Refactoring of builtins and annotations in the back-end.

Before, the back-end languages had distinct instructions
- Iannot for annotations, taking structured expressions (annot_arg)
  as arguments, and producing no results'
- Ibuiltin for other builtins, using simple pseudoregs/locations/registers
  as arguments and results.

This branch enriches Ibuiltin instructions so that they take structured
expressions (builtin_arg and builtin_res) as arguments and results.
This way,
- Annotations fit the general pattern of builtin functions,
  so Iannot instructions are removed.
- EF_vload_global and EF_vstore_global become useless, as the
  same optimization can be achieved by EF_vload/vstore taking
  a structured argument of the "address of global" kind.
- Better code can be generated for builtin_memcpy between stack locations,
  or volatile accesses to stack locations.

Finally, this commit also introduces a new kind of external function,
EF_debug, which is like EF_annot but produces no observable events.
It will be used later to transport debug info through the back-end,
without preventing optimizations.

1 files changed, 3 insertions, 4 deletions

diff --git a/backend/PrintLTL.ml b/backend/PrintLTL.ml
index 27936f9b..0f78bc58 100644
--- a/backend/PrintLTL.ml
+++ b/backend/PrintLTL.ml
@@ -79,10 +79,9 @@ let print_instruction pp succ = function
       fprintf pp "tailcall %a" ros fn
   | Lbuiltin(ef, args, res) ->
       fprintf pp "%a = %s(%a)"
-        mregs res (name_of_external ef) mregs args
-  | Lannot(ef, args) ->
-      fprintf pp "%s(%a)\n"
-        (name_of_external ef) (print_annot_args loc) args
+        (print_builtin_res mreg) res
+        (name_of_external ef)
+        (print_builtin_args loc) args
   | Lbranch s ->
       print_succ pp s succ
   | Lcond(cond, args, s1, s2) ->