Catch non-string subject in RegExpExecStub.

src/x64/code-stubs-x64.cc

Index: src/x64/code-stubs-x64.cc
diff --git a/src/x64/code-stubs-x64.cc b/src/x64/code-stubs-x64.cc
index b8f820d7f5581e9727731f61fa8481a751258aa0..3c0d11b09c0389a4804a1764a7bd5f5472be2c7e 100644
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -2663,10 +2663,15 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   Label cons_string, check_encoding;
   STATIC_ASSERT(kConsStringTag < kExternalStringTag);
   STATIC_ASSERT(kSlicedStringTag > kExternalStringTag);
+  STATIC_ASSERT(kIsNotStringMask > kExternalStringTag);
   __ cmpq(rbx, Immediate(kExternalStringTag));
   __ j(less, &cons_string, Label::kNear);
   __ j(equal, &runtime);
 
+  // Catch non-string subject (should already have been guarded against).
+  __ testb(ebx, Immediate(kIsNotStringMask));
+  __ j(zero, &runtime);
+
   // String is sliced.
   __ SmiToInteger32(r14, FieldOperand(rdi, SlicedString::kOffsetOffset));
   __ movq(rdi, FieldOperand(rdi, SlicedString::kParentOffset));