https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97707
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
CC| |jakub at gcc dot gnu.org
Blocks| |53947
Target| |x86_64-*-* i?86-*-*
Ever confirmed|0 |1
Last reconfirmed| |2020-11-04
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
-mprefer-vector-width=256 means it _prefers_ AVX256 but then in case
vectorization fails (for whatever bogus reason) with AVX256 it will still try
AVX512:
static unsigned int
ix86_autovectorize_vector_modes (vector_modes *modes, bool all)
{
if (TARGET_AVX512F && !TARGET_PREFER_AVX256)
{
modes->safe_push (V64QImode);
modes->safe_push (V32QImode);
modes->safe_push (V16QImode);
}
else if (TARGET_AVX512F && all)
{
modes->safe_push (V32QImode);
modes->safe_push (V16QImode);
modes->safe_push (V64QImode);
}
the odd thing is that the dumps suggest we use V4DFmode. We use a VF of 8
because of V8SI and it seems that call vectorization then chooses the
larger vector mode because it is supported - it seems to have its own
idea of costing there (probably reasonable).
Do you think this is a bad idea?
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations
