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/PrintMach.ml b/backend/PrintMach.ml
index 8484a5c3..0ce2e87b 100644
--- a/backend/PrintMach.ml
+++ b/backend/PrintMach.ml
@@ -67,10 +67,9 @@ let print_instruction pp i =
       fprintf pp "\ttailcall %a\n" ros fn
   | Mbuiltin(ef, args, res) ->
       fprintf pp "\t%a = %s(%a)\n"
-        regs res (name_of_external ef) regs args
-  | Mannot(ef, args) ->
-      fprintf pp "\t%s(%a)\n"
-        (name_of_external ef) (print_annot_args reg) args
+        (print_builtin_res reg) res
+        (name_of_external ef)
+        (print_builtin_args reg) args
   | Mlabel lbl ->
       fprintf pp "%5d:" (P.to_int lbl)
   | Mgoto lbl ->