[cfe-dev] [RFC] Opt-in vector of bool type
Simon Moll via cfe-dev
cfe-dev at lists.llvm.org
Fri May 15 06:16:23 PDT 2020
On 5/14/20 6:23 PM, Richard Sandiford wrote:
> FWIW, this would also be useful for SVE predicates when generating
> fixed-length code.
Yes, i imagine that a lot of SIMD/vector targets would benefit from this.
> It's convenient that both GCC and clang reject boolean element types
> as thing stand, e.g.:
> typedef bool foo __attribute__((vector_size(32)));
> I think this means that it should be possible to treat packed boolean
> vectors as a pure extension to what exists today. Compatibility with
> older compilers shouldn't be a concern, it would just be a new feature.
> GCC is a moving target too, and I don't know of any reason in principle
> why GCC would never support this. A lot of the necessary plumbing
> already exists.
> So far the principle has been that vector_size should work the same
> way regardless of the current target, with the compiler deciding
> how best to implement the code. I think it would be good to follow
> that for any extension too, rather than making the feature opt-in and
> introducing a new target dependency.
I have to say i am pleasantly surprised by the positive feedback for
this proposal :) If there are no principal reservations against going
ahead with this, i'll submit a patch on Phabricator that enables 'bool'
in vector_size by default for all targets, so, basically a revert of:
Author: Aaron Ballman <aaron at aaronballman.com>
Date: Fri Sep 13 20:43:08 2013 +0000
vector_size cannot be applied to Booleans. Updated the semantic
checking logic, as well as the comment and added a test case. Fixes PR12649
We can flesh out the details during review.
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