On Friday, 10 May 2019 at 23:58:37 UTC, Mike Franklin wrote:
I don't know how a proper assembly implementation would not be
performant. Perhaps you could elaborate.
Inline assembly prevents a lot of optimizations that give large
performance gains such as constant propagation. Say you implement
a memcpy with a different signature than C's mempcy (because of
slices instead of pointers), then the optimizer does not know
what the semantics of that function are and will need the
function to be transparent (not assembly) to do such
optimizations.
But I'm sure you know all that, so that's not your question. :)
In the case of reimplementing memcpy/mem* in a function with the
same signature as libc, that is not supposed to be inlined (like
the current libc functions), then I also think the use of inline
asm will not give a perf penalty. Be careful to recreate the
exact same semantics as those libc functions because the
optimizer is going to _assume_ it knows _exactly_ what those
functions are doing.
cheers,
Johan
