cmd/compile, cmd/link, reflect, runtime: remove type.zero field

No longer used after previous hashmap change.

Change-Id: I558470f872281e84a78406132df4e391d077b833
Reviewed-on: https://go-review.googlesource.com/13785
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/compile/internal/gc/reflect.go

@@ -796,11 +796,6 @@ func dcommontype(s *Sym, ot int, t *Type) int {
 
 	gcsym, useGCProg, ptrdata := dgcsym(t)
 
-	// We use size 0 here so we get the pointer to the zero value,
-	// but don't allocate space for the zero value unless we need it.
-	// TODO: how do we get this symbol into bss?  We really want
-	// a read-only bss, but I don't think such a thing exists.
-
 	// ../../pkg/reflect/type.go:/^type.commonType
 	// actual type structure
 	//	type commonType struct {
@@ -816,7 +811,6 @@ func dcommontype(s *Sym, ot int, t *Type) int {
 	//		string        *string
 	//		*extraType
 	//		ptrToThis     *Type
-	//		zero          unsafe.Pointer
 	//	}
 	ot = duintptr(s, ot, uint64(t.Width))
 	ot = duintptr(s, ot, uint64(ptrdata))
@@ -869,7 +863,6 @@ func dcommontype(s *Sym, ot int, t *Type) int {
 	ot += Widthptr
 
 	ot = dsymptr(s, ot, sptr, 0) // ptrto type
-	ot = duintptr(s, ot, 0)      // ptr to zero value (unused)
 	return ot
 }
 
@@ -1052,7 +1045,7 @@ ok:
 	switch t.Etype {
 	default:
 		ot = dcommontype(s, ot, t)
-		xt = ot - 3*Widthptr
+		xt = ot - 2*Widthptr
 
 	case TARRAY:
 		if t.Bound >= 0 {
@@ -1064,7 +1057,7 @@ ok:
 			t2.Bound = -1 // slice
 			s2 := dtypesym(t2)
 			ot = dcommontype(s, ot, t)
-			xt = ot - 3*Widthptr
+			xt = ot - 2*Widthptr
 			ot = dsymptr(s, ot, s1, 0)
 			ot = dsymptr(s, ot, s2, 0)
 			ot = duintptr(s, ot, uint64(t.Bound))
@@ -1073,7 +1066,7 @@ ok:
 			s1 := dtypesym(t.Type)
 
 			ot = dcommontype(s, ot, t)
-			xt = ot - 3*Widthptr
+			xt = ot - 2*Widthptr
 			ot = dsymptr(s, ot, s1, 0)
 		}
 
@@ -1082,7 +1075,7 @@ ok:
 		s1 := dtypesym(t.Type)
 
 		ot = dcommontype(s, ot, t)
-		xt = ot - 3*Widthptr
+		xt = ot - 2*Widthptr
 		ot = dsymptr(s, ot, s1, 0)
 		ot = duintptr(s, ot, uint64(t.Chan))
 
@@ -1101,7 +1094,7 @@ ok:
 		}
 
 		ot = dcommontype(s, ot, t)
-		xt = ot - 3*Widthptr
+		xt = ot - 2*Widthptr
 		ot = duint8(s, ot, uint8(obj.Bool2int(isddd)))
 
 		// two slice headers: in and out.
@@ -1140,7 +1133,7 @@ ok:
 		// ../../runtime/type.go:/InterfaceType
 		ot = dcommontype(s, ot, t)
 
-		xt = ot - 3*Widthptr
+		xt = ot - 2*Widthptr
 		ot = dsymptr(s, ot, s, ot+Widthptr+2*Widthint)
 		ot = duintxx(s, ot, uint64(n), Widthint)
 		ot = duintxx(s, ot, uint64(n), Widthint)
@@ -1160,7 +1153,7 @@ ok:
 		s3 := dtypesym(mapbucket(t))
 		s4 := dtypesym(hmap(t))
 		ot = dcommontype(s, ot, t)
-		xt = ot - 3*Widthptr
+		xt = ot - 2*Widthptr
 		ot = dsymptr(s, ot, s1, 0)
 		ot = dsymptr(s, ot, s2, 0)
 		ot = dsymptr(s, ot, s3, 0)
@@ -1196,7 +1189,7 @@ ok:
 		s1 := dtypesym(t.Type)
 
 		ot = dcommontype(s, ot, t)
-		xt = ot - 3*Widthptr
+		xt = ot - 2*Widthptr
 		ot = dsymptr(s, ot, s1, 0)
 
 		// ../../runtime/type.go:/StructType
@@ -1210,7 +1203,7 @@ ok:
 		}
 
 		ot = dcommontype(s, ot, t)
-		xt = ot - 3*Widthptr
+		xt = ot - 2*Widthptr
 		ot = dsymptr(s, ot, s, ot+Widthptr+2*Widthint)
 		ot = duintxx(s, ot, uint64(n), Widthint)
 		ot = duintxx(s, ot, uint64(n), Widthint)

src/cmd/link/internal/ld/decodesym.go

@@ -47,7 +47,7 @@ func decode_inuxi(p []byte, sz int) uint64 {
 // commonsize returns the size of the common prefix for all type
 // structures (runtime._type).
 func commonsize() int {
-	return 8*Thearch.Ptrsize + 8
+	return 7*Thearch.Ptrsize + 8
 }
 
 // Type.commonType.kind

src/reflect/type.go

@@ -247,17 +247,16 @@ const (
 type rtype struct {
 	size          uintptr
 	ptrdata       uintptr
-	hash          uint32         // hash of type; avoids computation in hash tables
+	hash          uint32   // hash of type; avoids computation in hash tables
-	_             uint8          // unused/padding
+	_             uint8    // unused/padding
-	align         uint8          // alignment of variable with this type
+	align         uint8    // alignment of variable with this type
-	fieldAlign    uint8          // alignment of struct field with this type
+	fieldAlign    uint8    // alignment of struct field with this type
-	kind          uint8          // enumeration for C
+	kind          uint8    // enumeration for C
-	alg           *typeAlg       // algorithm table
+	alg           *typeAlg // algorithm table
-	gcdata        *byte          // garbage collection data
+	gcdata        *byte    // garbage collection data
-	string        *string        // string form; unnecessary but undeniably useful
+	string        *string  // string form; unnecessary but undeniably useful
-	*uncommonType                // (relatively) uncommon fields
+	*uncommonType          // (relatively) uncommon fields
-	ptrToThis     *rtype         // type for pointer to this type, if used in binary or has methods
+	ptrToThis     *rtype   // type for pointer to this type, if used in binary or has methods
-	zero          unsafe.Pointer // unused
 }
 
 // a copy of runtime.typeAlg

src/runtime/type.go

@@ -8,8 +8,8 @@ package runtime
 
 import "unsafe"
 
-// Needs to be in sync with ../cmd/internal/ld/decodesym.go:/^func.commonsize,
+// Needs to be in sync with ../cmd/compile/internal/ld/decodesym.go:/^func.commonsize,
-// ../cmd/internal/gc/reflect.go:/^func.dcommontype and
+// ../cmd/compile/internal/gc/reflect.go:/^func.dcommontype and
 // ../reflect/type.go:/^type.rtype.
 type _type struct {
 	size       uintptr
@@ -27,7 +27,6 @@ type _type struct {
 	_string *string
 	x       *uncommontype
 	ptrto   *_type
-	zero    *byte // unused
 }
 
 type method struct {