[Bug rtl-optimization/109311] New: [13 Regression] bb_is_just_return miss to realize some bb from r13-6873-g776a5bb5894315

[Bug rtl-optimization/109311] New: [13 Regression] bb_is_just_return miss to realize some bb from r13-6873-g776a5bb5894315

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109311

            Bug ID: 109311
           Summary: [13 Regression] bb_is_just_return miss to realize some
                    bb from r13-6873-g776a5bb5894315
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: critical
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: linkw at gcc dot gnu.org
  Target Milestone: ---

Commit r13-6873-g776a5bb5894315 changed BB insns walking order under the
assumption that the handlings in the loop is order independent. But
unfortunately some failures shows it's not.

For a BB:

   15: L15:
   20: NOTE_INSN_BASIC_BLOCK 5
   19: use %3:SI
   32: NOTE_INSN_EPILOGUE_BEG
   33: simple_return
;;  succ:       EXIT

Previously function bb_is_just_return would return true while now it returns
false, since backward walking will meet return insn first, the USE insn isn't
considered as one use to be in *use but instead is taken as unexpected insn
then return false.

By adjusting it not to check !*ret for use can workaround it, 

         if (!*ret && ANY_RETURN_P (pat))
           *ret = insn;
-        else if (!*ret && !*use && GET_CODE (pat) == USE
+        else if (!*use && GET_CODE (pat) == USE
             && REG_P (XEXP (pat, 0))
             && REG_FUNCTION_VALUE_P (XEXP (pat, 0)))
           *use = insn;

but I'm not sure if there is some reason to check both !*ret && !*use, such as
to exclude something like:

    simple_return
    use %3:SI

[Bug rtl-optimization/109311] [13 Regression] bb_is_just_return miss to realize some bb from r13-6873-g776a5bb5894315

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109311

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
                 CC|                            |bergner at gcc dot gnu.org,
                   |                            |rguenth at gcc dot gnu.org,
                   |                            |segher at gcc dot gnu.org,
                   |                            |seurer at linux dot vnet.ibm.com
             Target|                            |powerpc*-linux-gnu

--- Comment #1 from Kewen Lin <linkw at gcc dot gnu.org> ---
Failures on both LE and BE:

< FAIL: gcc.target/powerpc/conditional-return.c scan-assembler \\\\mbeqlr\\\\M
< FAIL: gcc.target/powerpc/vec-stril-11.c scan-assembler-times
\\\\mvstribr\\\\. 2
< FAIL: gcc.target/powerpc/vec-stril-13.c scan-assembler-times
\\\\mvstrihr\\\\. 2
< FAIL: gcc.target/powerpc/vec-stril-15.c scan-assembler-times
\\\\mvstrihr\\\\. 2
< FAIL: gcc.target/powerpc/vec-stril-9.c scan-assembler-times \\\\mvstribr\\\\.
2
< FAIL: gcc.target/powerpc/vec-strir-11.c scan-assembler-times
\\\\mvstribl\\\\. 2
< FAIL: gcc.target/powerpc/vec-strir-13.c scan-assembler-times
\\\\mvstrihl\\\\. 2
< FAIL: gcc.target/powerpc/vec-strir-15.c scan-assembler-times
\\\\mvstrihl\\\\. 2
< FAIL: gcc.target/powerpc/vec-strir-9.c scan-assembler-times \\\\mvstribl\\\\.
2

[Bug rtl-optimization/109311] [13 Regression] bb_is_just_return miss to realize some bb from r13-6873-g776a5bb5894315

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109311

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED
   Target Milestone|---                         |13.0
   Last reconfirmed|                            |2023-03-28
     Ever confirmed|0                           |1
           Priority|P2                          |P1

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Doh - thanks for reporting, I'll revert the offending revision and revisit
during stage1.  I think for the forward walk it indeed wants to reject
use-after-return, so to make it identical for the backward walk the check
then should be *ret && !*use instead of !*ret && !*use I think.

[Bug rtl-optimization/109311] [13 Regression] bb_is_just_return miss to realize some bb from r13-6873-g776a5bb5894315

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109311

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:b462947dae9f8c0dd7c11165ccfdf6acd6f12a1c

commit r13-6889-gb462947dae9f8c0dd7c11165ccfdf6acd6f12a1c
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Mar 28 09:31:36 2023 +0200

    Revert "rtl-optimization/109237 - speedup bb_is_just_return"

    This reverts commit 776a5bb5894315ab144dc74222fc580fde8fdd87.

            PR rtl-optimization/109311
            * cfgcleanup.cc (bb_is_just_return): Revert previous change.

[Bug rtl-optimization/109311] [13 Regression] bb_is_just_return miss to realize some bb from r13-6873-g776a5bb5894315

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109311

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.