[LLVMdev] IRBuilder and "ad hoc" optimizations

[Krzysztof Parzyszek]

On 4/23/2015 3:50 AM, Paweł Bylica wrote:
> Hi LLVM,
>
> IRBuilder can fold constants (that behaviour can be controlled by Folder
> type). What do you think about optionally allow IRBuilder to eliminate
> no-op instructions like `add %a, 0` or `memcpy(%a, %b, 0)`?
>
> - Paweł
>

You mean in cases when the builder is creating an instruction that is a 
no-op?  The problem may be with handling cases like this:

MachineInstr *MI = BuildMI(ADD, DstReg).addReg(SrcReg).addImm(0);
if (C != 0)
   MI->getOperand(2).setImm(C);

If the builder doesn't create the initial SrcReg+0, then this code will 
fail.

-Krzysztof

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