Add high-level support for @cast()ing

This handles all of the parsing, traversal, and optimization.  It
doesn't actually resolve the cast yet though.

* staptree.h (struct cast_op, visitor::visit_cast_op): New.
* staptree.cxx (cast_op::print/visit, various visitor::visit_cast_op's):
Incorporate cast_op into the basic tree operations.
* parse.cxx (parser::parse_symbol): Parse @cast operator with an
expression operand, type string, and optional module string.
* translate.cxx (c_unparser::visit_cast_op): Error out if a @cast
survives to translation.
* elaborate.cxx (typeresolution_info::visit_cast_op): Error out if a
@cast survives to type resolution.
(symbol_fetcher::visit_cast_op): treat @casts as a symbol target
(void_statement_reducer::visit_cast_op): unused @casts can be discarded,
but the operand should still be evaluated.

1 files changed, 31 insertions, 0 deletions

diff --git a/elaborate.cxx b/elaborate.cxx
index ba50defb..981fc7c7 100644
--- a/elaborate.cxx
+++ b/elaborate.cxx
@@ -701,6 +701,11 @@ struct symbol_fetcher
     e->base->visit_indexable (this);
   }
 
+  void visit_cast_op (cast_op* e)
+  {
+    sym = e;
+  }
+
   void throwone (const token* t)
   {
     throw semantic_error ("Expecting symbol or array index expression", t);
@@ -2505,6 +2510,7 @@ struct void_statement_reducer: public update_visitor
   void visit_concatenation (concatenation* e);
   void visit_functioncall (functioncall* e);
   void visit_print_format (print_format* e);
+  void visit_cast_op (cast_op* e);
 
   // these are a bit hairy to grok due to the intricacies of indexables and
   // stats, so I'm chickening out and skipping them...
@@ -2772,6 +2778,19 @@ void_statement_reducer::visit_print_format (print_format* e)
   provide (e);
 }
 
+void
+void_statement_reducer::visit_cast_op (cast_op* e)
+{
+  // When the result of a cast operation isn't needed, it's just as good to
+  // evaluate the operand directly
+
+  if (session.verbose>2)
+    clog << "Eliding unused typecast " << *e->tok << endl;
+
+  relaxed_p = false;
+  e->operand->visit(this);
+}
+
 
 void semantic_pass_opt5 (systemtap_session& s, bool& relaxed_p)
 {
@@ -3399,6 +3418,18 @@ typeresolution_info::visit_target_symbol (target_symbol* e)
 
 
 void
+typeresolution_info::visit_cast_op (cast_op* e)
+{
+  // Like target_symbol, a cast_op shouldn't survive this far
+  // unless it was not resolved and its value is really needed.
+  if (e->saved_conversion_error)
+    throw (* (e->saved_conversion_error));
+  else
+    throw semantic_error("unresolved cast expression", e->tok);
+}
+
+
+void
 typeresolution_info::visit_arrayindex (arrayindex* e)
 {