Re: [tree-ssa] copy propagation and the abstraction penalty

[Richard Henderson <rth at redhat dot com>]

On Thu, May 15, 2003 at 10:10:22AM -0400, Diego Novillo wrote:
>         I'm also wondering if we could change the
>         may-alias between this and UV2150 to a must-alias, which would
>         completely free this program from aliasing problems:

Indeed.  And for this case I definitely think it's the right thing to do.

IMO constant propagation should be able to take

    T.8_2 = &<UVa150>;
    {
      struct complex * const this;

      this_3 = (struct complex * const)T.8_2;
      {
        this->re = 1.0e+0;

and turn it into

	(&<UVa150>)->re = 1.0e+0

which folds to

	<UVa150>.re = 1.0e+0

At which point we have no aliasing problem, and a subsequent round
of constant propagation ought to be able to send 1.0e+0 to its 
destination.


r~