[clang] [llvm] [RISCV] Inline Assembly Support for GPR Pairs ('Pr') (PR #112983)

[Sam Elliott via cfe-commits]

lenary wrote:


> I'm concerned that if we make i128 legal, we will have to write custom splitting code for every operation. Using v2i64 probably has other problems conflicting with the V extension fixed vector support.

I sort-of expected that making `i128` legal would be problematic, I didn't realise that `v2i64` would also conflict with something we're currently using.

> The Arch64 MVT::i64x8 may be a way to work around this. We could have a special pair MVT only used by inline assembly.

Ok, this sounds doable - so something like `MVT::xlen_pair` is the way I'll lean, rather than a different type for rv32/rv64.

https://github.com/llvm/llvm-project/pull/112983