First rough version of the JIT.

It can successfully parse SpeedMessage1.
Preliminary results: 750MB/s on Core2 2.4GHz.
This number is 2.5x proto2.
This isn't apples-to-apples, because
proto2 is parsing to a struct and we are
just doing stream parsing, but for apps
that are currently using proto2, this is the
improvement they would see if they could
move to stream-based processing.

Unfortunately perf-regression-test.py is
broken, and I'm not 100% sure why.  It would
be nice to fix it first (to ensure that
there are no performance regressions for
the table-based decoder) but I'm really
impatient to get the JIT checked in.

1 files changed, 10 insertions, 4 deletions

diff --git a/src/upb_string.h b/src/upb_string.h
index 88a513f..5aa5f3b 100644
--- a/src/upb_string.h
+++ b/src/upb_string.h
@@ -155,9 +155,13 @@ INLINE const char *upb_string_getbufend(upb_string *str) {
 }
 
 // Attempts to recycle the string "str" so it may be reused and have different
-// data written to it.  After the function returns, "str" points to a writable
-// string, which is either the original string if it had no other references
-// or a newly created string if it did have other references.
+// data written to it.  The caller MUST own a reference on the given string
+// prior to making this call (ie. the caller must have either created the
+// string or obtained a reference with upb_string_getref()).
+//
+// After the function returns, "str" points to a writable string, which is
+// either the original string if it had no other references or a newly created
+// string if it did have other references.
 //
 // As a special case, passing a pointer to NULL will allocate a new string.
 // This is convenient for the pattern:
@@ -171,7 +175,9 @@ INLINE const char *upb_string_getbufend(upb_string *str) {
 //   }
 INLINE void upb_string_recycle(upb_string **_str) {
   upb_string *str = *_str;
-  if(str && upb_atomic_only(&str->refcount)) {
+  int r;
+  if(str && ((r = upb_atomic_read(&str->refcount)) == 1 ||
+             (r == _UPB_STRING_REFCOUNT_STACK))) {
     str->ptr = NULL;
     str->len = 0;
     _upb_string_release(str);