[Bug tree-optimization/110450] New: [14 Regression] Dead Code Elimination Regression at -O2 since r14-261-g0ef3756adf0

[Bug tree-optimization/110450] New: [14 Regression] Dead Code Elimination Regression at -O2 since r14-261-g0ef3756adf0

[theodort at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110450

            Bug ID: 110450
           Summary: [14 Regression] Dead Code Elimination Regression at
                    -O2 since r14-261-g0ef3756adf0
           Product: gcc
           Version: 14.0
            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: ---

https://godbolt.org/z/KqcYxfevj

Given the following code:

void foo(void);
static int a = 1;
static int *b = &a, *c = &a;
static short d, e;
static char f = 11;
static char(g)(char h, int i) { return h << i; }
int main() {
    if (f) *c = g(0 >= a, 3);
    e = *c;
    d = e % f;
    if (d) {
        __builtin_unreachable();
    } else if (*b)
        foo();
    ;
}

gcc-trunk -O2 does not eliminate the call to foo:

main:
        movl    a(%rip), %eax
        xorl    %edx, %edx
        testl   %eax, %eax
        setle   %dl
        leal    0(,%rdx,8), %edx
        movl    %edx, a(%rip)
        jle     .L8
        xorl    %eax, %eax
        ret
.L8:
        pushq   %rax
        call    foo
        xorl    %eax, %eax
        popq    %rdx
        ret

gcc-13.1.0 -O2 eliminates the call to foo:

main:
        movl    a(%rip), %edx
        xorl    %eax, %eax
        testl   %edx, %edx
        setle   %al
        leal    0(,%rax,8), %eax
        movl    %eax, a(%rip)
        xorl    %eax, %eax
        ret

Bisects to r14-261-g0ef3756adf0

[Bug tree-optimization/110450] [14 Regression] Dead Code Elimination Regression at -O2 since r14-261-g0ef3756adf0

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110450

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
   Target Milestone|---                         |14.0

[Bug tree-optimization/110450] [14 Regression] Dead Code Elimination Regression at -O2 since r14-261-g0ef3756adf0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110450

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2023-07-01

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
In VRP:
trunk:
```
Folding statement: _11 = _9 % 11;
Matching expression match.pd:2480, gimple-match-4.cc:35
Matching expression match.pd:2483, gimple-match-3.cc:66
Matching expression match.pd:2490, gimple-match-2.cc:58
Matching expression match.pd:1991, gimple-match-5.cc:23
Matching expression match.pd:2480, gimple-match-4.cc:35
Matching expression match.pd:2483, gimple-match-3.cc:66
Matching expression match.pd:2490, gimple-match-2.cc:58
Matching expression match.pd:1948, gimple-match-7.cc:20
Matching expression match.pd:2480, gimple-match-4.cc:35
Matching expression match.pd:2483, gimple-match-3.cc:66
Matching expression match.pd:2490, gimple-match-2.cc:58
Applying pattern match.pd:5319, gimple-match-8.cc:2688
Applying pattern match.pd:6000, gimple-match-10.cc:587
Applying pattern match.pd:2102, gimple-match-1.cc:6289
Applying pattern match.pd:6000, gimple-match-10.cc:587
Applying pattern match.pd:5284, gimple-match-4.cc:1099
Applying pattern match.pd:1378, gimple-match-3.cc:7680
Applying pattern match.pd:4720, gimple-match-1.cc:16033
gimple_simplified to _14 = a.1_2 <= 0;
_15 = (int) _14;
_11 = _15 << 3;
Global Exported: _11 = [irange] int [0, 0][8, 8] NONZERO 0x8
Folded into: _11 = _15 << 3;
```

And the relationship between _5 and _11 is completely lost.


while in GCC 13:
```
Folding statement: _11 = _9 % 11;
Global Exported: _11 = [irange] int [0, 0][8, 8] NONZERO 0x8
Folded into: _11 = _9;
```

And then we remove the __builtin_unreachable even though we infer that _5 would
be 0 and therefore _11 would never be 8 .

[Bug tree-optimization/110450] [14 Regression] Dead Code Elimination Regression at -O2 since r14-261-g0ef3756adf0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110450

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |needs-bisection

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Looks to be fixed on the trunk.

[Bug tree-optimization/110450] [14 Regression] Dead Code Elimination Regression at -O2 since r14-261-g0ef3756adf0

[jamborm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110450

Martin Jambor <jamborm at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|needs-bisection             |
                 CC|                            |jamborm at gcc dot gnu.org

--- Comment #3 from Martin Jambor <jamborm at gcc dot gnu.org> ---
This has been fixed with r14-4141-gbf6b107e2a3423 (Andrew MacLeod: New early
__builtin_unreachable processing).

[Bug tree-optimization/110450] [14 Regression] Dead Code Elimination Regression at -O2 since r14-261-g0ef3756adf0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110450

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |pinskia at gcc dot gnu.org

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Will commit the testcase and close it as fixed. The fix seems like the correct
one based on my comment:

> And then we remove the __builtin_unreachable even though we infer that _5 would be 0 and therefore _11 would never be 8 .

[Bug tree-optimization/110450] [14 Regression] Dead Code Elimination Regression at -O2 since r14-261-g0ef3756adf0

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110450

--- Comment #5 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Andrew Pinski <pinskia@gcc.gnu.org>:

https://gcc.gnu.org/g:34a827039fabcf24ce78da25984a1cc8be7ca2c3

commit r14-7221-g34a827039fabcf24ce78da25984a1cc8be7ca2c3
Author: Andrew Pinski <quic_apinski@quicinc.com>
Date:   Fri Jan 12 20:24:34 2024 -0800

    Add a few testcases for fix missed optimization regressions

    Adds a few new testcases for some missed optimization regressions.
    The analysis on how each should be optimized is in the testcases
    themselves (and in the bug report).

    Committed as obvious after running the testsuite to make sure they pass.

            PR tree-optimization/107823
            PR tree-optimization/110768
            PR tree-optimization/110941
            PR tree-optimization/110450
            PR tree-optimization/110841

    gcc/testsuite/ChangeLog:

            * gcc.dg/tree-ssa/ssa-thread-22.c: New test.
            * gcc.dg/tree-ssa/vrp-loop-1.c: New test.
            * gcc.dg/tree-ssa/vrp-loop-2.c: New test.
            * gcc.dg/tree-ssa/vrp-unreachable-1.c: New test.
            * gcc.dg/tree-ssa/vrp-unreachable-2.c: New test.

    Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

[Bug tree-optimization/110450] [14 Regression] Dead Code Elimination Regression at -O2 since r14-261-g0ef3756adf0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110450

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

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

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed.