Catch non-string subject in RegExpExecStub.

src/ia32/code-stubs-ia32.cc

Index: src/ia32/code-stubs-ia32.cc
diff --git a/src/ia32/code-stubs-ia32.cc b/src/ia32/code-stubs-ia32.cc
index c6c1009c8cf7d28e2d8bf6ea12259783b5424a64..1d54c9ad7eaaa253ccc4ee919e4ff18f40bbb7c2 100644
--- a/src/ia32/code-stubs-ia32.cc
+++ b/src/ia32/code-stubs-ia32.cc
@@ -3616,10 +3616,15 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   Label cons_string, check_encoding;
   STATIC_ASSERT(kConsStringTag < kExternalStringTag);
   STATIC_ASSERT(kSlicedStringTag > kExternalStringTag);
+  STATIC_ASSERT(kIsNotStringMask > kExternalStringTag);
   __ cmp(ebx, Immediate(kExternalStringTag));
   __ j(less, &cons_string);
   __ j(equal, &runtime);
 
+  // Catch non-string subject (should already have been guarded against).
+  __ test(ebx, Immediate(kIsNotStringMask));
+  __ j(zero, &runtime);
+
   // String is sliced.
   __ mov(edi, FieldOperand(eax, SlicedString::kOffsetOffset));
   __ mov(eax, FieldOperand(eax, SlicedString::kParentOffset));