[dev.typeparams] cmd/compile: start using sub-dictionary entries where needed

Added new struct instInfo for information about an instantiation (of a
generic function/method with gcshapes or concrete types). We use this to
remember the dictionary param node, the nodes where sub-dictionaries
need to be used, etc. The instInfo map replaces the Stencil map in
Package.

Added code to access sub-dictionary entries at the appropriate call
sites. We are currently still calculating the corresponding main
dictionary, even when we really only need a sub-dictionary. I'll clean
that up in a follow-up CL.

Added code to deal with "generic" closures (closures that reference some
generic variables/types). We decided that closures will share the same
dictionary as the containing function (accessing the dictionary via a
closure variable). So, the getGfInfo function now traverses all the
nodes of each closure in a function that it is analyzing, so that a
function's dictionary has all the entries needed for all its closures as
well. Also, the instInfo of a closure is largely shared with its
containing function. A good test for generic closures already exists
with orderedmap.go.

Other improvements:
 - Only create sub-dictionary entries when the function/method
   call/value or closure actually has type params in it. Added new test
   file subdict.go with an example where a generic method has an
   instantiated method call that does not depend not have type params.

Change-Id: I691b9dc024a89d2305fcf1d8ba8540e53c9d103f
Reviewed-on: https://go-review.googlesource.com/c/go/+/331516
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 42 insertions, 0 deletions

diff --git a/test/typeparam/subdict.go b/test/typeparam/subdict.go
new file mode 100644
index 0000000000..c899af6d0d
--- /dev/null
+++ b/test/typeparam/subdict.go
@@ -0,0 +1,42 @@
+// run -gcflags=-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.
+
+// Test cases where a main dictionary is needed inside a generic function/method, because 
+// we are calling a method on a fully-instantiated type or a fully-instantiated function.
+// (probably not common situations, of course)
+
+package main
+
+import (
+	"fmt"
+)
+
+type value[T comparable] struct {
+	val T
+}
+
+func (v *value[T]) test(def T) bool {
+	return (v.val == def)
+}
+
+func (v *value[T]) get(def T) T {
+	var c value[int]
+	if c.test(32) {
+		return def
+	} else if v.test(def) {
+		return def
+	} else {
+		return v.val
+	}
+}
+
+
+func main() {
+	var s value[string]
+	if got, want := s.get("ab"), ""; got != want {
+		panic(fmt.Sprintf("get() == %d, want %d", got, want))
+	}
+}