Re: [PATCH 3/3] AVX512 fully masked vectorization

[Richard Sandiford <richard.sandiford@arm.com>]

Andrew Stubbs <ams@codesourcery.com> writes:
> One 
> comment: building a vector constant {0, 1, 2, 3, ...., 63} results in a 
> very large entry in the constant pool and an unnecessary memory load (it 
> literally has to use this sequence to generate the addresses to load the 
> constant!) Generating the sequence via VEC_SERIES would be a no-op, for 
> GCN, because we have an ABI-mandated register that already holds that 
> value. (Perhaps I have another piece missing here, IDK?)

A constant like that should become a CONST_VECTOR in RTL, so I think
the way to handle it would be to treat such a CONST_VECTOR as a valid
immediate operand, including providing an alternative for it in the
move patterns.  const_vec_series_p provides a quick way to test.

Thanks,
Richard