[WebAssembly][SDAG] Use partial reduction ISD nodes

[MacDue]

WebAssembly is the only target now using the (poorly named) TargetLowering::shouldExpandPartialReductionIntrinsic hook. Once it moves to the PARTIAL_REDUCE_* ISD nodes, the hook can be removed.

The WebAssembly target implements some patterns that match the intrinsics (via INTRINSIC_WO_CHAIN) that need to be ported to using the PARTIAL_REDUCE_* opcodes.

[llvmbot]

@llvm/issue-subscribers-backend-webassembly

Author: Benjamin Maxwell (MacDue)

WebAssembly is the only target now using the (poorly named) `TargetLowering::shouldExpandPartialReductionIntrinsic` hook. Once it moves to the `PARTIAL_REDUCE_*` ISD nodes, the hook can be removed.

The WebAssembly target implements some patterns that match the intrinsics (via INTRINSIC_WO_CHAIN) that need to be ported to using the PARTIAL_REDUCE_* opcodes.

[dschuff]

@sparker-arm has recently implemented this in the Wasm backend. Do you have an opinion on this? Would you be able to update it?

[sparker-arm]

Yeah, I'll look into it.

[MacDue]

Resolved in #161184