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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/96135] [9/10/11 regression] bswap not
 detected by bswap pass, unexpected results between optimization levels
Date: Thu, 11 Mar 2021 09:07:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96135

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Created attachment 50361
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D50361&action=3Dedit
WIP

On current trunk at -O3 f() again works via store-merging / vectorizing:

-  _21 =3D {_3, _4, _5, _6, _7, _8, _9, _10};
+  bswapsrc_22 =3D (long unsigned int) i_2(D);
+  bswapdst_19 =3D __builtin_bswap64 (bswapsrc_22);
+  _21 =3D VIEW_CONVERT_EXPR<vector(8) char>(bswapdst_19);

but g() does not, because init_symbolic_number doesn't like non-integral ty=
pes.
Fixing that generates

_Z1gd:
.LFB2:
        .cfi_startproc
        movq    %xmm0, %rax
        bswap   %rax
        ret

but with -m32 it has the issue that we bswap only the lower part since
vectorizing produced two vector CTORs.  So we'd need to use a BIT_FIELD_REF
to extract the integer representation.

WIP patch attached.=