cmd/compile: add clear(x) builtin

To clear map, and zero content of slice.

Updates golang#56351

Change-Id: I5f81dfbc465500f5acadaf2c6beb9b5f0d2c4045
Reviewed-on: https://go-review.googlesource.com/c/go/+/453395
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Run-TryBot: Cuong Manh Le <[email protected]>
Auto-Submit: Cuong Manh Le <[email protected]>

Author: cuonglm

src/cmd/compile/internal/escape/call.go

@@ -179,7 +179,7 @@ func (e *escape) callCommon(ks []hole, call ir.Node, init *ir.Nodes, wrapper *ir
 			argument(e.discardHole(), &call.Args[i])
 		}
 
-	case ir.OLEN, ir.OCAP, ir.OREAL, ir.OIMAG, ir.OCLOSE:
+	case ir.OLEN, ir.OCAP, ir.OREAL, ir.OIMAG, ir.OCLOSE, ir.OCLEAR:
 		call := call.(*ir.UnaryExpr)
 		argument(e.discardHole(), &call.X)
 

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

@@ -180,7 +180,7 @@ func (e *escape) stmt(n ir.Node) {
 			dsts[i] = res.Nname.(*ir.Name)
 		}
 		e.assignList(dsts, n.Results, "return", n)
-	case ir.OCALLFUNC, ir.OCALLMETH, ir.OCALLINTER, ir.OINLCALL, ir.OCLOSE, ir.OCOPY, ir.ODELETE, ir.OPANIC, ir.OPRINT, ir.OPRINTN, ir.ORECOVER:
+	case ir.OCALLFUNC, ir.OCALLMETH, ir.OCALLINTER, ir.OINLCALL, ir.OCLEAR, ir.OCLOSE, ir.OCOPY, ir.ODELETE, ir.OPANIC, ir.OPRINT, ir.OPRINTN, ir.ORECOVER:
 		e.call(nil, n)
 	case ir.OGO, ir.ODEFER:
 		n := n.(*ir.GoDeferStmt)

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

@@ -747,7 +747,7 @@ func (n *UnaryExpr) SetOp(op Op) {
 	default:
 		panic(n.no("SetOp " + op.String()))
 	case OBITNOT, ONEG, ONOT, OPLUS, ORECV,
-		OALIGNOF, OCAP, OCLOSE, OIMAG, OLEN, ONEW,
+		OALIGNOF, OCAP, OCLEAR, OCLOSE, OIMAG, OLEN, ONEW,
 		OOFFSETOF, OPANIC, OREAL, OSIZEOF,
 		OCHECKNIL, OCFUNC, OIDATA, OITAB, OSPTR,
 		OUNSAFESTRINGDATA, OUNSAFESLICEDATA:

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

@@ -39,6 +39,7 @@ var OpNames = []string{
 	OCALL:             "function call", // not actual syntax
 	OCAP:              "cap",
 	OCASE:             "case",
+	OCLEAR:            "clear",
 	OCLOSE:            "close",
 	OCOMPLEX:          "complex",
 	OBITNOT:           "^",
@@ -182,6 +183,7 @@ var OpPrec = []int{
 	OCALLMETH:         8,
 	OCALL:             8,
 	OCAP:              8,
+	OCLEAR:            8,
 	OCLOSE:            8,
 	OCOMPLIT:          8,
 	OCONVIFACE:        8,
@@ -767,6 +769,7 @@ func exprFmt(n Node, s fmt.State, prec int) {
 	case OREAL,
 		OIMAG,
 		OCAP,
+		OCLEAR,
 		OCLOSE,
 		OLEN,
 		ONEW,

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

@@ -159,6 +159,7 @@ const (
 	OCALLMETH  // X(Args) (direct method call x.Method(args))
 	OCALLINTER // X(Args) (interface method call x.Method(args))
 	OCAP       // cap(X)
+	OCLEAR     // clear(X)
 	OCLOSE     // close(X)
 	OCLOSURE   // func Type { Func.Closure.Body } (func literal)
 	OCOMPLIT   // Type{List} (composite literal, not yet lowered to specific form)

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

@@ -743,6 +743,7 @@ func callOrChan(n ir.Node) bool {
 		ir.OCALLINTER,
 		ir.OCALLMETH,
 		ir.OCAP,
+		ir.OCLEAR,
 		ir.OCLOSE,
 		ir.OCOMPLEX,
 		ir.OCOPY,

src/cmd/compile/internal/typecheck/const.go

@@ -260,7 +260,7 @@ func tcCall(n *ir.CallExpr, top int) ir.Node {
 			n.SetTypecheck(0) // re-typechecking new op is OK, not a loop
 			return typecheck(n, top)
 
-		case ir.OCAP, ir.OCLOSE, ir.OIMAG, ir.OLEN, ir.OPANIC, ir.OREAL, ir.OUNSAFESTRINGDATA, ir.OUNSAFESLICEDATA:
+		case ir.OCAP, ir.OCLEAR, ir.OCLOSE, ir.OIMAG, ir.OLEN, ir.OPANIC, ir.OREAL, ir.OUNSAFESTRINGDATA, ir.OUNSAFESLICEDATA:
 			typecheckargs(n)
 			fallthrough
 		case ir.ONEW, ir.OALIGNOF, ir.OOFFSETOF, ir.OSIZEOF:
@@ -441,6 +441,28 @@ func tcAppend(n *ir.CallExpr) ir.Node {
 	return n
 }
 
+// tcClear typechecks an OCLEAR node.
+func tcClear(n *ir.UnaryExpr) ir.Node {
+	n.X = Expr(n.X)
+	n.X = DefaultLit(n.X, nil)
+	l := n.X
+	t := l.Type()
+	if t == nil {
+		n.SetType(nil)
+		return n
+	}
+
+	switch {
+	case t.IsMap(), t.IsSlice():
+	default:
+		base.Errorf("invalid operation: %v (argument must be a map or slice)", n)
+		n.SetType(nil)
+		return n
+	}
+
+	return n
+}
+
 // tcClose typechecks an OCLOSE node.
 func tcClose(n *ir.UnaryExpr) ir.Node {
 	n.X = Expr(n.X)

src/cmd/compile/internal/typecheck/func.go

@@ -273,6 +273,7 @@ func tcGoDefer(n *ir.GoDeferStmt) {
 	case ir.OCALLINTER,
 		ir.OCALLMETH,
 		ir.OCALLFUNC,
+		ir.OCLEAR,
 		ir.OCLOSE,
 		ir.OCOPY,
 		ir.ODELETE,

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

@@ -336,7 +336,7 @@ func typecheck(n ir.Node, top int) (res ir.Node) {
 	case ir.OAPPEND:
 		// Must be used (and not BinaryExpr/UnaryExpr).
 		isStmt = false
-	case ir.OCLOSE, ir.ODELETE, ir.OPANIC, ir.OPRINT, ir.OPRINTN:
+	case ir.OCLEAR, ir.OCLOSE, ir.ODELETE, ir.OPANIC, ir.OPRINT, ir.OPRINTN:
 		// Must not be used.
 		isExpr = false
 		isStmt = true
@@ -621,6 +621,10 @@ func typecheck1(n ir.Node, top int) ir.Node {
 		n := n.(*ir.BinaryExpr)
 		return tcComplex(n)
 
+	case ir.OCLEAR:
+		n := n.(*ir.UnaryExpr)
+		return tcClear(n)
+
 	case ir.OCLOSE:
 		n := n.(*ir.UnaryExpr)
 		return tcClose(n)

src/cmd/compile/internal/typecheck/typecheck.go

@@ -34,6 +34,7 @@ var builtinFuncs = [...]struct {
 }{
 	{"append", ir.OAPPEND},
 	{"cap", ir.OCAP},
+	{"clear", ir.OCLEAR},
 	{"close", ir.OCLOSE},
 	{"complex", ir.OCOMPLEX},
 	{"copy", ir.OCOPY},