runtime: remove unused m->racepc

The original plan was to collect allocation stacks
for all memory blocks. But it was never implemented
and it's not in near plans and it's unclear how to do it at all.

R=golang-dev, dave, bradfitz
CC=golang-dev
https://golang.org/cl/12724044

src/pkg/runtime/malloc.goc

@@ -141,10 +141,8 @@ runtime·mallocgc(uintptr size, uintptr typ, uint32 flag)
 	if(!(flag & FlagNoInvokeGC) && mstats.heap_alloc >= mstats.next_gc)
 		runtime·gc(0);
 
-	if(raceenabled) {
-		runtime·racemalloc(v, size, m->racepc);
-		m->racepc = nil;
-	}
+	if(raceenabled)
+		runtime·racemalloc(v, size);
 	return v;
 }
 
@@ -702,8 +700,6 @@ runtime·mal(uintptr n)
 void
 runtime·new(Type *typ, uint8 *ret)
 {
-	if(raceenabled)
-		m->racepc = runtime·getcallerpc(&typ);
 	ret = runtime·mallocgc(typ->size, (uintptr)typ | TypeInfo_SingleObject, typ->kind&KindNoPointers ? FlagNoPointers : 0);
 	FLUSH(&ret);
 }

src/pkg/runtime/race.c

@@ -138,13 +138,13 @@ runtime·racefuncexit(void)
 }
 
 void
-runtime·racemalloc(void *p, uintptr sz, void *pc)
+runtime·racemalloc(void *p, uintptr sz)
 {
 	// use m->curg because runtime·stackalloc() is called from g0
 	if(m->curg == nil)
 		return;
 	m->racecall = true;
-	runtime∕race·Malloc(m->curg->racectx, p, sz, pc);
+	runtime∕race·Malloc(m->curg->racectx, p, sz, /* unused pc */ 0);
 	m->racecall = false;
 }
 

src/pkg/runtime/race.h

@@ -16,7 +16,7 @@ uintptr	runtime·raceinit(void);
 void	runtime·racefini(void);
 
 void	runtime·racemapshadow(void *addr, uintptr size);
-void	runtime·racemalloc(void *p, uintptr sz, void *pc);
+void	runtime·racemalloc(void *p, uintptr sz);
 void	runtime·racefree(void *p);
 uintptr	runtime·racegostart(void *pc);
 void	runtime·racegoend(void);

src/pkg/runtime/race0.c

@@ -105,11 +105,10 @@ runtime·racefingo(void)
 }
 
 void
-runtime·racemalloc(void *p, uintptr sz, void *pc)
+runtime·racemalloc(void *p, uintptr sz)
 {
 	USED(p);
 	USED(sz);
-	USED(pc);
 }
 
 void

src/pkg/runtime/runtime.h

@@ -339,7 +339,6 @@ struct	M
 	GCStats	gcstats;
 	bool	racecall;
 	bool	needextram;
-	void*	racepc;
 	void	(*waitunlockf)(Lock*);
 	void*	waitlock;