[llvm-commits] [llvm] r75531 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/zext-bool-add-sub.ll

[Chris Lattner]

On Jul 13, 2009, at 3:27 PM, Eli Friedman wrote:
> URL: http://llvm.org/viewvc/llvm-project?rev=75531&view=rev
> Log:
> Canonicalize boolean +/- a constant to a select.
>
> (I think it's reasonably clear that we want to have a canonical form  
> for
> constructs like this; if anyone thinks that a select is not the best
> canonical form, please tell me.)

I think "select c, -1, 0" -> "sext c" and  "select c, 0, -1" -> "sext ! 
c" would make sense, what do you think?

> +    // C - zext(bool) -> bool ? C - 1 : C
> +    if (ZExtInst *ZI = dyn_cast<ZExtInst>(Op1))
> +      if (ZI->getSrcTy() == Type::Int1Ty)
> +        return SelectInst::Create(ZI->getOperand(0), SubOne(C,  
> Context), C);

This one seems reasonable though,

-Chris