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@rrafols
the bytecode
mumbo-jumbo
#perfmatters
@rrafols
Disclaimer:
This presentation contains
bytecode
Content is my own experimentation and
might differ on other environments
@rrafols
Competitions
Work
2015 Local winner
2016+ Ambassador
Runner up
Demoscene
Speaker
Author Entrepreneurship
@rrafols
Our friend the java
compiler.
@rrafols
*.java → [javac] → *.class
@rrafols
Or, for example, on
Android
@rrafols
*.java → [javac] → *.class
*.class → [dx] → dex file
@rrafols
*.java → [javac] → *.class
*.class → [dx] → dex
dex → [dexopt] → opt. dex
dex → [dex2oat] → native
@rrafols
but change is coming!
Jack & Jill
@rrafols
but change is coming!
Jack & Jill
@rrafols
*.java → [jack] → dex file
@rrafols
Let’s focus on javac
Javac vs other compilers
@rrafols
Compilers
Produces optimized code
for the target platform
@rrafols
javac
Does not produce
optimized code*
@rrafols
javac
Does not know on which
architecture the code will
be executed
@rrafols
Source: Oracle
@rrafols
For this reason
Java bytecode &
operations are stack
based
@rrafols
Easy to interpret
But not the most
performant solution
@rrafols
Quick example
Stack based integer
addition
@rrafols
j = j + i
@rrafols
Java bytecode
@rrafols
iload_3
iload_2
iadd
istore_2
@rrafols
Register based approach
@rrafols
add r01, r02, r01
or
add eax, ebx
@rrafols
Let’s make things
interesting…
j = j + i + k + w + h * 2 + p * p;
@rrafols
Java bytecode
@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
@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
@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
@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
@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
@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
@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
@rrafols
Register based approach
@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
@rrafols
Java VM (JVM)
Only the JVM knows the
architecture where is running.
In this case, for example, we used up to
8 registers
@rrafols
Java VM (JVM)
All optimizations are left to
be done by the JVM
@rrafols
Maybe takes this concept
a bit too far...
@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);
}
@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
@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
...
@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);
}
@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
@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
@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);
}
@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);
}
@rrafols
On Android there is jack
to the rescue...
@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
...
@rrafols
And on Java there is the
JIT compiler to the rescue
@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
@rrafols
Language additions
Thinks to consider
@rrafols
Autoboxing
Transparent to the developer
but compiler adds some
'extra' code
@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
@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
@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
@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:
@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
@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
@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
@rrafols
Autoboxing
Long total = 0;
for(Integer i = 0; i < N; i++) {
total += i;
}
@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
@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
@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
@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
@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
@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
@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
@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
@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())
}
@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())
}
@rrafols
Autoboxing
What about Jack?
@rrafols
Autoboxing
Jack does not help in this
situation
@rrafols
Autoboxing
What about the JIT compiler?
@rrafols
Autoboxing
Let's run that loop
N times
(on my desktop computer)
N = 10.000.000.000
@rrafols
Autoboxing
@rrafols
Autoboxing
Let’s try it on Android
Dalvik VM & ART
@rrafols
Autoboxing
@rrafols
Language Additions
Use them wisely!
@rrafols
Sorting
No bytecode mumbo-jumbo
here
@rrafols
Let's sort some numbers…
Arrays.sort(...)
@rrafols
Difference between sorting
primitive types & objects
@rrafols
Using int & Integer
@rrafols
Sorting objects is a stable
sort
Default java algorithm:
TimSort adaptation
@rrafols
Sorting primitives does not
require to be stable sort
Default java algorithm:
Dual-Pivot quicksort
@rrafols
Sorting
Use primitive types as much
as possible
@rrafols
Loops
What is going on behind the
scenes
@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;
}
@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
@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
@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
@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
@rrafols
Loops - foreach
ArrayList<Integer> list = new …
static long loopForeachList() {
long result = 0;
for(int v : list) {
result += v;
}
return result;
}
@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
@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
@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
@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;
}
@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
@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
@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
@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;
}
@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
@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
@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;
}
@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
@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
@rrafols
@rrafols
@rrafols
Loops – foreach II
static long loopForeachArray(int[] array) {
long result = 0;
for(int v : array) {
result += v;
}
return result;
}
@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 -
@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 -
@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 -
@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 -
@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 -
@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 -
@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 -
@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 -
@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 -
@rrafols
@rrafols
@rrafols
Loops
Use arrays instead of lists
@rrafols
Loops
When using lists, avoid foreach
or iterator constructions if
performance is a requirement
@rrafols
Manual bytecode
optimization
Worth it?
@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
@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
-
-
-
@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
@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
@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
@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
@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
@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
@rrafols
@rrafols
Worth it?
Only in very specific, rare, unique,
special, peculiar cases.
Too much effort involved.
@rrafols
Calling a method
Is there an overhead?
@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
@rrafols
@rrafols
String concatenation
The evil + sign
@rrafols
String concatenation
String str = "";
for(int i = 0; i < N; i++) {
str += OTHER_STR;
}
@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
@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
@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
@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
@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
@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
@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
@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
@rrafols
String concatenation
alternatives
@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);
}
@rrafols
String.concat()
Object creation:
String str = "";
for(int i = 0; i < N; i++) {
str = str.concat(OTHER_STR);
}
@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();
@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
@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
@rrafols
Object creation:
StringBuilder sb = new StringBuilder();
for(int i = 0; i < N; i++) {
sb.append(OTHER_STR);
}
str = sb.toString();
StringBuilder
@rrafols
String concatenation
Use StringBuilder (properly) as
much as possible. StringBuffer
is the thread safe
implementation.
@rrafols
Strings in case statements
@rrafols
public void taskStateMachine(String status) {
switch(status) {
case "PENDING":
System.out.println("Status pending");
break;
case "EXECUTING":
System.out.println("Status executing");
break;
}
}
@rrafols
@rrafols
@rrafols
Tooling
@rrafols
Tooling - Disassembler
Java
• javap -c <classfile>
Android:
•Dexdump -d <dexfile>
@rrafols
Tooling - Assembler
Krakatau
https://github.com/Storyyeller/Krakatau
@rrafols
Tooling – Disassembler - ART
adb pull /data/dalvik-
cache/arm/data@app@<package>-1@base
apk@classes.dex
gobjdump -D <file>
@rrafols
Tooling – Disassembler - ART
adb shell oatdump --oat-file=/data/dalvik-
cache/arm/data@app@<package>-
1@base.apk@classes.dex
@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
@rrafols
Always measure
example - yuv2rgb
optimization
@rrafols
Source: Wikipedia
@rrafols
@rrafols
Slightly optimized version
precalc tables, fixed point
operations, 2 pixels per loop…
@rrafols
@rrafols
@rrafols
Lets compare:
Normal, minified, minified
with optimizations & jack
Minified = obfuscated using Proguard
@rrafols
Normal Minified Minified & optimized Jack
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
non-optimized
optimized
@rrafols
Performance measurements
Avoid doing multiple tests in one run
JIT might be evil!
@rrafols
Thank you!
http://blog.rafols.org
@rrafols
https://es.linkedin.com/in/raimonrafols

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The bytecode mumbo-jumbo

  • 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.
  • 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
  • 12. @rrafols Let’s focus on javac Javac vs other compilers
  • 15. @rrafols javac Does not know on which architecture the code will be executed
  • 17. @rrafols For this reason Java bytecode & operations are stack based
  • 18. @rrafols Easy to interpret But not the most performant solution
  • 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;
  • 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
  • 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
  • 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()) }
  • 72. @rrafols Autoboxing Jack does not help in this situation
  • 74. @rrafols Autoboxing Let's run that loop N times (on my desktop computer) N = 10.000.000.000
  • 76. @rrafols Autoboxing Let’s try it on Android Dalvik VM & ART
  • 80. @rrafols Let's sort some numbers… Arrays.sort(...)
  • 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
  • 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
  • 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 -
  • 121. @rrafols Loops When using lists, avoid foreach or iterator constructions if performance is a requirement
  • 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
  • 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
  • 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
  • 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.
  • 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; } }
  • 159. @rrafols Tooling - Disassembler Java • javap -c <classfile> Android: •Dexdump -d <dexfile>
  • 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
  • 167. @rrafols Slightly optimized version precalc tables, fixed point operations, 2 pixels per loop…
  • 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!