromParent();
54   }
55   return !GCRelocates.empty();
56 }
57 
58 PreservedAnalyses StripGCRelocates::run(Function &F,
59                                         FunctionAnalysisManager &AM) {
60   if (!stripGCRelocates(F))
61     return PreservedAnalyses::all();
62 
63   // Removing gc.relocate preserves the CFG, but most other analysis probably
64   // need to re-run.
65   PreservedAnalyses PA;
66   PA.preserveSet<CFGAnalyses>();
67   return PA;
68 }
69 
70 namespace {
71 struct StripGCRelocatesLegacy : public FunctionPass {
72   static char ID; // Pass identification, replacement for typeid
73   StripGCRelocatesLegacy() : FunctionPass(ID) {
74     initializeStripGCRelocatesLegacyPass(*PassRegistry::getPassRegistry());
75   }
76 
77   void getAnalysisUsage(AnalysisUsage &Info) const override {}
78 
79   bool runOnFunction(Function &F) override { return ::stripGCRelocates(F); }
80 };
81 char StripGCRelocatesLegacy::ID = 0;
82 } // namespace
83 
84 INITIALIZE_PASS(StripGCRelocatesLegacy, "strip-gc-relocates",
85                 "Strip gc.relocates inserted through RewriteStatepointsForGC",
86                 true, false)
87