runtime: pass key/value to map accessors by reference, not by value.

This change is part of the plan to get rid of all vararg C calls
which are a pain for getting exact stack scanning.

We allocate a chunk of zero memory to return a pointer to when a
map access doesn't find the key.  This is simpler than returning nil
and fixing things up in the caller.  Linker magic allocates a single
zero memory area that is shared by all (non-reflect-generated) map
types.

Passing things by reference gets rid of some copies, so it speeds
up code with big keys/values.

benchmark             old ns/op    new ns/op    delta
BenchmarkBigKeyMap           34           31   -8.48%
BenchmarkBigValMap           37           30  -18.62%
BenchmarkSmallKeyMap         26           23  -11.28%

R=golang-dev, dvyukov, khr, rsc
CC=golang-dev
https://golang.org/cl/14794043

1 files changed, 0 insertions, 6 deletions

diff --git a/src/pkg/runtime/runtime.h b/src/pkg/runtime/runtime.h
index f7c2adb121..129dc7d152 100644
--- a/src/pkg/runtime/runtime.h
+++ b/src/pkg/runtime/runtime.h
@@ -1037,12 +1037,6 @@ void	runtime·osyield(void);
 void	runtime·lockOSThread(void);
 void	runtime·unlockOSThread(void);
 
-void	runtime·mapassign(MapType*, Hmap*, byte*, byte*);
-void	runtime·mapaccess(MapType*, Hmap*, byte*, byte*, bool*);
-void	runtime·mapiternext(struct hash_iter*);
-bool	runtime·mapiterkey(struct hash_iter*, void*);
-Hmap*	runtime·makemap_c(MapType*, int64);
-
 Hchan*	runtime·makechan_c(ChanType*, int64);
 void	runtime·chansend(ChanType*, Hchan*, byte*, bool*, void*);
 void	runtime·chanrecv(ChanType*, Hchan*, byte*, bool*, bool*);