[llvm] [GlobalIsel] Combine logic of floating point compares (PR #81886)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

InstCombine combines the overflow intrinsics to the fullest. GlobalIsel and the Dag have named opcodes for overflow intrinsics.
GlobalIsel: G_SADDO reads as signed addition overflow.

What is the policy for the GlobalIsel combiner:
* refuse to combine them
* combine the to the fullest with even new tricks
* something in the middle
?

https://github.com/llvm/llvm-project/pull/81886