[llvm] [InstCombine] Canonicalize xor with disjoint ops to or disjoint (PR #133139)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> > What was the original sequence that exceeds the limit?
> 
> See for a representation of the original sequence
> 
> https://godbolt.org/z/9rE9dneT9
> 
> There is an opportunity for another instcombine in this sequence -- we can transform
> 
> ```
> %i48 = and i32 %i28, 1
> %i.not2 = icmp eq i32 %i48, 0
> %i144 = select i1 %i.not2, i32 0, i32 72
> ```
> 
> into
> 
> ```
> %i48 = and %i28, 1
> %i144 = mul i32 %i48, 72
> ```
> 

I don't think this transformation is profitable. Generally cmov is cheaper than mul.
InstCombiner performs similar transformations in foldSelectICmpAndBinOp for add/xor/shl/lshr/ashr/..., but not for mul.


https://github.com/llvm/llvm-project/pull/133139