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Date: Sat, 22 Nov 2008 19:10:00 -0000
Subject: [Bug tree-optimization/38230]  New: SCCVN doesn't do expression lookups during stmt walks
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Related to PR38207, SCCVN doesn't CSE the load of c->a in

/* { dg-do compile } */
/* { dg-options "-O -fdump-tree-fre" } */

struct a
{
  union
  {
    int a;
    int b;
  };
  union
  {
    int c;
    int d;
  };
  int e;
};

int f(struct a *c)
{
  int d; 
  c->e = 2;
  d = c->a;
  c->c = 1;
  return c->a + d;
}

/* We should have CSEd the load from c->a.  */

/* { dg-final { scan-tree-dump-times "c_.*\\\.a" 1 "fre" } } */
/* { dg-final { cleanup-tree-dump "fre" } } */


which is because it doesn't do expression hashtable lookups for intermediate
VUSEs it walks.  Without proper caching this will probably be too expensive.


-- 
           Summary: SCCVN doesn't do expression lookups during stmt walks
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38230