cmd/compile: copy blank parameter node when substituting function type

When a function type is copied (e.g. for substituting type
parameters), we make copies of its parameter ir.Name nodes, so
they are not shared with the old function type. But currently a
blank (_) identifier is not copied but shared. The parameter
node's frame offset is assigned (in ABI analysis) and then used in
the concurrent backend. Shared node can cause a data race. Make a
new blank parameter node to avoid sharing. (Unified IR does already
not have this problem. This fixes non-unified-IR mode.)

This seems to fix #55357.

Change-Id: Ie27f08e5589ac7d5d3f0d0d5de1a21e4fd2765c9
Reviewed-on: https://go-review.googlesource.com/c/go/+/443158
Reviewed-by: Keith Randall <[email protected]>
Run-TryBot: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Keith Randall <[email protected]>

Author: cherrymui

src/cmd/compile/internal/test/race.go

@@ -0,0 +1,64 @@
+// Copyright 2022 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.
+
+//go:build !compiler_bootstrap
+
+package test
+
+// The racecompile builder only builds packages, but does not build
+// or run tests. This is a non-test file to hold cases that (used
+// to) trigger compiler data races, so they will be exercised on
+// the racecompile builder.
+//
+// This package is not imported so functions here are not included
+// in the actual compiler.
+
+// Issue 55357: data race when building multiple instantiations of
+// generic closures with _ parameters.
+func Issue55357() {
+	type U struct {
+		A int
+		B string
+		C string
+	}
+	var q T55357[U]
+	q.Count()
+	q.List()
+
+	type M struct {
+		A int64
+		B uint32
+		C uint32
+	}
+	var q2 T55357[M]
+	q2.Count()
+	q2.List()
+}
+
+type T55357[T any] struct{}
+
+//go:noinline
+func (q *T55357[T]) do(w, v bool, fn func(bk []byte, v T) error) error {
+	return nil
+}
+
+func (q *T55357[T]) Count() (n int, rerr error) {
+	err := q.do(false, false, func(kb []byte, _ T) error {
+		n++
+		return nil
+	})
+	return n, err
+}
+
+func (q *T55357[T]) List() (list []T, rerr error) {
+	var l []T
+	err := q.do(false, true, func(_ []byte, v T) error {
+		l = append(l, v)
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return l, nil
+}

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

@@ -1358,14 +1358,22 @@ func (ts *Tsubster) tstruct(t *types.Type, force bool) *types.Type {
 				newfields[i].SetNointerface(true)
 			}
 			if f.Nname != nil && ts.Vars != nil {
-				v := ts.Vars[f.Nname.(*ir.Name)]
+				n := f.Nname.(*ir.Name)
+				v := ts.Vars[n]
 				if v != nil {
 					// This is the case where we are
 					// translating the type of the function we
 					// are substituting, so its dcls are in
 					// the subst.ts.vars table, and we want to
 					// change to reference the new dcl.
 					newfields[i].Nname = v
+				} else if ir.IsBlank(n) {
+					// Blank variable is not dcl list. Make a
+					// new one to not share.
+					m := ir.NewNameAt(n.Pos(), ir.BlankNode.Sym())
+					m.SetType(n.Type())
+					m.SetTypecheck(1)
+					newfields[i].Nname = m
 				} else {
 					// This is the case where we are
 					// translating the type of a function