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riscv-non-isa / riscv-c-api-doc

Documentation of the RISC-V C API
https://lf-riscv.atlassian.net/browse/RVG-4
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Support for C operators on RVV types #50

Open jacquesguan opened 1 year ago

jacquesguan commented 1 year ago

Now clang support some C operators (such as: arithmetic, bitwise and subscript) for SVE sizeless types. I think we could support these operator for RVV sizeless too. Actually in some real cases where vl=vlmax and without mask, using operators instead of builtin is more clear and would enable more ir/backend optimizations. I create a llvm patch here: https://reviews.llvm.org/D158259

jacquesguan commented 1 year ago

I am not sure this issue should discuss here or in https://github.com/riscv-non-isa/rvv-intrinsic-doc since it isn't an instrinsic problem.

cmuellner commented 1 year ago

Thanks for bringing this topic up! We briefly touched this today in the SIG Toolchain call. @eopXD (chair of the vector intrinsics TG) will discuss this within the Vector Intrinsics TG.

eopXD commented 1 year ago

Hi @jacquesguan,

We will be discussing this in the RVV C intrinsics meeting today [0]. If possible, may you attend the meeting and propose what you have in hand?

Thank you.

[0] Meeting reminder 10/03

jacquesguan commented 1 year ago

Hi @jacquesguan,

We will be discussing this in the RVV C intrinsics meeting today [0]. If possible, may you attend the meeting and propose what you have in hand?

Thank you.

[0] Meeting reminder 10/03

Sorry, I was on vocation in that day and just read this comment right now.

eopXD commented 1 year ago

Hi JianJian,

No problem. It was discussed on the meeting that there is not much push back for this syntax sugar that can help porting for libraries that targets other architectures. So I guess we can proceed by proposing your targeting behavior in the intrinsics document.

On the other hand, I am curious about the optimizations you mentioned that would be enabled. Wouldn't it be the same if vlmax is specified in the intrinsic functions?

jacquesguan commented 1 year ago

Hi JianJian,

No problem. It was discussed on the meeting that there is not much push back for this syntax sugar that can help porting for libraries that targets other architectures. So I guess we can proceed by proposing your targeting behavior in the intrinsics document.

On the other hand, I am curious about the optimizations you mentioned that would be enabled. Wouldn't it be the same if vlmax is specified in the intrinsic functions?

If we use intrinsics, I believe that IR combiner and DAG combine wouldn't work.

by example,

vec_c = vec_a + vec_b; vec_d = vec_c - vec_b;

If we write it in intrinsic, vec_d will still be calculated by vadd and vsub not directly the value of vec_a.