[llvm-commits] [llvm] r42864 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/2007-10-10-EliminateMemCpy.ll

[Dan Gohman]

> +      // If MemCpyInst length is 1/2/4/8 bytes then replace memcpy with load/store

Neat!

> +      ConstantInt *MemOpLength = dyn_cast<ConstantInt>(CI.getOperand(3));
> +      if (isa<MemCpyInst>(MI))
> +        if (MemOpLength) {

Can you replace these two if statements with

     if (isa<MemCpyInst>(MI) && MemOpLength) {

?

Then the indentation of what follows won't be wrong either :-)

> +        unsigned Size = MemOpLength->getZExtValue();
> +        unsigned Align = cast<ConstantInt>(CI.getOperand(4))->getZExtValue();
> +        const PointerType *PTy = cast<PointerType>(CI.getOperand(1)->getType());
> +        const Type *MTy = PTy->getElementType();
> +        PointerType *NewPtrTy = NULL;
> +        if (MTy == Type::Int8Ty) {
> +          if (Size == 8)
> +            NewPtrTy = PointerType::get(Type::Int64Ty);
> +          else if (Size == 4)
> +            NewPtrTy = PointerType::get(Type::Int32Ty);
> +          else if (Size == 2)
> +            NewPtrTy = PointerType::get(Type::Int16Ty);
> +          else if (Size == 1)
> +            NewPtrTy = PointerType::get(Type::Int8Ty);
> +        } else if (MTy == Type::Int16Ty) {
> +          if (Size == 4)
> +            NewPtrTy = PointerType::get(Type::Int64Ty);
> +          else if (Size == 2)
> +            NewPtrTy = PointerType::get(Type::Int32Ty);
> +          else if (Size == 1)
> +            NewPtrTy = PointerType::get(Type::Int16Ty);
> +        } else if (MTy == Type::Int32Ty) {
> +          if (Size == 2)
> +            NewPtrTy = PointerType::get(Type::Int64Ty);
> +          else if (Size == 1)
> +            NewPtrTy = PointerType::get(Type::Int32Ty);
> +        } else if (MTy == Type::Int64Ty) {
> +          if (Size == 1)
> +            NewPtrTy = PointerType::get(Type::Int64Ty);
> +        }

It'd be great it this worked for non-scalar-integer types as well.

Maybe you could do something like (warning, untested):

  if (Size == 1 && MTy->isFirstClassType())
    NewPtrTy = PointerType::get(MTy)
  else {
    CopySize = Size * TD->getABITypeSizeInBits(MTy);
    if (CopySize == 8 || CopySize == 4 || CopySize == 2 || CopySize == 1)
      NewPtrTy = PointerType::get(IntegerType::get(CopySize));
  }

?

> +        if (NewPtrTy)
> +        {

LLVM style.

> +          Value *Src = InsertCastBefore(Instruction::BitCast, CI.getOperand(2), NewPtrTy, CI);
> +          Value *Dest = InsertCastBefore(Instruction::BitCast, CI.getOperand(1), NewPtrTy, CI);

This is more than 80 columns.

> +          Value *L = new LoadInst(Src, "tmp", false, Align, &CI);
> +          Value *NS = new StoreInst(L, Dest, false, Align, &CI);
> +          CI.replaceAllUsesWith(NS);
> +          Changed = true;
> +          return EraseInstFromFunction(CI);
> +        }
> +      }