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, 0 insertions, 2 deletions

diff --git a/backend/Linearize.v b/backend/Linearize.v
index b1102e23..78cdd743 100644
--- a/backend/Linearize.v
+++ b/backend/Linearize.v
@@ -187,8 +187,6 @@ Fixpoint linearize_block (b: LTL.bblock) (k: code) : code :=
       Ltailcall sig ros :: k
   | LTL.Lbuiltin ef args res :: b' =>
       Lbuiltin ef args res :: linearize_block b' k
-  | LTL.Lannot ef args :: b' =>
-      Lannot ef args :: linearize_block b' k
   | LTL.Lbranch s :: b' =>
       add_branch s k
   | LTL.Lcond cond args s1 s2 :: b' =>