[release-branch.go1.20] cmd/compile: re-compile instantiated generic methods in linkshared mode

For G[T] that was seen and compiled in imported package, it is not added
to typecheck.Target.Decls, prevent wasting compile time re-creating
DUPOKS symbols. However, the linker do not support a type symbol
referencing a method symbol across DSO boundary. That causes unreachable
sym error when building under -linkshared mode.

To fix it, always re-compile generic methods in linkshared mode.

Fixes #59236

Change-Id: I894b417cfe8234ae1fe809cc975889345df22cef
Reviewed-on: https://go-review.googlesource.com/c/go/+/477375
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-on: https://go-review.googlesource.com/c/go/+/479355

misc/cgo/testshared/shared_test.go

@@ -1112,8 +1112,13 @@ func TestStd(t *testing.T) {
 		t.Skip("skip in short mode")
 	}
 	t.Parallel()
+	tmpDir := t.TempDir()
 	// Use a temporary pkgdir to not interfere with other tests, and not write to GOROOT.
 	// Cannot use goCmd as it runs with cloned GOROOT which is incomplete.
 	runWithEnv(t, "building std", []string{"GOROOT=" + oldGOROOT},
-		filepath.Join(oldGOROOT, "bin", "go"), "install", "-buildmode=shared", "-pkgdir="+t.TempDir(), "std")
+		filepath.Join(oldGOROOT, "bin", "go"), "install", "-buildmode=shared", "-pkgdir="+tmpDir, "std")
+
+	// Issue #58966.
+	runWithEnv(t, "testing issue #58966", []string{"GOROOT=" + oldGOROOT},
+		filepath.Join(oldGOROOT, "bin", "go"), "run", "-linkshared", "-pkgdir="+tmpDir, "./issue58966/main.go")
 }

misc/cgo/testshared/testdata/issue58966/main.go

@@ -0,0 +1,15 @@
+// Copyright 2023 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 "crypto/elliptic"
+
+var curve elliptic.Curve
+
+func main() {
+	switch curve {
+	case elliptic.P224():
+	}
+}

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

@@ -158,7 +158,11 @@ func readBodies(target *ir.Package, duringInlining bool) {
 			// Instantiated generic function: add to Decls for typechecking
 			// and compilation.
 			if fn.OClosure == nil && len(pri.dict.targs) != 0 {
-				if duringInlining {
+				// cmd/link does not support a type symbol referencing a method symbol
+				// across DSO boundary, so force re-compiling methods on a generic type
+				// even it was seen from imported package in linkshared mode, see #58966.
+				canSkipNonGenericMethod := !(base.Ctxt.Flag_linkshared && ir.IsMethod(fn))
+				if duringInlining && canSkipNonGenericMethod {
 					inlDecls = append(inlDecls, fn)
 				} else {
 					target.Decls = append(target.Decls, fn)