Revert "Remove unnecessary check in RegExpExecStub."

src/mips/code-stubs-mips.cc

Index: src/mips/code-stubs-mips.cc
diff --git a/src/mips/code-stubs-mips.cc b/src/mips/code-stubs-mips.cc
index 18f3a9a395a182fee85d5fc0b688ddbd6b482c9d..68d81bbfc74cc75d4cd7da8cf2c2df33d9f3878e 100644
--- a/src/mips/code-stubs-mips.cc
+++ b/src/mips/code-stubs-mips.cc
@@ -2670,12 +2670,16 @@ void RegExpExecStub::Generate(MacroAssembler* masm) {
   __ Branch(&failure, eq, v0, Operand(NativeRegExpMacroAssembler::FAILURE));
   // If not exception it can only be retry. Handle that in the runtime system.
   __ Branch(&runtime, ne, v0, Operand(NativeRegExpMacroAssembler::EXCEPTION));
-
-  // 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.
   __ li(a1, Operand(isolate()->factory()->the_hole_value()));
   __ li(a2, Operand(ExternalReference(Isolate::kPendingExceptionAddress,
                                       isolate())));
   __ lw(v0, MemOperand(a2, 0));
+  __ Branch(&runtime, eq, v0, Operand(a1));
+
   __ sw(a1, MemOperand(a2, 0));  // Clear pending exception.
 
   // Check if the exception is a termination. If so, throw as uncatchable.