cmd/gc: allocate backing storage for non-escaping interfaces on stack

Extend escape analysis to convT2E and conT2I. If the interface value
does not escape supply runtime with a stack buffer for the object copy.

This is a straight port from .c to .go of Dmitry's patch

Change-Id: Ic315dd50d144d94dd3324227099c116be5ca70b6
Reviewed-on: https://go-review.googlesource.com/8201
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

src/cmd/internal/gc/builtin.go

@@ -50,8 +50,8 @@ const runtimeimport = "" +
 	"func @\"\".typ2Itab (@\"\".typ·2 *byte, @\"\".typ2·3 *byte, @\"\".cache·4 **byte) (@\"\".ret·1 *byte)\n" +
 	"func @\"\".convI2E (@\"\".elem·2 any) (@\"\".ret·1 any)\n" +
 	"func @\"\".convI2I (@\"\".typ·2 *byte, @\"\".elem·3 any) (@\"\".ret·1 any)\n" +
-	"func @\"\".convT2E (@\"\".typ·2 *byte, @\"\".elem·3 *any) (@\"\".ret·1 any)\n" +
-	"func @\"\".convT2I (@\"\".typ·2 *byte, @\"\".typ2·3 *byte, @\"\".cache·4 **byte, @\"\".elem·5 *any) (@\"\".ret·1 any)\n" +
+	"func @\"\".convT2E (@\"\".typ·2 *byte, @\"\".elem·3 *any, @\"\".buf·4 *any) (@\"\".ret·1 any)\n" +
+	"func @\"\".convT2I (@\"\".typ·2 *byte, @\"\".typ2·3 *byte, @\"\".cache·4 **byte, @\"\".elem·5 *any, @\"\".buf·6 *any) (@\"\".ret·1 any)\n" +
 	"func @\"\".assertE2E (@\"\".typ·1 *byte, @\"\".iface·2 any, @\"\".ret·3 *any)\n" +
 	"func @\"\".assertE2E2 (@\"\".typ·2 *byte, @\"\".iface·3 any, @\"\".ret·4 *any) (? bool)\n" +
 	"func @\"\".assertE2I (@\"\".typ·1 *byte, @\"\".iface·2 any, @\"\".ret·3 *any)\n" +

src/cmd/internal/gc/builtin/runtime.go

@@ -63,8 +63,8 @@ func slicestringcopy(to any, fr any) int
 func typ2Itab(typ *byte, typ2 *byte, cache **byte) (ret *byte)
 func convI2E(elem any) (ret any)
 func convI2I(typ *byte, elem any) (ret any)
-func convT2E(typ *byte, elem *any) (ret any)
-func convT2I(typ *byte, typ2 *byte, cache **byte, elem *any) (ret any)
+func convT2E(typ *byte, elem, buf *any) (ret any)
+func convT2I(typ *byte, typ2 *byte, cache **byte, elem, buf *any) (ret any)
 
 // interface type assertions  x.(T)
 func assertE2E(typ *byte, iface any, ret *any)

src/cmd/internal/gc/esc.go

@@ -653,12 +653,11 @@ func esc(e *EscState, n *Node, up *Node) {
 			}
 		}
 
-	case OCONV, OCONVNOP:
+	case OCONV,
+		OCONVNOP:
 		escassign(e, n, n.Left)
 
 	case OCONVIFACE:
-		// We don't allocate storage for OCONVIFACE on stack yet,
-		// but mark it as EscNone merely to get debug output for tests.
 		n.Esc = EscNone // until proven otherwise
 		e.noesc = list(e.noesc, n)
 		n.Escloopdepth = e.loopdepth

src/cmd/internal/gc/walk.go

@@ -1040,9 +1040,25 @@ func walkexpr(np **Node, init **NodeList) {
 			} else {
 				ll = list(ll, Nod(OADDR, copyexpr(n.Left, n.Left.Type, init), nil))
 			}
+			dowidth(n.Left.Type)
+			r := nodnil()
+			if n.Esc == EscNone && n.Left.Type.Width <= 1024 {
+				// Allocate stack buffer for value stored in interface.
+				r = temp(n.Left.Type)
+				r = Nod(OAS, r, nil) // zero temp
+				typecheck(&r, Etop)
+				*init = list(*init, r)
+				r = Nod(OADDR, r.Left, nil)
+				typecheck(&r, Erv)
+			}
+			ll = list(ll, r)
 		}
 
-		substArgTypes(fn, n.Left.Type, n.Type)
+		if !Isinter(n.Left.Type) {
+			substArgTypes(fn, n.Left.Type, n.Left.Type, n.Type)
+		} else {
+			substArgTypes(fn, n.Left.Type, n.Type)
+		}
 		dowidth(fn.Type)
 		n = Nod(OCALL, fn, nil)
 		n.List = ll

src/runtime/iface.go

@@ -130,13 +130,15 @@ func typ2Itab(t *_type, inter *interfacetype, cache **itab) *itab {
 	return tab
 }
 
-func convT2E(t *_type, elem unsafe.Pointer) (e interface{}) {
+func convT2E(t *_type, elem unsafe.Pointer, x unsafe.Pointer) (e interface{}) {
 	ep := (*eface)(unsafe.Pointer(&e))
 	if isDirectIface(t) {
 		ep._type = t
 		typedmemmove(t, unsafe.Pointer(&ep.data), elem)
 	} else {
-		x := newobject(t)
+		if x == nil {
+			x = newobject(t)
+		}
 		// TODO: We allocate a zeroed object only to overwrite it with
 		// actual data.  Figure out how to avoid zeroing.  Also below in convT2I.
 		typedmemmove(t, x, elem)
@@ -146,7 +148,7 @@ func convT2E(t *_type, elem unsafe.Pointer) (e interface{}) {
 	return
 }
 
-func convT2I(t *_type, inter *interfacetype, cache **itab, elem unsafe.Pointer) (i fInterface) {
+func convT2I(t *_type, inter *interfacetype, cache **itab, elem unsafe.Pointer, x unsafe.Pointer) (i fInterface) {
 	tab := (*itab)(atomicloadp(unsafe.Pointer(cache)))
 	if tab == nil {
 		tab = getitab(inter, t, false)
@@ -157,7 +159,9 @@ func convT2I(t *_type, inter *interfacetype, cache **itab, elem unsafe.Pointer)
 		pi.tab = tab
 		typedmemmove(t, unsafe.Pointer(&pi.data), elem)
 	} else {
-		x := newobject(t)
+		if x == nil {
+			x = newobject(t)
+		}
 		typedmemmove(t, x, elem)
 		pi.tab = tab
 		pi.data = x

src/runtime/iface_test.go

@@ -221,3 +221,43 @@ func BenchmarkAssertE2E2Blank(b *testing.B) {
 		_, ok = e.(interface{})
 	}
 }
+
+func TestNonEscapingConvT2E(t *testing.T) {
+	m := make(map[interface{}]bool)
+	m[42] = true
+	if !m[42] {
+		t.Fatalf("42 is not present in the map")
+	}
+	if m[0] {
+		t.Fatalf("0 is present in the map")
+	}
+
+	n := testing.AllocsPerRun(1000, func() {
+		if m[0] {
+			t.Fatalf("0 is present in the map")
+		}
+	})
+	if n != 0 {
+		t.Fatalf("want 0 allocs, got %v", n)
+	}
+}
+
+func TestNonEscapingConvT2I(t *testing.T) {
+	m := make(map[I1]bool)
+	m[TM(42)] = true
+	if !m[TM(42)] {
+		t.Fatalf("42 is not present in the map")
+	}
+	if m[TM(0)] {
+		t.Fatalf("0 is present in the map")
+	}
+
+	n := testing.AllocsPerRun(1000, func() {
+		if m[TM(0)] {
+			t.Fatalf("0 is present in the map")
+		}
+	})
+	if n != 0 {
+		t.Fatalf("want 0 allocs, got %v", n)
+	}
+}

test/escape2.go

@@ -1787,7 +1787,7 @@ func makemap1() map[int]int {
 
 func makemap2() {
 	m := make(map[int]int) // ERROR "make\(map\[int\]int\) escapes to heap"
-	sink = m	// ERROR "m escapes to heap"
+	sink = m               // ERROR "m escapes to heap"
 }
 
 func nonescapingEface(m map[interface{}]bool) bool { // ERROR "m does not escape"