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cmd/compile: avoid extra mapaccess in "m[k] op= r"

Currently, order desugars map assignment operations like

    m[k] op= r

into

    m[k] = m[k] op r

which in turn is transformed during walk into:

    tmp := *mapaccess(m, k)
    tmp = tmp op r
    *mapassign(m, k) = tmp

However, this is suboptimal, as we could instead produce just:

    *mapassign(m, k) op= r

One complication though is if "r == 0", then "m[k] /= r" and "m[k] %=
r" will panic, and they need to do so *before* calling mapassign,
otherwise we may insert a new zero-value element into the map.

It would be spec compliant to just emit the "r != 0" check before
calling mapassign (see #23735), but currently these checks aren't
generated until SSA construction. For now, it's simpler to continue
desugaring /= and %= into two map indexing operations.

Fixes #23661.

Change-Id: I46e3739d9adef10e92b46fdd78b88d5aabe68952
Reviewed-on: https://go-review.googlesource.com/91557
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Vladimir Kuzmin 2018-02-01 21:33:56 -08:00 committed by Matthew Dempsky
parent 85a8d25d53
commit 7395083136
5 changed files with 158 additions and 32 deletions

View File

@ -14,7 +14,7 @@ import (
// order of evaluation. Makes walk easier, because it
// can (after this runs) reorder at will within an expression.
//
// Rewrite x op= y into x = x op y.
// Rewrite m[k] op= r into m[k] = m[k] op r if op is / or %.
//
// Introduce temporaries as needed by runtime routines.
// For example, the map runtime routines take the map key
@ -434,7 +434,7 @@ func (o *Order) mapAssign(n *Node) {
default:
Fatalf("ordermapassign %v", n.Op)
case OAS:
case OAS, OASOP:
if n.Left.Op == OINDEXMAP {
// Make sure we evaluate the RHS before starting the map insert.
// We need to make sure the RHS won't panic. See issue 22881.
@ -514,26 +514,31 @@ func (o *Order) stmt(n *Node) {
o.cleanTemp(t)
case OASOP:
// Special: rewrite l op= r into l = l op r.
// This simplifies quite a few operations;
// most important is that it lets us separate
// out map read from map write when l is
// a map index expression.
t := o.markTemp()
n.Left = o.expr(n.Left, nil)
n.Right = o.expr(n.Right, nil)
n.Left = o.safeExpr(n.Left)
tmp1 := treecopy(n.Left, src.NoXPos)
if tmp1.Op == OINDEXMAP {
tmp1.SetIndexMapLValue(false)
if instrumenting || n.Left.Op == OINDEXMAP && (n.SubOp() == ODIV || n.SubOp() == OMOD) {
// Rewrite m[k] op= r into m[k] = m[k] op r so
// that we can ensure that if op panics
// because r is zero, the panic happens before
// the map assignment.
n.Left = o.safeExpr(n.Left)
l := treecopy(n.Left, src.NoXPos)
if l.Op == OINDEXMAP {
l.SetIndexMapLValue(false)
}
l = o.copyExpr(l, n.Left.Type, false)
n.Right = nod(n.SubOp(), l, n.Right)
n.Right = typecheck(n.Right, Erv)
n.Right = o.expr(n.Right, nil)
n.Op = OAS
n.ResetAux()
}
tmp1 = o.copyExpr(tmp1, n.Left.Type, false)
n.Right = nod(n.SubOp(), tmp1, n.Right)
n.Right = typecheck(n.Right, Erv)
n.Right = o.expr(n.Right, nil)
n.Op = OAS
n.ResetAux()
o.mapAssign(n)
o.cleanTemp(t)

View File

@ -667,12 +667,21 @@ opswitch:
updateHasCall(n.Left)
n.List.Set(reorder1(ll))
case OAS:
case OAS, OASOP:
init.AppendNodes(&n.Ninit)
n.Left = walkexpr(n.Left, init)
n.Left = safeexpr(n.Left, init)
if n.Op == OASOP {
// Rewrite x op= y into x = x op y.
n.Right = nod(n.SubOp(), n.Left, n.Right)
n.Right = typecheck(n.Right, Erv)
n.Op = OAS
n.ResetAux()
}
if oaslit(n, init) {
break
}

View File

@ -52,14 +52,7 @@ func TestNegativeZero(t *testing.T) {
}
}
// nan is a good test because nan != nan, and nan has
// a randomized hash value.
func TestNan(t *testing.T) {
m := make(map[float64]int, 0)
nan := math.NaN()
m[nan] = 1
m[nan] = 2
m[nan] = 4
func testMapNan(t *testing.T, m map[float64]int) {
if len(m) != 3 {
t.Error("length wrong")
}
@ -78,6 +71,49 @@ func TestNan(t *testing.T) {
}
}
// nan is a good test because nan != nan, and nan has
// a randomized hash value.
func TestMapAssignmentNan(t *testing.T) {
m := make(map[float64]int, 0)
nan := math.NaN()
// Test assignment.
m[nan] = 1
m[nan] = 2
m[nan] = 4
testMapNan(t, m)
}
// nan is a good test because nan != nan, and nan has
// a randomized hash value.
func TestMapOperatorAssignmentNan(t *testing.T) {
m := make(map[float64]int, 0)
nan := math.NaN()
// Test assignment operations.
m[nan] += 1
m[nan] += 2
m[nan] += 4
testMapNan(t, m)
}
func TestMapOperatorAssignment(t *testing.T) {
m := make(map[int]int, 0)
// "m[k] op= x" is rewritten into "m[k] = m[k] op x"
// differently when op is / or % than when it isn't.
// Simple test to make sure they all work as expected.
m[0] = 12345
m[0] += 67890
m[0] /= 123
m[0] %= 456
const want = (12345 + 67890) / 123 % 456
if got := m[0]; got != want {
t.Errorf("got %d, want %d", got, want)
}
}
// Maps aren't actually copied on assignment.
func TestAlias(t *testing.T) {
m := make(map[int]int, 0)
@ -92,18 +128,25 @@ func TestAlias(t *testing.T) {
func TestGrowWithNaN(t *testing.T) {
m := make(map[float64]int, 4)
nan := math.NaN()
// Use both assignment and assignment operations as they may
// behave differently.
m[nan] = 1
m[nan] = 2
m[nan] = 4
m[nan] += 4
cnt := 0
s := 0
growflag := true
for k, v := range m {
if growflag {
// force a hashtable resize
for i := 0; i < 100; i++ {
for i := 0; i < 50; i++ {
m[float64(i)] = i
}
for i := 50; i < 100; i++ {
m[float64(i)] += i
}
growflag = false
}
if k != k {
@ -128,8 +171,8 @@ func TestGrowWithNegativeZero(t *testing.T) {
negzero := math.Copysign(0.0, -1.0)
m := make(map[FloatInt]int, 4)
m[FloatInt{0.0, 0}] = 1
m[FloatInt{0.0, 1}] = 2
m[FloatInt{0.0, 2}] = 4
m[FloatInt{0.0, 1}] += 2
m[FloatInt{0.0, 2}] += 4
m[FloatInt{0.0, 3}] = 8
growflag := true
s := 0
@ -211,9 +254,12 @@ func TestIterGrowAndDelete(t *testing.T) {
// an iterator is still using them.
func TestIterGrowWithGC(t *testing.T) {
m := make(map[int]int, 4)
for i := 0; i < 16; i++ {
for i := 0; i < 8; i++ {
m[i] = i
}
for i := 8; i < 16; i++ {
m[i] += i
}
growflag := true
bitmask := 0
for k := range m {
@ -786,6 +832,13 @@ func benchmarkMapAssignInt32(b *testing.B, n int) {
}
}
func benchmarkMapOperatorAssignInt32(b *testing.B, n int) {
a := make(map[int32]int)
for i := 0; i < b.N; i++ {
a[int32(i&(n-1))] += i
}
}
func benchmarkMapDeleteInt32(b *testing.B, n int) {
a := make(map[int32]int, n)
b.ResetTimer()
@ -808,6 +861,13 @@ func benchmarkMapAssignInt64(b *testing.B, n int) {
}
}
func benchmarkMapOperatorAssignInt64(b *testing.B, n int) {
a := make(map[int64]int)
for i := 0; i < b.N; i++ {
a[int64(i&(n-1))] += i
}
}
func benchmarkMapDeleteInt64(b *testing.B, n int) {
a := make(map[int64]int, n)
b.ResetTimer()
@ -835,6 +895,19 @@ func benchmarkMapAssignStr(b *testing.B, n int) {
}
}
func benchmarkMapOperatorAssignStr(b *testing.B, n int) {
k := make([]string, n)
for i := 0; i < len(k); i++ {
k[i] = strconv.Itoa(i)
}
b.ResetTimer()
a := make(map[string]string)
for i := 0; i < b.N; i++ {
key := k[i&(n-1)]
a[key] += key
}
}
func benchmarkMapDeleteStr(b *testing.B, n int) {
i2s := make([]string, n)
for i := 0; i < n; i++ {
@ -870,6 +943,12 @@ func BenchmarkMapAssign(b *testing.B) {
b.Run("Str", runWith(benchmarkMapAssignStr, 1<<8, 1<<16))
}
func BenchmarkMapOperatorAssign(b *testing.B) {
b.Run("Int32", runWith(benchmarkMapOperatorAssignInt32, 1<<8, 1<<16))
b.Run("Int64", runWith(benchmarkMapOperatorAssignInt64, 1<<8, 1<<16))
b.Run("Str", runWith(benchmarkMapOperatorAssignStr, 1<<8, 1<<16))
}
func BenchmarkMapDelete(b *testing.B) {
b.Run("Int32", runWith(benchmarkMapDeleteInt32, 100, 1000, 10000))
b.Run("Int64", runWith(benchmarkMapDeleteInt64, 100, 1000, 10000))

View File

@ -28,10 +28,38 @@ func del(m map[interface{}]interface{}, key interface{}) (err error) {
return nil
}
func addInt(m map[interface{}]int, key interface{}) (err error) {
defer func() {
if r := recover(); r != nil {
err = fmt.Errorf("addInt failed: %v", r)
}
}()
m[key] += 2018
return nil
}
func addStr(m map[interface{}]string, key interface{}) (err error) {
defer func() {
if r := recover(); r != nil {
err = fmt.Errorf("addStr failed: %v", r)
}
}()
m[key] += "hello, go"
return nil
}
func main() {
m := make(map[interface{}]interface{})
set(m, []int{1, 2, 3})
set(m, "abc") // used to throw
del(m, []int{1, 2, 3})
del(m, "abc") // used to throw
mi := make(map[interface{}]int)
addInt(mi, []int{1, 2, 3})
addInt(mi, "abc") // used to throw
ms := make(map[interface{}]string)
addStr(ms, []int{1, 2, 3})
addStr(ms, "abc") // used to throw
}

View File

@ -13,7 +13,7 @@ import "fmt"
func main() {
for i, f := range []func(map[int]int){
f0, f1, f2, f3, f4, f5, f6, f7,
f0, f1, f2, f3, f4, f5, f6, f7, f8,
} {
m := map[int]int{}
func() { // wrapper to scope the defer.
@ -69,4 +69,9 @@ func f7(m map[int]int) {
m[0] = a[0]
}
func f8(m map[int]int) {
var z int
m[0] %= z
}
var sink bool