diff --git a/llvm/lib/Transforms/Scalar/SCCP.cpp b/llvm/lib/Transforms/Scalar/SCCP.cpp
--- a/llvm/lib/Transforms/Scalar/SCCP.cpp
+++ b/llvm/lib/Transforms/Scalar/SCCP.cpp
@@ -20,6 +20,7 @@
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/STLExtras.h"
@@ -219,6 +220,7 @@
   // The BasicBlock work list
   SmallVector<BasicBlock *, 64>  BBWorkList;
 
+
   /// KnownFeasibleEdges - Entries in this set are edges which have already had
   /// PHI nodes retriggered.
   using Edge = std::pair<BasicBlock *, BasicBlock *>;
@@ -228,6 +230,7 @@
   DenseMap<Value *, SmallPtrSet<User *, 2>> AdditionalUsers;
 
 public:
+  SetVector<Function *> PossiblyUndefined;
   void addAnalysis(Function &F, AnalysisResultsForFn A) {
     AnalysisResults.insert({&F, std::move(A)});
   }
@@ -258,6 +261,7 @@
       return false;
     LLVM_DEBUG(dbgs() << "Marking Block Executable: " << BB->getName() << '\n');
     BBWorkList.push_back(BB);  // Add the block to the work list!
+    PossiblyUndefined.insert(BB->getParent());
     return true;
   }
 
@@ -1862,13 +1866,16 @@
   while (ResolvedUndefs) {
     LLVM_DEBUG(dbgs() << "RESOLVING UNDEFS\n");
     ResolvedUndefs = false;
-    for (Function &F : M)
+    while (!Solver.PossiblyUndefined.empty()) {
+      Function &F = *Solver.PossiblyUndefined.back();
       if (Solver.ResolvedUndefsIn(F)) {
         // We run Solve() after we resolved an undef in a function, because
         // we might deduce a fact that eliminates an undef in another function.
         Solver.Solve();
         ResolvedUndefs = true;
-      }
+      } else
+        Solver.PossiblyUndefined.pop_back();
+    }
   }
 
   bool MadeChanges = false;