[PATCH] Teach instcombine how to combine multiply of constant splat of known power-of-2

[Andrea_DiBiagio at sn.scee.net]

Hi Rafael,

Rafael Espíndola <rafael.espindola at gmail.com> wrote on 29/05/2013 
20:18:46:

> The testcases take and return scalars that are bitcast to and from a
> vector. For example, you have:
> 
> define i32 @AddToSelf_i8(i32 %InVec)  {
> entry:
>   %0 = bitcast i32 %InVec to <4 x i8>
>   %mul = mul <4 x i8> %0, <i8 2, i8 2, i8 2, i8 2>
>   %1 = bitcast <4 x i8> %mul to i32
>   ret i32 %1
> }
> 
> Why not the simpler:
> 
> define <4 x i8> @AddToSelf_i8(<4 x i8> %InVec)  {
> entry:
>   %mul = mul <4 x i8> %InVec, <i8 2, i8 2, i8 2, i8 2>
>   ret <4 x i8> %mul
> }
> 
> A really small nit is that you don't need the "-o -" in the command
> line, opt will print to stdout when reading from stdin.
> 

I simplified the test case removing all the unnecessary bitcasts.
The test case now definitely looks better, thanks for the feedback!
I also removed the "-o -" in the command line as you suggested.

> The current style is to start function names with lower case and they
> should be verb phrases
> (http://llvm.org/docs/CodingStandards.html#name-types-functions-
> variables-and-enumerators-properly),
> so please use something like getLogBase2Vector.
> 
> It looks like the function is only ever used with ConstantDataVector,
> so please use
> 
> static Constant *getLogBase2Vector(const ConstantDataVector *C)
> 
> as the signature and simplify.

True, sorry about that..
I renamed the function into `getLogBase2Vector' and I simplified the body 
of that
function since now it expects a ConstantDataVector in input.

The updated patch can be found in attachment to this email.

P.s.: I forgot to mention on my initial post that I don't have
commit access to the repository.

Thanks,
Andrea Di Biagio
SN Systems - Sony Computer Entertainment Group



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