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[dev.unified] cmd/compile/internal/noder: add optExpr for optional expressions

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Previously, {writer,reader}.expr would allow for nil
expressions (i.e., no expression at all, not a "nil" identifier). But
only a few contexts allow this, and it simplifies some logic if we can
assume the expression is non-nil.

So this CL introduces optExpr as a wrapper method for handling nil
expressions specially.

Change-Id: I438bae7a3191126f7790ec0bf5b77320fe855514
Reviewed-on: https://go-review.googlesource.com/c/go/+/410099
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
This commit is contained in:
Matthew Dempsky 2022-06-03 12:49:11 -07:00
parent 6c33f1d52e
commit 55fc07e164
3 changed files with 25 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
src/cmd/compile/internal/noder/codes.go
View File

@ -38,11 +38,10 @@ func (c codeExpr) Value() int { return int(c) }
// TODO(mdempsky): Split expr into addr, for lvalues.
const (
exprNone codeExpr = iota
exprConst
exprType // type expression
exprLocal // local variable
exprGlobal // global variable or function
exprConst codeExpr = iota
exprType // type expression
exprLocal // local variable
exprGlobal // global variable or function
exprBlank
exprCompLit
exprFuncLit

16
src/cmd/compile/internal/noder/reader.go
View File

@ -1380,7 +1380,7 @@ func (r *reader) forStmt(label *types.Sym) ir.Node {
pos := r.pos()
init := r.stmt()
cond := r.expr()
cond := r.optExpr()
post := r.stmt()
body := r.blockStmt()
r.closeAnotherScope()
@ -1450,7 +1450,7 @@ func (r *reader) switchStmt(label *types.Sym) ir.Node {
iface = x.Type()
tag = ir.NewTypeSwitchGuard(pos, ident, x)
} else {
tag = r.expr()
tag = r.optExpr()
}
clauses := make([]*ir.CaseClause, r.Len())
@ -1551,9 +1551,6 @@ func (r *reader) expr() (res ir.Node) {
default:
panic("unhandled expression")
case exprNone:
return nil
case exprBlank:
// blank only allowed in LHS of assignments
// TODO(mdempsky): Handle directly in assignList instead?
@ -1622,7 +1619,7 @@ func (r *reader) expr() (res ir.Node) {
pos := r.pos()
var index [3]ir.Node
for i := range index {
index[i] = r.expr()
index[i] = r.optExpr()
}
op := ir.OSLICE
if index[2] != nil {
@ -1701,6 +1698,13 @@ func (r *reader) expr() (res ir.Node) {
}
}
func (r *reader) optExpr() ir.Node {
if r.Bool() {
return r.expr()
}
return nil
}
func (r *reader) compLit() ir.Node {
r.Sync(pkgbits.SyncCompLit)
pos := r.pos()

17
src/cmd/compile/internal/noder/writer.go
View File

@ -1077,7 +1077,7 @@ func (w *writer) forStmt(stmt *syntax.ForStmt) {
} else {
w.pos(stmt)
w.stmt(stmt.Init)
w.expr(stmt.Cond)
w.optExpr(stmt.Cond)
w.stmt(stmt.Post)
}
@ -1136,7 +1136,7 @@ func (w *writer) switchStmt(stmt *syntax.SwitchStmt) {
}
w.expr(guard.X)
} else {
w.expr(stmt.Tag)
w.optExpr(stmt.Tag)
}
w.Len(len(stmt.Body))
@ -1201,6 +1201,8 @@ func (w *writer) optLabel(label *syntax.Name) {
// @@@ Expressions
func (w *writer) expr(expr syntax.Expr) {
base.Assertf(expr != nil, "missing expression")
expr = unparen(expr) // skip parens; unneeded after typecheck
obj, inst := lookupObj(w.p.info, expr)
@ -1254,9 +1256,6 @@ func (w *writer) expr(expr syntax.Expr) {
default:
w.p.unexpected("expression", expr)
case nil: // absent slice index, for condition, or switch tag
w.Code(exprNone)
case *syntax.Name:
assert(expr.Value == "_")
w.Code(exprBlank)
@ -1292,7 +1291,7 @@ func (w *writer) expr(expr syntax.Expr) {
w.expr(expr.X)
w.pos(expr)
for _, n := range &expr.Index {
w.expr(n)
w.optExpr(n)
}
case *syntax.AssertExpr:
@ -1356,6 +1355,12 @@ func (w *writer) expr(expr syntax.Expr) {
}
}
func (w *writer) optExpr(expr syntax.Expr) {
if w.Bool(expr != nil) {
w.expr(expr)
}
}
func (w *writer) compLit(lit *syntax.CompositeLit) {
tv, ok := w.p.info.Types[lit]
assert(ok)