[llvm] [GISEL] Add G_INSERT_SUBVECTOR and G_EXTRACT_SUBVECTOR (PR #84538)

[Craig Topper via llvm-commits]

topperc wrote:

I just read the description of G_INSERT and G_EXTRACT. They sound exactly like G_INSERT_SUBVECTOR and G_EXTRACT_SUBVECTOR. They don't use a subreg index.

https://github.com/llvm/llvm-project/pull/84538