Re: [PATCH] middle-end/114070 - VEC_COND_EXPR folding

[Jeff Law <jeffreyalaw@gmail.com>]

On 2/29/24 01:35, Richard Biener wrote:
> The following amends the PR114070 fix to optimistically allow
> the folding when we cannot expand the current vec_cond using
> vcond_mask and we're still before vector lowering.  This leaves
> a small window between vectorization and lowering where we could
> break vec_conds that can be expanded via vcond{,u,eq}, most
> susceptible is the loop unrolling pass which applies VN and thus
> possibly folding to the unrolled body of a vectorized loop.
> 
> This gets back the folding for targets that cannot do vectorization.
> It doesn't get back the folding for x86 with AVX512 for example
> since that can handle the original IL but not the folded since
> it misses some vcond_mask expanders.
> 
> Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
> 
> As said for stage1 I want to move vector lowering before vectorization.
> While I'm not entirely happy with this patch it forces us into the
> correct direction, getting vcond_mask and vcmp{,u,eq} patterns
> implemented.  We could use canonicalize_math_p () to close the
> vectorizer -> vector lowering gap but this only works when that
> pass is run (not with -Og or when disabled).  We could add a new
> PROP_vectorizer_il and disable the folding if the vectorizer ran.
> 
> Or we could simply live with the regression.
> 
> Any preferences?
Not really.  As I think I said, I consider the regression insignificant 
an I could certainly live with it.

jeff