[dev.typeparams] cmd/compile: put shape types in their own package

Put shape types in the top level package called ".shape".
Name them using the serialization of the shape name, instead of
the .shapeN names.

This allows the linker to deduplicate instantiations across packages.

Not sure that this is entirely correct, as shapes in this package
may reference other packages (e.g. a field of a struct). But it seems
to work for now.

For the added test, when you look at the resulting binary (use the -k
option with run.go) it has only one instantiation of F, and 4 call sites:

$ objdump -d a.exe | grep _a\.F
 1053cb0:	e8 8b 00 00 00 	callq	139 <_a.F[.shape.*uint8]>
 1053ce9:	e8 52 00 00 00 	callq	82 <_a.F[.shape.*uint8]>
_a.F[.shape.*uint8]:
 1053d90:	e8 ab ff ff ff 	callq	-85 <_a.F[.shape.*uint8]>
 1053dc9:	e8 72 ff ff ff 	callq	-142 <_a.F[.shape.*uint8]>

Change-Id: I627f7e50210aabe4a10d0e2717d87b75ac82e99b
Reviewed-on: https://go-review.googlesource.com/c/go/+/339595
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

8 files changed, 78 insertions, 5 deletions

diff --git a/src/cmd/compile/internal/reflectdata/reflect.go b/src/cmd/compile/internal/reflectdata/reflect.go
index 19cf2a0a12..a8df7a1a24 100644
--- a/src/cmd/compile/internal/reflectdata/reflect.go
+++ b/src/cmd/compile/internal/reflectdata/reflect.go
@@ -947,7 +947,7 @@ func writeType(t *types.Type) *obj.LSym {
 	}
 
 	dupok := 0
-	if tbase.Sym() == nil { // TODO(mdempsky): Probably need DUPOK for instantiated types too.
+	if tbase.Sym() == nil || tbase.HasShape() { // TODO(mdempsky): Probably need DUPOK for instantiated types too.
 		dupok = obj.DUPOK
 	}
 
@@ -1738,6 +1738,11 @@ func NeedEmit(typ *types.Type) bool {
 		// Need to emit to be safe (however, see TODO above).
 		return true
 
+	case typ.HasShape():
+		// Shape type; need to emit even though it lives in the .shape package.
+		// TODO: make sure the linker deduplicates them (see dupok in writeType above).
+		return true
+
 	default:
 		// Should have been emitted by an imported package.
 		return false
diff --git a/src/cmd/compile/internal/typecheck/subr.go b/src/cmd/compile/internal/typecheck/subr.go
index 25db24259c..53c3933370 100644
--- a/src/cmd/compile/internal/typecheck/subr.go
+++ b/src/cmd/compile/internal/typecheck/subr.go
@@ -1362,8 +1362,7 @@ func Shapify(t *types.Type) *types.Type {
 		return s
 	}
 
-	sym := Lookup(fmt.Sprintf(".shape%d", snum))
-	snum++
+	sym := shapePkg.Lookup(u.LinkString())
 	name := ir.NewDeclNameAt(u.Pos(), ir.OTYPE, sym)
 	s := types.NewNamed(name)
 	s.SetUnderlying(u)
@@ -1375,6 +1374,6 @@ func Shapify(t *types.Type) *types.Type {
 	return s
 }
 
-var snum int
-
 var shaped = map[*types.Type]*types.Type{}
+
+var shapePkg = types.NewPkg(".shape", ".shape")
diff --git a/test/typeparam/dedup.dir/a.go b/test/typeparam/dedup.dir/a.go
new file mode 100644
index 0000000000..f5cb6dc762
--- /dev/null
+++ b/test/typeparam/dedup.dir/a.go
@@ -0,0 +1,10 @@
+// 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
+
+//go:noinline
+func F[T comparable](a, b T) bool {
+	return a == b
+}
diff --git a/test/typeparam/dedup.dir/b.go b/test/typeparam/dedup.dir/b.go
new file mode 100644
index 0000000000..ce037e2d8a
--- /dev/null
+++ b/test/typeparam/dedup.dir/b.go
@@ -0,0 +1,14 @@
+// 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 b
+
+import "a"
+
+func B() {
+	var x int64
+	println(a.F(&x, &x))
+	var y int32
+	println(a.F(&y, &y))
+}
diff --git a/test/typeparam/dedup.dir/c.go b/test/typeparam/dedup.dir/c.go
new file mode 100644
index 0000000000..11a5d97642
--- /dev/null
+++ b/test/typeparam/dedup.dir/c.go
@@ -0,0 +1,14 @@
+// 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 c
+
+import "a"
+
+func C() {
+	var x int64
+	println(a.F(&x, &x))
+	var y int32
+	println(a.F(&y, &y))
+}
diff --git a/test/typeparam/dedup.dir/main.go b/test/typeparam/dedup.dir/main.go
new file mode 100644
index 0000000000..dc3ff6f75f
--- /dev/null
+++ b/test/typeparam/dedup.dir/main.go
@@ -0,0 +1,15 @@
+// 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 (
+	"b"
+	"c"
+)
+
+func main() {
+	b.B()
+	c.C()
+}
diff --git a/test/typeparam/dedup.go b/test/typeparam/dedup.go
new file mode 100644
index 0000000000..dca4cf3a84
--- /dev/null
+++ b/test/typeparam/dedup.go
@@ -0,0 +1,12 @@
+// 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.
+
+// Note: this doesn't really test the deduplication of
+// instantiations. It just provides an easy mechanism to build a
+// binary that you can then check with objdump manually to make sure
+// deduplication is happening. TODO: automate this somehow?
+
+package ignored
diff --git a/test/typeparam/dedup.out b/test/typeparam/dedup.out
new file mode 100644
index 0000000000..1140ff52e2
--- /dev/null
+++ b/test/typeparam/dedup.out
@@ -0,0 +1,4 @@
+true
+true
+true
+true