[PATCH] D112268: [LegalizeTypes][RISCV][PowerPC] Expand CTLZ/CTTZ/CTPOP instead of promoting if they'll be expanded later.

[Thomas Preud'homme via Phabricator via llvm-commits]

thopre added a comment.

In D112268#3138877 <https://reviews.llvm.org/D112268#3138877>, @craig.topper wrote:

> In D112268#3138874 <https://reviews.llvm.org/D112268#3138874>, @thopre wrote:
>
>> In D112268#3138471 <https://reviews.llvm.org/D112268#3138471>, @craig.topper wrote:
>>
>>> In D112268#3137708 <https://reviews.llvm.org/D112268#3137708>, @thopre wrote:
>>>
>>>> Hi @craig.topper ,
>>>>
>>>> This caused a regression for us for i16 cttz with is_undef_zero true because cttz is expanded to a sequence using ctpop which loses the fact that any output is ok for the 0 case.
>>>>
>>>>   t17: i16 = sub t9, Constant:i16<1>
>>>>   t19: i16 = xor t9, Constant:i16<-1>
>>>>   t20: i16 = and t19, t17
>>>>   t21: i16 = ctpop t20
>>>>
>>>> So when this gets promoted, a mask is inserted to not have the result of ctpop change when `t9` is 0.
>>>>
>>>>   t15: i32 = extract_vector_elt t2, Constant:i32<0>
>>>>   t25: i32 = xor t15, Constant:i32<-1>
>>>>   t23: i32 = sub t15, Constant:i32<1>
>>>>   t26: i32 = and t25, t23
>>>>   t28: i32 = and t26, Constant:i32<65535>
>>>>   t29: i32 = ctpop t28
>>>>
>>>> Prior to this patch, we'd get:
>>>>
>>>>   t19: i32 = sub t15, Constant:i32<1>
>>>>   t21: i32 = xor t15, Constant:i32<-1>
>>>>   t22: i32 = and t21, t19
>>>>   t23: i32 = ctpop t22
>>>>
>>>> I thought about inserting some llvm.assume saying the value is non zero when expanding but those work at IR level. Any pointer on how to solve this? Best regards.
>>>
>>> I take it i32 ctpop is legal for your target or the i16 ctpop would have gotten expanded too?
>>
>> Correct.
>
> I just pushed d78fdf111dda26307e88d16f5f5d1411f3bd7e61 <https://reviews.llvm.org/rGd78fdf111dda26307e88d16f5f5d1411f3bd7e61> can you let me know if that fixes the issue?

It does yes, codegen back to where it was. Thanks a lot!


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  https://reviews.llvm.org/D112268/new/

https://reviews.llvm.org/D112268