NVPTXLowerAlloca.cpp

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//===-- NVPTXLowerAlloca.cpp - Make alloca to use local memory =====--===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// For all alloca instructions, and add a pair of cast to local address for
// each of them. For example,
//
//   %A = alloca i32
//   store i32 0, i32* %A ; emits st.u32
//
// will be transformed to
//
//   %A = alloca i32
//   %Local = addrspacecast i32* %A to i32 addrspace(5)*
//   %Generic = addrspacecast i32 addrspace(5)* %A to i32*
//   store i32 0, i32 addrspace(5)* %Generic ; emits st.local.u32
//
// And we will rely on NVPTXInferAddressSpaces to combine the last two
// instructions.
//
//===----------------------------------------------------------------------===//

#include "NVPTX.h"
#include "NVPTXUtilities.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/Pass.h"

using namespace llvm;

namespace llvm {
void initializeNVPTXLowerAllocaPass(PassRegistry &);
}

namespace {
class NVPTXLowerAlloca : public BasicBlockPass {
  bool runOnBasicBlock(BasicBlock &BB) override;

public:
  static char ID; // Pass identification, replacement for typeid
  NVPTXLowerAlloca() : BasicBlockPass(ID) {}
  StringRef getPassName() const override {
    return "convert address space of alloca'ed memory to local";
  }
};
} // namespace

char NVPTXLowerAlloca::ID = 1;

INITIALIZE_PASS(NVPTXLowerAlloca, "nvptx-lower-alloca",
                "Lower Alloca", false, false)

// =============================================================================
// Main function for this pass.
// =============================================================================
bool NVPTXLowerAlloca::runOnBasicBlock(BasicBlock &BB) {
  if (skipBasicBlock(BB))
    return false;

  bool Changed = false;
  for (auto &I : BB) {
    if (auto allocaInst = dyn_cast<AllocaInst>(&I)) {
      Changed = true;
      auto PTy = dyn_cast<PointerType>(allocaInst->getType());
      auto ETy = PTy->getElementType();
      auto LocalAddrTy = PointerType::get(ETy, ADDRESS_SPACE_LOCAL);
      auto NewASCToLocal = new AddrSpaceCastInst(allocaInst, LocalAddrTy, "");
      auto GenericAddrTy = PointerType::get(ETy, ADDRESS_SPACE_GENERIC);
      auto NewASCToGeneric = new AddrSpaceCastInst(NewASCToLocal,
                                                    GenericAddrTy, "");
      NewASCToLocal->insertAfter(allocaInst);
      NewASCToGeneric->insertAfter(NewASCToLocal);
      for (Value::use_iterator UI = allocaInst->use_begin(),
                                UE = allocaInst->use_end();
            UI != UE; ) {
        // Check Load, Store, GEP, and BitCast Uses on alloca and make them
        // use the converted generic address, in order to expose non-generic
        // addrspacecast to NVPTXInferAddressSpaces. For other types
        // of instructions this is unnecessary and may introduce redundant
        // address cast.
        const auto &AllocaUse = *UI++;
        auto LI = dyn_cast<LoadInst>(AllocaUse.getUser());
        if (LI && LI->getPointerOperand() == allocaInst && !LI->isVolatile()) {
          LI->setOperand(LI->getPointerOperandIndex(), NewASCToGeneric);
          continue;
        }
        auto SI = dyn_cast<StoreInst>(AllocaUse.getUser());
        if (SI && SI->getPointerOperand() == allocaInst && !SI->isVolatile()) {
          SI->setOperand(SI->getPointerOperandIndex(), NewASCToGeneric);
          continue;
        }
        auto GI = dyn_cast<GetElementPtrInst>(AllocaUse.getUser());
        if (GI && GI->getPointerOperand() == allocaInst) {
          GI->setOperand(GI->getPointerOperandIndex(), NewASCToGeneric);
          continue;
        }
        auto BI = dyn_cast<BitCastInst>(AllocaUse.getUser());
        if (BI && BI->getOperand(0) == allocaInst) {
          BI->setOperand(0, NewASCToGeneric);
          continue;
        }
      }
    }
  }
  return Changed;
}

BasicBlockPass *llvm::createNVPTXLowerAllocaPass() {
  return new NVPTXLowerAlloca();
}