https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113080
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2023-12-19
Ever confirmed|0 |1
Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot
gnu.org
Status|UNCONFIRMED |ASSIGNED
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed. We're considering the final value replacement of the 't' reduction
expensive. It's
((b_lsm.10_8 + a_lsm.9_9) + t_10(D)) + (b_lsm.10_8 + a_lsm.9_9) * 99
and since there's a shared tree (b_lsm.10_8 + a_lsm.9_9) which we'd
duplicate (materializing as GIMPLE fails to immediately CSE).
bool
expression_expensive_p (tree expr, bool *cond_overflow_p)
{
hash_map<tree, uint64_t> cache;
uint64_t expanded_size = 0;
*cond_overflow_p = false;
return (expression_expensive_p (expr, cond_overflow_p, cache, expanded_size)
|| expanded_size > cache.elements ());
}
where expanded_size is 5 but cache.elements () is 4 (we grow because
of unsharing).
Allowing a little bit of unsharing fixes this. Even better would be of
course an unsharing mechanism that would "save" the shared parts to
a gimple sequence (we need to unshare because gimplification is destructive
and the SCEV result contains trees that can be part of the SCEV cache
which we may not alter).
