[dev.typeparams] cmd/compile: implement generic .(T) operations

Introduce new dynamic dottype operations which take a dynamic
instead of static type to convert to.

Change-Id: I5824a1fea056fe811b1226ce059e1e8da1baa335
Reviewed-on: https://go-review.googlesource.com/c/go/+/337609
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

11 files changed, 209 insertions, 53 deletions

diff --git a/src/cmd/compile/internal/escape/expr.go b/src/cmd/compile/internal/escape/expr.go
index b7423e114a..4a6304d47a 100644
--- a/src/cmd/compile/internal/escape/expr.go
+++ b/src/cmd/compile/internal/escape/expr.go
@@ -74,6 +74,10 @@ func (e *escape) exprSkipInit(k hole, n ir.Node) {
 	case ir.ODOTTYPE, ir.ODOTTYPE2:
 		n := n.(*ir.TypeAssertExpr)
 		e.expr(k.dotType(n.Type(), n, "dot"), n.X)
+	case ir.ODYNAMICDOTTYPE, ir.ODYNAMICDOTTYPE2:
+		n := n.(*ir.DynamicTypeAssertExpr)
+		e.expr(k.dotType(n.Type(), n, "dot"), n.X)
+		// n.T doesn't need to be tracked; it always points to read-only storage.
 	case ir.OINDEX:
 		n := n.(*ir.IndexExpr)
 		if n.X.Type().IsArray() {
diff --git a/src/cmd/compile/internal/ir/expr.go b/src/cmd/compile/internal/ir/expr.go
index 86323e6b8f..9c5fbbc9aa 100644
--- a/src/cmd/compile/internal/ir/expr.go
+++ b/src/cmd/compile/internal/ir/expr.go
@@ -677,6 +677,29 @@ func (n *TypeAssertExpr) SetOp(op Op) {
 	}
 }
 
+// A DynamicTypeAssertExpr asserts that X is of dynamic type T.
+type DynamicTypeAssertExpr struct {
+	miniExpr
+	X Node
+	// N = not an interface
+	// E = empty interface
+	// I = nonempty interface
+	// For E->N, T is a *runtime.type for N
+	// For I->N, T is a *runtime.itab for N+I
+	// For E->I, T is a *runtime.type for I
+	// For I->I, ditto
+	// For I->E, T is a *runtime.type for interface{} (unnecessary, but just to fill in the slot)
+	// For E->E, ditto
+	T Node
+}
+
+func NewDynamicTypeAssertExpr(pos src.XPos, op Op, x, t Node) *DynamicTypeAssertExpr {
+	n := &DynamicTypeAssertExpr{X: x, T: t}
+	n.pos = pos
+	n.op = op
+	return n
+}
+
 // A UnaryExpr is a unary expression Op X,
 // or Op(X) for a builtin function that does not end up being a call.
 type UnaryExpr struct {
diff --git a/src/cmd/compile/internal/ir/node.go b/src/cmd/compile/internal/ir/node.go
index 0fbc867c1d..e5f0c38f86 100644
--- a/src/cmd/compile/internal/ir/node.go
+++ b/src/cmd/compile/internal/ir/node.go
@@ -319,6 +319,10 @@ const (
 	OINLMARK       // start of an inlined body, with file/line of caller. Xoffset is an index into the inline tree.
 	OLINKSYMOFFSET // offset within a name
 
+	// opcodes for generics
+	ODYNAMICDOTTYPE
+	ODYNAMICDOTTYPE2
+
 	// arch-specific opcodes
 	OTAILCALL    // tail call to another function
 	OGETG        // runtime.getg() (read g pointer)
diff --git a/src/cmd/compile/internal/ir/node_gen.go b/src/cmd/compile/internal/ir/node_gen.go
index 9a4858d037..56db6bb9cf 100644
--- a/src/cmd/compile/internal/ir/node_gen.go
+++ b/src/cmd/compile/internal/ir/node_gen.go
@@ -463,6 +463,34 @@ func (n *Decl) editChildren(edit func(Node) Node) {
 	}
 }
 
+func (n *DynamicTypeAssertExpr) Format(s fmt.State, verb rune) { fmtNode(n, s, verb) }
+func (n *DynamicTypeAssertExpr) copy() Node {
+	c := *n
+	c.init = copyNodes(c.init)
+	return &c
+}
+func (n *DynamicTypeAssertExpr) doChildren(do func(Node) bool) bool {
+	if doNodes(n.init, do) {
+		return true
+	}
+	if n.X != nil && do(n.X) {
+		return true
+	}
+	if n.T != nil && do(n.T) {
+		return true
+	}
+	return false
+}
+func (n *DynamicTypeAssertExpr) editChildren(edit func(Node) Node) {
+	editNodes(n.init, edit)
+	if n.X != nil {
+		n.X = edit(n.X).(Node)
+	}
+	if n.T != nil {
+		n.T = edit(n.T).(Node)
+	}
+}
+
 func (n *ForStmt) Format(s fmt.State, verb rune) { fmtNode(n, s, verb) }
 func (n *ForStmt) copy() Node {
 	c := *n
diff --git a/src/cmd/compile/internal/ir/op_string.go b/src/cmd/compile/internal/ir/op_string.go
index 0235d5eab3..7b08ee287a 100644
--- a/src/cmd/compile/internal/ir/op_string.go
+++ b/src/cmd/compile/internal/ir/op_string.go
@@ -162,16 +162,18 @@ func _() {
 	_ = x[ORESULT-151]
 	_ = x[OINLMARK-152]
 	_ = x[OLINKSYMOFFSET-153]
-	_ = x[OTAILCALL-154]
-	_ = x[OGETG-155]
-	_ = x[OGETCALLERPC-156]
-	_ = x[OGETCALLERSP-157]
-	_ = x[OEND-158]
+	_ = x[ODYNAMICDOTTYPE-154]
+	_ = x[ODYNAMICDOTTYPE2-155]
+	_ = x[OTAILCALL-156]
+	_ = x[OGETG-157]
+	_ = x[OGETCALLERPC-158]
+	_ = x[OGETCALLERSP-159]
+	_ = x[OEND-160]
 }
 
-const _Op_name = "XXXNAMENONAMETYPEPACKLITERALNILADDSUBORXORADDSTRADDRANDANDAPPENDBYTES2STRBYTES2STRTMPRUNES2STRSTR2BYTESSTR2BYTESTMPSTR2RUNESSLICE2ARRPTRASAS2AS2DOTTYPEAS2FUNCAS2MAPRAS2RECVASOPCALLCALLFUNCCALLMETHCALLINTERCAPCLOSECLOSURECOMPLITMAPLITSTRUCTLITARRAYLITSLICELITPTRLITCONVCONVIFACECONVIDATACONVNOPCOPYDCLDCLFUNCDCLCONSTDCLTYPEDELETEDOTDOTPTRDOTMETHDOTINTERXDOTDOTTYPEDOTTYPE2EQNELTLEGEGTDEREFINDEXINDEXMAPKEYSTRUCTKEYLENMAKEMAKECHANMAKEMAPMAKESLICEMAKESLICECOPYMULDIVMODLSHRSHANDANDNOTNEWNOTBITNOTPLUSNEGORORPANICPRINTPRINTNPARENSENDSLICESLICEARRSLICESTRSLICE3SLICE3ARRSLICEHEADERRECOVERRECOVERFPRECVRUNESTRSELRECV2IOTAREALIMAGCOMPLEXALIGNOFOFFSETOFSIZEOFUNSAFEADDUNSAFESLICEMETHEXPRMETHVALUEBLOCKBREAKCASECONTINUEDEFERFALLFORFORUNTILGOTOIFLABELGORANGERETURNSELECTSWITCHTYPESWFUNCINSTTCHANTMAPTSTRUCTTINTERTFUNCTARRAYTSLICEINLCALLEFACEITABIDATASPTRCFUNCCHECKNILVARDEFVARKILLVARLIVERESULTINLMARKLINKSYMOFFSETTAILCALLGETGGETCALLERPCGETCALLERSPEND"
+const _Op_name = "XXXNAMENONAMETYPEPACKLITERALNILADDSUBORXORADDSTRADDRANDANDAPPENDBYTES2STRBYTES2STRTMPRUNES2STRSTR2BYTESSTR2BYTESTMPSTR2RUNESSLICE2ARRPTRASAS2AS2DOTTYPEAS2FUNCAS2MAPRAS2RECVASOPCALLCALLFUNCCALLMETHCALLINTERCAPCLOSECLOSURECOMPLITMAPLITSTRUCTLITARRAYLITSLICELITPTRLITCONVCONVIFACECONVIDATACONVNOPCOPYDCLDCLFUNCDCLCONSTDCLTYPEDELETEDOTDOTPTRDOTMETHDOTINTERXDOTDOTTYPEDOTTYPE2EQNELTLEGEGTDEREFINDEXINDEXMAPKEYSTRUCTKEYLENMAKEMAKECHANMAKEMAPMAKESLICEMAKESLICECOPYMULDIVMODLSHRSHANDANDNOTNEWNOTBITNOTPLUSNEGORORPANICPRINTPRINTNPARENSENDSLICESLICEARRSLICESTRSLICE3SLICE3ARRSLICEHEADERRECOVERRECOVERFPRECVRUNESTRSELRECV2IOTAREALIMAGCOMPLEXALIGNOFOFFSETOFSIZEOFUNSAFEADDUNSAFESLICEMETHEXPRMETHVALUEBLOCKBREAKCASECONTINUEDEFERFALLFORFORUNTILGOTOIFLABELGORANGERETURNSELECTSWITCHTYPESWFUNCINSTTCHANTMAPTSTRUCTTINTERTFUNCTARRAYTSLICEINLCALLEFACEITABIDATASPTRCFUNCCHECKNILVARDEFVARKILLVARLIVERESULTINLMARKLINKSYMOFFSETDYNAMICDOTTYPEDYNAMICDOTTYPE2TAILCALLGETGGETCALLERPCGETCALLERSPEND"
 
-var _Op_index = [...]uint16{0, 3, 7, 13, 17, 21, 28, 31, 34, 37, 39, 42, 48, 52, 58, 64, 73, 85, 94, 103, 115, 124, 136, 138, 141, 151, 158, 165, 172, 176, 180, 188, 196, 205, 208, 213, 220, 227, 233, 242, 250, 258, 264, 268, 277, 286, 293, 297, 300, 307, 315, 322, 328, 331, 337, 344, 352, 356, 363, 371, 373, 375, 377, 379, 381, 383, 388, 393, 401, 404, 413, 416, 420, 428, 435, 444, 457, 460, 463, 466, 469, 472, 475, 481, 484, 487, 493, 497, 500, 504, 509, 514, 520, 525, 529, 534, 542, 550, 556, 565, 576, 583, 592, 596, 603, 611, 615, 619, 623, 630, 637, 645, 651, 660, 671, 679, 688, 693, 698, 702, 710, 715, 719, 722, 730, 734, 736, 741, 743, 748, 754, 760, 766, 772, 780, 785, 789, 796, 802, 807, 813, 819, 826, 831, 835, 840, 844, 849, 857, 863, 870, 877, 883, 890, 903, 911, 915, 926, 937, 940}
+var _Op_index = [...]uint16{0, 3, 7, 13, 17, 21, 28, 31, 34, 37, 39, 42, 48, 52, 58, 64, 73, 85, 94, 103, 115, 124, 136, 138, 141, 151, 158, 165, 172, 176, 180, 188, 196, 205, 208, 213, 220, 227, 233, 242, 250, 258, 264, 268, 277, 286, 293, 297, 300, 307, 315, 322, 328, 331, 337, 344, 352, 356, 363, 371, 373, 375, 377, 379, 381, 383, 388, 393, 401, 404, 413, 416, 420, 428, 435, 444, 457, 460, 463, 466, 469, 472, 475, 481, 484, 487, 493, 497, 500, 504, 509, 514, 520, 525, 529, 534, 542, 550, 556, 565, 576, 583, 592, 596, 603, 611, 615, 619, 623, 630, 637, 645, 651, 660, 671, 679, 688, 693, 698, 702, 710, 715, 719, 722, 730, 734, 736, 741, 743, 748, 754, 760, 766, 772, 780, 785, 789, 796, 802, 807, 813, 819, 826, 831, 835, 840, 844, 849, 857, 863, 870, 877, 883, 890, 903, 917, 932, 940, 944, 955, 966, 969}
 
 func (i Op) String() string {
 	if i >= Op(len(_Op_index)-1) {
diff --git a/src/cmd/compile/internal/noder/stencil.go b/src/cmd/compile/internal/noder/stencil.go
index 02a380e63f..70a2c7b97f 100644
--- a/src/cmd/compile/internal/noder/stencil.go
+++ b/src/cmd/compile/internal/noder/stencil.go
@@ -1039,6 +1039,7 @@ func (subst *subster) checkDictionary(name *ir.Name, targs []*types.Type) (code
 	d.SetTypecheck(1)
 	d = ir.NewConvExpr(pos, ir.OCONVNOP, types.NewArray(types.Types[types.TUINTPTR], int64(len(targs))).PtrTo(), d)
 	d.SetTypecheck(1)
+	types.CheckSize(d.Type().Elem())
 
 	// Check that each type entry in the dictionary is correct.
 	for i, t := range targs {
@@ -1079,6 +1080,7 @@ func getDictionaryEntry(pos src.XPos, dict *ir.Name, i int, size int) ir.Node {
 	d.SetTypecheck(1)
 	d = ir.NewConvExpr(pos, ir.OCONVNOP, types.NewArray(types.Types[types.TUINTPTR], int64(size)).PtrTo(), d)
 	d.SetTypecheck(1)
+	types.CheckSize(d.Type().Elem())
 
 	// Load entry i out of the dictionary.
 	deref := ir.NewStarExpr(pos, d)
@@ -1367,7 +1369,31 @@ func (subst *subster) node(n ir.Node) ir.Node {
 				m = subst.convertUsingDictionary(m.Pos(), m.(*ir.ConvExpr).X, x, m.Type(), x.X.Type())
 			}
 		case ir.ODOTTYPE, ir.ODOTTYPE2:
-			m.SetType(subst.unshapifyTyp(m.Type()))
+			dt := m.(*ir.TypeAssertExpr)
+			var rt ir.Node
+			if dt.Type().IsInterface() || dt.X.Type().IsEmptyInterface() {
+				ix := subst.findDictType(x.Type())
+				assert(ix >= 0)
+				rt = subst.getDictionaryType(dt.Pos(), ix)
+			} else {
+				// nonempty interface to noninterface. Need an itab.
+				ix := -1
+				for i, ic := range subst.info.gfInfo.itabConvs {
+					if ic == x {
+						ix = subst.info.startItabConv + i
+						break
+					}
+				}
+				assert(ix >= 0)
+				rt = getDictionaryEntry(dt.Pos(), subst.info.dictParam, ix, subst.info.dictLen)
+			}
+			op := ir.ODYNAMICDOTTYPE
+			if x.Op() == ir.ODOTTYPE2 {
+				op = ir.ODYNAMICDOTTYPE2
+			}
+			m = ir.NewDynamicTypeAssertExpr(dt.Pos(), op, dt.X, rt)
+			m.SetType(dt.Type())
+			m.SetTypecheck(1)
 
 		case ir.OMETHEXPR:
 			se := m.(*ir.SelectorExpr)
@@ -1696,7 +1722,8 @@ func (g *irgen) finalizeSyms() {
 		// Emit an entry for each itab
 		for _, n := range info.itabConvs {
 			var srctype, dsttype *types.Type
-			if n.Op() == ir.OXDOT {
+			switch n.Op() {
+			case ir.OXDOT:
 				se := n.(*ir.SelectorExpr)
 				srctype = subst.Typ(se.X.Type())
 				dsttype = subst.Typ(se.X.Type().Bound())
@@ -1712,10 +1739,14 @@ func (g *irgen) finalizeSyms() {
 					}
 				}
 				assert(found)
-			} else {
-				assert(n.Op() == ir.OCONVIFACE)
+			case ir.ODOTTYPE, ir.ODOTTYPE2:
+				srctype = subst.Typ(n.(*ir.TypeAssertExpr).Type())
+				dsttype = subst.Typ(n.(*ir.TypeAssertExpr).X.Type())
+			case ir.OCONVIFACE:
 				srctype = subst.Typ(n.(*ir.ConvExpr).X.Type())
 				dsttype = subst.Typ(n.Type())
+			default:
+				base.Fatalf("itab entry with unknown op %s", n.Op())
 			}
 			itabLsym := reflectdata.ITabLsym(srctype, dsttype)
 			d.off = objw.SymPtr(lsym, d.off, itabLsym, 0)
@@ -1859,6 +1890,10 @@ func (g *irgen) getGfInfo(gn *ir.Name) *gfInfo {
 			infoPrint("  Itab for interface conv: %v\n", n)
 			info.itabConvs = append(info.itabConvs, n)
 		}
+		if (n.Op() == ir.ODOTTYPE || n.Op() == ir.ODOTTYPE2) && !n.(*ir.TypeAssertExpr).Type().IsInterface() && !n.(*ir.TypeAssertExpr).X.Type().IsEmptyInterface() {
+			infoPrint("  Itab for dot type: %v\n", n)
+			info.itabConvs = append(info.itabConvs, n)
+		}
 		if n.Op() == ir.OCLOSURE {
 			// Visit the closure body and add all relevant entries to the
 			// dictionary of the outer function (closure will just use
diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index d2e0d57b28..7e2f6a7471 100644
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -1423,7 +1423,12 @@ func (s *state) stmt(n ir.Node) {
 
 	case ir.OAS2DOTTYPE:
 		n := n.(*ir.AssignListStmt)
-		res, resok := s.dottype(n.Rhs[0].(*ir.TypeAssertExpr), true)
+		var res, resok *ssa.Value
+		if n.Rhs[0].Op() == ir.ODOTTYPE2 {
+			res, resok = s.dottype(n.Rhs[0].(*ir.TypeAssertExpr), true)
+		} else {
+			res, resok = s.dynamicDottype(n.Rhs[0].(*ir.DynamicTypeAssertExpr), true)
+		}
 		deref := false
 		if !TypeOK(n.Rhs[0].Type()) {
 			if res.Op != ssa.OpLoad {
@@ -2680,6 +2685,11 @@ func (s *state) expr(n ir.Node) *ssa.Value {
 		res, _ := s.dottype(n, false)
 		return res
 
+	case ir.ODYNAMICDOTTYPE:
+		n := n.(*ir.DynamicTypeAssertExpr)
+		res, _ := s.dynamicDottype(n, false)
+		return res
+
 	// binary ops
 	case ir.OLT, ir.OEQ, ir.ONE, ir.OLE, ir.OGE, ir.OGT:
 		n := n.(*ir.BinaryExpr)
@@ -5147,9 +5157,13 @@ func (s *state) addr(n ir.Node) *ssa.Value {
 	case ir.OCALLFUNC, ir.OCALLINTER:
 		n := n.(*ir.CallExpr)
 		return s.callAddr(n, callNormal)
-	case ir.ODOTTYPE:
-		n := n.(*ir.TypeAssertExpr)
-		v, _ := s.dottype(n, false)
+	case ir.ODOTTYPE, ir.ODYNAMICDOTTYPE:
+		var v *ssa.Value
+		if n.Op() == ir.ODOTTYPE {
+			v, _ = s.dottype(n.(*ir.TypeAssertExpr), false)
+		} else {
+			v, _ = s.dynamicDottype(n.(*ir.DynamicTypeAssertExpr), false)
+		}
 		if v.Op != ssa.OpLoad {
 			s.Fatalf("dottype of non-load")
 		}
@@ -6043,14 +6057,38 @@ func (s *state) floatToUint(cvttab *f2uCvtTab, n ir.Node, x *ssa.Value, ft, tt *
 func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Value) {
 	iface := s.expr(n.X)              // input interface
 	target := s.reflectType(n.Type()) // target type
-	byteptr := s.f.Config.Types.BytePtr
+	var targetItab *ssa.Value
+	if n.Itab != nil {
+		targetItab = s.expr(n.Itab)
+	}
+	return s.dottype1(n.Pos(), n.X.Type(), n.Type(), iface, target, targetItab, commaok)
+}
 
-	if n.Type().IsInterface() {
-		if n.Type().IsEmptyInterface() {
+func (s *state) dynamicDottype(n *ir.DynamicTypeAssertExpr, commaok bool) (res, resok *ssa.Value) {
+	iface := s.expr(n.X)
+	target := s.expr(n.T)
+	var itab *ssa.Value
+	if !n.X.Type().IsEmptyInterface() && !n.Type().IsInterface() {
+		byteptr := s.f.Config.Types.BytePtr
+		itab = target
+		target = s.load(byteptr, s.newValue1I(ssa.OpOffPtr, byteptr, int64(types.PtrSize), itab)) // itab.typ
+	}
+	return s.dottype1(n.Pos(), n.X.Type(), n.Type(), iface, target, itab, commaok)
+}
+
+// dottype1 implements a x.(T) operation. iface is the argument (x), dst is the type we're asserting to (T)
+// and src is the type we're asserting from.
+// target is the *runtime._type of dst.
+// If src is a nonempty interface and dst is not an interface, targetItab is an itab representing (dst, src). Otherwise it is nil.
+// commaok is true if the caller wants a boolean success value. Otherwise, the generated code panics if the conversion fails.
+func (s *state) dottype1(pos src.XPos, src, dst *types.Type, iface, target, targetItab *ssa.Value, commaok bool) (res, resok *ssa.Value) {
+	byteptr := s.f.Config.Types.BytePtr
+	if dst.IsInterface() {
+		if dst.IsEmptyInterface() {
 			// Converting to an empty interface.
 			// Input could be an empty or nonempty interface.
 			if base.Debug.TypeAssert > 0 {
-				base.WarnfAt(n.Pos(), "type assertion inlined")
+				base.WarnfAt(pos, "type assertion inlined")
 			}
 
 			// Get itab/type field from input.
@@ -6058,7 +6096,7 @@ func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Val
 			// Conversion succeeds iff that field is not nil.
 			cond := s.newValue2(ssa.OpNeqPtr, types.Types[types.TBOOL], itab, s.constNil(byteptr))
 
-			if n.X.Type().IsEmptyInterface() && commaok {
+			if src.IsEmptyInterface() && commaok {
 				// Converting empty interface to empty interface with ,ok is just a nil check.
 				return iface, cond
 			}
@@ -6080,7 +6118,7 @@ func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Val
 
 				// On success, return (perhaps modified) input interface.
 				s.startBlock(bOk)
-				if n.X.Type().IsEmptyInterface() {
+				if src.IsEmptyInterface() {
 					res = iface // Use input interface unchanged.
 					return
 				}
@@ -6088,7 +6126,7 @@ func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Val
 				off := s.newValue1I(ssa.OpOffPtr, byteptr, int64(types.PtrSize), itab)
 				typ := s.load(byteptr, off)
 				idata := s.newValue1(ssa.OpIData, byteptr, iface)
-				res = s.newValue2(ssa.OpIMake, n.Type(), typ, idata)
+				res = s.newValue2(ssa.OpIMake, dst, typ, idata)
 				return
 			}
 
@@ -6110,62 +6148,62 @@ func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Val
 			bFail.AddEdgeTo(bEnd)
 			s.startBlock(bEnd)
 			idata := s.newValue1(ssa.OpIData, byteptr, iface)
-			res = s.newValue2(ssa.OpIMake, n.Type(), s.variable(typVar, byteptr), idata)
+			res = s.newValue2(ssa.OpIMake, dst, s.variable(typVar, byteptr), idata)
 			resok = cond
 			delete(s.vars, typVar)
 			return
 		}
 		// converting to a nonempty interface needs a runtime call.
 		if base.Debug.TypeAssert > 0 {
-			base.WarnfAt(n.Pos(), "type assertion not inlined")
+			base.WarnfAt(pos, "type assertion not inlined")
 		}
 		if !commaok {
 			fn := ir.Syms.AssertI2I
-			if n.X.Type().IsEmptyInterface() {
+			if src.IsEmptyInterface() {
 				fn = ir.Syms.AssertE2I
 			}
 			data := s.newValue1(ssa.OpIData, types.Types[types.TUNSAFEPTR], iface)
 			tab := s.newValue1(ssa.OpITab, byteptr, iface)
 			tab = s.rtcall(fn, true, []*types.Type{byteptr}, target, tab)[0]
-			return s.newValue2(ssa.OpIMake, n.Type(), tab, data), nil
+			return s.newValue2(ssa.OpIMake, dst, tab, data), nil
 		}
 		fn := ir.Syms.AssertI2I2
-		if n.X.Type().IsEmptyInterface() {
+		if src.IsEmptyInterface() {
 			fn = ir.Syms.AssertE2I2
 		}
-		res = s.rtcall(fn, true, []*types.Type{n.Type()}, target, iface)[0]
-		resok = s.newValue2(ssa.OpNeqInter, types.Types[types.TBOOL], res, s.constInterface(n.Type()))
+		res = s.rtcall(fn, true, []*types.Type{dst}, target, iface)[0]
+		resok = s.newValue2(ssa.OpNeqInter, types.Types[types.TBOOL], res, s.constInterface(dst))
 		return
 	}
 
 	if base.Debug.TypeAssert > 0 {
-		base.WarnfAt(n.Pos(), "type assertion inlined")
+		base.WarnfAt(pos, "type assertion inlined")
 	}
 
 	// Converting to a concrete type.
-	direct := types.IsDirectIface(n.Type())
+	direct := types.IsDirectIface(dst)
 	itab := s.newValue1(ssa.OpITab, byteptr, iface) // type word of interface
 	if base.Debug.TypeAssert > 0 {
-		base.WarnfAt(n.Pos(), "type assertion inlined")
+		base.WarnfAt(pos, "type assertion inlined")
 	}
-	var targetITab *ssa.Value
-	if n.X.Type().IsEmptyInterface() {
+	var wantedFirstWord *ssa.Value
+	if src.IsEmptyInterface() {
 		// Looking for pointer to target type.
-		targetITab = target
+		wantedFirstWord = target
 	} else {
 		// Looking for pointer to itab for target type and source interface.
-		targetITab = s.expr(n.Itab)
+		wantedFirstWord = targetItab
 	}
 
 	var tmp ir.Node     // temporary for use with large types
 	var addr *ssa.Value // address of tmp
-	if commaok && !TypeOK(n.Type()) {
+	if commaok && !TypeOK(dst) {
 		// unSSAable type, use temporary.
 		// TODO: get rid of some of these temporaries.
-		tmp, addr = s.temp(n.Pos(), n.Type())
+		tmp, addr = s.temp(pos, dst)
 	}
 
-	cond := s.newValue2(ssa.OpEqPtr, types.Types[types.TBOOL], itab, targetITab)
+	cond := s.newValue2(ssa.OpEqPtr, types.Types[types.TBOOL], itab, wantedFirstWord)
 	b := s.endBlock()
 	b.Kind = ssa.BlockIf
 	b.SetControl(cond)
@@ -6179,8 +6217,8 @@ func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Val
 	if !commaok {
 		// on failure, panic by calling panicdottype
 		s.startBlock(bFail)
-		taddr := s.reflectType(n.X.Type())
-		if n.X.Type().IsEmptyInterface() {
+		taddr := s.reflectType(src)
+		if src.IsEmptyInterface() {
 			s.rtcall(ir.Syms.PanicdottypeE, false, nil, itab, target, taddr)
 		} else {
 			s.rtcall(ir.Syms.PanicdottypeI, false, nil, itab, target, taddr)
@@ -6189,10 +6227,10 @@ func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Val
 		// on success, return data from interface
 		s.startBlock(bOk)
 		if direct {
-			return s.newValue1(ssa.OpIData, n.Type(), iface), nil
+			return s.newValue1(ssa.OpIData, dst, iface), nil
 		}
-		p := s.newValue1(ssa.OpIData, types.NewPtr(n.Type()), iface)
-		return s.load(n.Type(), p), nil
+		p := s.newValue1(ssa.OpIData, types.NewPtr(dst), iface)
+		return s.load(dst, p), nil
 	}
 
 	// commaok is the more complicated case because we have
@@ -6206,14 +6244,14 @@ func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Val
 	s.startBlock(bOk)
 	if tmp == nil {
 		if direct {
-			s.vars[valVar] = s.newValue1(ssa.OpIData, n.Type(), iface)
+			s.vars[valVar] = s.newValue1(ssa.OpIData, dst, iface)
 		} else {
-			p := s.newValue1(ssa.OpIData, types.NewPtr(n.Type()), iface)
-			s.vars[valVar] = s.load(n.Type(), p)
+			p := s.newValue1(ssa.OpIData, types.NewPtr(dst), iface)
+			s.vars[valVar] = s.load(dst, p)
 		}
 	} else {
-		p := s.newValue1(ssa.OpIData, types.NewPtr(n.Type()), iface)
-		s.move(n.Type(), addr, p)
+		p := s.newValue1(ssa.OpIData, types.NewPtr(dst), iface)
+		s.move(dst, addr, p)
 	}
 	s.vars[okVar] = s.constBool(true)
 	s.endBlock()
@@ -6222,9 +6260,9 @@ func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Val
 	// type assertion failed
 	s.startBlock(bFail)
 	if tmp == nil {
-		s.vars[valVar] = s.zeroVal(n.Type())
+		s.vars[valVar] = s.zeroVal(dst)
 	} else {
-		s.zero(n.Type(), addr)
+		s.zero(dst, addr)
 	}
 	s.vars[okVar] = s.constBool(false)
 	s.endBlock()
@@ -6233,10 +6271,10 @@ func (s *state) dottype(n *ir.TypeAssertExpr, commaok bool) (res, resok *ssa.Val
 	// merge point
 	s.startBlock(bEnd)
 	if tmp == nil {
-		res = s.variable(valVar, n.Type())
+		res = s.variable(valVar, dst)
 		delete(s.vars, valVar)
 	} else {
-		res = s.load(n.Type(), addr)
+		res = s.load(dst, addr)
 		s.vars[memVar] = s.newValue1A(ssa.OpVarKill, types.TypeMem, tmp.(*ir.Name), s.mem())
 	}
 	resok = s.variable(okVar, types.Types[types.TBOOL])
diff --git a/src/cmd/compile/internal/walk/expr.go b/src/cmd/compile/internal/walk/expr.go
index f0d37198d3..f95b6f4639 100644
--- a/src/cmd/compile/internal/walk/expr.go
+++ b/src/cmd/compile/internal/walk/expr.go
@@ -136,6 +136,10 @@ func walkExpr1(n ir.Node, init *ir.Nodes) ir.Node {
 		n := n.(*ir.TypeAssertExpr)
 		return walkDotType(n, init)
 
+	case ir.ODYNAMICDOTTYPE, ir.ODYNAMICDOTTYPE2:
+		n := n.(*ir.DynamicTypeAssertExpr)
+		return walkDynamicDotType(n, init)
+
 	case ir.OLEN, ir.OCAP:
 		n := n.(*ir.UnaryExpr)
 		return walkLenCap(n, init)
@@ -669,6 +673,13 @@ func walkDotType(n *ir.TypeAssertExpr, init *ir.Nodes) ir.Node {
 	return n
 }
 
+// walkDynamicdotType walks an ODYNAMICDOTTYPE or ODYNAMICDOTTYPE2 node.
+func walkDynamicDotType(n *ir.DynamicTypeAssertExpr, init *ir.Nodes) ir.Node {
+	n.X = walkExpr(n.X, init)
+	n.T = walkExpr(n.T, init)
+	return n
+}
+
 // walkIndex walks an OINDEX node.
 func walkIndex(n *ir.IndexExpr, init *ir.Nodes) ir.Node {
 	n.X = walkExpr(n.X, init)
diff --git a/src/cmd/compile/internal/walk/order.go b/src/cmd/compile/internal/walk/order.go
index fe6ae3fda0..c5fd0c1e1d 100644
--- a/src/cmd/compile/internal/walk/order.go
+++ b/src/cmd/compile/internal/walk/order.go
@@ -686,6 +686,10 @@ func (o *orderState) stmt(n ir.Node) {
 		case ir.ODOTTYPE2:
 			r := r.(*ir.TypeAssertExpr)
 			r.X = o.expr(r.X, nil)
+		case ir.ODYNAMICDOTTYPE2:
+			r := r.(*ir.DynamicTypeAssertExpr)
+			r.X = o.expr(r.X, nil)
+			r.T = o.expr(r.T, nil)
 		case ir.ORECV:
 			r := r.(*ir.UnaryExpr)
 			r.X = o.expr(r.X, nil)
diff --git a/test/typeparam/dottype.go b/test/typeparam/dottype.go
index 89a9b02111..c9c900c096 100644
--- a/test/typeparam/dottype.go
+++ b/test/typeparam/dottype.go
@@ -69,6 +69,11 @@ func main() {
 	println(h[int](struct{ a, b int }{3, 5}).a)
 
 	println(k[int](mybar(3)).bar())
+
+	type large struct {a,b,c,d,e,f int}
+	println(f[large](large{}).a)
+	l2, ok := f2[large](large{})
+	println(l2.a, ok)
 }
 func shouldpanic(x func()) {
 	defer func() {
diff --git a/test/typeparam/dottype.out b/test/typeparam/dottype.out
index 058c923a5c..8e6a3c2552 100644
--- a/test/typeparam/dottype.out
+++ b/test/typeparam/dottype.out
@@ -6,3 +6,5 @@
 0 false
 3
 3
+0
+0 true