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From: "law at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/103278] New: [12 Regression] Recent change to
 cddce inhibits switch optimization
Date: Tue, 16 Nov 2021 17:16:21 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103278

            Bug ID: 103278
           Summary: [12 Regression] Recent change to cddce inhibits switch
                    optimization
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: law at gcc dot gnu.org
  Target Milestone: ---

On iq2000-elf this change:

commit 045206450386bcd774db3bde0c696828402361c6
Author: Richard Biener <rguenther@suse.de>
Date:   Fri Nov 12 10:21:22 2021 +0100

    tree-optimization/102880 - improve CD-DCE
[ ... ]

Is inhibiting switch optimization for tree-ssa/if-to-switch-3.c from conver=
ting
an if statement into a switch statement:

/* { dg-do compile } */
/* { dg-options "-O2 -fdump-tree-iftoswitch-optimized" } */

int IsMySuperRandomChar(int aChar)
{
  return aChar =3D=3D 0x0009 || aChar =3D=3D 0x000A ||
         aChar =3D=3D 0x000C || aChar =3D=3D 0x000D ||
         aChar =3D=3D 0x0020 || aChar =3D=3D 0x0030;
}

/* { dg-final { scan-tree-dump "Condition chain with \[^\n\r]\* BBs transfo=
rmed
into a switch statement." "iftoswitch" } } */


After today's cd-dce change we no longer turn that into a switch:

Before:

;; Canonical GIMPLE case clusters: 9-10 12 13 32 48
;; JT can be built: JT(values:6 comparisons:10 range:40 density: 25.00%):9-=
48
j.c:8:26: optimized: Condition chain with 3 BBs transformed into a switch
statement.


After:
;; Canonical GIMPLE case clusters: 9-10 12-13 32 48=