Index: lib/Analysis/LazyValueInfo.cpp
===================================================================
--- lib/Analysis/LazyValueInfo.cpp
+++ lib/Analysis/LazyValueInfo.cpp
@@ -930,6 +930,37 @@
     if (EdgesMissing)
       continue;
 
+    // If this is an identity arc, we cannot be less specific now than we were
+    // before.
+    if (PhiVal == PN)
+      EdgeResult = intersect(EdgeResult, Result);
+
+    // If the PHI has known bounds already and this is an increment, we can
+    // produce a much more accurate lattice value than overdefined.
+    if ((EdgeResult.isOverdefined() ||
+         (EdgeResult.isConstantRange() &&
+          EdgeResult.getConstantRange().isFullSet())) &&
+        (Result.isConstant() || Result.isConstantRange())) {
+      // Can we determine this is a monotonically increasing increment?
+      ConstantInt *Inc;
+      bool NSW = match(PhiVal, m_NSWAdd(m_Specific(PN), m_ConstantInt(Inc)));
+      bool NUW =
+        !NSW && match(PhiVal, m_NUWAdd(m_Specific(PN), m_ConstantInt(Inc)));
+      if ((NSW || NUW) && !Inc->isNegative()) {
+        APInt Start = Result.isConstant()
+          ? cast<ConstantInt>(Result.getConstant())->getValue()
+          : Result.getConstantRange().getLower();
+        APInt End = NSW ? APInt::getSignedMaxValue(Start.getBitWidth())
+          : APInt::getMaxValue(Start.getBitWidth());
+        EdgeResult = LVILatticeVal::getRange(ConstantRange(Start, End));
+
+        // We've discovered that this is a monotonically increasing increment.
+        // PhiVal may have been cached; in this case we must erase it so that
+        // it is recomputed based on this new information.
+        TheCache.eraseValue(PhiVal);
+      }
+    }
+
     Result.mergeIn(EdgeResult, DL);
 
     // If we hit overdefined, exit early.  The BlockVals entry is already set
Index: test/Transforms/CorrelatedValuePropagation/monotonic.ll
===================================================================
--- /dev/null
+++ test/Transforms/CorrelatedValuePropagation/monotonic.ll
@@ -0,0 +1,27 @@
+; RUN: opt -S < %s -correlated-propagation | FileCheck %s
+
+; CHECK-LABEL: @f
+; CHECK:  = phi i32 {{.*}} [ 3, %select.unfold ]
+define void @f() {
+entry:
+  br label %while.cond
+
+select.unfold:                                    ; preds = %while.body
+  br label %while.cond
+
+while.cond:                                       ; preds = %while.body, %select.unfold, %entry
+  %i.0 = phi i32 [ 2, %entry ], [ %i.0, %while.body ], [ %add, %select.unfold ]
+  %cmp = icmp slt i32 %i.0, 3
+  br i1 %cmp, label %while.body, label %return
+
+while.body:                                       ; preds = %while.cond
+  %add = add nsw i32 %i.0, 1
+  %call = call i32 @g()
+  %cmp3 = icmp eq i32 %call, 0
+  br i1 %cmp3, label %select.unfold, label %while.cond
+
+return:
+  ret void
+}
+
+declare i32 @g()