//===- SPIRVLowerMemmove.cpp - Lower llvm.memmove to llvm.memcpys ---------===//
//
//                     The LLVM/SPIRV Translator
//
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//===----------------------------------------------------------------------===//
//
// This file implements lowering llvm.memmove into several llvm.memcpys.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "spvmemmove"

#include "SPIRVInternal.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Verifier.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"

using namespace llvm;
using namespace SPIRV;

namespace SPIRV {
cl::opt<bool> SPIRVLowerMemmoveValidate(
    "spvmemmove-validate",
    cl::desc("Validate module after lowering llvm.memmove instructions into "
             "llvm.memcpy"));

class SPIRVLowerMemmove : public ModulePass,
                          public InstVisitor<SPIRVLowerMemmove> {
public:
  SPIRVLowerMemmove() : ModulePass(ID), Context(nullptr) {
    initializeSPIRVLowerMemmovePass(*PassRegistry::getPassRegistry());
  }
  virtual void visitMemMoveInst(MemMoveInst &I) {
    IRBuilder<> Builder(I.getParent());
    Builder.SetInsertPoint(&I);
    auto *Dest = I.getRawDest();
    auto *Src = I.getRawSource();
    auto *SrcTy = Src->getType();
    if (!isa<ConstantInt>(I.getLength()))
      // ToDo: for non-constant length, could use a loop to copy a
      // fixed length chunk at a time. For now simply fail
      report_fatal_error("llvm.memmove of non-constant length not supported",
                         false);
    auto *Length = cast<ConstantInt>(I.getLength());
    auto *S = Src;
    // The source could be bit-cast or addrspacecast from another type,
    // need the original type for the allocation of the temporary variable
    while (isa<BitCastInst>(S) || isa<AddrSpaceCastInst>(S))
      S = cast<CastInst>(S)->getOperand(0);
    SrcTy = S->getType();
    MaybeAlign Align = I.getSourceAlign();
    auto Volatile = I.isVolatile();
    Value *NumElements = nullptr;
    uint64_t ElementsCount = 1;
    if (SrcTy->isArrayTy()) {
      NumElements = Builder.getInt32(SrcTy->getArrayNumElements());
      ElementsCount = SrcTy->getArrayNumElements();
    }
    if (((ElementsCount > 1) && (Mod->getDataLayout().getTypeSizeInBits(
                                     SrcTy->getPointerElementType()) *
                                     ElementsCount !=
                                 Length->getZExtValue() * 8)) ||
        ((ElementsCount == 1) &&
         (Mod->getDataLayout().getTypeSizeInBits(
              SrcTy->getPointerElementType()) < Length->getZExtValue() * 8)))
      report_fatal_error("Size of the memcpy should match the allocated memory",
                         false);

    auto *Alloca =
        Builder.CreateAlloca(SrcTy->getPointerElementType(), NumElements);
    if (Align.hasValue()) {
      Alloca->setAlignment(Align.getValue());
    }
    Builder.CreateLifetimeStart(Alloca);
    Builder.CreateMemCpy(Alloca, Align, Src, Align, Length, Volatile);
    auto *SecondCpy = Builder.CreateMemCpy(Dest, I.getDestAlign(), Alloca,
                                           Align, Length, Volatile);
    Builder.CreateLifetimeEnd(Alloca);

    SecondCpy->takeName(&I);
    I.replaceAllUsesWith(SecondCpy);
    I.dropAllReferences();
    I.eraseFromParent();
  }
  bool runOnModule(Module &M) override {
    Context = &M.getContext();
    Mod = &M;
    visit(M);

    if (SPIRVLowerMemmoveValidate) {
      LLVM_DEBUG(dbgs() << "After SPIRVLowerMemmove:\n" << M);
      std::string Err;
      raw_string_ostream ErrorOS(Err);
      if (verifyModule(M, &ErrorOS)) {
        Err = std::string("Fails to verify module: ") + Err;
        report_fatal_error(Err.c_str(), false);
      }
    }
    return true;
  }

  static char ID;

private:
  LLVMContext *Context;
  Module *Mod;
};

char SPIRVLowerMemmove::ID = 0;
} // namespace SPIRV

INITIALIZE_PASS(SPIRVLowerMemmove, "spvmemmove",
                "Lower llvm.memmove into llvm.memcpy", false, false)

ModulePass *llvm::createSPIRVLowerMemmove() { return new SPIRVLowerMemmove(); }
