[llvm] [RISCV][GISel] Remove support for s32 G_VAARG on RV64. (PR #102533)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

I thought the point of promoting to s64 is to get better codegen. Why not keep this as legal even if it emits non-optimal code? 

https://github.com/llvm/llvm-project/pull/102533