[dev.typeparams] Add CONVIFACE nodes in noder2, where possible

Changes to add CONVIFACE nodes where possible in noder2, even when the
args are typeparams. The transformation to insert a CONVIFACE node can
usually happen when there an obvious assignment/conversion to an
interface type from a non-interface type. So, we now do this
tranformation for:

 - direct conversions to an interface type

 - function arguments that are implicitly converted to an interface
   based on the parameter types.

 - EQ/NE comparison of an interface and a non-interface

With this change, we can remove some special case checks for CONVIFACE
nodes after transformation in node(), and instead just have the one
check in the CONVIFACE check.

Change-Id: I7cf2ef920aebf9e5553210aeaf19f344e128ca62
Reviewed-on: https://go-review.googlesource.com/c/go/+/336992
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

3 files changed, 41 insertions, 61 deletions

diff --git a/src/cmd/compile/internal/noder/helpers.go b/src/cmd/compile/internal/noder/helpers.go
index 15b3277908..2b00a9d7a6 100644
--- a/src/cmd/compile/internal/noder/helpers.go
+++ b/src/cmd/compile/internal/noder/helpers.go
@@ -116,9 +116,12 @@ func Call(pos src.XPos, typ *types.Type, fun ir.Node, args []ir.Node, dots bool)
 
 	if fun.Op() == ir.OTYPE {
 		// Actually a type conversion, not a function call.
-		if fun.Type().HasTParam() || args[0].Type().HasTParam() {
-			// For type params, don't typecheck until we actually know
-			// the type.
+		if !fun.Type().IsInterface() &&
+			(fun.Type().HasTParam() || args[0].Type().HasTParam()) {
+			// For type params, we can transform if fun.Type() is known
+			// to be an interface (in which case a CONVIFACE node will be
+			// inserted). Otherwise, don't typecheck until we actually
+			// know the type.
 			return typed(typ, n)
 		}
 		typed(typ, n)
@@ -169,11 +172,15 @@ func Call(pos src.XPos, typ *types.Type, fun ir.Node, args []ir.Node, dots bool)
 	}
 
 	if fun.Type().HasTParam() {
-		// If the fun arg is or has a type param, don't do any extra
-		// transformations, since we may not have needed properties yet
-		// (e.g. number of return values, etc). The type param is probably
-		// described by a structural constraint that requires it to be a
-		// certain function type, etc., but we don't want to analyze that.
+		// If the fun arg is or has a type param, we can't do all the
+		// transformations, since we may not have needed properties yet.
+		// (e.g. number of return values, etc). However, if we do have the
+		// function type (even though it is parameterized), then can add in
+		// any needed CONVIFACE nodes. We can't do anything if fun is a type
+		// param (which is probably described by a structural constraint)
+		if fun.Type().Kind() == types.TFUNC {
+			typecheckaste(ir.OCALL, fun, n.IsDDD, fun.Type().Params(), n.Args, true)
+		}
 		return typed(typ, n)
 	}
 
@@ -203,11 +210,18 @@ func Call(pos src.XPos, typ *types.Type, fun ir.Node, args []ir.Node, dots bool)
 func Compare(pos src.XPos, typ *types.Type, op ir.Op, x, y ir.Node) ir.Node {
 	n := ir.NewBinaryExpr(pos, op, x, y)
 	if x.Type().HasTParam() || y.Type().HasTParam() {
-		// Delay transformCompare() if either arg has a type param, since
-		// it needs to know the exact types to decide on any needed conversions.
-		n.SetType(typ)
-		n.SetTypecheck(3)
-		return n
+		xIsInt := x.Type().IsInterface()
+		yIsInt := y.Type().IsInterface()
+		if !(xIsInt && !yIsInt || !xIsInt && yIsInt) {
+			// If either arg is a type param, then we can still do the
+			// transformCompare() if we know that one arg is an interface
+			// and the other is not. Otherwise, we delay
+			// transformCompare(), since it needs to know the exact types
+			// to decide on any needed conversions.
+			n.SetType(typ)
+			n.SetTypecheck(3)
+			return n
+		}
 	}
 	typed(typ, n)
 	transformCompare(n)
diff --git a/src/cmd/compile/internal/noder/stencil.go b/src/cmd/compile/internal/noder/stencil.go
index 59f11bbe23..a8f9cf3b3e 100644
--- a/src/cmd/compile/internal/noder/stencil.go
+++ b/src/cmd/compile/internal/noder/stencil.go
@@ -1251,21 +1251,13 @@ func (subst *subster) node(n ir.Node) ir.Node {
 
 		case ir.OCALL:
 			call := m.(*ir.CallExpr)
-			convcheck := false
 			switch call.X.Op() {
 			case ir.OTYPE:
 				// Transform the conversion, now that we know the
 				// type argument.
 				m = transformConvCall(call)
-				if m.Op() == ir.OCONVIFACE {
-					// Note: srcType uses x.Args[0], not m.X or call.Args[0], because
-					// we need the type before the type parameter -> type argument substitution.
-					srcType := x.(*ir.CallExpr).Args[0].Type()
-					if ix := subst.findDictType(srcType); ix >= 0 {
-						c := m.(*ir.ConvExpr)
-						m = subst.convertUsingDictionary(c.Pos(), c.X, c.Type(), srcType, ix)
-					}
-				}
+				// CONVIFACE transformation was already done in node2
+				assert(m.Op() != ir.OCONVIFACE)
 
 			case ir.OMETHVALUE, ir.OMETHEXPR:
 				// Redo the transformation of OXDOT, now that we
@@ -1275,7 +1267,6 @@ func (subst *subster) node(n ir.Node) ir.Node {
 				transformDot(call.X.(*ir.SelectorExpr), true)
 				call.X.SetType(subst.unshapifyTyp(call.X.Type()))
 				transformCall(call)
-				convcheck = true
 
 			case ir.ODOT, ir.ODOTPTR:
 				// An OXDOT for a generic receiver was resolved to
@@ -1283,7 +1274,6 @@ func (subst *subster) node(n ir.Node) ir.Node {
 				// value. Transform the call to that function, now
 				// that the OXDOT was resolved.
 				transformCall(call)
-				convcheck = true
 
 			case ir.ONAME:
 				name := call.X.Name()
@@ -1308,12 +1298,10 @@ func (subst *subster) node(n ir.Node) ir.Node {
 					// type parameter (implied to be a function via a
 					// structural constraint) which is now resolved.
 					transformCall(call)
-					convcheck = true
 				}
 
 			case ir.OCLOSURE:
 				transformCall(call)
-				convcheck = true
 
 			case ir.OFUNCINST:
 				// A call with an OFUNCINST will get transformed
@@ -1323,16 +1311,6 @@ func (subst *subster) node(n ir.Node) ir.Node {
 			default:
 				base.FatalfAt(call.Pos(), fmt.Sprintf("Unexpected op with CALL during stenciling: %v", call.X.Op()))
 			}
-			if convcheck {
-				for i, arg := range x.(*ir.CallExpr).Args {
-					if arg.Type().HasTParam() && arg.Op() != ir.OCONVIFACE &&
-						call.Args[i].Op() == ir.OCONVIFACE {
-						ix := subst.findDictType(arg.Type())
-						assert(ix >= 0)
-						call.Args[i] = subst.convertUsingDictionary(arg.Pos(), call.Args[i].(*ir.ConvExpr).X, call.Args[i].Type(), arg.Type(), ix)
-					}
-				}
-			}
 
 		case ir.OCLOSURE:
 			// We're going to create a new closure from scratch, so clear m
@@ -1391,21 +1369,6 @@ func (subst *subster) node(n ir.Node) ir.Node {
 			if ix := subst.findDictType(t); ix >= 0 {
 				m = subst.convertUsingDictionary(x.Pos(), m.(*ir.ConvExpr).X, m.Type(), t, ix)
 			}
-		case ir.OEQ, ir.ONE:
-			// Equality between a non-interface and an interface requires the non-interface
-			// to be promoted to an interface.
-			x := x.(*ir.BinaryExpr)
-			m := m.(*ir.BinaryExpr)
-			if i := x.Y.Type(); i.IsInterface() {
-				if ix := subst.findDictType(x.X.Type()); ix >= 0 {
-					m.X = subst.convertUsingDictionary(m.X.Pos(), m.X, i, x.X.Type(), ix)
-				}
-			}
-			if i := x.X.Type(); i.IsInterface() {
-				if ix := subst.findDictType(x.Y.Type()); ix >= 0 {
-					m.Y = subst.convertUsingDictionary(m.Y.Pos(), m.Y, i, x.X.Type(), ix)
-				}
-			}
 
 		case ir.ONEW:
 			// New needs to pass a concrete type to the runtime.
diff --git a/src/cmd/compile/internal/noder/transform.go b/src/cmd/compile/internal/noder/transform.go
index 86bdb91395..f89ae13237 100644
--- a/src/cmd/compile/internal/noder/transform.go
+++ b/src/cmd/compile/internal/noder/transform.go
@@ -156,7 +156,7 @@ func transformCall(n *ir.CallExpr) {
 		n.SetOp(ir.OCALLFUNC)
 	}
 
-	typecheckaste(ir.OCALL, n.X, n.IsDDD, t.Params(), n.Args)
+	typecheckaste(ir.OCALL, n.X, n.IsDDD, t.Params(), n.Args, false)
 	if l.Op() == ir.ODOTMETH && len(deref(n.X.Type().Recv().Type).RParams()) == 0 {
 		typecheck.FixMethodCall(n)
 	}
@@ -194,7 +194,7 @@ func transformCompare(n *ir.BinaryExpr) {
 			aop, _ := typecheck.Assignop(lt, rt)
 			if aop != ir.OXXX {
 				types.CalcSize(lt)
-				if rt.IsInterface() == lt.IsInterface() || lt.Width >= 1<<16 {
+				if lt.HasTParam() || rt.IsInterface() == lt.IsInterface() || lt.Width >= 1<<16 {
 					l = ir.NewConvExpr(base.Pos, aop, rt, l)
 					l.SetTypecheck(1)
 				}
@@ -207,7 +207,7 @@ func transformCompare(n *ir.BinaryExpr) {
 			aop, _ := typecheck.Assignop(rt, lt)
 			if aop != ir.OXXX {
 				types.CalcSize(rt)
-				if rt.IsInterface() == lt.IsInterface() || rt.Width >= 1<<16 {
+				if rt.HasTParam() || rt.IsInterface() == lt.IsInterface() || rt.Width >= 1<<16 {
 					r = ir.NewConvExpr(base.Pos, aop, lt, r)
 					r.SetTypecheck(1)
 				}
@@ -468,8 +468,11 @@ func assignconvfn(n ir.Node, t *types.Type) ir.Node {
 	return r
 }
 
-// Corresponds to typecheck.typecheckaste.
-func typecheckaste(op ir.Op, call ir.Node, isddd bool, tstruct *types.Type, nl ir.Nodes) {
+// Corresponds to typecheck.typecheckaste, but we add an extra flag convifaceOnly
+// only. If convifaceOnly is true, we only do interface conversion. We use this to do
+// early insertion of CONVIFACE nodes during noder2, when the function or args may
+// have typeparams.
+func typecheckaste(op ir.Op, call ir.Node, isddd bool, tstruct *types.Type, nl ir.Nodes, convifaceOnly bool) {
 	var t *types.Type
 	var i int
 
@@ -488,7 +491,7 @@ func typecheckaste(op ir.Op, call ir.Node, isddd bool, tstruct *types.Type, nl i
 			if isddd {
 				n = nl[i]
 				ir.SetPos(n)
-				if n.Type() != nil {
+				if n.Type() != nil && (!convifaceOnly || t.IsInterface()) {
 					nl[i] = assignconvfn(n, t)
 				}
 				return
@@ -498,7 +501,7 @@ func typecheckaste(op ir.Op, call ir.Node, isddd bool, tstruct *types.Type, nl i
 			for ; i < len(nl); i++ {
 				n = nl[i]
 				ir.SetPos(n)
-				if n.Type() != nil {
+				if n.Type() != nil && (!convifaceOnly || t.IsInterface()) {
 					nl[i] = assignconvfn(n, t.Elem())
 				}
 			}
@@ -507,7 +510,7 @@ func typecheckaste(op ir.Op, call ir.Node, isddd bool, tstruct *types.Type, nl i
 
 		n = nl[i]
 		ir.SetPos(n)
-		if n.Type() != nil {
+		if n.Type() != nil && (!convifaceOnly || t.IsInterface()) {
 			nl[i] = assignconvfn(n, t)
 		}
 		i++
@@ -529,7 +532,7 @@ func transformReturn(rs *ir.ReturnStmt) {
 		return
 	}
 
-	typecheckaste(ir.ORETURN, nil, false, ir.CurFunc.Type().Results(), nl)
+	typecheckaste(ir.ORETURN, nil, false, ir.CurFunc.Type().Results(), nl, false)
 }
 
 // transformSelect transforms a select node, creating an assignment list as needed