[dev.ssa] cmd/compile: implement len(map)

Implement len(map) values.

Change-Id: If92be96ec9a7a86aeb3ce566d6758aab01c2fa7d
Reviewed-on: https://go-review.googlesource.com/13961Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -1440,8 +1440,7 @@ func (s *state) expr(n *Node) *ssa.Value {
 		case n.Left.Type.IsString(): // string; not reachable for OCAP
 			return s.newValue1(ssa.OpStringLen, Types[TINT], s.expr(n.Left))
 		case n.Left.Type.IsMap():
-			s.Unimplementedf("unhandled len(map)")
-			return nil
+			return s.lenMap(n, s.expr(n.Left))
 		case n.Left.Type.IsChan():
 			if n.Op == OCAP {
 				s.Unimplementedf("unhandled cap(chan)")
@@ -1998,6 +1997,41 @@ func (s *state) uintTofloat(cvttab *u2fcvtTab, n *Node, x *ssa.Value, ft, tt *Ty
 	return s.variable(n, n.Type)
 }
 
+func (s *state) lenMap(n *Node, x *ssa.Value) *ssa.Value {
+	// if n == nil {
+	//   return 0
+	// } else {
+	//   return *((*int)n)
+	// }
+	lenType := n.Type
+	cmp := s.newValue2(ssa.OpEqPtr, Types[TBOOL], x, s.zeroVal(lenType))
+	b := s.endBlock()
+	b.Kind = ssa.BlockIf
+	b.Control = cmp
+	b.Likely = ssa.BranchUnlikely
+
+	bThen := s.f.NewBlock(ssa.BlockPlain)
+	bElse := s.f.NewBlock(ssa.BlockPlain)
+	bAfter := s.f.NewBlock(ssa.BlockPlain)
+
+	// length of a nil map is zero
+	addEdge(b, bThen)
+	s.startBlock(bThen)
+	s.vars[n] = s.zeroVal(lenType)
+	s.endBlock()
+	addEdge(bThen, bAfter)
+
+	// the length is stored in the first word
+	addEdge(b, bElse)
+	s.startBlock(bElse)
+	s.vars[n] = s.newValue2(ssa.OpLoad, lenType, x, s.mem())
+	s.endBlock()
+	addEdge(bElse, bAfter)
+
+	s.startBlock(bAfter)
+	return s.variable(n, lenType)
+}
+
 // checkgoto checks that a goto from from to to does not
 // jump into a block or jump over variable declarations.
 // It is a copy of checkgoto in the pre-SSA backend,

src/cmd/compile/internal/gc/testdata/map_ssa.go

+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// map_ssa.go tests map operations.
+package main
+
+import "fmt"
+
+var failed = false
+
+func lenMap_ssa(v map[int]int) int {
+	switch { // prevent inlining
+
+	}
+	return len(v)
+}
+
+func testLenMap() {
+
+	v := make(map[int]int)
+	v[0] = 0
+	v[1] = 0
+	v[2] = 0
+
+	if want, got := 3, lenMap_ssa(v); got != want {
+		fmt.Printf("expected len(map) = %d, got %d", want, got)
+		failed = true
+	}
+}
+
+func testLenNilMap() {
+
+	var v map[int]int
+	if want, got := 0, lenMap_ssa(v); got != want {
+		fmt.Printf("expected len(nil) = %d, got %d", want, got)
+		failed = true
+	}
+}
+func main() {
+	testLenMap()
+	testLenNilMap()
+
+	if failed {
+		panic("failed")
+	}
+}

src/cmd/compile/internal/gc/testdata/string_ssa.go

+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
 // string_ssa.go tests string operations.
 package main