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Date: Thu, 19 Jul 2007 17:14:00 -0000
Subject: [Bug tree-optimization/32826]  New: Reduction into a global variable causes a Load Hit Store Hazard (for the Cell)
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Testcase (compile at -O2 -maltivec -ftree-vectorize):
int a[16*100];
int e;
float f(void)
{
  int i;
  int e1;
  e1 = e;
  for(i = 0;i<16*100;i++)
    e1 += a[i];
  e = e1;
}

----------- cut ------
Currently you get:
        stvewx v1,0,r2
        lis r2,ha16(_e)
        lwz r0,-20(r1)   <---- LHS hazard
        stw r0,lo16(_e)(r2)

Even though the elements of v1 will all be the same, so GCC could do:
        lis r2,ha16(_e)
        add r2, lo16(_e)(r2)
        stvewx v1,0,r2


-- 
           Summary: Reduction into a global variable causes a Load Hit Store
                    Hazard (for the Cell)
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pinskia at gcc dot gnu dot org
GCC target triplet: powerpc*-*-*


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32826