[llvm] [GlobalIsel] Visit ICmp (PR #105991)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

I may be blind, but I couldn't find any requests for known bits in visitICmp. matchCmpOfZero has requests for known bits. It is the icmp x, 0 C++ part.

In the AMDGPU tests, there are many hits of the icmp x, 0 combine. In many case, I could find something like, e.g., 
`v_cmp_eq_u32_e64 s[4:5], 0, v5` . To me it reads like an icmp with a zero on the left hand side.

If you ask me to split the canonicalization of constants on icmps to the right and the icmp x, 0 combine into two PRs, then both PRs are not profitable.



There is exactly one combine, which relies on known bits. The icmp x, 0 combine, which has a precise MIR pattern.

https://github.com/llvm/llvm-project/pull/105991