Index: lib/Analysis/ScalarEvolution.cpp
===================================================================
--- lib/Analysis/ScalarEvolution.cpp
+++ lib/Analysis/ScalarEvolution.cpp
@@ -127,6 +127,11 @@
     cl::desc("Threshold for inlining multiplication operands into a SCEV"),
     cl::init(1000));
 
+static cl::opt<unsigned>
+    MaxCompareDepth("scalar-evolution-max-compare-depth", cl::Hidden,
+                    cl::desc("Maximum depth of recursive compare complexity"),
+                    cl::init(10));
+
 //===----------------------------------------------------------------------===//
 //                           SCEV class definitions
 //===----------------------------------------------------------------------===//
@@ -551,7 +556,7 @@
 // than RHS, respectively. A three-way result allows recursive comparisons to be
 // more efficient.
 static int CompareSCEVComplexity(const LoopInfo *const LI, const SCEV *LHS,
-                                 const SCEV *RHS) {
+                                 const SCEV *RHS, unsigned Depth = 0) {
   // Fast-path: SCEVs are uniqued so we can do a quick equality check.
   if (LHS == RHS)
     return 0;
@@ -561,6 +566,10 @@
   if (LType != RType)
     return (int)LType - (int)RType;
 
+  // Limit recursion depth
+  if (Depth > MaxCompareDepth)
+    return 0;
+
   // Aside from the getSCEVType() ordering, the particular ordering
   // isn't very important except that it's beneficial to be consistent,
   // so that (a + b) and (b + a) don't end up as different expressions.
@@ -605,7 +614,8 @@
 
     // Lexicographically compare.
     for (unsigned i = 0; i != LNumOps; ++i) {
-      long X = CompareSCEVComplexity(LI, LA->getOperand(i), RA->getOperand(i));
+      long X = CompareSCEVComplexity(LI, LA->getOperand(i), RA->getOperand(i),
+                                     Depth + 1);
       if (X != 0)
         return X;
     }
@@ -628,7 +638,8 @@
     for (unsigned i = 0; i != LNumOps; ++i) {
       if (i >= RNumOps)
         return 1;
-      long X = CompareSCEVComplexity(LI, LC->getOperand(i), RC->getOperand(i));
+      long X = CompareSCEVComplexity(LI, LC->getOperand(i), RC->getOperand(i),
+                                     Depth + 1);
       if (X != 0)
         return X;
     }
@@ -640,10 +651,10 @@
     const SCEVUDivExpr *RC = cast<SCEVUDivExpr>(RHS);
 
     // Lexicographically compare udiv expressions.
-    long X = CompareSCEVComplexity(LI, LC->getLHS(), RC->getLHS());
+    long X = CompareSCEVComplexity(LI, LC->getLHS(), RC->getLHS(), Depth + 1);
     if (X != 0)
       return X;
-    return CompareSCEVComplexity(LI, LC->getRHS(), RC->getRHS());
+    return CompareSCEVComplexity(LI, LC->getRHS(), RC->getRHS(), Depth + 1);
   }
 
   case scTruncate:
@@ -653,7 +664,7 @@
     const SCEVCastExpr *RC = cast<SCEVCastExpr>(RHS);
 
     // Compare cast expressions by operand.
-    return CompareSCEVComplexity(LI, LC->getOperand(), RC->getOperand());
+    return CompareSCEVComplexity(LI, LC->getOperand(), RC->getOperand(), Depth + 1);
   }
 
   case scCouldNotCompute: