erichkeane added inline comments.
================
Comment at: clang/include/clang/Basic/Specifiers.h:283
CC_AArch64VectorCall, // __attribute__((aarch64_vector_pcs))
+ CC_AArch64SVEPcs, // __attribute__((aarch64_sve_pcs))
};
----------------
aaron.ballman wrote:
> I continue to be concerned with how many custom calling conventions we're
> adding. We're running out of bits to store them and when we bump up against
> the next limitation (32 possible calling conventions, this patch brings us up
> to 20), we're going to lose a significant amount of performance due to extra
> memory overhead pressure (which, in turn, will greatly reduce our maximum
> template instantiation depth) with no clear path forward. We've looked into
> this before and once we hit that 32 calling convention limit, we won't be
> adding any new calling conventions until we solve the memory pressure problem.
>
> Are there other alternatives than making a new calling convention? (e.g., can
> this be handled with a backend pass somehow, or some other implementation
> strategy?)
> Is this calling convention going to be used often enough to warrant adding
> it? (e.g., will this be showing up in system headers or other major
> third-party library headers, or is this a one-off for people trying to eek
> the last ounce of performance out of a function call?)
I agree with this, our list of calling conventions needs to find a way to get
smaller, not larger. our `ExtInfo` is already shocking/frighteningly large use
of bits with calling conventions taking 5. IMO, we should reduce this to 4
bits if at all possible, particularly since we're likely to need more bits in
the function-type thanks to the C++ committee.
Internally, Ive been fighting pretty hard to keep us from extending this list
unless at all possible, and I think we need to do so here.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D124998/new/
https://reviews.llvm.org/D124998
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