[LLVMdev] Simplifying boolean expressions

[Chris Lattner]

On Wed, 4 May 2005, Vladimir Prus wrote:
> Suppose I have a code like this:
>
>       %tmp.aux = cast bool %tmp.24 to int
>        %tmp.x = xor int  %tmp.aux, 1                    ; negates tmp.24
>        %tmp.xx = cast int %tmp.x to bool
>        %tmp.y = or bool %tmp.xx, %tmp.24          ;  will be always true
>        br bool %tmp.y, label %next6, label %next7
>
> Is there an optimization in LLVM that will recognize that %tmp.y is always
> true, and replace the entire basic block with unconditional jump?
>
> I've tried running 'opt' on the attached file, but did not get the desired
> effect.
>
> The full story is that I'll be generating code like above, and while I
> probably can detect such redundant situation, I was hoping I can save myself
> some work, and just run LLVM optimizer at the produced code.

I will enhance the -instcombine pass to do this, hopefully today.

-Chris

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