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

[Dale Johannesen]

You aren't checking alignment when choosing the new pointer type.
Are you sure this works on machines that don't have misaligned load/ 
store?

In general memcpy handling is highly target specific.  I'd be wary of  
doing too
much in target-independent code, although I think the general idea  
here is OK.

> +      // If MemCpyInst length is 1/2/4/8 bytes then replace memcpy  
> with load/store
> +      ConstantInt *MemOpLength = dyn_cast<ConstantInt> 
> (CI.getOperand(3));
> +      if (isa<MemCpyInst>(MI))
> +        if (MemOpLength) {
> +        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);
> +        }
> +        if (NewPtrTy)
> +        {
> +          Value *Src = InsertCastBefore(Instruction::BitCast,  
> CI.getOperand(2), NewPtrTy, CI);
> +          Value *Dest = InsertCastBefore(Instruction::BitCast,  
> CI.getOperand(1), NewPtrTy, CI);
> +          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);
> +        }
> +      }
>      } else if (isa<MemSetInst>(MI)) {
>        unsigned Alignment = GetOrEnforceKnownAlignment(MI->getDest 
> (), TD);
>        if (MI->getAlignment()->getZExtValue() < Alignment) {
>
> Added: llvm/trunk/test/Transforms/InstCombine/2007-10-10- 
> EliminateMemCpy.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/ 
> InstCombine/2007-10-10-EliminateMemCpy.ll?rev=42864&view=auto
>
> ====================================================================== 
> ========
> --- llvm/trunk/test/Transforms/InstCombine/2007-10-10- 
> EliminateMemCpy.ll (added)
> +++ llvm/trunk/test/Transforms/InstCombine/2007-10-10- 
> EliminateMemCpy.ll Thu Oct 11 12:21:57 2007
> @@ -0,0 +1,18 @@
> +; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep call
> + at .str = internal constant [4 x i8] c"xyz\00"		; <[4 x i8]*> [#uses=1]
> +
> +define void @foo(i8* %P) {
> +entry:
> +	%P_addr = alloca i8*		; <i8**> [#uses=2]
> +	%"alloca point" = bitcast i32 0 to i32		; <i32> [#uses=0]
> +	store i8* %P, i8** %P_addr
> +	%tmp = load i8** %P_addr, align 4		; <i8*> [#uses=1]
> +	%tmp1 = getelementptr [4 x i8]* @.str, i32 0, i32 0		; <i8*>  
> [#uses=1]
> +	call void @llvm.memcpy.i32( i8* %tmp, i8* %tmp1, i32 4, i32 1 )
> +	br label %return
> +
> +return:		; preds = %entry
> +	ret void
> +}
> +
> +declare void @llvm.memcpy.i32(i8*, i8*, i32, i32)
>
>
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