lib/Transforms/Utils/StripGCRelocates.cpp

   1 //===- StripGCRelocates.cpp - Remove gc.relocates inserted by RewriteStatePoints===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This is a little utility pass that removes the gc.relocates inserted by
  11 // RewriteStatepointsForGC. Note that the generated IR is incorrect,
  12 // but this is useful as a single pass in itself, for analysis of IR, without
  13 // the GC.relocates. The statepoint and gc.result instrinsics would still be
  14 // present.
  15 //===----------------------------------------------------------------------===//
  16
  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/IR/Type.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 (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
  74 INITIALIZE_PASS(StripGCRelocates, "strip-gc-relocates",
  75                 "Strip gc.relocates inserted through RewriteStatepointsForGC",
  76                 true, false)