[llvm] [InstCombine] Fix fail to fold (A >> C1) Pred C2 if shr is used multple times #83430 (PR #83563)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> @dtcxzyw, I was experimenting with SPF code and added some logic before the `if (TrueVal == CmpLHS && FalseVal == CmpRHS)` statement. but it didn't work because of this:
> 
> ```llvm
> (lldb) expr SI->getCondition()->dump()
>  %switch.i = xor i1 %cmp4.i, true
> ```

You should match this with `m_Not`, then update the cmp predicate with `CmpInst::getInversePredicate`.
```
bool Invert = false;
Value *Condition = SI->getCondition();
Value *X;
if (match(Condition, m_Not(X)) {
  Invert = true;
  Condition = X;
}

CmpInst::Predicate Pred;
Value *CmpLHS, *CmpRHS;
if (!match(Condition, m_ICmp(Pred, m_Value(CmpLHS), m_Value(CmpRHS)))
   fail...

if (Invert)
  Pred = CmpInst::getInversePredicate(Pred);

...
```


https://github.com/llvm/llvm-project/pull/83563