[llvm-dev] Compiler hint for vectors.

[David Greene via llvm-dev]

Deepak Rajendrakumaran via llvm-dev <llvm-dev at lists.llvm.org> writes:

> I'm thinking of adding 'llvm.assume' intrinsics into the IR as optimization
> hints . It works great for scalar values. However I have a number of use
> cases where I deal with vector conditions. Assuming I have '<8 x i1> %cond'
>
> 1. Is there an option other than looping and calling llvm.assume for each
> scalar value?

Maybe?  What kinds of patterns are you looking for?  You could do
various reductions on the i1 vector to detect all 1's/0's, parity,
popcount, etc.  Your targeted optimizations would have to understand the
expressions you construct of course.

> 2. Another open question is, if there any point in introducing the above
> loop if that's the only option i.e, are the relevant optimizations likely
> to kick in this way? p.s. I'll obviously check this out but it'll to good
> to hear if anyone has any experience/opinion.

That's impossible to say without understanding the use cases for vector
assume.

                -David