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, 12 insertions, 11 deletions

diff --git a/backend/Mach.v b/backend/Mach.v
index fe00d42d..08fe7c0a 100644
--- a/backend/Mach.v
+++ b/backend/Mach.v
@@ -60,8 +60,7 @@ Inductive instruction: Type :=
   | Mstore: memory_chunk -> addressing -> list mreg -> mreg -> instruction
   | Mcall: signature -> mreg + ident -> instruction
   | Mtailcall: signature -> mreg + ident -> instruction
-  | Mbuiltin: external_function -> list mreg -> list mreg -> instruction
-  | Mannot: external_function -> list (annot_arg mreg) -> instruction
+  | Mbuiltin: external_function -> list (builtin_arg mreg) -> builtin_res mreg -> instruction
   | Mlabel: label -> instruction
   | Mgoto: label -> instruction
   | Mcond: condition -> list mreg -> label -> instruction
@@ -163,6 +162,13 @@ Fixpoint set_regs (rl: list mreg) (vl: list val) (rs: regset) : regset :=
   | _, _ => rs
   end.
 
+Fixpoint set_res (res: builtin_res mreg) (v: val) (rs: regset) : regset :=
+  match res with
+  | BR r => Regmap.set r v rs
+  | BR_none => rs
+  | BR_longofwords hi lo => set_res lo (Val.loword v) (set_res hi (Val.hiword v) rs)
+  end.
+
 Definition is_label (lbl: label) (instr: instruction) : bool :=
   match instr with
   | Mlabel lbl' => if peq lbl lbl' then true else false
@@ -328,17 +334,12 @@ Inductive step: state -> trace -> state -> Prop :=
       step (State s fb (Vptr stk soff) (Mtailcall sig ros :: c) rs m)
         E0 (Callstate s f' rs m')
   | exec_Mbuiltin:
-      forall s f sp rs m ef args res b t vl rs' m',
-      external_call' ef ge rs##args m t vl m' ->
-      rs' = set_regs res vl (undef_regs (destroyed_by_builtin ef) rs) ->
+      forall s f sp rs m ef args res b vargs t vres rs' m',
+      eval_builtin_args ge rs sp m args vargs ->
+      external_call ef ge vargs m t vres m' ->
+      rs' = set_res res vres (undef_regs (destroyed_by_builtin ef) rs) ->
       step (State s f sp (Mbuiltin ef args res :: b) rs m)
          t (State s f sp b rs' m')
-  | exec_Mannot:
-      forall s f sp rs m ef args b vargs t v m',
-      eval_annot_args ge rs sp m args vargs ->
-      external_call ef ge vargs m t v m' ->
-      step (State s f sp (Mannot ef args :: b) rs m)
-         t (State s f sp b rs m')
   | exec_Mgoto:
       forall s fb f sp lbl c rs m c',
       Genv.find_funct_ptr ge fb = Some (Internal f) ->