Sync from internal Google development.

Many improvements, too many to mention.  One significant
perf regression warrants investigation:

omitfp.parsetoproto2_googlemessage1.upb_jit: 343 -> 252 (-26.53)
plain.parsetoproto2_googlemessage1.upb_jit: 334 -> 251 (-24.85)

25% regression for this benchmark is bad, but since I don't think
there's any fundamental design issue that caused it I'm going to
go ahead with the commit anyway.  Can investigate and fix later.

Other benchmarks were neutral or showed slight improvement.

1 files changed, 83 insertions, 0 deletions

diff --git a/upb/descriptor/reader.h b/upb/descriptor/reader.h
new file mode 100644
index 0000000..0e1bfa0
--- /dev/null
+++ b/upb/descriptor/reader.h
@@ -0,0 +1,83 @@
+/*
+ * upb - a minimalist implementation of protocol buffers.
+ *
+ * Copyright (c) 2011 Google Inc.  See LICENSE for details.
+ * Author: Josh Haberman <jhaberman@gmail.com>
+ *
+ * upb_descreader provides a set of sink handlers that will build defs from a
+ * data source that uses the descriptor.proto schema (like a protobuf binary
+ * descriptor).
+ */
+
+#ifndef UPB_DESCRIPTOR_H
+#define UPB_DESCRIPTOR_H
+
+#include "upb/handlers.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* upb_deflist ****************************************************************/
+
+// upb_deflist is an internal-only dynamic array for storing a growing list of
+// upb_defs.
+typedef struct {
+  upb_def **defs;
+  size_t len;
+  size_t size;
+  bool owned;
+} upb_deflist;
+
+void upb_deflist_init(upb_deflist *l);
+void upb_deflist_uninit(upb_deflist *l);
+void upb_deflist_push(upb_deflist *l, upb_def *d);
+
+/* upb_descreader  ************************************************************/
+
+// We keep a stack of all the messages scopes we are currently in, as well as
+// the top-level file scope.  This is necessary to correctly qualify the
+// definitions that are contained inside.  "name" tracks the name of the
+// message or package (a bare name -- not qualified by any enclosing scopes).
+typedef struct {
+  char *name;
+  // Index of the first def that is under this scope.  For msgdefs, the
+  // msgdef itself is at start-1.
+  int start;
+} upb_descreader_frame;
+
+typedef struct {
+  upb_deflist defs;
+  upb_descreader_frame stack[UPB_MAX_TYPE_DEPTH];
+  int stack_len;
+  upb_status status;
+
+  uint32_t number;
+  char *name;
+  bool saw_number;
+  bool saw_name;
+
+  char *default_string;
+
+  upb_fielddef *f;
+} upb_descreader;
+
+void upb_descreader_init(upb_descreader *r);
+void upb_descreader_uninit(upb_descreader *r);
+
+// Registers handlers that will build the defs.  Pass the descreader as the
+// closure.
+upb_mhandlers *upb_descreader_reghandlers(upb_handlers *h);
+
+// Gets the array of defs that have been parsed and removes them from the
+// descreader.  Ownership of the defs is passed to the caller using the given
+// owner), but the ownership of the returned array is retained and is
+// invalidated by any other call into the descreader.  The defs will not have
+// been resolved, and are ready to be added to a symtab.
+upb_def **upb_descreader_getdefs(upb_descreader *r, void *owner, int *n);
+
+#ifdef __cplusplus
+}  /* extern "C" */
+#endif
+
+#endif