go/ssa: monomorphize generic instantiations.

Monomorphize the instantiation of generic functions. Applies type
substitution while building the function instantiation.

Adds a new BuilderMode, ssa.InstantiateGenerics, to enable
monomorphization. InstantiateGenerics is turned on by the flag 'G' in
tools that specify the BuilderMode.

Adds a parameterized field to Program to detect when a MethodValue is
parameterized.

Thunk creation creates new MethodExpr selections. Adds a new methodExpr
type to construct a MethodExpr from outside of types, and selection
interface to generalize a *methodExpr and *types.Selection.

Tests x/tools/go/ssa/interp against the runnable examples in
$GOROOT/test/typeparam/*.go. Some additional models to support files.

Misc. cleanup:
- adding (*canonizer).instantiateMethod to create a canonical
  representative of a method.
- documenting builder.go
- adding (*subster).types that applies type substitution to a list.

Updates golang/go#48525

Change-Id: I885a4223900feaa3664e35caf8618d11ba16a2a7
Reviewed-on: https://go-review.googlesource.com/c/tools/+/356315
Reviewed-by: Dominik Honnef <dominik@honnef.co>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Zvonimir Pavlinovic <zpavlinovic@google.com>
Run-TryBot: Tim King <taking@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/go/ssa/sanity.go b/go/ssa/sanity.go
index ba08c41d6..7d7130275 100644
--- a/go/ssa/sanity.go
+++ b/go/ssa/sanity.go
@@ -402,6 +402,8 @@ func (s *sanity) checkFunction(fn *Function) bool {
 	// - check params match signature
 	// - check transient fields are nil
 	// - warn if any fn.Locals do not appear among block instructions.
+
+	// TODO(taking): Sanity check _Origin, _TypeParams, and _TypeArgs.
 	s.fn = fn
 	if fn.Prog == nil {
 		s.errorf("nil Prog")
@@ -418,14 +420,19 @@ func (s *sanity) checkFunction(fn *Function) bool {
 			strings.HasPrefix(fn.Synthetic, "bound ") ||
 			strings.HasPrefix(fn.Synthetic, "thunk ") ||
 			strings.HasSuffix(fn.name, "Error") ||
-			strings.HasPrefix(fn.Synthetic, "instantiation") {
+			strings.HasPrefix(fn.Synthetic, "instantiation") ||
+			(fn.parent != nil && len(fn._TypeArgs) > 0) /* anon fun in instance */ {
 			// ok
 		} else {
 			s.errorf("nil Pkg")
 		}
 	}
 	if src, syn := fn.Synthetic == "", fn.Syntax() != nil; src != syn {
-		s.errorf("got fromSource=%t, hasSyntax=%t; want same values", src, syn)
+		if strings.HasPrefix(fn.Synthetic, "instantiation") && fn.Prog.mode&InstantiateGenerics != 0 {
+			// ok
+		} else {
+			s.errorf("got fromSource=%t, hasSyntax=%t; want same values", src, syn)
+		}
 	}
 	for i, l := range fn.Locals {
 		if l.Parent() != fn {