cmd/compile: inline {i,e}facethash

These functions are really simple, the overhead of calling
them (in both time and code size) is larger than the inlined versions.

Reorganize how the nil case in a type switch is handled, as we have
to check for nil explicitly now anyway.

Saves about 0.8% in the binary size of the go tool.

Change-Id: I8501b62d72fde43650b79f52b5f699f1fbd0e7e7
Reviewed-on: https://go-review.googlesource.com/19814
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

4 files changed, 53 insertions, 43 deletions

diff --git a/src/cmd/compile/internal/gc/builtin.go b/src/cmd/compile/internal/gc/builtin.go
index 7583e8fa13..4a6e56fe47 100644
--- a/src/cmd/compile/internal/gc/builtin.go
+++ b/src/cmd/compile/internal/gc/builtin.go
@@ -66,8 +66,6 @@ const runtimeimport = "" +
 	"func @\"\".panicdottype (@\"\".have·1 *byte, @\"\".want·2 *byte, @\"\".iface·3 *byte)\n" +
 	"func @\"\".ifaceeq (@\"\".i1·2 any, @\"\".i2·3 any) (@\"\".ret·1 bool)\n" +
 	"func @\"\".efaceeq (@\"\".i1·2 any, @\"\".i2·3 any) (@\"\".ret·1 bool)\n" +
-	"func @\"\".ifacethash (@\"\".i1·2 any) (@\"\".ret·1 uint32)\n" +
-	"func @\"\".efacethash (@\"\".i1·2 any) (@\"\".ret·1 uint32)\n" +
 	"func @\"\".makemap (@\"\".mapType·2 *byte, @\"\".hint·3 int64, @\"\".mapbuf·4 *any, @\"\".bucketbuf·5 *any) (@\"\".hmap·1 map[any]any)\n" +
 	"func @\"\".mapaccess1 (@\"\".mapType·2 *byte, @\"\".hmap·3 map[any]any, @\"\".key·4 *any) (@\"\".val·1 *any)\n" +
 	"func @\"\".mapaccess1_fast32 (@\"\".mapType·2 *byte, @\"\".hmap·3 map[any]any, @\"\".key·4 any) (@\"\".val·1 *any)\n" +
diff --git a/src/cmd/compile/internal/gc/builtin/runtime.go b/src/cmd/compile/internal/gc/builtin/runtime.go
index 08f925f41c..0fe6242e74 100644
--- a/src/cmd/compile/internal/gc/builtin/runtime.go
+++ b/src/cmd/compile/internal/gc/builtin/runtime.go
@@ -83,8 +83,6 @@ func panicdottype(have, want, iface *byte)
 
 func ifaceeq(i1 any, i2 any) (ret bool)
 func efaceeq(i1 any, i2 any) (ret bool)
-func ifacethash(i1 any) (ret uint32)
-func efacethash(i1 any) (ret uint32)
 
 // *byte is really *runtime.Type
 func makemap(mapType *byte, hint int64, mapbuf *any, bucketbuf *any) (hmap map[any]any)
diff --git a/src/cmd/compile/internal/gc/swt.go b/src/cmd/compile/internal/gc/swt.go
index f0433f3df7..661b3ee5a9 100644
--- a/src/cmd/compile/internal/gc/swt.go
+++ b/src/cmd/compile/internal/gc/swt.go
@@ -549,20 +549,6 @@ func (s *typeSwitch) walk(sw *Node) {
 	// set up labels and jumps
 	casebody(sw, s.facename)
 
-	// calculate type hash
-	t := cond.Right.Type
-	if isnilinter(t) {
-		a = syslook("efacethash", 1)
-	} else {
-		a = syslook("ifacethash", 1)
-	}
-	substArgTypes(a, t)
-	a = Nod(OCALL, a, nil)
-	a.List = list1(s.facename)
-	a = Nod(OAS, s.hashname, a)
-	typecheck(&a, Etop)
-	cas = list(cas, a)
-
 	cc := caseClauses(sw, switchKindType)
 	sw.List = nil
 	var def *Node
@@ -572,22 +558,66 @@ func (s *typeSwitch) walk(sw *Node) {
 	} else {
 		def = Nod(OBREAK, nil, nil)
 	}
+	var typenil *Node
+	if len(cc) > 0 && cc[0].typ == caseKindTypeNil {
+		typenil = cc[0].node.Right
+		cc = cc[1:]
+	}
+
+	// For empty interfaces, do:
+	//     if e._type == nil {
+	//         do nil case if it exists, otherwise default
+	//     }
+	//     h := e._type.hash
+	// Use a similar strategy for non-empty interfaces.
+
+	// Get interface descriptor word.
+	typ := Nod(OITAB, s.facename, nil)
+
+	// Check for nil first.
+	i := Nod(OIF, nil, nil)
+	i.Left = Nod(OEQ, typ, nodnil())
+	if typenil != nil {
+		// Do explicit nil case right here.
+		i.Nbody = list1(typenil)
+	} else {
+		// Jump to default case.
+		lbl := newCaseLabel()
+		i.Nbody = list1(Nod(OGOTO, lbl, nil))
+		// Wrap default case with label.
+		blk := Nod(OBLOCK, nil, nil)
+		blk.List = list(list1(Nod(OLABEL, lbl, nil)), def)
+		def = blk
+	}
+	typecheck(&i.Left, Erv)
+	cas = list(cas, i)
+
+	if !isnilinter(cond.Right.Type) {
+		// Load type from itab.
+		typ = Nod(ODOTPTR, typ, nil)
+		typ.Type = Ptrto(Types[TUINT8])
+		typ.Typecheck = 1
+		typ.Xoffset = int64(Widthptr) // offset of _type in runtime.itab
+		typ.Bounded = true            // guaranteed not to fault
+	}
+	// Load hash from type.
+	h := Nod(ODOTPTR, typ, nil)
+	h.Type = Types[TUINT32]
+	h.Typecheck = 1
+	h.Xoffset = int64(2 * Widthptr) // offset of hash in runtime._type
+	h.Bounded = true                // guaranteed not to fault
+	a = Nod(OAS, s.hashname, h)
+	typecheck(&a, Etop)
+	cas = list(cas, a)
 
 	// insert type equality check into each case block
 	for _, c := range cc {
 		n := c.node
 		switch c.typ {
-		case caseKindTypeNil:
-			var v Val
-			v.U = new(NilVal)
-			a = Nod(OIF, nil, nil)
-			a.Left = Nod(OEQ, s.facename, nodlit(v))
-			typecheck(&a.Left, Erv)
-			a.Nbody = list1(n.Right) // if i==nil { goto l }
-			n.Right = a
-
 		case caseKindTypeVar, caseKindTypeConst:
 			n.Right = s.typeone(n)
+		default:
+			Fatalf("typeSwitch with bad kind: %d", c.typ)
 		}
 	}
 
diff --git a/src/runtime/iface.go b/src/runtime/iface.go
index 71dc865e07..50dff77e42 100644
--- a/src/runtime/iface.go
+++ b/src/runtime/iface.go
@@ -398,22 +398,6 @@ func assertE2E2(inter *interfacetype, e eface, r *eface) bool {
 	return true
 }
 
-func ifacethash(i iface) uint32 {
-	tab := i.tab
-	if tab == nil {
-		return 0
-	}
-	return tab._type.hash
-}
-
-func efacethash(e eface) uint32 {
-	t := e._type
-	if t == nil {
-		return 0
-	}
-	return t.hash
-}
-
 func iterate_itabs(fn func(*itab)) {
 	for _, h := range &hash {
 		for ; h != nil; h = h.link {