[dev.typeparams] Fix issues related to dictionaries and method calls with embedded fields

 - Fix handling of method expressions with embedded fields. Fix an
   incorrect lookup for method expressions, which have only the
   top-level type (and don't have DOT operations for the embedded
   fields). Add the embedded field dot operations into the closure.

 - Don't need a dictionary and so don't build a closure if the last
   embedded field reached in a method expression is an interface value.

 - Fix methodWrapper() to use the computed 'dot' node in the
   generic-only part of the code.

 - For a method expression, don't create a generic wrapper if the last
   embedded field reached before the method lookup is an interface.

Copied cmd/compile/internal/types2/testdata/fixedbugs/issue44688.go2 to
test/typeparam/issue44688.go, made it fully runnable (rather than just
for compilation), and added a bunch more tests.

Change-Id: I90c1aa569e1c7272e986c9d2ae683e553c3a38a1
Reviewed-on: https://go-review.googlesource.com/c/go/+/329550
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 11 insertions, 2 deletions

diff --git a/src/cmd/compile/internal/reflectdata/reflect.go b/src/cmd/compile/internal/reflectdata/reflect.go
index 9e070895a0..52534db70d 100644
--- a/src/cmd/compile/internal/reflectdata/reflect.go
+++ b/src/cmd/compile/internal/reflectdata/reflect.go
@@ -1786,6 +1786,11 @@ func methodWrapper(rcvr *types.Type, method *types.Field, forItab bool) *obj.LSy
 	}
 
 	dot := typecheck.AddImplicitDots(ir.NewSelectorExpr(base.Pos, ir.OXDOT, nthis, method.Sym))
+	if generic && dot.X != nthis && dot.X.Type().IsInterface() {
+		// We followed some embedded fields, and the last type was
+		// actually an interface, so no need for a dictionary.
+		generic = false
+	}
 
 	// generate call
 	// It's not possible to use a tail call when dynamic linking on ppc64le. The
@@ -1824,9 +1829,13 @@ func methodWrapper(rcvr *types.Type, method *types.Field, forItab bool) *obj.LSy
 			}
 			args = append(args, getDictionary(".inst."+ir.MethodSym(orig, method.Sym).Name, targs)) // TODO: remove .inst.
 			if indirect {
-				args = append(args, ir.NewStarExpr(base.Pos, nthis))
+				args = append(args, ir.NewStarExpr(base.Pos, dot.X))
+			} else if methodrcvr.IsPtr() && methodrcvr.Elem() == dot.X.Type() {
+				// Case where method call is via a non-pointer
+				// embedded field with a pointer method.
+				args = append(args, typecheck.NodAddrAt(base.Pos, dot.X))
 			} else {
-				args = append(args, nthis)
+				args = append(args, dot.X)
 			}
 			args = append(args, ir.ParamNames(tfn.Type())...)