[Bug c/59424] New: Optimization issue on min/max

[Bug c/59424] New: Optimization issue on min/max

[jmvalin at jmvalin dot ca]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59424

            Bug ID: 59424
           Summary: Optimization issue on min/max
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jmvalin at jmvalin dot ca

gcc seems to be having problems optimizing float min/max code and behaves
unpredictably. If I compile the following code on an x86-64 (SSE enabled):

#include <math.h>

float func1(float a, float b) {
  return (a < b ? a : b);
}

float func2(float a, float b) {
  return sqrtf(a < b ? a : b);
}

float func3(float a, float b) {
  return fabsf(a < b ? a : b);
}

I get the following disassembly:

0000000000000000 <func1>:
func1():
   0:   f3 0f 5d c1             minss  %xmm1,%xmm0
   4:   c3                      retq   
   5:   66 66 2e 0f 1f 84 00    data32 nopw %cs:0x0(%rax,%rax,1)
   c:   00 00 00 00 

0000000000000010 <func2>:
func2():
  10:   f3 0f 5d c1             minss  %xmm1,%xmm0
  14:   f3 0f 51 c0             sqrtss %xmm0,%xmm0
  18:   c3                      retq   
  19:   0f 1f 80 00 00 00 00    nopl   0x0(%rax)

0000000000000020 <func3>:
func3():
  20:   0f 2f c8                comiss %xmm0,%xmm1
  23:   77 13                   ja     38 <func3+0x18>
  25:   f3 0f 10 05 00 00 00    movss  0x0(%rip),%xmm0        # 2d <func3+0xd>
  2c:   00 
  2d:   0f 54 c1                andps  %xmm1,%xmm0
  30:   c3                      retq   
  31:   0f 1f 80 00 00 00 00    nopl   0x0(%rax)
  38:   f3 0f 10 0d 00 00 00    movss  0x0(%rip),%xmm1        # 40 <func3+0x20>
  3f:   00 
  40:   0f 54 c1                andps  %xmm1,%xmm0
  43:   c3                      retq   


So gcc is correctly using maxss in func1 and func2, but not in func2. In
practice, I'm using MIN/MAX macros extensively in libopus and gcc is missing
the optimization most of the time, slowing down the code.

[Bug c/59424] Optimization issue on min/max

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59424

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I can observe the same behavior with trunk.

For func2, we compute a < b ? a : b first and then call sqrtf on that, while
for func3 we have return a < b ? ABS_EXPR <a> : ABS_EXPR <b>;.  Perhaps that's
the reason why ifcvt doesn't optimize this using UNSPEC_IEEE_MIN.

[Bug c/59424] Optimization issue on min/max

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59424

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #1)
> I can observe the same behavior with trunk.
> 
> For func2, we compute a < b ? a : b first and then call sqrtf on that, while
> for func3 we have return a < b ? ABS_EXPR <a> : ABS_EXPR <b>;.  Perhaps
> that's the reason why ifcvt doesn't optimize this using UNSPEC_IEEE_MIN.

Yep.  Obviously it cannot after that distribution of ABS_EXPR.

[Bug c/59424] Optimization issue on min/max

[jmvalin at jmvalin dot ca]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59424

--- Comment #3 from Jean-Marc Valin <jmvalin at jmvalin dot ca> ---
What's strange is that adding -ffast-math makes gcc use maxss on func3() too,
even though it was already allowed to without -ffast-math. I had the same
problem with absolute value, although in that case fabs() solved the problem.
In the case of max(), using fmax() doesn't help because it's too strict about
NaN behaviour to match maxss.

[Bug middle-end/59424] Optimization issue on min/max

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59424

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

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

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I have a fix which I was working on for PR 56223.
Basically factor_out_conditional_conversion can be extended to support more
than conversions :).

[Bug middle-end/59424] Optimization issue on min/max

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59424

--- Comment #6 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:6d6c17e45f62cfe0b7de502af299348fca548b01

commit r14-575-g6d6c17e45f62cfe0b7de502af299348fca548b01
Author: Andrew Pinski <apinski@marvell.com>
Date:   Thu Apr 27 12:21:54 2023 -0700

    PHIOPT: factor out unary operations instead of just conversions

    After using factor_out_conditional_conversion with diamond bb,
    we should be able do use it also for all normal unary gimple and not
    just conversions. This allows to optimize PR 59424 for an example.
    This is also a start to optimize PR 64700 and a few others.

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

    An example of this is:
    ```
    static inline unsigned long long g(int t)
    {
      unsigned t1 = t;
      return t1;
    }
    static int abs1(int a)
    {
      if (a < 0)
        a = -a;
      return a;
    }
    unsigned long long f(int c, int d, int e)
    {
      unsigned long long t;
      if (d > e)
        t = g(abs1(d));
      else
        t = g(abs1(e));
      return t;
    }
    ```

    Which should be optimized to:
      _9 = MAX_EXPR <d_5(D), e_6(D)>;
      _4 = ABS_EXPR <_9>;
      t_3 = (long long unsigned intD.16) _4;

    gcc/ChangeLog:

            * tree-ssa-phiopt.cc (factor_out_conditional_conversion): Rename to
...
            (factor_out_conditional_operation): This and add support for all
unary
            operations.
            (pass_phiopt::execute): Update call to
factor_out_conditional_conversion
            to call factor_out_conditional_operation instead.

            PR tree-optimization/109424
            PR tree-optimization/59424

    gcc/testsuite/ChangeLog:

            * gcc.dg/tree-ssa/abs-2.c: Update tree scan for
            details change in wording.
            * gcc.dg/tree-ssa/minmax-17.c: Likewise.
            * gcc.dg/tree-ssa/pr103771.c: Likewise.
            * gcc.dg/tree-ssa/minmax-18.c: New test.
            * gcc.dg/tree-ssa/minmax-19.c: New test.

[Bug middle-end/59424] Optimization issue on min/max

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59424

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
   Target Milestone|---                         |14.0
             Status|ASSIGNED                    |RESOLVED

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed.