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, 2 insertions, 3 deletions

diff --git a/backend/Liveness.v b/backend/Liveness.v
index ce1a798a..b8a5f965 100644
--- a/backend/Liveness.v
+++ b/backend/Liveness.v
@@ -92,9 +92,8 @@ Definition transfer
       | Itailcall sig ros args =>
           reg_list_live args (reg_sum_live ros Regset.empty)
       | Ibuiltin ef args res s =>
-          reg_list_live args (reg_dead res after)
-      | Iannot ef args s =>
-          reg_list_live (params_of_annot_args args) after
+          reg_list_live (params_of_builtin_args args)
+            (reg_list_dead (params_of_builtin_res res) after)
       | Icond cond args ifso ifnot =>
           reg_list_live args after
       | Ijumptable arg tbl =>