[llvm] [DemandedBits] Track demanded bits for clmul instrinsics (PR #202415)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

The clmul support is available now (see https://github.com/AliveToolkit/alive2/pull/1318). But it hasn't been deployed to alive2.llvm.org.

```
; ./alive-tv --disable-undef-input test.ll
define i8 @src(i8 %x, i8 %y, i8 range(i8 1, 0) %demanded) {
  %clmul = call i8 @llvm.clmul.i8(i8 %x, i8 %y)
  %masked = and i8 %clmul, %demanded
  ret i8 %masked
}

define i8 @tgt(i8 %x, i8 %y, i8 %demanded) {
  %lz = call i8 @llvm.ctlz.i8(i8 %demanded, i1 true)
  %mask = lshr i8 -1, %lz
  %masked_x = and i8 %x, %mask
  %masked_y = and i8 %y, %mask
  %clmul = call i8 @llvm.clmul.i8(i8 %masked_x, i8 %masked_y)
  %masked = and i8 %clmul, %demanded
  ret i8 %masked
}
```
```
----------------------------------------
define i8 @src(i8 %x, i8 %y, i8 %demanded) {
init:
  %#range_0_%demanded = !range i8 %demanded, i8 1, i8 0
  br label %#0

#0:
  %clmul = clmul i8 %x, %y
  %masked = and i8 %clmul, %#range_0_%demanded
  ret i8 %masked
}
=>
define i8 @tgt(i8 %x, i8 %y, i8 %demanded) {
#0:
  %lz = ctlz i8 %demanded, 1
  %mask = lshr i8 255, %lz
  %masked_x = and i8 %x, %mask
  %masked_y = and i8 %y, %mask
  %clmul = clmul i8 %masked_x, %masked_y
  %masked = and i8 %clmul, %demanded
  ret i8 %masked
}
Transformation seems to be correct!
```

https://github.com/llvm/llvm-project/pull/202415