[llvm] [InstCombine] Combine and->cmp->sel->or-disjoint into and->mul (PR #135274)

[Jeffrey Byrnes via llvm-commits]

jrbyrnes wrote:

> I thought the conclusion in a previous PR was to avoid introducing mul?

I would say its more of an open concern rather than a conclusion.

My thought was that 

```
%T1 = and %X, %BitMask
%T2 = mul %T1, %Factor
```

was the canonical form of

```
%T1 = and %X, %BitMask
%Cmp = icmp eq i32 %T1, 0
%T2 = select i1 %Cmp, i32 0, %C
```

given certain conditions.

In https://github.com/llvm/llvm-project/pull/133139#issuecomment-2773977867 we discussed the case where %BitMask is 1 (should be lowered into trunc). And for the general case there was concern over the `mul` form due to CodeGen concerns. However, I think there is still a valid argument that the `mul` form is canonical.

That said, this PR most certainly produces canonical form as its combining 2 `and`s, 2 `icmp`s and 2 `select`s into 1 `and` and 1 `mul`

https://github.com/llvm/llvm-project/pull/135274