Re: [tree-ssa] More aliasing fixes

[Diego Novillo <dnovillo at redhat dot com>]

On Wed, 2003-12-17 at 07:59, Diego Novillo wrote:

> With the current implementation we'd generate 14 vops, the new one would
> generate 18 vops.  But we would have to experiment with real code.  I
> can see definite advantages to the new scheme in pointer-heavy code.
> 
Wait.  There's a fatal flaw in this scheme that I didn't realize
yesterday.  You will be relating variables that cannot possibly alias
each other and block VN based optimizations and DCE.  Consider:

foo (int i)
{
   int a, b;
   int *p;

   p = (i > 50) ? &a : &b;
   a = 50;
   b = 3;
   if (a > 0)
      *p = 5;
}

The assignment to 'b' will block DOM from propagating 50 into (a > 0),
because the assignment to b will create a new version of p's MT.


Diego.