[llvm] [GlobalIsel] Combine G_ADD and G_SUB with constants (PR #97771)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

They are running commercial static analyzers over the project. They will scream when they find unchecked access to optionals.
We have our own unchecked access checker:
https://github.com/llvm/llvm-project/blob/main/clang/lib/Analysis/FlowSensitive/Models/UncheckedOptionalAccessModel.cpp
The LLVM community decided to check optionals before accessing them.
Even if the probability of `std::nullopt` is a joke, we still need to check before accessing optionals.

This is the wrong approach.

https://github.com/llvm/llvm-project/pull/97771