upb_stream: all callbacks registered ahead-of-time.

This is a significant change to the upb_stream
protocol, and should hopefully be the last
significant change.

All callbacks are now registered ahead-of-time
instead of having delegated callbacks registered
at runtime, which makes it much easier to
aggressively optimize ahead-of-time (like with a
JIT).

Other impacts of this change:

- You no longer need to have loaded descriptor.proto
  as a upb_def to load other descriptors!  This means
  the special-case code we used for bootstrapping is
  no longer necessary, and we no longer need to link
  the descriptor for descriptor.proto into upb.

- A client can now register any upb_value as what
  will be delivered to their value callback, not
  just a upb_fielddef*.  This should allow for other
  clients to get more bang out of the streaming
  decoder.

This change unfortunately causes a bit of a performance
regression -- I think largely due to highly
suboptimal code that GCC generates when structs
are returned by value.  See:
  http://blog.reverberate.org/2011/03/19/when-a-compilers-slow-code-actually-bites-you/

On the other hand, once we have a JIT this should
no longer matter.

Performance numbers:

plain.parsestream_googlemessage1.upb_table: 374 -> 396 (5.88)
plain.parsestream_googlemessage2.upb_table: 616 -> 449 (-27.11)
plain.parsetostruct_googlemessage1.upb_table_byref: 268 -> 269 (0.37)
plain.parsetostruct_googlemessage1.upb_table_byval: 215 -> 204 (-5.12)
plain.parsetostruct_googlemessage2.upb_table_byref: 307 -> 281 (-8.47)
plain.parsetostruct_googlemessage2.upb_table_byval: 297 -> 272 (-8.42)
omitfp.parsestream_googlemessage1.upb_table: 423 -> 410 (-3.07)
omitfp.parsestream_googlemessage2.upb_table: 679 -> 483 (-28.87)
omitfp.parsetostruct_googlemessage1.upb_table_byref: 287 -> 282 (-1.74)
omitfp.parsetostruct_googlemessage1.upb_table_byval: 226 -> 219 (-3.10)
omitfp.parsetostruct_googlemessage2.upb_table_byref: 315 -> 298 (-5.40)
omitfp.parsetostruct_googlemessage2.upb_table_byval: 297 -> 287 (-3.37)

1 files changed, 10 insertions, 21 deletions

diff --git a/src/upb_msg.h b/src/upb_msg.h
index fd5750f..4895c4b 100644
--- a/src/upb_msg.h
+++ b/src/upb_msg.h
@@ -17,8 +17,7 @@
 #ifndef UPB_MSG_H
 #define UPB_MSG_H
 
-#include "upb.h"
-#include "upb_def.h"
+#include "upb_stream.h"
 #include <stdlib.h>
 
 #ifdef __cplusplus
@@ -274,26 +273,16 @@ INLINE void upb_msg_clear(upb_msg *msg, upb_msgdef *md) {
   memset(msg->data, 0, md->set_flags_bytes);
 }
 
-// A non-resumable upb_src that pushes the current contents of the message to
-// the given handlers.
+// Registers handlers for populating a msg for the given upb_msgdef.
+// The upb_msg itself must be passed as the param to the src.
+void upb_msg_reghandlers(upb_handlers *h, upb_msgdef *md);
+
+// Registers handlers that are suitable for populating a msg of *any*
+// upb_msgdef ("dynamic" handlers).  May be slower than upb_msg_reghandlers().
+void upb_msg_regdhandlers(upb_handlers *h);
+
 void upb_msg_runhandlers(upb_msg *msg, upb_msgdef *md, upb_handlers *h,
-                         upb_status *status);
-
-typedef struct {
-  upb_msg *msg;
-  upb_msgdef *msgdef;
-} upb_msgpopulator_frame;
-
-typedef struct {
-  upb_msgpopulator_frame *top, *limit;
-  upb_status status;
-  upb_msgpopulator_frame stack[UPB_MAX_NESTING];
-} upb_msgpopulator;
-
-void upb_msgpopulator_init(upb_msgpopulator *p);
-void upb_msgpopulator_uninit(upb_msgpopulator *p);
-void upb_msgpopulator_reset(upb_msgpopulator *p, upb_msg *m, upb_msgdef *md);
-void upb_msgpopulator_register_handlers(upb_msgpopulator *p, upb_handlers *h);
+                         void *closure, upb_status *status);
 
 #ifdef __cplusplus
 }  /* extern "C" */