diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -597,17 +597,10 @@
   if (Inv->getParent() != CxtI->getParent())
     return false;
 
-  // If we have a dom tree, then we now know that the assume doesn't dominate
-  // the other instruction.  If we don't have a dom tree then we can check if
-  // the assume is first in the BB.
-  if (!DT) {
-    // Search forward from the assume until we reach the context (or the end
-    // of the block); the common case is that the assume will come first.
-    for (auto I = std::next(BasicBlock::const_iterator(Inv)),
-         IE = Inv->getParent()->end(); I != IE; ++I)
-      if (&*I == CxtI)
-        return true;
-  }
+  // If Inv and CtxI are in the same block, check if the assume (Inv) is first
+  // in the BB.
+  if (Inv->comesBefore(CxtI))
+    return true;
 
   // Don't let an assume affect itself - this would cause the problems
   // `isEphemeralValueOf` is trying to prevent, and it would also make