[PATCH] Fix up wi::lrshift (PR c++/69399)

[Richard Biener]

On Wed, Jan 27, 2016 at 12:41 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Tue, Jan 26, 2016 at 01:55:41PM -0800, Mike Stump wrote:
>> On Jan 26, 2016, at 1:26 PM, Jakub Jelinek <jakub@redhat.com> wrote:
>> > will do cc1plus size comparison afterwards.
>>
>> We know the dynamic check is larger.  You can’t tell the advantage of
>> speed from size.  Better would be to time compiling any random large
>> translation unit.
>>
>> Nice to see that only 14 calls remain, that’s way better than the 34 I
>> thought.
>
> So, it seems probably the PR65656 changes made things actually significantly
> worse, while I see a (small) difference in the generated code between the two
> patches if I compile say tree-ssa-ccp.c with g++ 5.x, in the bootstrapped
> compiler there is no difference at all, the compilers with either patch
> have identical objdump -dr cc1plus.  Already at *.gimple time all the
> relevant __builtin_constant_p are resolved and it seems all to 0.
>
> So please agree on one of the two patches (don't care which), and I'll try
> to distill a testcase to look at for PR65656.

I don't care if the wi::lshift by LOG2_BITS_PER_UNIT done by
get_ref_base_and_extent
are compiled to as good quality as before (I suspect it doesn't matter
in this case
as the shift amount is constant, but maybe due to PR65656 the
non-STATIC_CONSTANT_P
variant is better).

Richard.

>         Jakub