[Bug rtl-optimization/44214] New: Compiler does not optimize vector divide with -freciprocal-math (or -ffast-math)

[Bug rtl-optimization/44214] New: Compiler does not optimize vector divide with -freciprocal-math (or -ffast-math)

[meissner at gcc dot gnu dot org]

If you have code that does division by a constant that can be auto vectorized
by the compiler, the compiler does not convert the division to multiplication
by the reciprocal if -freciprocal-math (or -ffast-math), but instead does the
division.

The bug is in fold-const.c near line 11254, where the code for handling
REAL_CST should be cloned to handle VECTOR_CST (and presumably COMPLEX_CST
also).


-- 
           Summary: Compiler does not optimize vector divide with -
                    freciprocal-math (or -ffast-math)
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: meissner at gcc dot gnu dot org
 GCC build triplet: powerpc64-unknown-linux-gnu
  GCC host triplet: powerpc64-unknown-linux-gnu
GCC target triplet: powerpc64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44214

[Bug rtl-optimization/44214] Compiler does not optimize vector divide with -freciprocal-math (or -ffast-math)

[meissner at gcc dot gnu dot org]

------- Comment #1 from meissner at gcc dot gnu dot org  2010-05-20 18:00 -------
Actually in looking at it further, I was wrong in the initial claim.  Auto
vectorization now handles division by a constant.  Explicit vectors like
PowerPC (and probably SPU) do show the problem.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44214

[Bug rtl-optimization/44214] Compiler does not optimize vector divide with -freciprocal-math (or -ffast-math)

[meissner at gcc dot gnu dot org]

------- Comment #2 from meissner at gcc dot gnu dot org  2010-05-20 18:02 -------
Created an attachment (id=20712)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=20712&action=view)
Example program that shows the issue on powerpc.

Compile with -mcpu=power7 on powerpc.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44214

[Bug rtl-optimization/44214] Compiler does not optimize vector divide with -freciprocal-math (or -ffast-math)

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2010-05-21 09:47 -------
The fold code should probably simply use fold_binary to do the constant
folding (which already should handle 1/x for x vector and complex.  There
is a build_one_cst to build the constant 1 for any type).  The exact
result check would need to use mpc (and I'm not sure its correct for
-frounding-math anyway).


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2010-05-21 09:47:56
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44214