1.
@rrafols
the bytecode
mumbo-jumbo
#perfmatters

2.
@rrafols
Disclaimer:
This presentation contains
bytecode
Content is my own experimentation and
might differ on other environments

3.
@rrafols
Competitions
Work
2015 Local winner
2016+ Ambassador
Runner up
Demoscene
Speaker
Author Entrepreneurship

4.
@rrafols
Our friend the java
compiler.

5.
@rrafols
*.java → [javac] → *.class

6.
@rrafols
Or, for example, on
Android

7.
@rrafols
*.java → [javac] → *.class
*.class → [dx] → dex file

8.
@rrafols
*.java → [javac] → *.class
*.class → [dx] → dex
dex → [dexopt] → opt. dex
dex → [dex2oat] → native

9.
@rrafols
but change is coming!
Jack & Jill

10.
@rrafols
but change is coming!
Jack & Jill

11.
@rrafols
*.java → [jack] → dex file

12.
@rrafols
Let’s focus on javac
Javac vs other compilers

13.
@rrafols
Compilers
Produces optimized code
for the target platform

14.
@rrafols
javac
Does not produce
optimized code*

15.
@rrafols
javac
Does not know on which
architecture the code will
be executed

16.
@rrafols
Source: Oracle

17.
@rrafols
For this reason
Java bytecode &
operations are stack
based

18.
@rrafols
Easy to interpret
But not the most
performant solution

19.
@rrafols
Quick example
Stack based integer
addition

20.
@rrafols
j = j + i

21.
@rrafols
Java bytecode

22.
@rrafols
iload_3
iload_2
iadd
istore_2

23.
@rrafols
Register based approach

24.
@rrafols
add r01, r02, r01
or
add eax, ebx

25.
@rrafols
Let’s make things
interesting…
j = j + i + k + w + h * 2 + p * p;

26.
@rrafols
Java bytecode

27.
@rrafols
0: iload_2
1: iload_1
2: iadd
3: iload_3
4: iadd
5: iload 4
7: iadd
8: iload 5
10: iconst_2
11: imul
12: iadd
13: iload 6
15: iload 6
17: imul
18: iadd
19: istore_2
j = j + i + k + w + h * 2 + p * p;
Local vars
1: i
2: j
3: k
4: w
5: h
6: p

28.
@rrafols
0: iload_2
1: iload_1
2: iadd
3: iload_3
4: iadd
5: iload 4
7: iadd
8: iload 5
10: iconst_2
11: imul
12: iadd
13: iload 6
15: iload 6
17: imul
18: iadd
19: istore_2
j = j + i + k + w + h * 2 + p * p;
Local vars
1: i
2: j
3: k
4: w
5: h
6: p

29.
@rrafols
0: iload_2
1: iload_1
2: iadd
3: iload_3
4: iadd
5: iload 4
7: iadd
8: iload 5
10: iconst_2
11: imul
12: iadd
13: iload 6
15: iload 6
17: imul
18: iadd
19: istore_2
j = j + i + k + w + h * 2 + p * p;
Local vars
1: i
2: j
3: k
4: w
5: h
6: p

30.
@rrafols
0: iload_2
1: iload_1
2: iadd
3: iload_3
4: iadd
5: iload 4
7: iadd
8: iload 5
10: iconst_2
11: imul
12: iadd
13: iload 6
15: iload 6
17: imul
18: iadd
19: istore_2
j = j + i + k + w + h * 2 + p * p;
Local vars
1: i
2: j
3: k
4: w
5: h
6: p

31.
@rrafols
0: iload_2
1: iload_1
2: iadd
3: iload_3
4: iadd
5: iload 4
7: iadd
8: iload 5
10: iconst_2
11: imul
12: iadd
13: iload 6
15: iload 6
17: imul
18: iadd
19: istore_2
j = j + i + k + w + h * 2 + p * p;
Local vars
1: i
2: j
3: k
4: w
5: h
6: p

32.
@rrafols
0: iload_2
1: iload_1
2: iadd
3: iload_3
4: iadd
5: iload 4
7: iadd
8: iload 5
10: iconst_2
11: imul
12: iadd
13: iload 6
15: iload 6
17: imul
18: iadd
19: istore_2
j = j + i + k + w + h * 2 + p * p;
Local vars
1: i
2: j
3: k
4: w
5: h
6: p

33.
@rrafols
0: iload_2
1: iload_1
2: iadd
3: iload_3
4: iadd
5: iload 4
7: iadd
8: iload 5
10: iconst_2
11: imul
12: iadd
13: iload 6
15: iload 6
17: imul
18: iadd
19: istore_2
j = j + i + k + w + h * 2 + p * p;
Local vars
1: i
2: j
3: k
4: w
5: h
6: p

34.
@rrafols
Register based approach

35.
@rrafols
add r01, r02, r01
add r01, r03, r01
add r01, r04, r01
mul r07, r05, #2
add r01, r07, r01
mul r08, r06, r06
add r02, r08, r01
j = j + i + k + w + h * 2 + p * p;
r01: i
r02: j
r03: k
r04: w
r05: h
r06: p

36.
@rrafols
Java VM (JVM)
Only the JVM knows the
architecture where is running.
In this case, for example, we used up to
8 registers

37.
@rrafols
Java VM (JVM)
All optimizations are left to
be done by the JVM

38.
@rrafols
Maybe takes this concept
a bit too far...

39.
@rrafols
Imagine this simple C code
#include <stdio.h>
int main() {
int a = 10;
int b = 1 + 2 + 3 + 4 + 5 + 6 + a;
printf("%dn", b);
}

40.
@rrafols
GCC compiler
#include <stdio.h>
int main() {
int a = 10;
int b = 1 + 2 + 3 + 4 + 5 + 6 + a;
printf("%dn", b);
}
…
movl $31, %esi
call _printf
…
* Using gcc & -O2 compiler option

41.
@rrafols
javac
public static void main(String
args[]) {
int a = 10;
int b = 1 + 2 + 3 + 4 + 5 + 6 + a;
System.out.println(b);
}
0: bipush 10
2: istore_1
3: bipush 21
5: iload_1
6: iadd
7: istore_2
...

42.
@rrafols
Let's do a small change
#include <stdio.h>
int main() {
int a = 10;
int b = 1 + 2 + 3 + 4 + 5 + a + 6;
printf("%dn", b);
}

43.
@rrafols
GCC compiler
#include <stdio.h>
int main() {
int a = 10;
int b = 1 + 2 + 3 + 4 + 5 + a + 6;
printf("%dn", b);
}
…
movl $31, %esi
call _printf
…
* Using gcc & -O2 compiler option

44.
@rrafols
javac
public static void main(String
args[]) {
int a = 10;
int b = 1 + 2 + 3 + 4 + 5 + a + 6;
System.out.println(b);
}
0: bipush 10
2: istore_1
3: bipush 15
5: iload_1
6: iadd
7: bipush 6
9: iadd
10: istore_2

45.
@rrafols
Let's do another quick
change..
public static void main(String args[]) {
int a = 10;
int b = a + 1 + 2 + 3 + 4 + 5 + 6;
System.out.println(b);
}

46.
@rrafols
javac
0: bipush 10
2: istore_1
3: iload_1
4: iconst_1
5: iadd
6: iconst_2
7: iadd
8: iconst_3
9: iadd
10: iconst_4
11: iadd
12: iconst_5
13: iadd
14: bipush 6
16: iadd
17: istore_2
public static void main(String args[]) {
int a = 10;
int b = a + 1 + 2 + 3 + 4 + 5 + 6;
System.out.println(b);
}

47.
@rrafols
On Android there is jack
to the rescue...

48.
@rrafols
jack
public static void main(String args[]) {
int a = 10;
int b = a + 1 + 2 + 3 + 4 + 5 + 6;
System.out.println(b);
}
...
0: const/16 v0, #int 31
2: sget-object v1,
Ljava/lang/System;
4: invoke-virtual {v1, v0}
7: return-void
...

49.
@rrafols
And on Java there is the
JIT compiler to the rescue

50.
@rrafols
JIT assembly output
public static void main(String args[]) {
int a = 10;
int b = a + 1 + 2 + 3 + 4 + 5 + 6;
System.out.println(b);
}
...
0x00000001104b2bff: mov eax, 0x0001f
...
0: bipush 10
2: istore_1
3: iload_1
4: iconst_1
5: iadd
6: iconst_2
7: iadd
8: iconst_3
9: iadd
10: iconst_4
11: iadd
12: iconst_5
13: iadd
14: bipush 6
16: iadd
17: istore_2

51.
@rrafols
Language additions
Thinks to consider

52.
@rrafols
Autoboxing
Transparent to the developer
but compiler adds some
'extra' code

53.
@rrafols
Autoboxing
long total = 0;
for(int i = 0; i < N; i++) {
total += i;
}
0: lconst_0
1: lstore_1
2: iconst_0
3: istore_3
4: iload_3
5: ldc #8 // N
7: if_icmpge 21
10: lload_1
11: iload_3
12: i2l
13: ladd
14: lstore_1
15: iinc 3, 1
18: goto 4

54.
@rrafols
Autoboxing
long total = 0;
for(int i = 0; i < N; i++) {
total += i;
}
0: lconst_0
1: lstore_1
2: iconst_0
3: istore_3
4: iload_3
5: ldc #8 // N
7: if_icmpge 21
10: lload_1
11: iload_3
12: i2l
13: ladd
14: lstore_1
15: iinc 3, 1
18: goto 4

55.
@rrafols
Autoboxing
long total = 0;
for(int i = 0; i < N; i++) {
total += i;
}
0: lconst_0
1: lstore_1
2: iconst_0
3: istore_3
4: iload_3
5: ldc #8 // N
7: if_icmpge 21
10: lload_1
11: iload_3
12: i2l
13: ladd
14: lstore_1
15: iinc 3, 1
18: goto 4

56.
@rrafols
Autoboxing
long total = 0;
for(int i = 0; i < N; i++) {
total += i;
}
0: lconst_0
1: lstore_1
2: iconst_0
3: istore_3
4: iload_3
5: ldc #8 // N
7: if_icmpge 21
10: lload_1
11: iload_3
12: i2l
13: ladd
14: lstore_1
15: iinc 3, 1
18: goto 4
21:

57.
@rrafols
Autoboxing
long total = 0;
for(int i = 0; i < N; i++) {
total += i;
}
0: lconst_0
1: lstore_1
2: iconst_0
3: istore_3
4: iload_3
5: ldc #8 // N
7: if_icmpge 21
10: lload_1
11: iload_3
12: i2l
13: ladd
14: lstore_1
15: iinc 3, 1
18: goto 4

58.
@rrafols
Autoboxing
long total = 0;
for(int i = 0; i < N; i++) {
total += i;
}
0: lconst_0
1: lstore_1
2: iconst_0
3: istore_3
4: iload_3
5: ldc #8 // N
7: if_icmpge 21
10: lload_1
11: iload_3
12: i2l
13: ladd
14: lstore_1
15: iinc 3, 1
18: goto 4

59.
@rrafols
Autoboxing
long total = 0;
for(int i = 0; i < N; i++) {
total += i;
}
0: lconst_0
1: lstore_1
2: iconst_0
3: istore_3
4: iload_3
5: ldc #8 // N
7: if_icmpge 21
10: lload_1
11: iload_3
12: i2l
13: ladd
14: lstore_1
15: iinc 3, 1
18: goto 4

60.
@rrafols
Autoboxing
Long total = 0;
for(Integer i = 0; i < N; i++) {
total += i;
}

61.
@rrafols
Autoboxing
Long total = 0;
for(Integer i = 0; i < N; i++) {
total += i;
}
00: lconst_0
01: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
04: astore_1
05: iconst_0
06: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
09: astore_2
10: aload_2
11: invokevirtual #9 // java/lang/Integer.intValue:()I
14: sipush N
17: if_icmpge 54
20: aload_1
21: invokevirtual #10 // java/lang/Long.longValue:()J
24: aload_2
25: invokevirtual #9 // java/lang/Integer.intValue:()I
28: i2l
29: ladd
30: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
33: astore_1
34: aload_2
35: astore_3
36: aload_2
37: invokevirtual #9 // java/lang/Integer.intValue:()I
40: iconst_1
41: iadd
42: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
45: dup
46: astore_2
47: astore 4
49: aload_3
50: pop
51: goto 10

62.
@rrafols
Autoboxing
Long total = 0;
for(Integer i = 0; i < N; i++) {
total += i;
}
00: lconst_0
01: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
04: astore_1
05: iconst_0
06: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
09: astore_2
10: aload_2
11: invokevirtual #9 // java/lang/Integer.intValue:()I
14: sipush N
17: if_icmpge 54
20: aload_1
21: invokevirtual #10 // java/lang/Long.longValue:()J
24: aload_2
25: invokevirtual #9 // java/lang/Integer.intValue:()I
28: i2l
29: ladd
30: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
33: astore_1
34: aload_2
35: astore_3
36: aload_2
37: invokevirtual #9 // java/lang/Integer.intValue:()I
40: iconst_1
41: iadd
42: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
45: dup
46: astore_2
47: astore 4
49: aload_3
50: pop
51: goto 10

63.
@rrafols
Autoboxing
Long total = 0;
for(Integer i = 0; i < N; i++) {
total += i;
}
00: lconst_0
01: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
04: astore_1
05: iconst_0
06: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
09: astore_2
10: aload_2
11: invokevirtual #9 // java/lang/Integer.intValue:()I
14: sipush N
17: if_icmpge 54
20: aload_1
21: invokevirtual #10 // java/lang/Long.longValue:()J
24: aload_2
25: invokevirtual #9 // java/lang/Integer.intValue:()I
28: i2l
29: ladd
30: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
33: astore_1
34: aload_2
35: astore_3
36: aload_2
37: invokevirtual #9 // java/lang/Integer.intValue:()I
40: iconst_1
41: iadd
42: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
45: dup
46: astore_2
47: astore 4
49: aload_3
50: pop
51: goto 10

64.
@rrafols
Autoboxing
Long total = 0;
for(Integer i = 0; i < N; i++) {
total += i;
}
00: lconst_0
01: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
04: astore_1
05: iconst_0
06: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
09: astore_2
10: aload_2
11: invokevirtual #9 // java/lang/Integer.intValue:()I
14: sipush N
17: if_icmpge 54
20: aload_1
21: invokevirtual #10 // java/lang/Long.longValue:()J
24: aload_2
25: invokevirtual #9 // java/lang/Integer.intValue:()I
28: i2l
29: ladd
30: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
33: astore_1
34: aload_2
35: astore_3
36: aload_2
37: invokevirtual #9 // java/lang/Integer.intValue:()I
40: iconst_1
41: iadd
42: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
45: dup
46: astore_2
47: astore 4
49: aload_3
50: pop
51: goto 10

65.
@rrafols
Autoboxing
Long total = 0;
for(Integer i = 0; i < N; i++) {
total += i;
}
00: lconst_0
01: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
04: astore_1
05: iconst_0
06: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
09: astore_2
10: aload_2
11: invokevirtual #9 // java/lang/Integer.intValue:()I
14: sipush N
17: if_icmpge 54
20: aload_1
21: invokevirtual #10 // java/lang/Long.longValue:()J
24: aload_2
25: invokevirtual #9 // java/lang/Integer.intValue:()I
28: i2l
29: ladd
30: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
33: astore_1
34: aload_2
35: astore_3
36: aload_2
37: invokevirtual #9 // java/lang/Integer.intValue:()I
40: iconst_1
41: iadd
42: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
45: dup
46: astore_2
47: astore 4
49: aload_3
50: pop
51: goto 10

66.
@rrafols
Autoboxing
Long total = 0;
for(Integer i = 0; i < N; i++) {
total += i;
}
00: lconst_0
01: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
04: astore_1
05: iconst_0
06: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
09: astore_2
10: aload_2
11: invokevirtual #9 // java/lang/Integer.intValue:()I
14: sipush N
17: if_icmpge 54
20: aload_1
21: invokevirtual #10 // java/lang/Long.longValue:()J
24: aload_2
25: invokevirtual #9 // java/lang/Integer.intValue:()I
28: i2l
29: ladd
30: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
33: astore_1
34: aload_2
35: astore_3
36: aload_2
37: invokevirtual #9 // java/lang/Integer.intValue:()I
40: iconst_1
41: iadd
42: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
45: dup
46: astore_2
47: astore 4
49: aload_3
50: pop
51: goto 10

67.
@rrafols
Autoboxing
Long total = 0;
for(Integer i = 0; i < N; i++) {
total += i;
}
00: lconst_0
01: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
04: astore_1
05: iconst_0
06: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
09: astore_2
10: aload_2
11: invokevirtual #9 // java/lang/Integer.intValue:()I
14: sipush N
17: if_icmpge 54
20: aload_1
21: invokevirtual #10 // java/lang/Long.longValue:()J
24: aload_2
25: invokevirtual #9 // java/lang/Integer.intValue:()I
28: i2l
29: ladd
30: invokestatic #7 // java/lang/Long.valueOf:(J)Ljava/la
33: astore_1
34: aload_2
35: astore_3
36: aload_2
37: invokevirtual #9 // java/lang/Integer.intValue:()I
40: iconst_1
41: iadd
42: invokestatic #8 // java/lang/Integer.valueOf:(I)Ljava/
45: dup
46: astore_2
47: astore 4
49: aload_3
50: pop
51: goto 10

68.
@rrafols
Autoboxing
Long total = 0;
for(Integer i = 0; i < N; i++) {
total += i;
}
// ?
00: lconst_0
01: invokestatic #7 // Method java/lang/Long.valueOf:(J)L
04: astore_1
05: iconst_0
06: invokestatic #8 // Method java/lang/Integer.valueOf:(I
09: astore_2
10: aload_2
11: invokevirtual #9 // Method java/lang/Integer.intValue:
14: sipush N
17: if_icmpge 54
20: aload_1
21: invokevirtual #10 // Method java/lang/Long.longValue:(
24: aload_2
25: invokevirtual #9 // Method java/lang/Integer.intValue:
28: i2l
29: ladd
30: invokestatic #7 // Method java/lang/Long.valueOf:(J)L
33: astore_1
34: aload_2
35: astore_3
36: aload_2
37: invokevirtual #9 // Method java/lang/Integer.intValue:
40: iconst_1
41: iadd
42: invokestatic #8 // Method java/lang/Integer.valueOf:(I
45: dup
46: astore_2
47: astore 4
49: aload_3
50: pop
51: goto 10

69.
@rrafols
Autoboxing
This is what that code is actually doing:
Long total = Long.valueOf(0);
for(Integer i = Integer.valueOf(0);
i.intValue() < N;
i = Integer.valueOf(i.intValue() + 1)) {
total = Long.valueOf(total.longValue() + (long)i.intValue())
}

70.
@rrafols
Autoboxing
Object creation
Long total = Long.valueOf(0);
for(Integer i = Integer.valueOf(0);
i.intValue() < N;
i = Integer.valueOf(i.intValue() + 1)) {
total = Long.valueOf(total.longValue() + (long)i.intValue())
}

71.
@rrafols
Autoboxing
What about Jack?

72.
@rrafols
Autoboxing
Jack does not help in this
situation

73.
@rrafols
Autoboxing
What about the JIT compiler?

74.
@rrafols
Autoboxing
Let's run that loop
N times
(on my desktop computer)
N = 10.000.000.000

75.
@rrafols
Autoboxing

76.
@rrafols
Autoboxing
Let’s try it on Android
Dalvik VM & ART

77.
@rrafols
Autoboxing

78.
@rrafols
Language Additions
Use them wisely!

79.
@rrafols
Sorting
No bytecode mumbo-jumbo
here

80.
@rrafols
Let's sort some numbers…
Arrays.sort(...)

81.
@rrafols
Difference between sorting
primitive types & objects

82.
@rrafols
Using int & Integer

83.
@rrafols
Sorting objects is a stable
sort
Default java algorithm:
TimSort adaptation

84.
@rrafols
Sorting primitives does not
require to be stable sort
Default java algorithm:
Dual-Pivot quicksort

85.
@rrafols
Sorting
Use primitive types as much
as possible

86.
@rrafols
Loops
What is going on behind the
scenes

87.
@rrafols
Loops - List
ArrayList<Integer> list = new …
static long loopStandardList() {
long result = 0;
for(int i = 0; i < list.size(); i++) {
result += list.get(i);
}
return result;
}

88.
@rrafols
ArrayList<Integer> list = new …
static long loopStandardList() {
long result = 0;
for(int i = 0; i < list.size(); i++) {
result += list.get(i);
}
return result;
}
07: lload_0
08: getstatic list
11: iload_2
12: invokevirtual java/util/ArrayList.get
15: checkcast java/lang/Integer
18: invokevirtual java/lang/Integer.intValue
21: i2l
22: ladd
23: lstore_0
24: iinc 2, 1
27: iload_2
28: getstatic list
31: invokevirtual java/util/ArrayList.size
34: if_icmplt 7
Loops - List

89.
@rrafols
ArrayList<Integer> list = new …
static long loopStandardList() {
long result = 0;
for(int i = 0; i < list.size(); i++) {
result += list.get(i);
}
return result;
}
Loops - List 07: lload_0
08: getstatic list
11: iload_2
12: invokevirtual java/util/ArrayList.get
15: checkcast java/lang/Integer
18: invokevirtual java/lang/Integer.intValue
21: i2l
22: ladd
23: lstore_0
24: iinc 2, 1
27: iload_2
28: getstatic list
31: invokevirtual java/util/ArrayList.size
34: if_icmplt 7

90.
@rrafols
ArrayList<Integer> list = new …
static long loopStandardList() {
long result = 0;
for(int i = 0; i < list.size(); i++) {
result += list.get(i);
}
return result;
}
Loops - List 07: lload_0
08: getstatic list
11: iload_2
12: invokevirtual java/util/ArrayList.get
15: checkcast java/lang/Integer
18: invokevirtual java/lang/Integer.intValue
21: i2l
22: ladd
23: lstore_0
24: iinc 2, 1
27: iload_2
28: getstatic list
31: invokevirtual java/util/ArrayList.size
34: if_icmplt 7

91.
@rrafols
ArrayList<Integer> list = new …
static long loopStandardList() {
long result = 0;
for(int i = 0; i < list.size(); i++) {
result += list.get(i);
}
return result;
}
Loops - List 07: lload_0
08: getstatic list
11: iload_2
12: invokevirtual java/util/ArrayList.get
15: checkcast java/lang/Integer
18: invokevirtual java/lang/Integer.intValue
21: i2l
22: ladd
23: lstore_0
24: iinc 2, 1
27: iload_2
28: getstatic list
31: invokevirtual java/util/ArrayList.size
34: if_icmplt 7

92.
@rrafols
Loops - foreach
ArrayList<Integer> list = new …
static long loopForeachList() {
long result = 0;
for(int v : list) {
result += v;
}
return result;
}

93.
@rrafols
ArrayList<Integer> list = new …
static long loopForeachList() {
long result = 0;
for(int v : list) {
result += v;
}
return result;
}
12: aload_3
13: invokeinterface java/util/Iterator.next
18: checkcast java/lang/Integer
21: invokevirtual java/lang/Integer.intValue
24: istore_2
25: lload_0
26: iload_2
27: i2l
28: ladd
29: lstore_0
30: aload_3
31: invokeinterface java/util/Iterator.hasNext
36: ifne 12
Loops - foreach

94.
@rrafols
ArrayList<Integer> list = new …
static long loopForeachList() {
long result = 0;
for(int v : list) {
result += v;
}
return result;
}
Loops - foreach
12: aload_3
13: invokeinterface java/util/Iterator.next
18: checkcast java/lang/Integer
21: invokevirtual java/lang/Integer.intValue
24: istore_2
25: lload_0
26: iload_2
27: i2l
28: ladd
29: lstore_0
30: aload_3
31: invokeinterface java/util/Iterator.hasNext
36: ifne 12

95.
@rrafols
ArrayList<Integer> list = new …
static long loopForeachList() {
long result = 0;
for(int v : list) {
result += v;
}
return result;
}
Loops - foreach
12: aload_3
13: invokeinterface java/util/Iterator.next
18: checkcast java/lang/Integer
21: invokevirtual java/lang/Integer.intValue
24: istore_2
25: lload_0
26: iload_2
27: i2l
28: ladd
29: lstore_0
30: aload_3
31: invokeinterface java/util/Iterator.hasNext
36: ifne 12

96.
@rrafols
Loops - Array
static int[] array = new ...
static long loopStandardArray() {
long result = 0;
for(int i = 0; i < array.length; i++) {
result += array[i];
}
return result;
}

97.
@rrafols
static int[] array = new ...
static long loopStandardArray() {
long result = 0;
for(int i = 0; i < array.length; i++) {
result += array[i];
}
return result;
}
07: lload_0
08: getstatic array
11: iload_2
12: iaload
13: i2l
14: ladd
15: lstore_0
16: iinc 2, 1
19: iload_2
20: getstatic array
23: arraylength
24: if_icmplt 7
Loops - Array

98.
@rrafols
static int[] array = new ...
static long loopStandardArray() {
long result = 0;
for(int i = 0; i < array.length; i++) {
result += array[i];
}
return result;
}
Loops - Array
07: lload_0
08: getstatic array
11: iload_2
12: iaload
13: i2l
14: ladd
15: lstore_0
16: iinc 2, 1
19: iload_2
20: getstatic array
23: arraylength
24: if_icmplt 7

99.
@rrafols
static int[] array = new ...
static long loopStandardArray() {
long result = 0;
for(int i = 0; i < array.length; i++) {
result += array[i];
}
return result;
}
Loops - Array
07: lload_0
08: getstatic array
11: iload_2
12: iaload
13: i2l
14: ladd
15: lstore_0
16: iinc 2, 1
19: iload_2
20: getstatic array
23: arraylength
24: if_icmplt 7

100.
@rrafols
Loops - size cached
static int[] array = new ...
static long loopStandardArray () {
long result = 0;
int length = array.length;
for(int i = 0; i < length; i++) {
result += array[i];
}
return result;
}

101.
@rrafols
static int[] array = new ...
static long loopStandardArray () {
long result = 0;
int length = array.length;
for(int i = 0; i < length; i++) {
result += array[i];
}
return result;
}
12: lload_0
13: getstatic array
16: iload_3
17: iaload
18: i2l
19: ladd
20: lstore_0
21: iinc 3, 1
24: iload_3
25: iload_2
26: if_icmplt 12
Loops - size cached

102.
@rrafols
static int[] array = new ...
static long loopStandardArray () {
long result = 0;
int length = array.length;
for(int i = 0; i < length; i++) {
result += array[i];
}
return result;
}
Loops - size cached
12: lload_0
13: getstatic array
16: iload_3
17: iaload
18: i2l
19: ladd
20: lstore_0
21: iinc 3, 1
24: iload_3
25: iload_2
26: if_icmplt 12

103.
@rrafols
Loops - backwards
static int[] array = new ...
static long loopStandardArray () {
long result = 0;
for(int i = array.length - 1; i >= 0; i--) {
result += array[i];
}
return result;
}

104.
@rrafols
static int[] array = new ...
static long loopStandardArray () {
long result = 0;
for(int i = array.length - 1; i >= 0; i--) {
result += array[i];
}
return result;
}
12: lload_0
13: getstatic array
16: iload_2
17: iaload
18: i2l
19: ladd
20: lstore_0
21: iinc 2, -1
24: iload_2
25: ifge 12
Loops - backwards

105.
@rrafols
static int[] array = new ...
static long loopStandardArray () {
long result = 0;
for(int i = array.length - 1; i >= 0; i--) {
result += array[i];
}
return result;
}
Loops - backwards
12: lload_0
13: getstatic array
16: iload_2
17: iaload
18: i2l
19: ladd
20: lstore_0
21: iinc 2, -1
24: iload_2
25: ifge 12

106.
@rrafols

107.
@rrafols

108.
@rrafols
Loops – foreach II
static long loopForeachArray(int[] array) {
long result = 0;
for(int v : array) {
result += v;
}
return result;
}

109.
@rrafols
Loops – foreach II
static long loopForeachArray(int[] array) {
long result = 0;
for(int v : array) {
result += v;
}
return result;
}
00: lconst_0
01: lstore_1
02: aload_0
03: dup
04: astore 6
06: arraylength
07: istore 5
09: iconst_0
10: istore 4
12: goto 29
15: aload 6
17: iload 4
19: iaload
20: istore_3
21: lload_1
22: iload_3
23: i2l
24: ladd
25: lstore_1
26: iinc 4, 1
29: iload 4
31: iload 5
33: if_icmplt 15
0 array 4 -
1 - 5 -
2 - 6 -
3 - 7 -

110.
@rrafols
Loops – foreach II
static long loopForeachArray(int[] array) {
long result = 0;
for(int v : array) {
result += v;
}
return result;
}
00: lconst_0
01: lstore_1
02: aload_0
03: dup
04: astore 6
06: arraylength
07: istore 5
09: iconst_0
10: istore 4
12: goto 29
15: aload 6
17: iload 4
19: iaload
20: istore_3
21: lload_1
22: iload_3
23: i2l
24: ladd
25: lstore_1
26: iinc 4, 1
29: iload 4
31: iload 5
33: if_icmplt 15
0 array 4 -
1 0 (result) 5 -
2 - 6 -
3 - 7 -

111.
@rrafols
Loops – foreach II
static long loopForeachArray(int[] array) {
long result = 0;
for(int v : array) {
result += v;
}
return result;
}
00: lconst_0
01: lstore_1
02: aload_0
03: dup
04: astore 6
06: arraylength
07: istore 5
09: iconst_0
10: istore 4
12: goto 29
15: aload 6
17: iload 4
19: iaload
20: istore_3
21: lload_1
22: iload_3
23: i2l
24: ladd
25: lstore_1
26: iinc 4, 1
29: iload 4
31: iload 5
33: if_icmplt 15
0 array 4 -
1 0 (result) 5 -
2 - 6 array
3 - 7 -

112.
@rrafols
Loops – foreach II
static long loopForeachArray(int[] array) {
long result = 0;
for(int v : array) {
result += v;
}
return result;
}
00: lconst_0
01: lstore_1
02: aload_0
03: dup
04: astore 6
06: arraylength
07: istore 5
09: iconst_0
10: istore 4
12: goto 29
15: aload 6
17: iload 4
19: iaload
20: istore_3
21: lload_1
22: iload_3
23: i2l
24: ladd
25: lstore_1
26: iinc 4, 1
29: iload 4
31: iload 5
33: if_icmplt 15
0 array 4 -
1 0 (result) 5 array.length
2 - 6 array
3 - 7 -

113.
@rrafols
Loops – foreach II
static long loopForeachArray(int[] array) {
long result = 0;
for(int v : array) {
result += v;
}
return result;
}
00: lconst_0
01: lstore_1
02: aload_0
03: dup
04: astore 6
06: arraylength
07: istore 5
09: iconst_0
10: istore 4
12: goto 29
15: aload 6
17: iload 4
19: iaload
20: istore_3
21: lload_1
22: iload_3
23: i2l
24: ladd
25: lstore_1
26: iinc 4, 1
29: iload 4
31: iload 5
33: if_icmplt 15
0 array 4 0 (loop index)
1 0 (result) 5 array.length
2 - 6 array
3 - 7 -

114.
@rrafols
Loops – foreach II
static long loopForeachArray(int[] array) {
long result = 0;
for(int v : array) {
result += v;
}
return result;
}
00: lconst_0
01: lstore_1
02: aload_0
03: dup
04: astore 6
06: arraylength
07: istore 5
09: iconst_0
10: istore 4
12: goto 29
15: aload 6
17: iload 4
19: iaload
20: istore_3
21: lload_1
22: iload_3
23: i2l
24: ladd
25: lstore_1
26: iinc 4, 1
29: iload 4
31: iload 5
33: if_icmplt 15
0 array 4 0 (loop index)
1 0 (result) 5 array.length
2 - 6 array
3 - 7 -

115.
@rrafols
Loops – foreach II
static long loopForeachArray(int[] array) {
long result = 0;
for(int v : array) {
result += v;
}
return result;
}
00: lconst_0
01: lstore_1
02: aload_0
03: dup
04: astore 6
06: arraylength
07: istore 5
09: iconst_0
10: istore 4
12: goto 29
15: aload 6
17: iload 4
19: iaload
20: istore_3
21: lload_1
22: iload_3
23: i2l
24: ladd
25: lstore_1
26: iinc 4, 1
29: iload 4
31: iload 5
33: if_icmplt 15
0 array 4 0 (loop index)
1 0 (result) 5 array.length
2 - 6 array
3 array[index] 7 -

116.
@rrafols
Loops – foreach II
static long loopForeachArray(int[] array) {
long result = 0;
for(int v : array) {
result += v;
}
return result;
}
00: lconst_0
01: lstore_1
02: aload_0
03: dup
04: astore 6
06: arraylength
07: istore 5
09: iconst_0
10: istore 4
12: goto 29
15: aload 6
17: iload 4
19: iaload
20: istore_3
21: lload_1
22: iload_3
23: i2l
24: ladd
25: lstore_1
26: iinc 4, 1
29: iload 4
31: iload 5
33: if_icmplt 15
0 array 4 0 (loop index)
1 0 + array[index] 5 array.length
2 - 6 array
3 array[index] 7 -

117.
@rrafols
Loops – foreach II
static long loopForeachArray(int[] array) {
long result = 0;
for(int v : array) {
result += v;
}
return result;
}
00: lconst_0
01: lstore_1
02: aload_0
03: dup
04: astore 6
06: arraylength
07: istore 5
09: iconst_0
10: istore 4
12: goto 29
15: aload 6
17: iload 4
19: iaload
20: istore_3
21: lload_1
22: iload_3
23: i2l
24: ladd
25: lstore_1
26: iinc 4, 1
29: iload 4
31: iload 5
33: if_icmplt 15
0 array 4 0 (loop index) + 1
1 0 + array[index] 5 array.length
2 - 6 array
3 array[index] 7 -

118.
@rrafols

119.
@rrafols

120.
@rrafols
Loops
Use arrays instead of lists

121.
@rrafols
Loops
When using lists, avoid foreach
or iterator constructions if
performance is a requirement

122.
@rrafols
Manual bytecode
optimization
Worth it?

123.
@rrafols
foreach loop 0: lconst_0
1: lstore_1
2: aload_0
3: dup
4: astore 6
6: arraylength
7: istore 5
9: iconst_0
10: istore 4
12: goto 29
15: aload 6
17: iload 4
19: iaload
20: istore_3
21: lload_1
22: iload_3
23: i2l
24: ladd
25: lstore_1
26: iinc 4, 1
29: iload 4
31: iload 5
33: if_icmplt 15
0: aload_0
1: arraylength
2: istore_3
3: iconst_0
4: istore_1
5: lconst_0
6: goto 17
9: aload_0
10: iload_1
11: iaload
12: i2l
13: ladd
14: iinc 1, 1
17: iload_1
18: iload_3
19: if_icmplt 9
Manual bytecode optimization

124.
@rrafols
Manual bytecode optimization
0: aload_0
1: arraylength
2: istore_3
3: iconst_0
4: istore_1
5: lconst_0
6: goto 17
9: aload_0
10: iload_1
11: iaload
12: i2l
13: ladd
14: iinc 1, 1
17: iload_1
18: iload_3
19: if_icmplt 9
Local variables
0 array 3 -
1 - 4 -
2 - 5 -
Stack
-
-
-

125.
@rrafols
0: aload_0
1: arraylength
2: istore_3
3: iconst_0
4: istore_1
5: lconst_0
6: goto 17
9: aload_0
10: iload_1
11: iaload
12: i2l
13: ladd
14: iinc 1, 1
17: iload_1
18: iload_3
19: if_icmplt 9
Local variables
0 array 3 array.length
1 - 4 -
2 - 5 -
Stack
-
-
-
Manual bytecode optimization

126.
@rrafols
0: aload_0
1: arraylength
2: istore_3
3: iconst_0
4: istore_1
5: lconst_0
6: goto 17
9: aload_0
10: iload_1
11: iaload
12: i2l
13: ladd
14: iinc 1, 1
17: iload_1
18: iload_3
19: if_icmplt 9
Local variables
0 array 3 array.length
1 0 (index) 4 -
2 - 5 -
Stack
-
-
-
Manual bytecode optimization

127.
@rrafols
0: aload_0
1: arraylength
2: istore_3
3: iconst_0
4: istore_1
5: lconst_0
6: goto 17
9: aload_0
10: iload_1
11: iaload
12: i2l
13: ladd
14: iinc 1, 1
17: iload_1
18: iload_3
19: if_icmplt 9
Local variables
0 array 3 array.length
1 0 (index) 4 -
2 - 5 -
Stack
0 (result)
-
-
Manual bytecode optimization

128.
@rrafols
0: aload_0
1: arraylength
2: istore_3
3: iconst_0
4: istore_1
5: lconst_0
6: goto 17
9: aload_0
10: iload_1
11: iaload
12: i2l
13: ladd
14: iinc 1, 1
17: iload_1
18: iload_3
19: if_icmplt 9
Local variables
0 array 3 array.length
1 0 (index) 4 -
2 - 5 -
Stack
0 (result)
array[index]
-
Manual bytecode optimization

129.
@rrafols
0: aload_0
1: arraylength
2: istore_3
3: iconst_0
4: istore_1
5: lconst_0
6: goto 17
9: aload_0
10: iload_1
11: iaload
12: i2l
13: ladd
14: iinc 1, 1
17: iload_1
18: iload_3
19: if_icmplt 9
Local variables
0 array 3 array.length
1 0 (index) 4 -
2 - 5 -
Stack
0 + array[index]
-
-
Manual bytecode optimization

130.
@rrafols
0: aload_0
1: arraylength
2: istore_3
3: iconst_0
4: istore_1
5: lconst_0
6: goto 17
9: aload_0
10: iload_1
11: iaload
12: i2l
13: ladd
14: iinc 1, 1
17: iload_1
18: iload_3
19: if_icmplt 9
Local variables
0 array 3 array.length
1 0 (index) + 1 4 -
2 - 5 -
Stack
0 + array[index]
-
-
Manual bytecode optimization

131.
@rrafols

132.
@rrafols
Worth it?
Only in very specific, rare, unique,
special, peculiar cases.
Too much effort involved.

133.
@rrafols
Calling a method
Is there an overhead?

134.
@rrafols
Overhead of calling a method
for(int i = 0; i < N; i++) {
setVal(getVal() + 1);
}
for(int i = 0; i < N; i++) {
val = val + 1;
}
vs

135.
@rrafols

136.
@rrafols
String concatenation
The evil + sign

137.
@rrafols
String concatenation
String str = "";
for(int i = 0; i < N; i++) {
str += OTHER_STR;
}

138.
@rrafols
String concatenation
String str = "";
for(int i = 0; i < N; i++) {
str += OTHER_STR;
}
0: ldc String
2: astore_1
3: iconst_0
4: istore_2
5: iload_2
6: sipush N
9: if_icmpge 40
12: new class java/lang/StringBuilder
15: dup
16: invokespecial java/lang/StringBuilder."<init>"
19: aload_1
20: invokevirtual java/lang/StringBuilder.append
23: aload_0
24: getfield OTHER_STR
27: invokevirtual java/lang/StringBuilder.append
30: invokevirtual java/lang/StringBuilder.toString
33: astore_1
34: iinc 2, 1
37: goto 5

139.
@rrafols
String concatenation
String str = "";
for(int i = 0; i < N; i++) {
str += OTHER_STR;
}
0: ldc String
2: astore_1
3: iconst_0
4: istore_2
5: iload_2
6: sipush N
9: if_icmpge 40
12: new class java/lang/StringBuilder
15: dup
16: invokespecial java/lang/StringBuilder."<init>"
19: aload_1
20: invokevirtual java/lang/StringBuilder.append
23: aload_0
24: getfield OTHER_STR
27: invokevirtual java/lang/StringBuilder.append
30: invokevirtual java/lang/StringBuilder.toString
33: astore_1
34: iinc 2, 1
37: goto 5

140.
@rrafols
String concatenation
String str = "";
for(int i = 0; i < N; i++) {
str += OTHER_STR;
}
0: ldc String
2: astore_1
3: iconst_0
4: istore_2
5: iload_2
6: sipush N
9: if_icmpge 40
12: new class java/lang/StringBuilder
15: dup
16: invokespecial java/lang/StringBuilder."<init>"
19: aload_1
20: invokevirtual java/lang/StringBuilder.append
23: aload_0
24: getfield OTHER_STR
27: invokevirtual java/lang/StringBuilder.append
30: invokevirtual java/lang/StringBuilder.toString
33: astore_1
34: iinc 2, 1
37: goto 5

141.
@rrafols
String concatenation
String str = "";
for(int i = 0; i < N; i++) {
str += OTHER_STR;
}
0: ldc String
2: astore_1
3: iconst_0
4: istore_2
5: iload_2
6: sipush N
9: if_icmpge 40
12: new class java/lang/StringBuilder
15: dup
16: invokespecial java/lang/StringBuilder."<init>"
19: aload_1
20: invokevirtual java/lang/StringBuilder.append
23: aload_0
24: getfield OTHER_STR
27: invokevirtual java/lang/StringBuilder.append
30: invokevirtual java/lang/StringBuilder.toString
33: astore_1
34: iinc 2, 1
37: goto 5

142.
@rrafols
String concatenation
String str = "";
for(int i = 0; i < N; i++) {
str += OTHER_STR;
}
0: ldc String
2: astore_1
3: iconst_0
4: istore_2
5: iload_2
6: sipush N
9: if_icmpge 40
12: new class java/lang/StringBuilder
15: dup
16: invokespecial java/lang/StringBuilder."<init>"
19: aload_1
20: invokevirtual java/lang/StringBuilder.append
23: aload_0
24: getfield OTHER_STR
27: invokevirtual java/lang/StringBuilder.append
30: invokevirtual java/lang/StringBuilder.toString
33: astore_1
34: iinc 2, 1
37: goto 5

143.
@rrafols
String concatenation
String str = "";
for(int i = 0; i < N; i++) {
str += OTHER_STR;
}
0: ldc String
2: astore_1
3: iconst_0
4: istore_2
5: iload_2
6: sipush N
9: if_icmpge 40
12: new class java/lang/StringBuilder
15: dup
16: invokespecial java/lang/StringBuilder."<init>"
19: aload_1
20: invokevirtual java/lang/StringBuilder.append
23: aload_0
24: getfield OTHER_STR
27: invokevirtual java/lang/StringBuilder.append
30: invokevirtual java/lang/StringBuilder.toString
33: astore_1
34: iinc 2, 1
37: goto 5

144.
@rrafols
String str = "";
for(int i = 0; i < N; i++) {
StringBuilder sb = new StringBuilder();
sb.append(str);
sb.append(OTHER_STR);
str = sb.toString();
}
String concatenation

145.
@rrafols
Object creation:
String str = "";
for(int i = 0; i < N; i++) {
StringBuilder sb = new StringBuilder();
sb.append(str);
sb.append(OTHER_STR);
str = sb.toString();
}
String concatenation

146.
@rrafols
String concatenation
alternatives

147.
@rrafols
String.concat()
• Concat cost is O(N) + O(M)
• Concat returns a new String Object.
String str = "";
for(int i = 0; i < N; i++) {
str = str.concat(OTHER_STR);
}

148.
@rrafols
String.concat()
Object creation:
String str = "";
for(int i = 0; i < N; i++) {
str = str.concat(OTHER_STR);
}

149.
@rrafols
StringBuilder
• StringBuilder.append cost is O(M) [M being the
length of appended String]
StringBuilder sb = new StringBuilder()
for(int i = 0; i < N; i++) {
sb.append(OTHER_STR);
}
str = sb.toString();

150.
@rrafols
StringBuilder
sb = new StringBuilder()
for(int i = 0; i < N; i++) {
sb.append(OTHER_STR);
}
str = sb.toString();
0: ldc String
2: astore_1
3: new java/lang/StringBuilder
6: dup
7: invokespecial java/lang/StringBuilder."<init>"
10: astore_2
11: iconst_0
12: istore_3
13: iload_3
14: sipush N
17: if_icmpge 35
20: aload_2
21: aload_0
22: getfield OTHER_STR
25: invokevirtual java/lang/StringBuilder.append
28: pop
29: iinc 3, 1
32: goto 13

151.
@rrafols
0: ldc String
2: astore_1
3: new java/lang/StringBuilder
6: dup
7: invokespecial java/lang/StringBuilder."<init>"
10: astore_2
11: iconst_0
12: istore_3
13: iload_3
14: sipush N
17: if_icmpge 35
20: aload_2
21: aload_0
22: getfield OTHER_STR
25: invokevirtual java/lang/StringBuilder.append
28: pop
29: iinc 3, 1
32: goto 13
sb = new StringBuilder()
for(int i = 0; i < N; i++) {
sb.append(OTHER_STR);
}
str = sb.toString();
StringBuilder

152.
@rrafols
Object creation:
StringBuilder sb = new StringBuilder();
for(int i = 0; i < N; i++) {
sb.append(OTHER_STR);
}
str = sb.toString();
StringBuilder

153.
@rrafols
String concatenation
Use StringBuilder (properly) as
much as possible. StringBuffer
is the thread safe
implementation.

154.
@rrafols
Strings in case statements

155.
@rrafols
public void taskStateMachine(String status) {
switch(status) {
case "PENDING":
System.out.println("Status pending");
break;
case "EXECUTING":
System.out.println("Status executing");
break;
}
}

156.
@rrafols

157.
@rrafols

158.
@rrafols
Tooling

159.
@rrafols
Tooling - Disassembler
Java
• javap -c <classfile>
Android:
•Dexdump -d <dexfile>

160.
@rrafols
Tooling - Assembler
Krakatau
https://github.com/Storyyeller/Krakatau

161.
@rrafols
Tooling – Disassembler - ART
adb pull /data/dalvik-
cache/arm/data@app@<package>-1@base
apk@classes.dex
gobjdump -D <file>

162.
@rrafols
Tooling – Disassembler - ART
adb shell oatdump --oat-file=/data/dalvik-
cache/arm/data@app@<package>-
1@base.apk@classes.dex

163.
@rrafols
Tooling – PrintAssembly - JIT
-XX:+UnlockDiagnosticVMOptions
-XX:+PrintAssembly
-XX:CompileCommand=print,com.raimon.test.Test::method
Under the Hood of the JVM: From Bytecode Through the JIT
to Assembly
http://alblue.bandlem.com/2016/09/javaone-hotspot.html

164.
@rrafols
Always measure
example - yuv2rgb
optimization

165.
@rrafols
Source: Wikipedia

166.
@rrafols

167.
@rrafols
Slightly optimized version
precalc tables, fixed point
operations, 2 pixels per loop…

168.
@rrafols

169.
@rrafols

170.
@rrafols
Lets compare:
Normal, minified, minified
with optimizations & jack
Minified = obfuscated using Proguard

171.
@rrafols
Normal Minified Minified & optimized Jack
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
non-optimized
optimized

172.
@rrafols
Performance measurements
Avoid doing multiple tests in one run
JIT might be evil!

173.
@rrafols
Thank you!
http://blog.rafols.org
@rrafols
https://es.linkedin.com/in/raimonrafols