[llvm] [AMDGPU][AggressiveInstCombine] Narrow 64 bit math to 32 bit if profitable (PR #130577)

[via llvm-commits]

Shoreshen wrote:

> > > > Hi @dtcxzyw , I'm a little bit confusing about the link posted, are you saying that function `@src` is equivalent to function `@tgt`??
> > > 
> > > 
> > > No. I mean `@src` can be optimized into `@tgt`.
> > 
> > 
> > Hi @dtcxzyw with trunc and sext yes, but with the cases added there is no trunc or sext in them.....
> 
> We don't need trunc. These trunc instructions in `@src` are used to make sure that both `%x` and `%y` have at least 10 sign bits.

Hi @dtcxzyw , by trunc + sext, the original value can be changed. If `%x` is b'1000000 then sext(trunc(%x)) = b'11111...1000

What I'm trying to say is that if I'm not wrong, the case `@src` is not equivalent to case as follow:
```
define i16 @src(i16 %x, i16 %y) {
#0:
  %ax = and i16 %x to b'1111111
  %ay = and i16 %y to b'1111111
  %add = add i16 %ax, %ay
  ret i16 %add
}
```

https://github.com/llvm/llvm-project/pull/130577