[LVI] Infer non-zero from equality icmp (#112838)

This following pattern is common in loop headers:
```
  %101 = sub nuw i64 %78, %98
  %103 = icmp eq i64 %78, %98
  br i1 %103, label %.thread.i.i, label %.preheader.preheader.i.i

.preheader.preheader.i.i:
  %invariant.umin.i.i = call i64 @llvm.umin.i64(i64 %101, i64 9)
  %umax.i = call i64 @llvm.umax.i64(i64 %invariant.umin.i.i, i64 1)
  br label %.preheader.i.i

.preheader.i.i:
  ...
  %116 = add nuw nsw i64 %.011.i.i, 1
  %exitcond.not.i = icmp eq i64 %116, %umax.i
  br i1 %exitcond.not.i, label %.critedge.i.i, label %.preheader.i.i
```
As `%78` is not equal to `%98` in BB `.preheader.preheader.i.i`, we can
prove `%101` is non-zero. Then we can simplify the loop exit condition.

Addresses regression introduced by
https://github.com/llvm/llvm-project/pull/112742.

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/LazyValueInfo.cpp b/llvm/lib/Analysis/LazyValueInfo.cpp
index 10ad470..42b04046 100644
--- a/llvm/lib/Analysis/LazyValueInfo.cpp
+++ b/llvm/lib/Analysis/LazyValueInfo.cpp
@@ -1188,6 +1188,20 @@ std::optional<ValueLatticeElement> LazyValueInfoImpl::getValueFromICmpCondition(
       return ValueLatticeElement::getRange(*CR);
   }
 
+  // a - b or ptrtoint(a) - ptrtoint(b) ==/!= 0 if a ==/!= b
+  Value *X, *Y;
+  if (ICI->isEquality() && match(Val, m_Sub(m_Value(X), m_Value(Y)))) {
+    // Peek through ptrtoints
+    match(X, m_PtrToIntSameSize(DL, m_Value(X)));
+    match(Y, m_PtrToIntSameSize(DL, m_Value(Y)));
+    if ((X == LHS && Y == RHS) || (X == RHS && Y == LHS)) {
+      Constant *NullVal = Constant::getNullValue(Val->getType());
+      if (EdgePred == ICmpInst::ICMP_EQ)
+        return ValueLatticeElement::get(NullVal);
+      return ValueLatticeElement::getNot(NullVal);
+    }
+  }
+
   return ValueLatticeElement::getOverdefined();
 }