Re: Update on A * (1 - uitofp i1 C) + B * uitofp i1 C —> select C, B, A

[Evan Cheng]

LGTM.

Evan

Sent from my iPad

On May 21, 2013, at 7:03 PM, Jean-Luc Duprat <jduprat at apple.com> wrote:

> This is an update to a previous commit (r181216).
> 
> The earlier change list introduced the following inst combines:
> B * (uitofp i1 C) —> select C, B, 0
> A * (1 - uitofp i1 C) —> select C, 0, A
> select C, 0, B + select C, A, 0 —> select C, A, B
> 
> Together these 3 changes would simplify :
> A * (1 - uitofp i1 C) + B * uitofp i1 C 
> down to :
> select C, B, A
> 
> In practice we found that the first two substitutions can have a negative effect on performance, because they reduce opportunities to use FMA contractions; between the two options FMAs are often the better choice.  This change list amends the previous one to enable just these inst combines:
> 
> select C, B, 0 + select C, 0, A —> select C, B, A
> A * (1 - uitofp i1 C) + B * uitofp i1 C —> select C, B, A
> 
> 
> Feedback appreciated,
> 
> JL
> 
> 
> <blendWithoutCompromisingFMA.patch>
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