cmd/compile, etc: use name offset in method tables

Introduce and start using nameOff for two encoded names. This pair
of changes is best done together because the linker's method decoder
expects the method layouts to match.

Precursor to converting all existing name and *string fields to
nameOff.

linux/amd64:
	cmd/go:  -45KB (0.5%)
	jujud:  -389KB (0.6%)

linux/amd64 PIE:
	cmd/go: -170KB (1.4%)
	jujud:  -1.5MB (1.8%)

For #6853.

Change-Id: Ia044423f010fb987ce070b94c46a16fc78666ff6
Reviewed-on: https://go-review.googlesource.com/21396
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 29 insertions, 17 deletions

diff --git a/src/runtime/type.go b/src/runtime/type.go
index 711753bab5..31f7ff81b8 100644
--- a/src/runtime/type.go
+++ b/src/runtime/type.go
@@ -161,11 +161,17 @@ func resolveNameOff(ptrInModule unsafe.Pointer, off nameOff) name {
 		}
 	}
 	if md == nil {
-		println("runtime: nameOff", hex(off), "base", hex(base), "not in ranges:")
-		for next := &firstmoduledata; next != nil; next = next.next {
-			println("\ttypes", hex(next.types), "etypes", hex(next.etypes))
+		lock(&reflectOffs.lock)
+		res, found := reflectOffs.m[int32(off)]
+		unlock(&reflectOffs.lock)
+		if !found {
+			println("runtime: nameOff", hex(off), "base", hex(base), "not in ranges:")
+			for next := &firstmoduledata; next != nil; next = next.next {
+				println("\ttypes", hex(next.types), "etypes", hex(next.etypes))
+			}
+			throw("runtime: name offset base pointer out of range")
 		}
-		throw("runtime: name offset base pointer out of range")
+		return name{(*byte)(res)}
 	}
 	res := md.types + uintptr(off)
 	if res > md.etypes {
@@ -175,6 +181,10 @@ func resolveNameOff(ptrInModule unsafe.Pointer, off nameOff) name {
 	return name{(*byte)(unsafe.Pointer(res))}
 }
 
+func (t *_type) nameOff(off nameOff) name {
+	return resolveNameOff(unsafe.Pointer(t), off)
+}
+
 func (t *_type) typeOff(off typeOff) *_type {
 	if off == 0 {
 		return nil
@@ -269,7 +279,7 @@ type typeOff int32
 type textOff int32
 
 type method struct {
-	name name
+	name nameOff
 	mtyp typeOff
 	ifn  textOff
 	tfn  textOff
@@ -282,8 +292,8 @@ type uncommontype struct {
 }
 
 type imethod struct {
-	name  name
-	_type *_type
+	name nameOff
+	ityp typeOff
 }
 
 type interfacetype struct {
@@ -354,19 +364,19 @@ type name struct {
 	bytes *byte
 }
 
-func (n *name) data(off int) *byte {
+func (n name) data(off int) *byte {
 	return (*byte)(add(unsafe.Pointer(n.bytes), uintptr(off)))
 }
 
-func (n *name) isExported() bool {
+func (n name) isExported() bool {
 	return (*n.bytes)&(1<<0) != 0
 }
 
-func (n *name) nameLen() int {
+func (n name) nameLen() int {
 	return int(uint16(*n.data(1))<<8 | uint16(*n.data(2)))
 }
 
-func (n *name) tagLen() int {
+func (n name) tagLen() int {
 	if *n.data(0)&(1<<1) == 0 {
 		return 0
 	}
@@ -374,7 +384,7 @@ func (n *name) tagLen() int {
 	return int(uint16(*n.data(off))<<8 | uint16(*n.data(off + 1)))
 }
 
-func (n *name) name() (s string) {
+func (n name) name() (s string) {
 	if n.bytes == nil {
 		return ""
 	}
@@ -388,7 +398,7 @@ func (n *name) name() (s string) {
 	return s
 }
 
-func (n *name) tag() (s string) {
+func (n name) tag() (s string) {
 	tl := n.tagLen()
 	if tl == 0 {
 		return ""
@@ -400,7 +410,7 @@ func (n *name) tag() (s string) {
 	return s
 }
 
-func (n *name) pkgPath() string {
+func (n name) pkgPath() string {
 	if n.bytes == nil || *n.data(0)&(1<<2) == 0 {
 		return ""
 	}
@@ -545,13 +555,15 @@ func typesEqual(t, v *_type) bool {
 		for i := range it.mhdr {
 			tm := &it.mhdr[i]
 			vm := &iv.mhdr[i]
-			if tm.name.name() != vm.name.name() {
+			tname := it.typ.nameOff(tm.name)
+			vname := iv.typ.nameOff(vm.name)
+			if tname.name() != vname.name() {
 				return false
 			}
-			if tm.name.pkgPath() != vm.name.pkgPath() {
+			if tname.pkgPath() != vname.pkgPath() {
 				return false
 			}
-			if !typesEqual(tm._type, vm._type) {
+			if !typesEqual(it.typ.typeOff(tm.ityp), iv.typ.typeOff(vm.ityp)) {
 				return false
 			}
 		}