[Bug target/27827] [4.0 Regression] gcc 4 produces worse x87 code on all platforms than gcc 3

[aldyh at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=27827
Bug 27827 depends on bug 27855, which changed state.

Bug 27855 Summary: [6/7/8 regression] reassociation causes the RA to be confused
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=27855

   What|Removed |Added

 Status|NEW |RESOLVED
 Resolution|--- |FIXED

[Bug target/27827] [4.0 Regression] gcc 4 produces worse x87 code on all platforms than gcc 3

[pinskia at gcc dot gnu dot org]

--- Comment #70 from pinskia at gcc dot gnu dot org  2007-02-13 02:59 
---
Fixed, 4.0 branch is now been closed.


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pinskia at gcc dot gnu dot org changed:

   What|Removed |Added

 Status|ASSIGNED|RESOLVED
 Resolution||FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27827

[Bug target/27827] [4.0 Regression] gcc 4 produces worse x87 code on all platforms than gcc 3

[steven at gcc dot gnu dot org]

--- Comment #69 from steven at gcc dot gnu dot org  2006-10-07 10:06 ---
The linked-to patch is already on the trunk.


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steven at gcc dot gnu dot org changed:

   What|Removed |Added

URL|http://gcc.gnu.org/ml/gcc-  |
   |patches/2006-   |
   |08/msg00113.html|


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27827

[Bug target/27827] [4.0 Regression] gcc 4 produces worse x87 code on all platforms than gcc 3

[bonzini at gnu dot org]

--- Comment #66 from bonzini at gnu dot org  2006-08-11 14:10 ---
(on bugzilla because I had problems sending mail to you)

 Just got your most recent update.  From what I can tell, you have applied
 your patch to the 4.1 series, so that the next 4.1 release will have the fix?

Yes.

 So, my question is that I notice the comment says:
* config/i386/i386.md: Add peephole2 to avoid fld %st instructions.

 Which, if its what we've been doing should be something like:
* config/i386/i386.md: Add peephole2 to substitute fld for memory-source 
  fmul

No, what my patch does is exactly replacing fld reg + fmul mem with fld mem
+ fmul reg,reg.  Maybe the ChangeLog is not completely descriptive, but the PR
number is there and will make things clear enough.

 BTW, it's going to remain the case that you must do at least -O2 to get
 this peephole invoked?

You can add -fpeephole2.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27827

[Bug target/27827] [4.0 Regression] gcc 4 produces worse x87 code on all platforms than gcc 3

[whaley at cs dot utsa dot edu]

--- Comment #67 from whaley at cs dot utsa dot edu  2006-08-11 15:22 ---
Uros,

Slightly offtopic, but to put some numbers to comment #8 and comment #11,
equivalent SSE code now reaches only 50% of x87 single performance and 60% of
x87 double performance on AMD x86_64

FYI, you *may* get slightly better single SSE performance with these flags:
   -fomit-frame-pointer -march=athlon64 -O2 -mfpmath=sse \
   -msse -msse2 -msse3 -fargument-noalias-global

Also, when ATLAS is allowed to exercise the code generator to find the best
kernel, for double precision gcc 4's SSE could be made to almost tie gcc3's x87
performance (gcc3's double x87 performance is roughly 92% of the patched gcc 4
for this platform).  However, single precision SSE, even allowing the code
generator to go crazy, could only achieve about 2/3 of double *SSE*
performance, and since x87 single perf is actually greater for x87 . . .

You can find some details at:
  
https://sourceforge.net/mailarchive/forum.php?thread_id=10026092forum_id=426

Cheers,
Clint


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27827