Re: combine permutations in gimple

[Marc Glisse <marc dot glisse at inria dot fr>]

On Mon, 13 Aug 2012, Richard Guenther wrote:

> > > > +  /* Check that it is only used here. We cannot use has_single_use
> > > > +     since the expression is using it twice itself...  */
> > >
> > > Ah ... so then
> > >
> > >           || num_imm_uses (op0) != 2
> >
> > Ah, ok, that's simpler indeed, but there were such dire warnings to never
> > use that evil function unless absolutely necessary that I didn't dare use
> > it... Thanks for the permission.
>
> If your new predicate would match more places (can you do a quick search?)

You mean: if there are more optimizations that either already check for 
double use in the same statement, or could benefit from doing so? I'll 
take a look.

> then we want it in tree-flow-inline.h instead of in
> tree-ssa-forwprop.c.  But yes,
> num_imm_uses can be expensive.   For now just stick with the above.

I assume "the above" means "num_imm_uses (op0) != 2", since both versions 
are above ;-)

> The natural SSA (and forwprop) way is to look for BIT_FIELD_REF and see
> if the def stmt is a VEC_PERM_EXPR.

Thanks again,

--
Marc Glisse