Revert "Remove unnecessary check 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 0590ad466d23fa02ed4cbb515518ea04fdb0f48a..8a05e007639d432f33701b614d26d8993c197883 100644
--- a/src/ia32/code-stubs-ia32.cc
+++ b/src/ia32/code-stubs-ia32.cc
@@ -1596,14 +1596,19 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   __ cmp(eax, NativeRegExpMacroAssembler::EXCEPTION);
   // If not exception it can only be retry. Handle that in the runtime system.
   __ j(not_equal, &runtime);
-
-  // Result must now be exception.
+  // Result must now be exception. If there is no pending exception already a
+  // stack overflow (on the backtrack stack) was detected in RegExp code but
+  // haven't created the exception yet. Handle that in the runtime system.
+  // TODO(592): Rerunning the RegExp to get the stack overflow exception.
   ExternalReference pending_exception(Isolate::kPendingExceptionAddress,
                                       isolate());
   __ mov(edx, Immediate(isolate()->factory()->the_hole_value()));
   __ mov(eax, Operand::StaticVariable(pending_exception));
+  __ cmp(edx, eax);
+  __ j(equal, &runtime);
+  // For exception, throw the exception again.
 
-  // Clear pending exception.
+  // Clear the pending exception variable.
   __ mov(Operand::StaticVariable(pending_exception), edx);
 
   // Special handling of termination exceptions which are uncatchable