[Bug middle-end/110906] New: __attribute__((optimize("no-math-errno"))) has no effect.

[Bug middle-end/110906] New: __attribute__((optimize("no-math-errno"))) has no effect.

[cassio.neri at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110906

            Bug ID: 110906
           Summary: __attribute__((optimize("no-math-errno"))) has no
                    effect.
           Product: gcc
           Version: 13.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cassio.neri at gmail dot com
  Target Milestone: ---

Consider this C++ code compiled with -O3:

double g(double x) {
  return std::sqrt(x);
}

Usually this does call the library function std::sqrt because x might be
negative and errno needs to be set accordingly. Moreover, with -fno-math-errno
a single sqrtsd instruction is emitted. However, annotating g with

__attribute__((optimize("no-math-errno")))

has no effect. This attribute (and #pragma GCC optimize("no-math-errno") ) used
to work up to gcc 5.5.

https://godbolt.org/z/T1nb11bv5

[Bug middle-end/110906] __attribute__((optimize("no-math-errno"))) has no effect.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110906

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
well std::sqrt is not annotated with no-math-errno after all ...

[Bug middle-end/110906] __attribute__((optimize("no-math-errno"))) has no effect.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110906

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Created attachment 55692
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=55692&action=edit
Full testcase

[Bug middle-end/110906] __attribute__((optimize("no-math-errno"))) has no effect.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110906

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
But even:
```
__attribute__((optimize("no-math-errno")))
double g(double x) {
  return __builtin_sqrt(x);
}
```
Does not change here ...

[Bug middle-end/110906] __attribute__((optimize("no-math-errno"))) has no effect.

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110906

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Well "math-errno" has no effect if -fno-math-errno is supplied on the command
line either, well can produce incorrect code too.

Take:
```
__attribute__((optimize("math-errno")))
void g(double x) {
  __builtin_sqrt(x);
}
```
With `-O2`, a call happens but with `-O2 -fno-math-errno` does not happen. That
was true even in GCC 5.