[llvm] [X86][SimplifyCFG] Support hoisting load/store with conditional faulting (PR #96878)

[Shengchen Kan via llvm-commits]

KanRobert wrote:

> 1. run these three transforms of SimplifyCFG rightly before CodeGenPrepare if the target supports conditional faulting, to avoid the awkwardness?
> 2. extend LLVM IR to support scalar versioned masked.load/store.
> 3. enhance the support for masked loads/stores for 1x %T throughout the middle-end passes after SimplifyCFG
> 
> dtcxzyw: I prefer the second one.

@nikic @DianQK Vote?

https://github.com/llvm/llvm-project/pull/96878