Re: [PATCH 2/5][P1][tree-optimization/71437] Record more equivalences in some cases

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

On Thu, 16 Mar 2017, Jeff Law wrote:

> On 03/16/2017 06:54 AM, Trevor Saunders wrote:
> > > +	  if (TREE_CODE (op0) == SSA_NAME && integer_zerop (op1))
> > > +	    {
> > > +	      enum tree_code code = eq->cond.ops.binary.op;
> > > +	      if ((code == EQ_EXPR && eq->value == boolean_true_node)
> > > +		  || (code == NE_EXPR && eq->value == boolean_false_node))
> > > +		derive_equivalencs_from_bit_ior (op0, const_and_copies);
> > > +
> > > +	      /* TODO: We could handle BIT_AND_EXPR in a similar fashion
> > > +		 recording that the operands have a nonzero value.  */
> > > +
> > > +	      /* TODO: We can handle more cases here, particularly when OP0 
> > > is
> > > +		 known to have a boolean range.  */
> >
> > I don't think its necessarily useful to put a list here of all possible
> > improvements, but we could also handle things like if ((a | b) </> 0)
> > since those imply !=.
> The equivalences you derive here must hold for both objects.  So without 
> additional range information you can't really determine anything about (a | 
> b) > 0.

I didn't follow the discussion so I am probably completely off, but 
(a|b)>=0 is equivalent to (a>=0)&(b>=0) since it just tests for the sign 
bit (surprisingly we seem to generate different code for the 2 versions).

--
Marc Glisse