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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/103393] [12 Regression] Generating 256bit register
 usage with -mprefer-avx128 -mprefer-vector-width=128
Date: Fri, 26 Nov 2021 12:26:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103393

--- Comment #21 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note using MOVE_RATIO in gimple-fold but then always emitting just a single
stmt and not honoring MOVE_MAX on that is fishy - you seem to be expecting =
RTL
expansion to fix up but that's clearly not happening (for the reasons Jakub=
 is
talking about).  So one can either teach gimple-fold to emit multiple
load/store
stmts or go back to MOVE_MAX.  Note multiple load/store stmts wasn't done on
purpose to not complicate the code and bring in additional cost considerati=
ons
(size and register pressure).  But sure, in principle the whole *_by_pieces
machinery could be brought to GIMPLE and we could leave RTL expansion of
memcpy/memset and friends to always emit calls or use optabs.=