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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>
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dr2chase committed Mar 30, 2015
1 parent cf7461c commit 22701339817a591cd352ecd43b0439b84dbe8095
@@ -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" +
@@ -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)
@@ -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
@@ -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
@@ -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
@@ -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)
}
}
@@ -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"

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