[Bug tree-optimization/19347] New: Invariant load not moved out of loop

[Bug tree-optimization/19347] New: Invariant load not moved out of loop

[irar at il dot ibm dot com]

In mesa benchmark (osmesa.c:678) 

         GLuint i, n, *ptr4;
         n = osmesa->rowlength * osmesa->height;
         ptr4 = (GLuint *) osmesa->buffer;
         for (i=0;i<n;i++) {
            *ptr4++ = osmesa->clearpixel;
         }   

The load of osmesa->clearpixel is not taken outside the loop by LIM because of 
aliasing limitations. This in turn also prevents vectorization.

In this particular case we can actually get the load moved out of the loop even 
without resolving the aliasing issue (which requires whole-program), on 
account that even if the store aliases the load, it will not alter the value 
loaded (because we store the same value that we loaded).

I'm looking into this in the context of the vectorizer.

-- 
           Summary: Invariant load not moved out of loop
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: irar at il dot ibm dot com
        ReportedBy: irar at il dot ibm dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: powerpc-apple-darwin7.0.0
  GCC host triplet: powerpc-apple-darwin7.0.0
GCC target triplet: powerpc-apple-darwin7.0.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19347

[Bug tree-optimization/19347] Invariant load not moved out of loop

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-01-09 15:55 -------
Confirmed but add a full testcase here, thanks.

Actually I don't think it would require whole program analysis to do this in LIM (or LICM), we just need 
more information (which might be done on the structure-aliasing branch).

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |missed-optimization
   Last reconfirmed|0000-00-00 00:00:00         |2005-01-09 15:55:15
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19347

[Bug tree-optimization/19347] Invariant load not moved out of loop

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
   Last reconfirmed|2005-01-09 15:55:15         |2005-04-11 06:09:59
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19347