Re: [PATCH][RFH] Fix PR31169, bootstrap failure on SHIFT_COUNT_TRUNCATED targets

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 4/1/07, Richard Henderson <rth@redhat.com> wrote:
> On Sat, Mar 31, 2007 at 12:11:05PM +0200, Richard Guenther wrote:
> > It looks like a very bad design to have target dependencies in routines
> > computing with double HOST(!)_WIDE_INTs.
>
> I agree, but, as I said, I don't think we can *just* remove it.
>
> > After all, it's only combine and cse that seem to care about
> > SHIFT_COUNT_TRUNCATED.
>
> I'd agree that the check ought to be moved into some routine
> that only deals with rtl.
>
> OTOH, I don't agree that we ought to rely on particular shift
> behaviour at the tree level either, and that's what simply
> removing the check from rshift_double would do -- it would
> make tree-vrp rely on large-shift-generates-zero behaviour.
>
> I've given my previous patch some more thought, and think that
> the test I had isn't really correct either.  In this new patch,
> I fall back to varying in case the shift count can possibly be
> outside the range of defined values.
>
>
> r~
>
>
>         PR tree-optimization/31169
>         * tree-vrp.c (extract_range_from_binary_expr) <RSHIFT_EXPR>: Drop
>         to varying if the range is outside [0,  prec-1].

I have added the following testcase.

Richard.

2007-04-12  Richard Guenther  <rguenther@suse.de>

       PR tree-optimization/31169
       * gcc.c-torture/execute/pr31169.c: New testcase.

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