[Bug tree-optimization/111469] New: Wrong code at -Os on x86_64-linux-gnu since r14-573-g69f1a8af45

[Bug tree-optimization/111469] New: Wrong code at -Os on x86_64-linux-gnu since r14-573-g69f1a8af45

[shaohua.li at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111469

            Bug ID: 111469
           Summary: Wrong code at -Os on x86_64-linux-gnu since
                    r14-573-g69f1a8af45
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shaohua.li at inf dot ethz.ch
                CC: pinskia at gcc dot gnu.org
  Target Milestone: ---

gcc at -Os produced the wrong code.

Bisected to r14-573-g69f1a8af45

Compiler explorer: https://godbolt.org/z/fheon13dP

$ cat a.c
int printf(const char *, ...);
int a;
long b, c, e, f;
char *g;
unsigned short h = 5;
static unsigned short *i = &h;
unsigned j;
long k(long m, long n) {
  if (n)
    e = m;
  c = e;
  return e;
}
char o() {
  char l;
  while (f)
    ;
  l = *g;
  return l;
}
int main() {
  int p;
  int q;
  for (; j - 9 >= 29; j = k(-95, *i) + 127) {
    *i || o();
    long d = h;
    p = d == 0 ? 0 : b % d;
    q = p;
    int *r[1] = {&q};
  }
  printf("%d\n", a);
}
$
$ gcc a.c && ./a.out
0
$ gcc a.c -Os && ./a.out
segmentation fault
$

[Bug tree-optimization/111469] Wrong code at -Os on x86_64-linux-gnu since r14-573-g69f1a8af45

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111469

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I am 99% sure this is a latent bug. Will find a testcase later tomorrow.

[Bug tree-optimization/111469] [14 Regression] Wrong code at -Os on x86_64-linux-gnu since r14-573-g69f1a8af45

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111469

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.0
            Summary|Wrong code at -Os on        |[14 Regression] Wrong code
                   |x86_64-linux-gnu since      |at -Os on x86_64-linux-gnu
                   |r14-573-g69f1a8af45         |since r14-573-g69f1a8af45

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Looks like a latent bug in phiopt exposed by my phiopt patch. Still trying to
figure out what is going wrong.

[Bug tree-optimization/111469] [14 Regression] Wrong code at -Os on x86_64-linux-gnu since r14-573-g69f1a8af45

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111469

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed. it is a bug in minmax_replacement ...

[Bug tree-optimization/111469] [14 Regression] Wrong code at -Os on x86_64-linux-gnu since r14-573-g69f1a8af45

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111469

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-09-19
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.
Reduced further and fails at -O1 and above now:
```
long f;
char *g;
[[gnu::noinline]]
char o() {
  char l;
  while (f)
    ;
  l = *g;
  return l;
}
[[gnu::noinline]]
unsigned short gg(unsigned short a, unsigned short b)
{
  short d;
  if (a > b)
  {
    d= b;
  }
  else
  {
    o();
    d = a;
  }
  return d;
}

int main(void)
{
  gg(3, 2);
}


```

[Bug tree-optimization/111469] [14 Regression] Wrong code at -Os on x86_64-linux-gnu since r14-573-g69f1a8af45

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111469

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 #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I am going to fix minmax_replacement over the weekend.

[Bug tree-optimization/111469] [14 Regression] Wrong code at -Os on x86_64-linux-gnu since r14-573-g69f1a8af45

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111469

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |https://gcc.gnu.org/piperma
                   |                            |il/gcc-patches/2023-Septemb
                   |                            |er/631099.html
           Keywords|                            |patch

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Patch posted:
https://gcc.gnu.org/pipermail/gcc-patches/2023-September/631099.html

[Bug tree-optimization/111469] [14 Regression] Wrong code at -Os on x86_64-linux-gnu since r14-573-g69f1a8af45

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111469

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |19373742 at buaa dot edu.cn

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 111574 has been marked as a duplicate of this bug. ***

[Bug tree-optimization/111469] [14 Regression] Wrong code at -Os on x86_64-linux-gnu since r14-573-g69f1a8af45

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111469

--- Comment #8 from CVS 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:68fa82e2d8f868a233103102dff2449a416bc566

commit r14-4279-g68fa82e2d8f868a233103102dff2449a416bc566
Author: Andrew Pinski <apinski@marvell.com>
Date:   Thu Sep 21 03:05:17 2023 +0000

    PHIOPT: Fix minmax_replacement for three way

    So when diamond bb support was added to minmax_replacement in
r13-1950-g9bb19e143cfe,
    the code was not expecting the alt_middle_bb not to exist if it was empty
(for threeway_p).
    So when factor_out_conditional_conversion was used to factor out
conversions, it turns out
    the assumption for alt_middle_bb to be wrong and we ended up with
threeway_p being true but
    having middle_bb being empty but alt_middle_bb not being empty which causes
wrong code in
    many cases.

    This patch fixes the issue by adding a test for the 2 cases where the
assumption on
    threeway_p case having the other bb being empty.

    Changes made:
    v2: Fix test for `(a <= u) b = MAX(a, d) else b = u`.

    Note my plan for GCC 15 is remove minmax_replacement as match.pd will catch
all cases
    at that point.

    OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

            PR tree-optimization/111469

    gcc/ChangeLog:

            * tree-ssa-phiopt.cc (minmax_replacement): Fix
            the assumption for the `non-diamond` handling cases
            of diamond code.

    gcc/testsuite/ChangeLog:

            * gcc.c-torture/execute/pr111469-1.c: New test.

[Bug tree-optimization/111469] [14 Regression] Wrong code at -Os on x86_64-linux-gnu since r14-573-g69f1a8af45

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111469

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

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

--- Comment #9 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed.