PR11005: @defined($tvar) predicate, part 1

* staptree.h (defined_op): New class.
* all files: Extend all visitors as appropriate, mostly
  dummy/pass-through implementation.
* parse.cxx (parse_target_symbol): New function, factored out
  of parse_symbol().
  (parse_define_op): New function.
* NEWS: Mention it.
* parse.h: Corresponding changes.
* tapsets.cxx (var_expanding_visitor::visit_defined_op):
  Implement @defined() semantics.
  (dwarf_var_expanding_visitor::visit_target_symbol): Adjust.
* tapset-utrace.c (visit_target_symbol_arg): Avoid crashes
  on $argZZZ.
* tapsets.cxx (sdt_var_expanding_visitor): Ditto.
* semok/thirtysix.stp: New test.

1 files changed, 4 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 8d9fe2bf..85619f8e 100644
--- a/NEWS
+++ b/NEWS
@@ -1,5 +1,9 @@
 * What's new
 
+- A new predicate @defined is available for testing whether a
+  particular $variable/expression is resolvable at translate time:
+  probe foo { if (@defined($bar)) log ("$bar is available here") }
+
 - Adjacent string literals are glued together, making this
   construct valid:
      probe process("/usr" @1 "/bin").function("*") { ... }