https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113583
--- Comment #1 from JuzheZhong <juzhe.zhong at rivai dot ai> ---
It's interesting, for Clang only RISC-V can vectorize it.
I think there are 2 topics:
1. Support vectorization of this codes of in loop vectorizer.
2. Transform gather/scatter into strided load/store for RISC-V.
For 2nd topic: LLVM does it by RISC-V target specific lowering pass:
RISC-V gather/scatter lowering (riscv-gather-scatter-lowering)
This is the RISC-V LLVM backend codes:
if (II->getIntrinsicID() == Intrinsic::masked_gather)
Call = Builder.CreateIntrinsic(
Intrinsic::riscv_masked_strided_load,
{DataType, BasePtr->getType(), Stride->getType()},
{II->getArgOperand(3), BasePtr, Stride, II->getArgOperand(2)});
else
Call = Builder.CreateIntrinsic(
Intrinsic::riscv_masked_strided_store,
{DataType, BasePtr->getType(), Stride->getType()},
{II->getArgOperand(0), BasePtr, Stride, II->getArgOperand(3)});
I have ever tried to support strided load/store in GCC loop vectorizer,
but it seems to be unacceptable. Maybe we can support strided load/stores
by leveraging LLVM approach ???
Btw, LLVM risc-v gather/scatter didn't do a perfect job here:
vid.v v8
vmul.vx v8, v8, a3
....
vsoxei64.v v10, (s2), v14
This is in-order indexed store which is very costly in hardware.
It should be unorder indexed store or strided store.
Anyway, I think we should investigate first how to support vectorization of lbm
in loop vectorizer.
