runtime: rename FlagNoPointers to FlagNoScan. Better represents

the use of the flag, especially for objects which actually do have
pointers but we don't want the GC to scan them.

R=golang-dev, cshapiro
CC=golang-dev
https://golang.org/cl/13181045

src/pkg/runtime/malloc.goc

@@ -98,12 +98,14 @@ runtime·mallocgc(uintptr size, uintptr typ, uint32 flag)
 	}
 
 	if(!(flag & FlagNoGC))
-		runtime·markallocated(v, size, (flag&FlagNoPointers) != 0);
+		runtime·markallocated(v, size, (flag&FlagNoScan) != 0);
 
 	if(DebugTypeAtBlockEnd)
 		*(uintptr*)((uintptr)v+size-sizeof(uintptr)) = typ;
 
-	if(UseSpanType && !(flag & FlagNoPointers) && typ != 0) {
+	// TODO: save type even if FlagNoScan?  Potentially expensive but might help
+	// heap profiling/tracing.
+	if(UseSpanType && !(flag & FlagNoScan) && typ != 0) {
 		uintptr *buf, i;
 
 		buf = m->settype_buf;
@@ -114,7 +116,7 @@ runtime·mallocgc(uintptr size, uintptr typ, uint32 flag)
 	}
 
 	m->mallocing = 0;
-	if(UseSpanType && !(flag & FlagNoPointers) && typ != 0 && m->settype_bufsize == nelem(m->settype_buf))
+	if(UseSpanType && !(flag & FlagNoScan) && typ != 0 && m->settype_bufsize == nelem(m->settype_buf))
 		runtime·settype_flush(m);
 	m->locks--;
 	if(m->locks == 0 && g->preempt)  // restore the preemption request in case we've cleared it in newstack
@@ -601,7 +603,7 @@ runtime·settype_flush(M *mp)
 		case MTypes_Empty:
 			ntypes = (s->npages << PageShift) / size;
 			nbytes3 = 8*sizeof(uintptr) + 1*ntypes;
-			data3 = runtime·mallocgc(nbytes3, 0, FlagNoProfiling|FlagNoPointers|FlagNoInvokeGC);
+			data3 = runtime·mallocgc(nbytes3, 0, FlagNoProfiling|FlagNoScan|FlagNoInvokeGC);
 			s->types.compression = MTypes_Bytes;
 			s->types.data = (uintptr)data3;
 			((uintptr*)data3)[1] = typ;
@@ -628,7 +630,7 @@ runtime·settype_flush(M *mp)
 			} else {
 				ntypes = (s->npages << PageShift) / size;
 				nbytes2 = ntypes * sizeof(uintptr);
-				data2 = runtime·mallocgc(nbytes2, 0, FlagNoProfiling|FlagNoPointers|FlagNoInvokeGC);
+				data2 = runtime·mallocgc(nbytes2, 0, FlagNoProfiling|FlagNoScan|FlagNoInvokeGC);
 				s->types.compression = MTypes_Words;
 				s->types.data = (uintptr)data2;
 
@@ -699,7 +701,7 @@ runtime·mal(uintptr n)
 void
 runtime·new(Type *typ, uint8 *ret)
 {
-	ret = runtime·mallocgc(typ->size, (uintptr)typ | TypeInfo_SingleObject, typ->kind&KindNoPointers ? FlagNoPointers : 0);
+	ret = runtime·mallocgc(typ->size, (uintptr)typ | TypeInfo_SingleObject, typ->kind&KindNoPointers ? FlagNoScan : 0);
 	FLUSH(&ret);
 }
 
@@ -710,7 +712,7 @@ cnew(Type *typ, intgo n, int32 objtyp)
 		runtime·throw("runtime: invalid objtyp");
 	if(n < 0 || (typ->size > 0 && n > MaxMem/typ->size))
 		runtime·panicstring("runtime: allocation size out of range");
-	return runtime·mallocgc(typ->size*n, (uintptr)typ | objtyp, typ->kind&KindNoPointers ? FlagNoPointers : 0);
+	return runtime·mallocgc(typ->size*n, (uintptr)typ | objtyp, typ->kind&KindNoPointers ? FlagNoScan : 0);
 }
 
 // same as runtime·new, but callable from C

src/pkg/runtime/malloc.h

@@ -467,7 +467,7 @@ uintptr	runtime·gettype(void*);
 enum
 {
 	// flags to malloc
-	FlagNoPointers	= 1<<0,	// no pointers here
+	FlagNoScan	= 1<<0,	// GC doesn't have to scan object
 	FlagNoProfiling	= 1<<1,	// must not profile
 	FlagNoGC	= 1<<2,	// must not free or scan for pointers
 	FlagNoZero	= 1<<3, // don't zero memory

src/pkg/runtime/mfinal.c

@@ -123,7 +123,7 @@ resizefintab(Fintab *tab)
 		newtab.max *= 3;
 	}
 	
-	newtab.key = runtime·mallocgc(newtab.max*sizeof newtab.key[0], 0, FlagNoInvokeGC|FlagNoPointers);
+	newtab.key = runtime·mallocgc(newtab.max*sizeof newtab.key[0], 0, FlagNoInvokeGC|FlagNoScan);
 	newtab.val = runtime·mallocgc(newtab.max*sizeof newtab.val[0], 0, FlagNoInvokeGC);
 	
 	for(i=0; i<tab->max; i++) {

src/pkg/runtime/mgc0.c

@@ -51,7 +51,7 @@ enum {
 // The bits in the word are packed together by type first, then by
 // heap location, so each 64-bit bitmap word consists of, from top to bottom,
 // the 16 bitSpecial bits for the corresponding heap words, then the 16 bitMarked bits,
-// then the 16 bitNoPointers/bitBlockBoundary bits, then the 16 bitAllocated bits.
+// then the 16 bitNoScan/bitBlockBoundary bits, then the 16 bitAllocated bits.
 // This layout makes it easier to iterate over the bits of a given type.
 //
 // The bitmap starts at mheap.arena_start and extends *backward* from
@@ -68,7 +68,7 @@ enum {
 //	/* then test bits & bitAllocated, bits & bitMarked, etc. */
 //
 #define bitAllocated		((uintptr)1<<(bitShift*0))
-#define bitNoPointers		((uintptr)1<<(bitShift*1))	/* when bitAllocated is set */
+#define bitNoScan		((uintptr)1<<(bitShift*1))	/* when bitAllocated is set */
 #define bitMarked		((uintptr)1<<(bitShift*2))	/* when bitAllocated is set */
 #define bitSpecial		((uintptr)1<<(bitShift*3))	/* when bitAllocated is set - has finalizer or being profiled */
 #define bitBlockBoundary	((uintptr)1<<(bitShift*1))	/* when bitAllocated is NOT set */
@@ -454,7 +454,7 @@ flushptrbuf(PtrTarget *ptrbuf, PtrTarget **ptrbufpos, Obj **_wp, Workbuf **_wbuf
 			}
 
 			// If object has no pointers, don't need to scan further.
-			if((bits & bitNoPointers) != 0)
+			if((bits & bitNoScan) != 0)
 				continue;
 
 			// Ask span about size class.
@@ -1198,7 +1198,7 @@ debug_scanblock(byte *b, uintptr n)
 			runtime·printf("found unmarked block %p in %p\n", obj, vp+i);
 
 		// If object has no pointers, don't need to scan further.
-		if((bits & bitNoPointers) != 0)
+		if((bits & bitNoScan) != 0)
 			continue;
 
 		debug_scanblock(obj, size);
@@ -2345,9 +2345,9 @@ runfinq(void)
 					runtime·free(frame);
 					// The frame does not contain pointers interesting for GC,
 					// all not yet finalized objects are stored in finc.
-					// If we do not mark it as FlagNoPointers,
+					// If we do not mark it as FlagNoScan,
 					// the last finalized object is not collected.
-					frame = runtime·mallocgc(framesz, 0, FlagNoPointers|FlagNoInvokeGC);
+					frame = runtime·mallocgc(framesz, 0, FlagNoScan|FlagNoInvokeGC);
 					framecap = framesz;
 				}
 				if(f->fint == nil)
@@ -2381,9 +2381,9 @@ runfinq(void)
 }
 
 // mark the block at v of size n as allocated.
-// If noptr is true, mark it as having no pointers.
+// If noscan is true, mark it as not needing scanning.
 void
-runtime·markallocated(void *v, uintptr n, bool noptr)
+runtime·markallocated(void *v, uintptr n, bool noscan)
 {
 	uintptr *b, obits, bits, off, shift;
 
@@ -2400,8 +2400,8 @@ runtime·markallocated(void *v, uintptr n, bool noptr)
 	for(;;) {
 		obits = *b;
 		bits = (obits & ~(bitMask<<shift)) | (bitAllocated<<shift);
-		if(noptr)
-			bits |= bitNoPointers<<shift;
+		if(noscan)
+			bits |= bitNoScan<<shift;
 		if(runtime·gomaxprocs == 1) {
 			*b = bits;
 			break;

src/pkg/runtime/string.goc

@@ -47,7 +47,7 @@ gostringsize(intgo l)
 	if(l == 0)
 		return runtime·emptystring;
 	// leave room for NUL for C runtime (e.g., callers of getenv)
-	s.str = runtime·mallocgc(l+1, 0, FlagNoPointers|FlagNoZero);
+	s.str = runtime·mallocgc(l+1, 0, FlagNoScan|FlagNoZero);
 	s.len = l;
 	s.str[l] = 0;
 	for(;;) {
@@ -85,7 +85,7 @@ runtime·gobytes(byte *p, intgo n)
 {
 	Slice sl;
 
-	sl.array = runtime·mallocgc(n, 0, FlagNoPointers|FlagNoZero);
+	sl.array = runtime·mallocgc(n, 0, FlagNoScan|FlagNoZero);
 	sl.len = n;
 	sl.cap = n;
 	runtime·memmove(sl.array, p, n);
@@ -252,7 +252,7 @@ func slicebytetostring(b Slice) (s String) {
 }
 
 func stringtoslicebyte(s String) (b Slice) {
-	b.array = runtime·mallocgc(s.len, 0, FlagNoPointers|FlagNoZero);
+	b.array = runtime·mallocgc(s.len, 0, FlagNoScan|FlagNoZero);
 	b.len = s.len;
 	b.cap = s.len;
 	runtime·memmove(b.array, s.str, s.len);
@@ -301,7 +301,7 @@ func stringtoslicerune(s String) (b Slice) {
 		n++;
 	}
 
-	b.array = runtime·mallocgc(n*sizeof(r[0]), 0, FlagNoPointers|FlagNoZero);
+	b.array = runtime·mallocgc(n*sizeof(r[0]), 0, FlagNoScan|FlagNoZero);
 	b.len = n;
 	b.cap = n;
 	p = s.str;