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From: "b.buschinski at googlemail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/105740] New: missed optimization switch
 transformation for conditions with duplicate conditions
Date: Thu, 26 May 2022 11:26:46 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105740

            Bug ID: 105740
           Summary: missed optimization switch transformation for
                    conditions with duplicate conditions
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: b.buschinski at googlemail dot com
  Target Milestone: ---

Created attachment 53037
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D53037&action=3Dedit
Attached code + asm from the compiler explorer link

Compiler Explorer Link: https://godbolt.org/z/q76s99Gj9

The code on the left does not generate a switch statement.
The code on the right does generate a switch statement.

The code works similar, the only difference is that the duplicate "f->len >=
 3"
check is moved to the top for the "right" version.

The compiler explorer code is actually a minimized version of the code I wo=
rk
on (with way more conditions in a hot code path), where I can not easily mo=
ve
the length check to the top, because the "f-> len > 3 && ..." is done in a =
very
complicated macro, but that's just details.

I expected both code versions to generate the same assembler.

Tested with GCC-12.1 and 11.3. 10.3 does not generate a switch version for =
both
versions, as only 11 got this nice feature.
On x86_64 Linux.


Please let me know if you need any additional details or if this report was
useful at all.=