diff -r f55c4f82ab9d -r 4b29a725c43c src/share/vm/opto/library_call.cpp
--- a/src/share/vm/opto/library_call.cpp	Thu Aug 19 14:51:47 2010 -0700
+++ b/src/share/vm/opto/library_call.cpp	Fri Aug 20 23:40:30 2010 -0700
@@ -906,7 +906,8 @@
   const int count_offset = java_lang_String::count_offset_in_bytes();
   const int offset_offset = java_lang_String::offset_offset_in_bytes();
 
-  _sp += 2;
+  int nargs = 2;
+  _sp += nargs;
   Node* argument = pop();  // pop non-receiver first:  it was pushed second
   Node* receiver = pop();
 
@@ -914,11 +915,11 @@
   // null check technically happens in the wrong place, which can lead to
   // invalid stack traces when string compare is inlined into a method
   // which handles NullPointerExceptions.
-  _sp += 2;
+  _sp += nargs;
   receiver = do_null_check(receiver, T_OBJECT);
   //should not do null check for argument for String.equals(), because spec
   //allows to specify NULL as argument.
-  _sp -= 2;
+  _sp -= nargs;
 
   if (stopped()) {
     return true;
@@ -943,7 +944,9 @@
   ciInstanceKlass* klass = env()->String_klass();
 
   if (!stopped()) {
+    _sp += nargs;          // gen_instanceof might do an uncommon trap
     Node* inst = gen_instanceof(argument, makecon(TypeKlassPtr::make(klass)));
+    _sp -= nargs;
     Node* cmp  = _gvn.transform(new (C, 3) CmpINode(inst, intcon(1)));
     Node* bol  = _gvn.transform(new (C, 2) BoolNode(cmp, BoolTest::ne));
 
@@ -2935,7 +2938,9 @@
   switch (id) {
   case vmIntrinsics::_isInstance:
     // nothing is an instance of a primitive type
+    _sp += nargs;          // gen_instanceof might do an uncommon trap
     query_value = gen_instanceof(obj, kls);
+    _sp -= nargs;
     break;
 
   case vmIntrinsics::_getModifiers: