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RE: [MIPS] Add sbasic supoert ffor MSA (SIMD)


> You shouldn't need to declare __builtin_* functions anyway.  And if a
> function can be represented directly with GNU C vector extensions, it's
> preferred to implement it that way inline in the header rather than having
> built-in functions duplicating existing GNU C functionality.  (Look at
> what AArch64 arm_neon.h does where possible, and what ARM arm_neon.h has
> been moved towards lately.  I don't now what the msa.h functions do, so I
> don't know if this actually applies to any of them - but it's something to
> consider, so that built-in functions are only defined where actually
> needed.)

In the aarch64 arm_neon.h header there are a decent number of inline asm
implementations too instead of builtins. It is not immediately obvious to me
as to what the deciding factor is between adding a builtin and using inline
asm when vector extensions do not support the operation. Do you happen to
know why inline asm is used in places?

This looks like a reasonable idea to use GNU extensions where available. The
down-side to this approach is that it may be necessary to write quite
dis-similar headers for LLVM vs GCC which I think is part of the reason why
the header is written as it is. I don't know if that is a good reason to
require builtins or not though.

Regards,
Matthew


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