[llvm] Fold (a % b) lt/ge (b-1) where b is a power of 2 (PR #72504)

[via llvm-commits]

elhewaty wrote:

Does llvm.assume require special handling?

```
{
    Value *X;
    const APInt *C, *CC;
    ICmpInst::Predicate Pred = I.getPredicate();
    if ((Pred == ICmpInst::ICMP_SGE || Pred == ICmpInst::ICMP_SLT) &&
        match(Op0, m_OneUse(m_SRem(m_Value(X), m_APInt(C)))) &&
        match(Op1, m_OneUse(m_Add(m_SpecificInt(*C), m_APInt(CC)))) &&
        !(C->isNegative()) && *CC == -1) {
      // icmp slt (X % C), (C - 1) --> icmp ne (X % C), (C - 1)
      auto *NewCmp = Builder.CreateICmpNE(Op0, Op1);        
      // icmp sge (X % C), (C - 1) --> icmp eq (X % C), (C - 1)
      if (Pred == ICmpInst::ICMP_SGE)
        NewCmp = Builder.CreateICmpEQ(Op0, Op1);
      return replaceInstUsesWith(I, NewCmp);
    }
  }
```
This code doesn't change the tests.

https://github.com/llvm/llvm-project/pull/72504