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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/102543] New: -march=cascadelake performs odd alignment
 peeling
Date: Thu, 30 Sep 2021 10:13:23 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102543

            Bug ID: 102543
           Summary: -march=3Dcascadelake performs odd alignment peeling
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

For gcc.dg/torture/pr65270-1.c we choose to misalign an aligned store + load
combo for runtime aligning a single load because we have (skylake_cost):

  {6, 6, 6, 10, 20},                    /* cost of loading SSE register
                                           in 32bit, 64bit, 128bit, 256bit =
and
512bit */
  {8, 8, 8, 12, 24},                    /* cost of storing SSE register
                                           in 32bit, 64bit, 128bit, 256bit =
and
512bit */
  {6, 6, 6, 10, 20},                    /* cost of unaligned loads.  */
  {8, 8, 8, 8, 16},                     /* cost of unaligned stores.  */

which means that an unaligned store is cheaper than an aligned store for
%ymm and even more so for %zmm!??=