[llvm-dev] [RFC] Vector Predication

Luke Kenneth Casson Leighton via llvm-dev llvm-dev at lists.llvm.org
Fri Feb 1 16:39:22 PST 2019

On Friday, February 1, 2019, Simon Moll <moll at cs.uni-saarland.de> wrote:
> We could untie the mask length from the data length:
>   %result = call <scalable 4 x float> @llvm.evl.fsub.v4f32(<scalable 4 x
> float> %x, <scalable 4 x float> %y, <scalable 1 x i1> %M, i32 %L)
> would then indicate the mask %M applies to groups of "4 / 1" float
> elements.

That would provide the greatest flexibility, as a 1:1 ratio could mean 1
bit per element, covering the normal case.

Question: are there any circumstances under which it is desirable to
underspecify or overspecify the number of bits in the predicate?

ie to deliberately have a FP vector of length 11 and a mask of length 9 or

Or, is that just a runtime error.


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