cmd/compile: avoid re-instantiating method that is already imported

We can import an shape-instantiated function/method for inlining
purposes. If we are instantiating the methods of a instantiated type
that we have seen, and it happens to need a shape instantiation that we
have imported, then don't re-create the instantiation, since we will end
up with conflicting/duplicate definitions for the instantiation symbol.
Instead, we can just use the existing imported instantation, and enter
it in the instInfoMap[].

Fixes #50121

Change-Id: I6eeb8786faad71106e261e113048b579afad04fa
Reviewed-on: https://go-review.googlesource.com/c/go/+/371414
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

diff --git a/src/cmd/compile/internal/noder/stencil.go b/src/cmd/compile/internal/noder/stencil.go
index 004db54c3b4a80dd1995729295d176e21e8fd2fd..62c306b89e2e6862a725076a5b26e5cb9a89f68d 100644 (file)
--- a/src/cmd/compile/internal/noder/stencil.go
+++ b/src/cmd/compile/internal/noder/stencil.go
@@ -684,7 +684,22 @@ func (g *genInst) getInstantiation(nameNode *ir.Name, shapes []*types.Type, isMe
                }
                info.dictInfo.shapeToBound = make(map[*types.Type]*types.Type)
 
-               // genericSubst fills in info.dictParam and info.tparamToBound.
+               if sym.Def != nil {
+                       // This instantiation must have been imported from another
+                       // package (because it was needed for inlining), so we should
+                       // not re-generate it and have conflicting definitions for the
+                       // symbol (issue #50121). It will have already gone through the
+                       // dictionary transformations of dictPass, so we don't actually
+                       // need the info.dictParam and info.shapeToBound info filled in
+                       // below. We just set the imported instantiation as info.fun.
+                       assert(sym.Pkg != types.LocalPkg)
+                       info.fun = sym.Def.(*ir.Name).Func
+                       assert(info.fun != nil)
+                       g.instInfoMap[sym] = info
+                       return info
+               }
+
+               // genericSubst fills in info.dictParam and info.shapeToBound.
                st := g.genericSubst(sym, nameNode, shapes, isMeth, info)
                info.fun = st
                g.instInfoMap[sym] = info
@@ -722,7 +737,7 @@ type subster struct {
 // args shapes. For a method with a generic receiver, it returns an instantiated
 // function type where the receiver becomes the first parameter. For either a generic
 // method or function, a dictionary parameter is the added as the very first
-// parameter. genericSubst fills in info.dictParam and info.tparamToBound.
+// parameter. genericSubst fills in info.dictParam and info.shapeToBound.
 func (g *genInst) genericSubst(newsym *types.Sym, nameNode *ir.Name, shapes []*types.Type, isMethod bool, info *instInfo) *ir.Func {
        var tparams []*types.Type
        if isMethod {

diff --git a/test/typeparam/issue50121.dir/a.go b/test/typeparam/issue50121.dir/a.go
new file mode 100644 (file)
index 0000000..9918fa3
--- /dev/null
+++ b/test/typeparam/issue50121.dir/a.go
@@ -0,0 +1,22 @@
+// Copyright 2021 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 a
+
+import (
+       "constraints"
+       "math/rand"
+)
+
+type Builder[T constraints.Integer] struct{}
+
+func (r Builder[T]) New() T {
+       return T(rand.Int())
+}
+
+var IntBuilder = Builder[int]{}
+
+func BuildInt() int {
+       return IntBuilder.New()
+}

diff --git a/test/typeparam/issue50121.dir/main.go b/test/typeparam/issue50121.dir/main.go
new file mode 100644 (file)
index 0000000..71eb44f
--- /dev/null
+++ b/test/typeparam/issue50121.dir/main.go
@@ -0,0 +1,18 @@
+// Copyright 2021 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 (
+       "a"
+)
+
+//go:noinline
+func BuildInt() int {
+       return a.BuildInt()
+}
+
+func main() {
+       BuildInt()
+}

diff --git a/test/typeparam/issue50121.go b/test/typeparam/issue50121.go
new file mode 100644 (file)
index 0000000..76930e5
--- /dev/null
+++ b/test/typeparam/issue50121.go
@@ -0,0 +1,7 @@
+// rundir -G=3
+
+// Copyright 2021 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 ignored