[dev.unified] cmd/compile/internal/noder: push exprBlank up into assignment handling

Blanks can only appear on the LHS of an assignment. Instead of
handling them as an arbitrary expression, handle them as part of
assignee expression lists.

Change-Id: Iaeb0a5c471ffa1abd2bbbd9c95f7876533e5a607
Reviewed-on: https://go-review.googlesource.com/c/go/+/410100
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

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

@@ -42,7 +42,6 @@ const (
 	exprType            // type expression
 	exprLocal           // local variable
 	exprGlobal          // global variable or function
-	exprBlank
 	exprCompLit
 	exprFuncLit
 	exprSelector
@@ -55,6 +54,17 @@ const (
 	exprConvert
 )
 
+type codeAssign int
+
+func (c codeAssign) Marker() pkgbits.SyncMarker { return pkgbits.SyncAssign }
+func (c codeAssign) Value() int                 { return int(c) }
+
+const (
+	assignBlank codeAssign = iota
+	assignDef
+	assignExpr
+)
+
 type codeDecl int
 
 func (c codeDecl) Marker() pkgbits.SyncMarker { return pkgbits.SyncDecl }

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

@@ -1323,25 +1323,41 @@ func (r *reader) assignList() ([]*ir.Name, []ir.Node) {
 	var names []*ir.Name
 
 	for i := range lhs {
-		if r.Bool() {
+		expr, def := r.assign()
-			pos := r.pos()
+		lhs[i] = expr
-			_, sym := r.localIdent()
+		if def {
-			typ := r.typ()
+			names = append(names, expr.(*ir.Name))
-
-			name := ir.NewNameAt(pos, sym)
-			lhs[i] = name
-			names = append(names, name)
-			setType(name, typ)
-			r.addLocal(name, ir.PAUTO)
-			continue
 		}
-
-		lhs[i] = r.expr()
 	}
 
 	return names, lhs
 }
 
+// assign returns an assignee expression. It also reports whether the
+// returned expression is a newly declared variable.
+func (r *reader) assign() (ir.Node, bool) {
+	switch tag := codeAssign(r.Code(pkgbits.SyncAssign)); tag {
+	default:
+		panic("unhandled assignee expression")
+
+	case assignBlank:
+		return typecheck.AssignExpr(ir.BlankNode), false
+
+	case assignDef:
+		pos := r.pos()
+		_, sym := r.localIdent()
+		typ := r.typ()
+
+		name := ir.NewNameAt(pos, sym)
+		setType(name, typ)
+		r.addLocal(name, ir.PAUTO)
+		return name, true
+
+	case assignExpr:
+		return r.expr(), false
+	}
+}
+
 func (r *reader) blockStmt() []ir.Node {
 	r.Sync(pkgbits.SyncBlockStmt)
 	r.openScope()
@@ -1551,11 +1567,6 @@ func (r *reader) expr() (res ir.Node) {
 	default:
 		panic("unhandled expression")
 
-	case exprBlank:
-		// blank only allowed in LHS of assignments
-		// TODO(mdempsky): Handle directly in assignList instead?
-		return typecheck.AssignExpr(ir.BlankNode)
-
 	case exprLocal:
 		return typecheck.Expr(r.useLocal())
 

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

@@ -1023,25 +1023,36 @@ func (w *writer) assignList(expr syntax.Expr) {
 	w.Len(len(exprs))
 
 	for _, expr := range exprs {
-		if name, ok := expr.(*syntax.Name); ok && name.Value != "_" {
+		w.assign(expr)
-			if obj, ok := w.p.info.Defs[name]; ok {
+	}
-				obj := obj.(*types2.Var)
+}
 
-				w.Bool(true)
+func (w *writer) assign(expr syntax.Expr) {
-				w.pos(obj)
+	expr = unparen(expr)
-				w.localIdent(obj)
-				w.typ(obj.Type())
 
-				// TODO(mdempsky): Minimize locals index size by deferring
+	if name, ok := expr.(*syntax.Name); ok {
-				// this until the variables actually come into scope.
+		if name.Value == "_" {
-				w.addLocal(obj)
+			w.Code(assignBlank)
-				continue
+			return
-			}
 		}
 
-		w.Bool(false)
+		if obj, ok := w.p.info.Defs[name]; ok {
-		w.expr(expr)
+			obj := obj.(*types2.Var)
+
+			w.Code(assignDef)
+			w.pos(obj)
+			w.localIdent(obj)
+			w.typ(obj.Type())
+
+			// TODO(mdempsky): Minimize locals index size by deferring
+			// this until the variables actually come into scope.
+			w.addLocal(obj)
+			return
+		}
 	}
+
+	w.Code(assignExpr)
+	w.expr(expr)
 }
 
 func (w *writer) declStmt(decl syntax.Decl) {
@@ -1256,10 +1267,6 @@ func (w *writer) expr(expr syntax.Expr) {
 	default:
 		w.p.unexpected("expression", expr)
 
-	case *syntax.Name:
-		assert(expr.Value == "_")
-		w.Code(exprBlank)
-
 	case *syntax.CompositeLit:
 		w.Code(exprCompLit)
 		w.compLit(expr)

src/internal/pkgbits/sync.go

@@ -90,6 +90,7 @@ const (
 	SyncExprs
 	SyncExpr
 	SyncExprType
+	SyncAssign
 	SyncOp
 	SyncFuncLit
 	SyncCompLit

src/internal/pkgbits/syncmarker_string.go

@@ -45,39 +45,40 @@ func _() {
 	_ = x[SyncExprs-35]
 	_ = x[SyncExpr-36]
 	_ = x[SyncExprType-37]
-	_ = x[SyncOp-38]
+	_ = x[SyncAssign-38]
-	_ = x[SyncFuncLit-39]
+	_ = x[SyncOp-39]
-	_ = x[SyncCompLit-40]
+	_ = x[SyncFuncLit-40]
-	_ = x[SyncDecl-41]
+	_ = x[SyncCompLit-41]
-	_ = x[SyncFuncBody-42]
+	_ = x[SyncDecl-42]
-	_ = x[SyncOpenScope-43]
+	_ = x[SyncFuncBody-43]
-	_ = x[SyncCloseScope-44]
+	_ = x[SyncOpenScope-44]
-	_ = x[SyncCloseAnotherScope-45]
+	_ = x[SyncCloseScope-45]
-	_ = x[SyncDeclNames-46]
+	_ = x[SyncCloseAnotherScope-46]
-	_ = x[SyncDeclName-47]
+	_ = x[SyncDeclNames-47]
-	_ = x[SyncStmts-48]
+	_ = x[SyncDeclName-48]
-	_ = x[SyncBlockStmt-49]
+	_ = x[SyncStmts-49]
-	_ = x[SyncIfStmt-50]
+	_ = x[SyncBlockStmt-50]
-	_ = x[SyncForStmt-51]
+	_ = x[SyncIfStmt-51]
-	_ = x[SyncSwitchStmt-52]
+	_ = x[SyncForStmt-52]
-	_ = x[SyncRangeStmt-53]
+	_ = x[SyncSwitchStmt-53]
-	_ = x[SyncCaseClause-54]
+	_ = x[SyncRangeStmt-54]
-	_ = x[SyncCommClause-55]
+	_ = x[SyncCaseClause-55]
-	_ = x[SyncSelectStmt-56]
+	_ = x[SyncCommClause-56]
-	_ = x[SyncDecls-57]
+	_ = x[SyncSelectStmt-57]
-	_ = x[SyncLabeledStmt-58]
+	_ = x[SyncDecls-58]
-	_ = x[SyncUseObjLocal-59]
+	_ = x[SyncLabeledStmt-59]
-	_ = x[SyncAddLocal-60]
+	_ = x[SyncUseObjLocal-60]
-	_ = x[SyncLinkname-61]
+	_ = x[SyncAddLocal-61]
-	_ = x[SyncStmt1-62]
+	_ = x[SyncLinkname-62]
-	_ = x[SyncStmtsEnd-63]
+	_ = x[SyncStmt1-63]
-	_ = x[SyncLabel-64]
+	_ = x[SyncStmtsEnd-64]
-	_ = x[SyncOptLabel-65]
+	_ = x[SyncLabel-65]
+	_ = x[SyncOptLabel-66]
 }
 
-const _SyncMarker_name = "EOFBoolInt64Uint64StringValueValRelocsRelocUseRelocPublicPosPosBaseObjectObject1PkgPkgDefMethodTypeTypeIdxTypeParamNamesSignatureParamsParamCodeObjSymLocalIdentSelectorPrivateFuncExtVarExtTypeExtPragmaExprListExprsExprAssertTypeOpFuncLitCompLitDeclFuncBodyOpenScopeCloseScopeCloseAnotherScopeDeclNamesDeclNameStmtsBlockStmtIfStmtForStmtSwitchStmtRangeStmtCaseClauseCommClauseSelectStmtDeclsLabeledStmtUseObjLocalAddLocalLinknameStmt1StmtsEndLabelOptLabel"
+const _SyncMarker_name = "EOFBoolInt64Uint64StringValueValRelocsRelocUseRelocPublicPosPosBaseObjectObject1PkgPkgDefMethodTypeTypeIdxTypeParamNamesSignatureParamsParamCodeObjSymLocalIdentSelectorPrivateFuncExtVarExtTypeExtPragmaExprListExprsExprExprTypeAssignOpFuncLitCompLitDeclFuncBodyOpenScopeCloseScopeCloseAnotherScopeDeclNamesDeclNameStmtsBlockStmtIfStmtForStmtSwitchStmtRangeStmtCaseClauseCommClauseSelectStmtDeclsLabeledStmtUseObjLocalAddLocalLinknameStmt1StmtsEndLabelOptLabel"
 
-var _SyncMarker_index = [...]uint16{0, 3, 7, 12, 18, 24, 29, 32, 38, 43, 51, 57, 60, 67, 73, 80, 83, 89, 95, 99, 106, 120, 129, 135, 140, 147, 150, 160, 168, 175, 182, 188, 195, 201, 209, 214, 218, 228, 230, 237, 244, 248, 256, 265, 275, 292, 301, 309, 314, 323, 329, 336, 346, 355, 365, 375, 385, 390, 401, 412, 420, 428, 433, 441, 446, 454}
+var _SyncMarker_index = [...]uint16{0, 3, 7, 12, 18, 24, 29, 32, 38, 43, 51, 57, 60, 67, 73, 80, 83, 89, 95, 99, 106, 120, 129, 135, 140, 147, 150, 160, 168, 175, 182, 188, 195, 201, 209, 214, 218, 226, 232, 234, 241, 248, 252, 260, 269, 279, 296, 305, 313, 318, 327, 333, 340, 350, 359, 369, 379, 389, 394, 405, 416, 424, 432, 437, 445, 450, 458}
 
 func (i SyncMarker) String() string {
 	i -= 1