Simple bitop reassoc in match.pd

[Richard Biener]

On Wed, May 11, 2016 at 7:56 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
> On Wed, 11 May 2016, Jeff Law wrote:
>
>>> We could also simplify (int)(_Bool)x to x using VRP information that x
>>> is in [0, 1], but apparently when VRP replaces x==0 with y=x^1,(_Bool)y,
>>> it does not compute a range for the new variable y, and by the time the
>>> next VRP pass comes, it is too late.
>>
>> Seems like a clear oversight.
>
>
> In get_value_range, there is:
>   /* If we query the range for a new SSA name return an unmodifiable
> VARYING.
>      We should get here at most from the substitute-and-fold stage which
>      will never try to change values.  */
> so this is a known limitation.
>
> We could try to change that (XRESIZEVEC, memset(0) on the new elements,
> update num_vr_values to the new num_ssa_names, at this point vr_value should
> be replaced with a vector).
>
> We could also use set_range_info and make simplify_conversion_using_ranges
> use get_range_info instead of get_value_range. Might even move the whole
> function to match.pd then ;-)

Yeah - note that VRP already calls set_range_info before simplifying
stmts.  It's
just that substitute_and_fold doesn't apply fold_stmt (and thus match.pd) to
all stmts but it only applies the pass specific "fold" (vrp_fold_stmt)
to all stmts.

Richard.

> --
> Marc Glisse