Re: [PATCH 3/4 v2] Enhance SCEV to follow copies of SSA_NAMEs.

[Alan Lawrence <alan dot lawrence at foss dot arm dot com>]

On 15/01/16 10:07, Richard Biener wrote:
> On Fri, Jan 15, 2016 at 10:47 AM, Alan Lawrence <alan.lawrence@arm.com> wrote:
> > On Thu, Jan 14, 2016 at 12:30 PM, Richard Biener <richard.guenther@gmail.com> wrote:
> >
> > > The vuse test is not necessary
> > >
> > > > +              && (gimple_assign_rhs_code (def) == SSA_NAME
> > > > +                  || is_gimple_min_invariant (gimple_assign_rhs1 (def))))
> > >
> > > and the is_gimple_min_invariant (rhs1) test is not sufficient if you
> > > consider - (-INT_MIN) with -ftrapv for example.
> >
> > Thanks, I didn't realize gimple_min_invariant would allow such cases.
>
> Well, the invariant would be -INT_MIN but gimple_assign_rhs_code (def) would
> be NEGATE_EXPR.  Basically you forgot about unary operators.

Hmm, shouldn't those have get_gimple_rhs_class(gimple_assign_rhs_code(stmt)) == 
GIMPLE_UNARY_RHS, rather than GIMPLE_SINGLE_RHS as checked for by 
gimple_assign_single_p?

If SINGLE_RHS includes unary operators, the new version of the patch is as 
flawed as the previous, in that it drops the unary operator altogether.

--Alan