[Bug tree-optimization/111221] New: Floating point handling a*1.0 vs. a+0.0

[Bug tree-optimization/111221] New: Floating point handling a*1.0 vs. a+0.0

[tkoenig at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111221

            Bug ID: 111221
           Summary: Floating point handling a*1.0 vs. a+0.0
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tkoenig at gcc dot gnu.org
  Target Milestone: ---

I just noticed that gcc will optimize away multiplying a floating
point number with 1.0, but will not do for an addition with 0.0.
Example, with -O3,

double add0 (double a)
{
  return a + 0.0;
}

double mul1 (double a)
{
  return a * 1.0;
}

yields

add0:
.LFB0:
        .cfi_startproc
        pxor    %xmm1, %xmm1
        addsd   %xmm1, %xmm0
        ret

vs.

mul1:
.LFB1:
        .cfi_startproc
        ret

which seems inconsistent.  If this is the result of a deliberate design
decision, feel free to close as WONTFIX.

[Bug tree-optimization/111221] Floating point handling a*1.0 vs. a+0.0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111221

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
-0.0 * 1.0 is still -0.0
While -0.0 + 0.0 is 0.0 rather than -0.0.

[Bug tree-optimization/111221] Floating point handling a*1.0 vs. a+0.0

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111221

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
That is GCC will remove additions of -0.0:
double addneg0 (double a)
{
  return a + -0.0;
}

Gets optimized to just `return a;`.

[Bug tree-optimization/111221] Floating point handling a*1.0 vs. a+0.0

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111221

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |xry111 at gcc dot gnu.org

--- Comment #3 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
FWIW if you want "add0" to be optimized use -fno-signed-zeros.