[dev.typeparams] cmd/compile: change method instantiations back to being functions

Change all instantiated methods to being functions again. We found that
this is easier for adding the dictionary argument consistently. A method
wrapper will usually be added around the instantiation call, so that
eliminate the inconsistency in the type of the top-level method and the
the associated function node type.

Change-Id: I9034a0c5cc901e7a89e60756bff574c1346adbc7
Reviewed-on: https://go-review.googlesource.com/c/go/+/321609
Run-TryBot: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dan Scales <danscales@google.com>

1 files changed, 23 insertions, 29 deletions

diff --git a/src/cmd/compile/internal/noder/stencil.go b/src/cmd/compile/internal/noder/stencil.go
index e6498e5ef8..f9cf6d8a1a 100644
--- a/src/cmd/compile/internal/noder/stencil.go
+++ b/src/cmd/compile/internal/noder/stencil.go
@@ -86,21 +86,20 @@ func (g *irgen) stencil() {
 			// instantiation.
 			call := n.(*ir.CallExpr)
 			inst := call.X.(*ir.InstExpr)
+			// Replace the OFUNCINST with a direct reference to the
+			// new stenciled function
 			st := g.getInstantiationForNode(inst)
+			call.X = st.Nname
 			if inst.X.Op() == ir.OCALLPART {
-				// Replace the OFUNCINST with the selector
-				// expression, and update the selector expression
-				// to refer to the new stenciled function.
-				call.X = inst.X
-				se := call.X.(*ir.SelectorExpr)
-				se.Selection = types.NewField(se.Pos(), se.Sel, st.Type())
-				se.Selection.Nname = st.Nname
-				se.SetOp(ir.ODOTMETH)
-				se.SetType(st.Type())
-			} else {
-				// Replace the OFUNCINST with a direct reference to the
-				// new stenciled function
-				call.X = st.Nname
+				// When we create an instantiation of a method
+				// call, we make it a function. So, move the
+				// receiver to be the first arg of the function
+				// call.
+				withRecv := make([]ir.Node, len(call.Args)+1)
+				dot := inst.X.(*ir.SelectorExpr)
+				withRecv[0] = dot.X
+				copy(withRecv[1:], call.Args)
+				call.Args = withRecv
 			}
 			// Transform the Call now, which changes OCALL
 			// to OCALLFUNC and does typecheckaste/assignconvfn.
@@ -166,9 +165,13 @@ func (g *irgen) instantiateMethods() {
 		baseSym := typ.Sym().Pkg.Lookup(genericTypeName(typ.Sym()))
 		baseType := baseSym.Def.(*ir.Name).Type()
 		for j, m := range typ.Methods().Slice() {
+			name := m.Nname.(*ir.Name)
 			baseNname := baseType.Methods().Slice()[j].Nname.(*ir.Name)
-			f := g.getInstantiation(baseNname, typ.RParams(), true)
-			m.Nname = f.Nname
+			// Note: we are breaking an invariant here:
+			// m.Nname is now not equal m.Nname.Func.Nname.
+			// m.Nname has the type of a method, whereas m.Nname.Func.Nname has
+			// the type of a function, since it is an function instantiation.
+			name.Func = g.getInstantiation(baseNname, typ.RParams(), true)
 		}
 	}
 	g.instTypeList = nil
@@ -279,20 +282,11 @@ func (g *irgen) genericSubst(newsym *types.Sym, nameNode *ir.Name, targs []*type
 	// the function type. The current function type has no Nname fields set,
 	// because it came via conversion from the types2 type.
 	oldt := nameNode.Type()
-	dcl := newf.Dcl
-	var newrecv *types.Field
-	if oldt.Recv() != nil {
-		newrecv = subst.fields(ir.PPARAM, oldt.Recvs().FieldSlice(), dcl)[0]
-		if newrecv.Nname != nil {
-			// If we found the receiver in the dcl list, then skip it
-			// when we scan for the remaining params below.
-			assert(newrecv.Nname == dcl[0])
-			dcl = dcl[1:]
-		}
-	}
-	newt := types.NewSignature(oldt.Pkg(), newrecv, nil,
-		subst.fields(ir.PPARAM, oldt.Params().FieldSlice(), dcl),
-		subst.fields(ir.PPARAMOUT, oldt.Results().FieldSlice(), dcl))
+	// We also transform a generic method type to the corresponding
+	// instantiated function type where the receiver is the first parameter.
+	newt := types.NewSignature(oldt.Pkg(), nil, nil,
+		subst.fields(ir.PPARAM, append(oldt.Recvs().FieldSlice(), oldt.Params().FieldSlice()...), newf.Dcl),
+		subst.fields(ir.PPARAMOUT, oldt.Results().FieldSlice(), newf.Dcl))
 
 	newf.Nname.SetType(newt)
 	ir.MarkFunc(newf.Nname)