[Bug tree-optimization/105834] New: Dead Code Elimination Regression at -O2 (trunk vs. 12.1.0)

[Bug tree-optimization/105834] New: Dead Code Elimination Regression at -O2 (trunk vs. 12.1.0)

[theodort at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105834

            Bug ID: 105834
           Summary: Dead Code Elimination Regression at -O2 (trunk vs.
                    12.1.0)
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: theodort at inf dot ethz.ch
  Target Milestone: ---

cat case.c
static int a, b;

void foo();

int main() {
    for (int c = 0; c < 2; c = c + (unsigned)3)
        if (a)
            for (;;)
                if (c > 0)
                    b = 0;
    if (b)
        foo();
}

`gcc-1982fe2692b6c3b7f969ffc4edac59f9d4359e91 (trunk) -O2` can not eliminate
`foo` but `gcc-releases/gcc-12.1.0 -O2` can.

`gcc-1982fe2692b6c3b7f969ffc4edac59f9d4359e91 (trunk) -O2 -S -o /dev/stdout
case.c`
--------- OUTPUT ---------
main:
.LFB0:
        .cfi_startproc
        movl    b(%rip), %ecx
        testl   %ecx, %ecx
        jne     .L8
        xorl    %eax, %eax
        ret
.L8:
        pushq   %rax
        .cfi_def_cfa_offset 16
        xorl    %eax, %eax
        call    foo
        xorl    %eax, %eax
        popq    %rdx
        .cfi_def_cfa_offset 8
        ret
---------- END OUTPUT ---------


`gcc-releases/gcc-12.1.0 -O2 -S -o /dev/stdout case.c`
--------- OUTPUT ---------
main:
.LFB0:
        .cfi_startproc
        xorl    %eax, %eax
        ret
---------- END OUTPUT ---------


Bisects to:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=98e475a8f58ca3ba6e9bd5c9276efce4236f5d26

[Bug tree-optimization/105834] [13 Regression] Dead Code Elimination Regression at -O2 (trunk vs. 12.1.0)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105834

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Dead Code Elimination       |[13 Regression] Dead Code
                   |Regression at -O2 (trunk    |Elimination Regression at
                   |vs. 12.1.0)                 |-O2 (trunk vs. 12.1.0)
           Keywords|                            |missed-optimization
   Target Milestone|---                         |13.0

[Bug tree-optimization/105834] [13 Regression] Dead Code Elimination Regression at -O2 (trunk vs. 12.1.0)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105834

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2023-02-21
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  Not analyzed yet.

[Bug tree-optimization/105834] [13 Regression] Dead Code Elimination Regression at -O2 (trunk vs. 12.1.0)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105834

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
c_5  : int [0, 0][3, 3]
vs
c_5  : [irange] int [0, 3] NONZERO 0x3

Obvious the first range is more correct, c_5 can only be either 0 or 3.

[Bug tree-optimization/105834] [13 Regression] Dead Code Elimination Regression at -O2 (trunk vs. 12.1.0)

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105834

Jeffrey A. Law <law at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
                 CC|                            |law at gcc dot gnu.org

[Bug tree-optimization/105834] [13/14 Regression] Dead Code Elimination Regression at -O2 (trunk vs. 12.1.0)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105834

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|13.0                        |13.2

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 13.1 is being released, retargeting bugs to GCC 13.2.

[Bug tree-optimization/105834] [13/14 Regression] Dead Code Elimination Regression at -O2 (trunk vs. 12.1.0)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105834

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |needs-bisection
      Known to work|                            |14.0

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Looks to be fixed on the trunk.

We also now get from evrp:
Global Exported: c_5 = [irange] int [0, 0][3, 3]

[Bug tree-optimization/105834] [13/14 Regression] Dead Code Elimination Regression at -O2 (trunk vs. 12.1.0)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105834

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|13.2                        |13.3

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 13.2 is being released, retargeting bugs to GCC 13.3.

[Bug tree-optimization/105834] [13/14 Regression] Dead Code Elimination Regression at -O2 (trunk vs. 12.1.0)

[tkoenig at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105834

Thomas Koenig <tkoenig at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=109695
           Keywords|needs-bisection             |

--- Comment #6 from Thomas Koenig <tkoenig at gcc dot gnu.org> ---
On trunk, this was fixed by r14-1163-gd8b058d3ca4ebb, one of the
patchset which fixed PR 109695:

d8b058d3ca4ebbef5575105164417f125696f5ce is the first new commit
commit d8b058d3ca4ebbef5575105164417f125696f5ce
Author: Andrew MacLeod <amacleod@redhat.com>
Date:   Tue May 23 15:11:44 2023 -0400

    Choose better initial values for ranger.

    Instead of defaulting to VARYING, fold the stmt using just global ranges.

            PR tree-optimization/109695
            * gimple-range-cache.cc (ranger_cache::get_global_range): Call
            fold_range with global query to choose an initial value.

 gcc/gimple-range-cache.cc | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

Would this patch be something that could reasonably be backported?

[Bug tree-optimization/105834] [13 Regression] Dead Code Elimination Regression at -O2 (trunk vs. 12.1.0)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105834

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=110540

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note this change seems to have caused PR110540, so backporting would cause the
regression on the branch as well, sth. we'd want to avoid at this stage.

[Bug tree-optimization/105834] [13 Regression] Dead Code Elimination Regression at -O2 (trunk vs. 12.1.0)

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105834

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|13.3                        |13.4

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 13.3 is being released, retargeting bugs to GCC 13.4.