undo CL 12785045 / 71ce80dc4195

This has broken the 32-bit builds.

««« original CL description
cmd/gc, runtime: use type information to scan interface values

R=golang-dev, rsc, dvyukov
CC=golang-dev
https://golang.org/cl/12785045
»»»

R=khr, golang-dev, khr
CC=golang-dev
https://golang.org/cl/13010045

src/cmd/gc/pgen.c

@@ -257,6 +257,7 @@ walktype1(Type *t, vlong *xoffset, Bvec *bv)
 		bvset(bv, ((*xoffset / widthptr) * BitsPerPointer) + 1);
 		if(isnilinter(t))
 			bvset(bv, ((*xoffset / widthptr) * BitsPerPointer));
+		bvset(bv, ((*xoffset + widthptr) / widthptr) * BitsPerPointer);
 		*xoffset += t->width;
 		break;
 

src/pkg/runtime/mgc0.c

@@ -36,10 +36,6 @@ enum {
 
 	// Pointer map
 	BitsPerPointer = 2,
-	BitsNoPointer = 0,
-	BitsPointer = 1,
-	BitsIface = 2,
-	BitsEface = 3,
 };
 
 // Bits in per-word bitmap.
@@ -1402,52 +1398,26 @@ struct BitVector
 	uint32 data[];
 };
 
-// Scans an interface data value when the interface type indicates
-// that it is a pointer.
-static void
-scaninterfacedata(uintptr bits, byte *scanp, bool inprologue)
-{
-	Itab *tab;
-	Type *type;
-
-	if(!inprologue) {
-		if(bits == BitsIface) {
-			tab = *(Itab**)scanp;
-			if(tab->type->size <= sizeof(void*) && (tab->type->kind & KindNoPointers))
-				return;
-		} else { // bits == BitsEface
-			type = *(Type**)scanp;
-			if(type->size <= sizeof(void*) && (type->kind & KindNoPointers))
-				return;
-		}
-	}
-	addroot((Obj){scanp+PtrSize, PtrSize, 0});
-}
-
 // Starting from scanp, scans words corresponding to set bits.
 static void
-scanbitvector(byte *scanp, BitVector *bv, bool inprologue)
+scanbitvector(byte *scanp, BitVector *bv)
 {
-	uintptr word, bits;
-	uint32 *wordp;
+	uint32 *wp;
+	uint32 w;
 	int32 i, remptrs;
 
-	wordp = bv->data;
+	wp = bv->data;
 	for(remptrs = bv->n; remptrs > 0; remptrs -= 32) {
-		word = *wordp++;
+		w = *wp++;
 		if(remptrs < 32)
 			i = remptrs;
 		else
 			i = 32;
 		i /= BitsPerPointer;
 		for(; i > 0; i--) {
-			bits = word & 3;
-			if(bits != BitsNoPointer && *(void**)scanp != nil)
-				if(bits == BitsPointer)
-					addroot((Obj){scanp, PtrSize, 0});
-				else
-					scaninterfacedata(bits, scanp, inprologue);
-			word >>= BitsPerPointer;
+			if(w & 3)
+				addroot((Obj){scanp, PtrSize, 0});
+			w >>= BitsPerPointer;
 			scanp += PtrSize;
 		}
 	}
@@ -1460,14 +1430,12 @@ addframeroots(Stkframe *frame, void*)
 	Func *f;
 	BitVector *args, *locals;
 	uintptr size;
-	bool afterprologue;
 
 	f = frame->fn;
 
 	// Scan local variables if stack frame has been allocated.
 	// Use pointer information if known.
-	afterprologue = (frame->varp > (byte*)frame->sp);
-	if(afterprologue) {
+	if(frame->varp > (byte*)frame->sp) {
 		locals = runtime·funcdata(f, FUNCDATA_GCLocals);
 		if(locals == nil) {
 			// No locals information, scan everything.
@@ -1482,7 +1450,7 @@ addframeroots(Stkframe *frame, void*)
 			// Locals bitmap information, scan just the
 			// pointers in locals.
 			size = (locals->n*PtrSize) / BitsPerPointer;
-			scanbitvector(frame->varp - size, locals, false);
+			scanbitvector(frame->varp - size, locals);
 		}
 	}
 
@@ -1490,7 +1458,7 @@ addframeroots(Stkframe *frame, void*)
 	// Use pointer information if known.
 	args = runtime·funcdata(f, FUNCDATA_GCArgs);
 	if(args != nil && args->n > 0)
-		scanbitvector(frame->argp, args, !afterprologue);
+		scanbitvector(frame->argp, args);
 	else
 		addroot((Obj){frame->argp, frame->arglen, 0});
 }