[llvm-dev] [RFC] Vector Predication

Luke Kenneth Casson Leighton via llvm-dev llvm-dev at lists.llvm.org
Fri Feb 1 16:29:49 PST 2019

On Friday, February 1, 2019, Jacob Lifshay <programmerjake at gmail.com> wrote:

Neat! I did not know that about the V extension. So this sounds as though
> the V extension would like support for <VL x <4 x float>>-style vectors as
> well.
> We are currently thinking of defining the extension in terms of a 16-bit
> prefix that changes standard 32-bit instructions into vectorized 48-bit
> instructions,
(and Compressed 16-bit ones into vectorised 32-bit, unmodified)

 allowing most future or current standard/non-standard extensions to be
> vectorized, rather than having to wait for additional extensions to have
> vector versions added to the V extension (one reason we are not using the V
> extension instead), such as the B extension.

(and there isn't enough free RISCV 32 bit opcode space to add vectorised
versions of xBitManip, nor any future custom or standard ops. So the
simplest most powerful way to move forward quickly and without disruption
is a prefix)


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