[llvm] [SelectionDAG] Change SSUBO to do (LHS < RHS) XOR (RESULT < 0) (PR #191747)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> What's the motivation for this? Is it supposed to generate better code overall? (If so, that is not obvious to me from skimming the codegen changes.)

Some of the RISCV changes look like net -1 instruction 

https://github.com/llvm/llvm-project/pull/191747