[Bug middle-end/33675] Badly optimized negations on x86 with -frounding-math

[Bug middle-end/33675] Badly optimized negations on x86 with -frounding-math

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=33675

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

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

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
As said, we try to honor volatile automatic variables as such and they get a
stack slot assigned for this reason.  Without the volatile but with
-frounding-math -O2 we get

        fldl    20(%esp)
        movl    16(%esp), %eax
        fchs
        fstps   4(%esp)
        flds    4(%esp)
        fchs
        fstps   (%eax)

which is what you expect.  Fixed (or wontfix with the volatile).

[Bug middle-end/33675] Badly optimized negations on x86 with -frounding-math

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2007-10-08 08:53 -------
The first store is for the truncation to float, the second store is because
of the volatile.  Now we could combine the first into the second, but in
general we don't care too much to try optimize code which uses volatile.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2007-10-08 08:53:42
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33675

[Bug middle-end/33675] Badly optimized negations on x86 with -frounding-math

[bagnara at cs dot unipr dot it]

------- Comment #2 from bagnara at cs dot unipr dot it  2007-10-06 13:03 -------
I don't understand.  Do you mean that what I consider the natural compilation
of that piece of code (the shorter assembly listing) is incorrect?  In other
words: do you think that the shorter assembly listing does not properly honor
the volatile qualifier?
If so, why?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33675

[Bug middle-end/33675] Badly optimized negations on x86 with -frounding-math

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2007-10-06 11:45 -------
That is becasue there is a cast to volatile float which causes an extra store.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
          Component|c                           |middle-end


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33675