Index: include/clang/AST/Expr.h
===================================================================
--- include/clang/AST/Expr.h	(revision 187641)
+++ include/clang/AST/Expr.h	(working copy)
@@ -3451,9 +3451,9 @@
 
   void setExprs(ASTContext &C, ArrayRef<Expr *> Exprs);
 
-  unsigned getShuffleMaskIdx(ASTContext &Ctx, unsigned N) const {
+  llvm::APSInt getShuffleMaskIdx(ASTContext &Ctx, unsigned N) const {
     assert((N < NumExprs - 2) && "Shuffle idx out of range!");
-    return getExpr(N+2)->EvaluateKnownConstInt(Ctx).getZExtValue();
+    return getExpr(N+2)->EvaluateKnownConstInt(Ctx);
   }
 
   // Iterators
Index: lib/CodeGen/CGExprScalar.cpp
===================================================================
--- lib/CodeGen/CGExprScalar.cpp	(revision 187641)
+++ lib/CodeGen/CGExprScalar.cpp	(working copy)
@@ -955,8 +955,12 @@
 
   SmallVector<llvm::Constant*, 32> indices;
   for (unsigned i = 2; i < E->getNumSubExprs(); ++i) {
-    unsigned Idx = E->getShuffleMaskIdx(CGF.getContext(), i-2);
-    indices.push_back(Builder.getInt32(Idx));
+    llvm::APSInt Idx = E->getShuffleMaskIdx(CGF.getContext(), i-2);
+    // Check for -1 and output it as undef in the IR.
+    if (Idx.isSigned() && Idx.isAllOnesValue())
+      indices.push_back(llvm::UndefValue::get(CGF.Int32Ty));
+    else
+      indices.push_back(Builder.getInt32(Idx.getZExtValue()));
   }
 
   Value *SV = llvm::ConstantVector::get(indices);
Index: lib/Sema/SemaChecking.cpp
===================================================================
--- lib/Sema/SemaChecking.cpp	(revision 187644)
+++ lib/Sema/SemaChecking.cpp	(working copy)
@@ -1786,6 +1786,10 @@
                             diag::err_shufflevector_nonconstant_argument)
                        << TheCall->getArg(i)->getSourceRange());
 
+    // Allow -1 which will be translated to undef in the IR.
+    if (Result.isSigned() && Result.isAllOnesValue())
+      continue;
+
     if (Result.getActiveBits() > 64 || Result.getZExtValue() >= numElements*2)
       return ExprError(Diag(TheCall->getLocStart(),
                             diag::err_shufflevector_argument_too_large)