[llvm] Allow folding icmp eq (add X, C2), C when there is more than one-use when we can compute the range (PR #144566)

[via llvm-commits]

AZero13 wrote:

> > > > @topperc this is having too many side effects. I think we should do what I originally did for now and then I will invest working on a proper fix because this is not going to be easily done in one PR
> > > 
> > > 
> > > Ok. Is there a known workload that benefits from this?
> > 
> > 
> > Plenty. Let me ask @dtcxzyw
> 
> X86/RISCV/ARM/AArch64 all generates the same code for these two IR functions. Do I need a larger test case to show improved code generation?
> 
> ```
> define i32 @add_check_zero(i32 %num) {                                           
>   %add = add i32 %num, 1
>   %cmp = icmp eq i32 %add, 0
>   %cond = select i1 %cmp, i32 -1, i32 %add
>   ret i32 %cond
> }
>                                                                                  
> define i32 @add_check_zero_opt(i32 %num) {
>   %a = call i32 @llvm.uadd.sat.i32(i32 %num, i32 1)
>   ret i32 %a
> }
> ```

It's more about the IR optimization, not just codegen.

https://github.com/llvm/llvm-project/pull/144566