[llvm] r182499 - This is an update to a previous commit (r181216).

[Rafael Espíndola]

On 22 May 2013 14:29, Jean-Luc Duprat <jduprat at apple.com> wrote:
> Author: jduprat
> Date: Wed May 22 13:29:31 2013
> New Revision: 182499
>
> URL: http://llvm.org/viewvc/llvm-project?rev=182499&view=rev
> Log:
> 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:

Why not codegen those selects to FMA instead? The select looks like a
more natural canonical form.

Cheers,
Rafael