[Bug tree-optimization/113441] [14 Regression] Fail to fold the last element with multiple loop since g:2efe3a7de0107618397264017fb045f237764cc7

["rsandifo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113441

--- Comment #36 from Richard Sandiford <rsandifo at gcc dot gnu.org> ---
Created attachment 57602
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57602&action=edit
proof-of-concept patch to suppress peeling for gaps

This patch does what I suggested in the previous comment: if the loop needs
peeling for gaps, try again without that, and pick the better loop.  It seems
to restore the original style of code for SVE.

A more polished version would be a bit smarter about when to retry.  E.g. it's
pointless if the main loop already operates on full vectors (i.e. if peeling 1
iteration is natural in any case).  Perhaps the condition should be that either
(a) the number of epilogue iterations is known to be equal to the VF of the
main loop or (b) the target is known to support partial vectors for the loop's
vector_mode.

Any thoughts?