diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -11012,8 +11012,10 @@
                                              ICmpInst::Predicate Pred,
                                              const SCEV *LHS, const SCEV *RHS) {
   // Interpret a null as meaning no loop, where there is obviously no guard
-  // (interprocedural conditions notwithstanding).
-  if (!L) return true;
+  // (interprocedural conditions notwithstanding). Do not bother about
+  // unreachable loops.
+  if (!L || !DT.isReachableFromEntry(L->getHeader()))
+    return true;
 
   if (VerifyIR)
     assert(!verifyFunction(*L->getHeader()->getParent(), &dbgs()) &&
@@ -11070,12 +11072,6 @@
       return true;
   }
 
-  // If the loop is not reachable from the entry block, we risk running into an
-  // infinite loop as we walk up into the dom tree.  These loops do not matter
-  // anyway, so we just return a conservative answer when we see them.
-  if (!DT.isReachableFromEntry(L->getHeader()))
-    return false;
-
   if (isImpliedViaGuard(Latch, Pred, LHS, RHS))
     return true;
 
@@ -11121,6 +11117,9 @@
                                                      ICmpInst::Predicate Pred,
                                                      const SCEV *LHS,
                                                      const SCEV *RHS) {
+  // Do not bother proving facts for unreachable code.
+  if (!DT.isReachableFromEntry(BB))
+    return true;
   if (VerifyIR)
     assert(!verifyFunction(*BB->getParent(), &dbgs()) &&
            "This cannot be done on broken IR!");