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, 8 insertions, 0 deletions

diff --git a/backend/Locations.v b/backend/Locations.v
index 5674b93a..4ec24a14 100644
--- a/backend/Locations.v
+++ b/backend/Locations.v
@@ -377,6 +377,14 @@ Module Locmap.
     destruct vl; auto. destruct H. rewrite IHll; auto. apply gso; auto. apply Loc.diff_sym; auto.
   Qed.
 
+  Fixpoint setres (res: builtin_res mreg) (v: val) (m: t) : t :=
+    match res with
+    | BR r => set (R r) v m
+    | BR_none => m
+    | BR_longofwords hi lo => 
+        setres lo (Val.loword v) (setres hi (Val.hiword v) m)
+    end.
+
 End Locmap.
 
 (** * Total ordering over locations *)