From c10e3e1fc83cbccd1c8c3b377e2309ea8fa27572 Mon Sep 17 00:00:00 2001
From: Sverker Eriksson <sverker@erlang.org>
Date: Thu, 1 Mar 2018 12:27:48 +0100
Subject: erts: Optimize dist transcoding toward erl_/jinterface

to only transcode if output buffer actually contains
unsupported BIT_BINARY_EXT or EXPORT_EXT.
---
 erts/emulator/beam/dist.c            |  2 ++
 erts/emulator/beam/dist.h            |  6 +++---
 erts/emulator/beam/erl_node_tables.h |  1 +
 erts/emulator/beam/external.c        | 23 ++++++++++++++++-------
 4 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/erts/emulator/beam/dist.c b/erts/emulator/beam/dist.c
index c08a8ec832..132a0b9fba 100644
--- a/erts/emulator/beam/dist.c
+++ b/erts/emulator/beam/dist.c
@@ -2000,6 +2000,7 @@ erts_dsig_send(ErtsDSigData *dsdp, struct erts_dsig_send_context* ctx)
                 break;
             }
             ctx->u.ec.flags = ctx->flags;
+            ctx->u.ec.hopefull_flags = 0;
             ctx->u.ec.level = 0;
             ctx->u.ec.wstack.wstart = NULL;
             ctx->obuf->msg_start = ctx->obuf->ext_endp;
@@ -2023,6 +2024,7 @@ erts_dsig_send(ErtsDSigData *dsdp, struct erts_dsig_send_context* ctx)
 
 	    ctx->data_size = ctx->obuf->ext_endp - ctx->obuf->extp;
 
+            ctx->obuf->hopefull_flags = ctx->u.ec.hopefull_flags;
 	    /*
 	     * Signal encoded; now verify that the connection still exists,
 	     * and if so enqueue the signal and schedule it for send.
diff --git a/erts/emulator/beam/dist.h b/erts/emulator/beam/dist.h
index e8dcdb669d..000c66a00f 100644
--- a/erts/emulator/beam/dist.h
+++ b/erts/emulator/beam/dist.h
@@ -55,9 +55,8 @@
 
 /*
  * Additional optimistic flags when encoding toward pending connection.
- * If remote node does not supporting these (erl_interface)
- * then we will need to transcode all messages enqueued before
- * connection setup was finished.
+ * If remote node (erl_interface) does not supporting these then we may need
+ * to transcode messages enqueued before connection setup was finished.
  */
 #define DFLAG_DIST_HOPEFULLY (DFLAG_EXPORT_PTR_TAG              \
                               | DFLAG_BIT_BINARIES              \
@@ -355,6 +354,7 @@ typedef struct TTBSizeContext_ {
 
 typedef struct TTBEncodeContext_ {
     Uint flags;
+    Uint hopefull_flags;
     int level;
     byte* ep;
     Eterm obj;
diff --git a/erts/emulator/beam/erl_node_tables.h b/erts/emulator/beam/erl_node_tables.h
index 8d29c83e15..5822f97f55 100644
--- a/erts/emulator/beam/erl_node_tables.h
+++ b/erts/emulator/beam/erl_node_tables.h
@@ -86,6 +86,7 @@ struct ErtsDistOutputBuf_ {
     byte *alloc_endp;
 #endif
     ErtsDistOutputBuf *next;
+    Uint hopefull_flags;
     byte *extp;
     byte *ext_endp;
     byte *msg_start;
diff --git a/erts/emulator/beam/external.c b/erts/emulator/beam/external.c
index b12a021e41..b358685cc0 100644
--- a/erts/emulator/beam/external.c
+++ b/erts/emulator/beam/external.c
@@ -2873,6 +2873,8 @@ enc_term_int(TTBEncodeContext* ctx, ErtsAtomCacheMap *acmp, Eterm obj, byte* ep,
 		    ep[j] = 0;	/* Zero unused bits at end of binary */
 		    data_dst = ep;
 		    ep += j + 1;
+                    if (ctx)
+                        ctx->hopefull_flags |= DFLAG_BIT_BINARIES;
 		} else {
 		    /*
 		     * Bit-level binary, but the receiver doesn't support it.
@@ -2908,6 +2910,8 @@ enc_term_int(TTBEncodeContext* ctx, ErtsAtomCacheMap *acmp, Eterm obj, byte* ep,
 		    ep = enc_atom(acmp, exp->info.mfa.function, ep, dflags);
 		    ep = enc_term(acmp, make_small(exp->info.mfa.arity),
                                   ep, dflags, off_heap);
+                    if (ctx)
+                        ctx->hopefull_flags |= DFLAG_EXPORT_PTR_TAG;
 		} else {
 		    /* Tag, arity */
 		    *ep++ = SMALL_TUPLE_EXT;
@@ -4729,11 +4733,13 @@ Sint transcode_dist_obuf(ErtsDistOutputBuf* ob,
     struct transcode_context* ctx = dep->transcode_ctx;
 
     if (!ctx) { /* first call for 'ob' */
-
-        if (~dflags & (DFLAG_BIT_BINARIES | DFLAG_EXPORT_PTR_TAG)) {
+	ASSERT(!(ob->hopefull_flags & ~(Uint)(DFLAG_BIT_BINARIES |
+					      DFLAG_EXPORT_PTR_TAG)));
+        if (~dflags & ob->hopefull_flags) {
             /*
-             * Receiver does not support bitstrings and/or export funs.
-             * We need to transcode control and message terms to use tuple fallbacks.
+             * Receiver does not support bitstrings and/or export funs
+             * and output buffer contains such message tags (hopefull_flags).
+             * Must transcode control and message terms to use tuple fallbacks.
              */
             ctx = erts_alloc(ERTS_ALC_T_DIST_TRANSCODE, sizeof(struct transcode_context));
             dep->transcode_ctx = ctx;
@@ -4760,7 +4766,7 @@ Sint transcode_dist_obuf(ErtsDistOutputBuf* ob,
                 ctx->state = TRANSCODE_ENC_CTL;
             }
         }
-        else {
+        else if (!(dflags & DFLAG_DIST_HDR_ATOM_CACHE)) {
             /*
              * No need for full transcoding, but primitive receiver (erl_/jinterface)
              * expects VERSION_MAGIC before both control and message terms.
@@ -4777,8 +4783,10 @@ Sint transcode_dist_obuf(ErtsDistOutputBuf* ob,
             *--(ob->extp) = VERSION_MAGIC;
             goto done;
         }
+        else
+            goto done;
     }
-    else {
+    else {  /* continue after yield */
         ASSERT(ctx->dbg_ob == ob);
     }
     ctx->b2t.reds = reds * B2T_BYTES_PER_REDUCTION;
@@ -4831,6 +4839,7 @@ Sint transcode_dist_obuf(ErtsDistOutputBuf* ob,
         ob->msg_start = ob->ext_endp;
         ctx->ttb.wstack.wstart = NULL;
         ctx->ttb.flags = dflags;
+        ctx->ttb.hopefull_flags = 0;
         ctx->ttb.level = 0;
 
         ctx->state = TRANSCODE_ENC_MSG;
@@ -4843,7 +4852,7 @@ Sint transcode_dist_obuf(ErtsDistOutputBuf* ob,
         reds /= TERM_TO_BINARY_LOOP_FACTOR;
 
         ASSERT(ob->ext_endp <= ob->alloc_endp);
-
+        ASSERT(!ctx->ttb.hopefull_flags);
     }
     transcode_free_ctx(dep);
 
-- 
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