Re: [COMMITTED] [range-op] Take known set bits into account in popcount [PR107053]

[Aldy Hernandez <aldyh@redhat.com>]

On 7/12/23 23:50, Jeff Law wrote:
> 
> 
> On 7/12/23 15:15, Aldy Hernandez via Gcc-patches wrote:
>> This patch teaches popcount about known set bits which are now
>> available in the irange.
>>
>>     PR tree-optimization/107053
>>
>> gcc/ChangeLog:
>>
>>     * gimple-range-op.cc (cfn_popcount): Use known set bits.
>>
>> gcc/testsuite/ChangeLog:
>>
>>     * gcc.dg/tree-ssa/pr107053.c: New test.
> You could probably play similar games with ctz/clz, though it's hard to 
> know if it's worth the effort.
> 
> One way to find out might be to build jemalloc which uses those idioms 
> heavily.  Similarly for deepsjeng from spec2017.
> 
> Jeff
> 

See class cfn_clz and class cfn_ctz in gimple-range-op.cc.  There's 
already code for both of these, although they're throwback from the VRP 
era, so there's definitely room for improvement.  I think they came from 
vr-values.cc.

Aldy