optimization/10087: [3.3/3.4 regression] optimizer produces wrong code when indexing 2D array

[bangerth@dealii.org]

Old Synopsis: optimizer produces wrong code when indexing malloc'ed 2D array
New Synopsis: [3.3/3.4 regression] optimizer produces wrong code when indexing 2D array

State-Changed-From-To: open->analyzed
State-Changed-By: bangerth
State-Changed-When: Fri Mar 14 23:45:17 2003
State-Changed-Why:
    Confirmed also on x86 linux. Here's a slightly modified example:
    --------------------------
    void b(int*,int*);
    
    typedef struct {
        double T1;
        char c;
    } S;
    
    int main(void)
    {
      int i,j;
      double s;
    
      S x1[2][2];
      S *x[2] = { x1[0], x1[1] };
      S **E = x;
      
      for( i=0; i < 2; i++ )
        for( j=0; j < 2; j++ )
          E[j][i].T1 = 1;
    
      for( i=0; i < 2; i++ )
        for( j=0; j < 2; j++ )
          s = E[j][i].T1;
    
      b(&j,&i);
      printf( "result %.6e\n", s);
      return 0;
    }
    
    void b(int *i, int *j) {}
    -------------------------------
    
    This yields different results with and without -O2:
    g/x> /home/bangerth/bin/gcc-3.4-pre/bin/gcc x.c
    g/x> ./a.out
    result 1.000000e+00
    
    g/x> /home/bangerth/bin/gcc-3.4-pre/bin/gcc x.c -O2
    g/x> ./a.out
    result 2.171654e+00
    
    The same holds for 3.3, but 3.2.2 is ok, so it's a regression.
    
    W.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=10087