cmd/compile: fix handling of Defn field during stenciling

When the Defn field of a name node is not an ONAME (for a closure
variable), then it points to a body node of the same function/closure.
Therefore, we should not attempt to substitute it at the time we are
substituting the local variables. Instead, we remember a mapping from the
Defn node to the nodes that reference it, and update the Defn fields of
the copied name nodes at the time that we create the new copy of the
Defn node.

Added some comments to the Defn field of ir.Name.

Moved the Defn (and Outer code, for consistency) from namelist() to
localvar(), since Defn needs to updated for all local variables, not
just those in a closure. Fixed case where .Defn was not being set
properly in noder2 for type switches. Fixed another case where the Defn
field had to be updated during transformSelect() because the Defn node
was being completely changed to a new node.

Fixed some spacing in typeswitch2.go

Fixes #47676
Fixes #48016

Change-Id: Iae70dd76575f4a647c1db79e1eba9bbe44bfc226
Reviewed-on: https://go-review.googlesource.com/c/go/+/346290
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/ir/name.go

@@ -51,6 +51,8 @@ type Name struct {
 	// For a local variable (not param) or extern, the initializing assignment (OAS or OAS2).
 	// For a closure var, the ONAME node of the outer captured variable.
 	// For the case-local variables of a type switch, the type switch guard (OTYPESW).
+	// For a range variable, the range statement (ORANGE)
+	// For a recv variable in a case of a select statement, the receive assignment (OSELRECV2)
 	// For the name of a function, points to corresponding Func node.
 	Defn Node
 

src/cmd/compile/internal/noder/stencil.go

@@ -627,6 +627,9 @@ type subster struct {
 	newf     *ir.Func // Func node for the new stenciled function
 	ts       typecheck.Tsubster
 	info     *instInfo // Place to put extra info in the instantiation
+
+	// Map from non-nil, non-ONAME node n to slice of all m, where m.Defn = n
+	defnMap map[ir.Node][]**ir.Name
 }
 
 // genericSubst returns a new function with name newsym. The function is an
@@ -675,6 +678,7 @@ func (g *irgen) genericSubst(newsym *types.Sym, nameNode *ir.Name, shapes []*typ
 			Targs:   shapes,
 			Vars:    make(map[*ir.Name]*ir.Name),
 		},
+		defnMap: make(map[ir.Node][]**ir.Name),
 	}
 
 	newf.Dcl = make([]*ir.Name, 0, len(gf.Dcl)+1)
@@ -726,6 +730,10 @@ func (g *irgen) genericSubst(newsym *types.Sym, nameNode *ir.Name, shapes []*typ
 	// to many->1 shape to concrete mapping.
 	// newf.Body.Prepend(subst.checkDictionary(dictionaryName, shapes)...)
 
+	if len(subst.defnMap) > 0 {
+		base.Fatalf("defnMap is not empty")
+	}
+
 	ir.CurFunc = savef
 	// Add any new, fully instantiated types seen during the substitution to
 	// g.instTypeList.
@@ -764,6 +772,25 @@ func (subst *subster) localvar(name *ir.Name) *ir.Name {
 	m.Func = name.Func
 	subst.ts.Vars[name] = m
 	m.SetTypecheck(1)
+	if name.Defn != nil {
+		if name.Defn.Op() == ir.ONAME {
+			// This is a closure variable, so its Defn is the outer
+			// captured variable, which has already been substituted.
+			m.Defn = subst.node(name.Defn)
+		} else {
+			// The other values of Defn are nodes in the body of the
+			// function, so just remember the mapping so we can set Defn
+			// properly in node() when we create the new body node. We
+			// always call localvar() on all the local variables before
+			// we substitute the body.
+			slice := subst.defnMap[name.Defn]
+			subst.defnMap[name.Defn] = append(slice, &m)
+		}
+	}
+	if name.Outer != nil {
+		m.Outer = subst.node(name.Outer).(*ir.Name)
+	}
+
 	return m
 }
 
@@ -871,6 +898,18 @@ func (subst *subster) node(n ir.Node) ir.Node {
 			}
 		}
 		m := ir.Copy(x)
+
+		slice, ok := subst.defnMap[x]
+		if ok {
+			// We just copied a non-ONAME node which was the Defn value
+			// of a local variable. Set the Defn value of the copied
+			// local variable to this new Defn node.
+			for _, ptr := range slice {
+				(*ptr).Defn = m
+			}
+			delete(subst.defnMap, x)
+		}
+
 		if _, isExpr := m.(ir.Expr); isExpr {
 			t := x.Type()
 			if t == nil {
@@ -1312,12 +1351,6 @@ func (subst *subster) namelist(l []*ir.Name) []*ir.Name {
 	s := make([]*ir.Name, len(l))
 	for i, n := range l {
 		s[i] = subst.localvar(n)
-		if n.Defn != nil {
-			s[i].Defn = subst.node(n.Defn)
-		}
-		if n.Outer != nil {
-			s[i].Outer = subst.node(n.Outer).(*ir.Name)
-		}
 	}
 	return s
 }

src/cmd/compile/internal/noder/stmt.go

@@ -327,6 +327,8 @@ func (g *irgen) switchStmt(stmt *syntax.SwitchStmt) ir.Node {
 		if obj, ok := g.info.Implicits[clause]; ok {
 			cv = g.obj(obj)
 			cv.SetPos(g.makeXPos(clause.Colon))
+			assert(expr.Op() == ir.OTYPESW)
+			cv.Defn = expr
 		}
 		body[i] = ir.NewCaseStmt(g.pos(clause), g.exprList(clause.Cases), g.stmts(clause.Body))
 		body[i].Var = cv

src/cmd/compile/internal/noder/transform.go

@@ -493,10 +493,15 @@ func transformSelect(sel *ir.SelectStmt) {
 		if ncase.Comm != nil {
 			n := ncase.Comm
 			oselrecv2 := func(dst, recv ir.Node, def bool) {
-				n := ir.NewAssignListStmt(n.Pos(), ir.OSELRECV2, []ir.Node{dst, ir.BlankNode}, []ir.Node{recv})
+				selrecv := ir.NewAssignListStmt(n.Pos(), ir.OSELRECV2, []ir.Node{dst, ir.BlankNode}, []ir.Node{recv})
-				n.Def = def
+				if dst.Op() == ir.ONAME && dst.(*ir.Name).Defn == n {
-				n.SetTypecheck(1)
+					// Must fix Defn for dst, since we are
-				ncase.Comm = n
+					// completely changing the node.
+					dst.(*ir.Name).Defn = selrecv
+				}
+				selrecv.Def = def
+				selrecv.SetTypecheck(1)
+				ncase.Comm = selrecv
 			}
 			switch n.Op() {
 			case ir.OAS:

test/typeparam/issue47676.go

@@ -0,0 +1,23 @@
+// run -gcflags=-G=3
+
+// Copyright 2021 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.
+
+package main
+
+func main() {
+	d := diff([]int{}, func(int) string {
+		return "foo"
+	})
+	d()
+}
+
+func diff[T any](previous []T, uniqueKey func(T) string) func() {
+	return func() {
+		newJSON := map[string]T{}
+		for _, prev := range previous {
+			delete(newJSON, uniqueKey(prev))
+		}
+	}
+}

test/typeparam/issue48016.go

@@ -0,0 +1,35 @@
+// run -gcflags=-G=3
+
+// Copyright 2021 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.
+
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+func test1[T any](fn func(T) int, v T) int {
+	fn1 := func() int {
+		var i interface{} = v
+		val := fn(i.(T))
+		return val
+	}
+	return fn1()
+}
+
+func main() {
+	want := 123
+	got := test1(func(s string) int {
+		r, err := strconv.Atoi(s)
+		if err != nil {
+			return 0
+		}
+		return r
+	}, "123")
+	if got != want {
+		panic(fmt.Sprintf("got %f, want %f", got, want))
+	}
+}

test/typeparam/typeswitch2.go

@@ -16,7 +16,7 @@ func f[T any](i interface{}) {
 		println("int", x)
 	case int32, int16:
 		println("int32/int16", reflect.ValueOf(x).Int())
-	case struct { a, b T }:
+	case struct{ a, b T }:
 		println("struct{T,T}", x.a, x.b)
 	default:
 		println("other", reflect.ValueOf(x).Int())
@@ -26,6 +26,6 @@ func main() {
 	f[float64](float64(6))
 	f[float64](int(7))
 	f[float64](int32(8))
-	f[float64](struct{a, b float64}{a:1, b:2})
+	f[float64](struct{ a, b float64 }{a: 1, b: 2})
 	f[float64](int8(9))
 }