[llvm] [InstCombine] Canonicalize Bit Testing (PR #101822)

[Yingwei Zheng via llvm-commits]

================
@@ -2304,19 +2305,32 @@ Instruction *InstCombinerImpl::foldICmpShlConstant(ICmpInst &Cmp,
     if (C.isZero() || (Pred == ICmpInst::ICMP_SGT ? C.isAllOnes() : C.isOne()))
       return new ICmpInst(Pred, Shl->getOperand(0), Cmp.getOperand(1));
 
+  unsigned TypeBits = C.getBitWidth();
+  Value *X = Shl->getOperand(0);
+  Type *ShType = Shl->getType();
+
+  // (icmp slt (shl X, (sub bw, Y)), 0)  --> (icmp ne (and X, (shl 1, Y)), 0)
+  // (icmp sgt (shl X, (sub bw, Y)), -1) --> (icmp eq (and X, (shl 1, Y)), 0)
----------------
dtcxzyw wrote:

```suggestion
  // (icmp slt (shl X, (sub bw-1, Y)), 0)  --> (icmp ne (and X, (shl 1, Y)), 0)
  // (icmp sgt (shl X, (sub bw-1, Y)), -1) --> (icmp eq (and X, (shl 1, Y)), 0)
```

https://github.com/llvm/llvm-project/pull/101822