Index: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp
@@ -4085,37 +4085,49 @@
 
 namespace {
 
+/// Takes SCEV S and Loop L. For each AddRec sub-expression, use its start
+/// expression in case its Loop is L. If it is not L then
+/// if IgnoreOtherLoops is true then use AddRec itself
+/// otherwise rewrite cannot be done.
+/// If SCEV contains non-invariant unknown SCEV rewrite cannot be done.
 class SCEVInitRewriter : public SCEVRewriteVisitor<SCEVInitRewriter> {
 public:
-  static const SCEV *rewrite(const SCEV *S, const Loop *L,
-                             ScalarEvolution &SE) {
+  static const SCEV *rewrite(const SCEV *S, const Loop *L, ScalarEvolution &SE,
+                             bool IgnoreOtherLoops = false) {
     SCEVInitRewriter Rewriter(L, SE);
     const SCEV *Result = Rewriter.visit(S);
-    return Rewriter.isValid() ? Result : SE.getCouldNotCompute();
+    if (Rewriter.hasSeenLoopVariantSCEVUnknown())
+      return SE.getCouldNotCompute();
+    return Rewriter.hasSeenOtherLoops() && !IgnoreOtherLoops
+               ? SE.getCouldNotCompute()
+               : Result;
   }
 
   const SCEV *visitUnknown(const SCEVUnknown *Expr) {
     if (!SE.isLoopInvariant(Expr, L))
-      Valid = false;
+      SeenLoopVariantSCEVUnknown = true;
     return Expr;
   }
 
   const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) {
-    // Only allow AddRecExprs for this loop.
+    // Only re-write AddRecExprs for this loop.
     if (Expr->getLoop() == L)
       return Expr->getStart();
-    Valid = false;
+    SeenOtherLoops = true;
     return Expr;
   }
 
-  bool isValid() { return Valid; }
+  bool hasSeenLoopVariantSCEVUnknown() { return SeenLoopVariantSCEVUnknown; }
+
+  bool hasSeenOtherLoops() { return SeenOtherLoops; }
 
 private:
   explicit SCEVInitRewriter(const Loop *L, ScalarEvolution &SE)
       : SCEVRewriteVisitor(SE), L(L) {}
 
   const Loop *L;
-  bool Valid = true;
+  bool SeenLoopVariantSCEVUnknown = false;
+  bool SeenOtherLoops = false;
 };
 
 /// This class evaluates the compare condition by matching it against the