The bytecode hocus pocus - JavaOne 2016

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@rrafols The bytecode hocus-pocus #perfmatters

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@rrafols Disclaimer This presentation containsbytecode Content is my own experimentation and might differ on other environments

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@rrafols Competitions Work 2015 Local winner 2016Ambassador Runner up Demoscene Speaker Author Entrerpreneurship About me

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@rrafols Our friend thejava compiler

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@rrafols *.java → [javac]→ *.class

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@rrafols Or, for example,on Android

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

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

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@rrafols but change iscoming! Jack & Jill

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@rrafols *.java → [jack]→ dex file

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@rrafols Let’s focus onjavac Javac vs other compilers

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@rrafols Compilers Produces optimized codefor the target platform

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@rrafols Javac Does not produceoptimized code*

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@rrafols Javac Does not knowon which architecture the code will be executed

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@rrafols Source: Oracle

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@rrafols For this reason Javabytecode & operations are stack based

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@rrafols Easy to interpret Butnot the most optimal solution (regarding performance)

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@rrafols Quick example Stack basedinteger addition

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@rrafols j = j+ i

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@rrafols Java bytecode

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@rrafols iload_3 iload_2 iadd istore_2

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@rrafols Register based approach

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

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@rrafols Let’s make thingsinteresting… j = j + i + k + w + h * 2 + p * p;

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@rrafols Java bytecode

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@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

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@rrafols Register based approach

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@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

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@rrafols Java VM (JVM) Onlythe JVM knows on which architecture is running. In this case, for example, we used up to 8 registers

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@rrafols Java VM (JVM) Alloptimizations are left to be done by the JVM

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@rrafols Maybe takes thisconcept a bit too far...

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

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@rrafols GCC compiler #include <stdio.h> intmain() { 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

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@rrafols javac public static voidmain(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 ...

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

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@rrafols GCC compiler #include <stdio.h> intmain() { 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

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@rrafols javac public static voidmain(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 ...

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

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@rrafols javac public static voidmain(String args[]) { int a = 10; int b = a + 1 + 2 + 3 + 4 + 5 + 6; System.out.println(b); } 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

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@rrafols On Android thereis jack to the rescue...

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@rrafols jack public static voidmain(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 ...

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@rrafols And on Javathere is the JIT compiler to the rescue

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@rrafols JIT assembly output publicstatic void main(String args[]) { int a = 10; int b = a + 1 + 2 + 3 + 4 + 5 + 6; System.out.println(b); } ... 0x00000001104b2bff: mov eax, 0x000000000000001f ... 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

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@rrafols Compilers Produces optimised codefor target platform

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@rrafols Language additions Thinks toconsider

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@rrafols Autoboxing Transparent to thedeveloper but compiler adds some 'extra' code

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@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

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@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:

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

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@rrafols Autoboxing Long total =0; for(Integer i = 0; i < N; i++) { total += i; } 0: lconst_0 1: invokestatic #7 // Method java/lang/Long.valueOf:(J)Ljava/ 4: astore_1 5: iconst_0 6: invokestatic #8 // Method java/lang/Integer.valueOf:(I)Ljav 9: astore_2 10: aload_2 11: invokevirtual #9 // Method java/lang/Integer.intValue:()I 14: sipush N 17: if_icmpge 54 20: aload_1 21: invokevirtual #10 // Method java/lang/Long.longValue:()J 24: aload_2 25: invokevirtual #9 // Method java/lang/Integer.intValue:()I 28: i2l 29: ladd 30: invokestatic #7 // Method java/lang/Long.valueOf:(J)Ljava 33: astore_1 34: aload_2 35: astore_3 36: aload_2 37: invokevirtual #9 // Method java/lang/Integer.intValue:()I 40: iconst_1 41: iadd 42: invokestatic #8 // Method java/lang/Integer.valueOf:(I)Lja 45: dup 46: astore_2 47: astore 4 49: aload_3 50: pop 51: goto 10

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@rrafols Autoboxing Long total =0; for(Integer i = 0; i < N; i++) { total += i; } // ? 0: lconst_0 1: invokestatic #7 // Method java/lang/Long.valueOf:(J)Ljava/ 4: astore_1 5: iconst_0 6: invokestatic #8 // Method java/lang/Integer.valueOf:(I)Ljav 9: astore_2 10: aload_2 11: invokevirtual #9 // Method java/lang/Integer.intValue:()I 14: sipush N 17: if_icmpge 54 20: aload_1 21: invokevirtual #10 // Method java/lang/Long.longValue:()J 24: aload_2 25: invokevirtual #9 // Method java/lang/Integer.intValue:()I 28: i2l 29: ladd 30: invokestatic #7 // Method java/lang/Long.valueOf:(J)Ljava 33: astore_1 34: aload_2 35: astore_3 36: aload_2 37: invokevirtual #9 // Method java/lang/Integer.intValue:()I 40: iconst_1 41: iadd 42: invokestatic #8 // Method java/lang/Integer.valueOf:(I)Lja 45: dup 46: astore_2 47: astore 4 49: aload_3 50: pop 51: goto 10

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@rrafols Autoboxing This is whatthat 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()) }

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@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()) }

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@rrafols Autoboxing What about Jack?

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@rrafols Autoboxing Jack does nothelp in this situation

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@rrafols Autoboxing What about theJIT compiler?

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@rrafols Autoboxing Let's run thatloop 10.000.000.000 times (on my desktop computer)

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@rrafols Autoboxing

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@rrafols Autoboxing Let's run thatloop 100.000.000 Times on two Nexus 5 KitKat (Dalvik VM) & Lollipop (ART)

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@rrafols Autoboxing

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@rrafols Language Additions Use themwisely!

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@rrafols Sorting No bytecode mumbo-jumbohere

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@rrafols Let's sort somenumbers… Arrays.sort(...)

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@rrafols Difference between sorting primitivetypes & objects

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@rrafols Using int &Integer

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@rrafols Sorting objects isa stable sort Default java algorithm: TimSort adaptation

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@rrafols Sorting primitives doesnot require to be stable sort Default java algorithm: Dual-Pivot quicksort

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@rrafols Sorting Use primitive typesas much as possible

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@rrafols Loops

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@rrafols Loops What is goingon behind the scenes

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@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; }

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@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; } 7: lload_0 8: getstatic #26 // Field list:Ljava/util/ArrayList; 11: iload_2 12: invokevirtual #54 // Method java/util/ArrayList.get:(I) 15: checkcast #38 // class java/lang/Integer 18: invokevirtual #58 // Method java/lang/Integer.intValue:()I 21: i2l 22: ladd 23: lstore_0 24: iinc 2, 1 27: iload_2 28: getstatic #26 // Field list:Ljava/util/ArrayList; 31: invokevirtual #61 // Method java/util/ArrayList.size:()I 34: if_icmplt 7

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

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@rrafols Loops - foreach ArrayList<Integer>list = new … static long loopForeachList() { long result = 0; for(int v : list) { result += v; } return result; } 12: aload_3 13: invokeinterface #70, 1 // java/util/Iterator.next:() 18: checkcast #38 // class java/lang/Integer 21: invokevirtual #58 // Method 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 #76, 1 // java/util/Iterator.hasNext:()Z 36: ifne 12

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@rrafols Loops - foreach ArrayList<Integer>list = new … static long loopForeachList() { long result = 0; for(int v : list) { result += v; } return result; } 12: aload_3 13: invokeinterface #70, 1 // java/util/Iterator.next:() 18: checkcast #38 // class java/lang/Integer 21: invokevirtual #58 // Method java/lang/Integer.intValue:()I 24: istore_2 25: lload_0 26: iload_2 27: i2l 28: ladd 29: lstore_0 30: aload_3 31: invokeinterface #76, 1 // java/util/Iterator.hasNext:()Z 36: ifne 12

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@rrafols Loops - foreach ArrayList<Integer>list = new … static long loopForeachList() { long result = 0; for(int v : list) { result += v; } return result; } 12: aload_3 13: invokeinterface #70, 1 // java/util/Iterator.next:() 18: checkcast #38 // class java/lang/Integer 21: invokevirtual #58 // Method java/lang/Integer.intValue:()I 24: istore_2 25: lload_0 26: iload_2 27: i2l 28: ladd 29: lstore_0 30: aload_3 31: invokeinterface #76, 1 // java/util/Iterator.hasNext:()Z 36: ifne 12

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

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@rrafols Loops - Array staticint[] array = new ... static long loopStandardArray() { long result = 0; for(int i = 0; i < array.length; i++) { result += array[i]; } return result; } 7: lload_0 8: getstatic #28 // Field array:[I 11: iload_2 12: iaload 13: i2l 14: ladd 15: lstore_0 16: iinc 2, 1 19: iload_2 20: getstatic #28 // Field array:[I 23: arraylength 24: if_icmplt 7

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@rrafols Loops - sizecached 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; }

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@rrafols Loops - sizecached 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 #28 // Field array:[I 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

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@rrafols Loops - sizecached 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 #28 // Field array:[I 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

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

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@rrafols Loops - backwards staticint[] 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 #28 // Field array:[I 16: iload_2 17: iaload 18: i2l 19: ladd 20: lstore_0 21: iinc 2, -1 24: iload_2 25: ifge 12

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@rrafols Loops - backwards staticint[] 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 #28 // Field array:[I 16: iload_2 17: iaload 18: i2l 19: ladd 20: lstore_0 21: iinc 2, -1 24: iload_2 25: ifge 12

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@rrafols

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@rrafols

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

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@rrafols Loops – foreachII static long loopForeachArray(int[] array) { long result = 0; for(int v : array) { result += v; } return result; } 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 array 4 - 1 - 5 - 2 - 6 - 3 - 7 -

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@rrafols Loops – foreachII static long loopForeachArray(int[] array) { long result = 0; for(int v : array) { result += v; } return result; } 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 array 4 - 1 0 (result) 5 - 2 - 6 - 3 - 7 -

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@rrafols Loops – foreachII static long loopForeachArray(int[] array) { long result = 0; for(int v : array) { result += v; } return result; } 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 array 4 - 1 0 (result) 5 - 2 - 6 array 3 - 7 -

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@rrafols Loops – foreachII static long loopForeachArray(int[] array) { long result = 0; for(int v : array) { result += v; } return result; } 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 array 4 - 1 0 (result) 5 array.length 2 - 6 array 3 - 7 -

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@rrafols Loops – foreachII static long loopForeachArray(int[] array) { long result = 0; for(int v : array) { result += v; } return result; } 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 array 4 0 (loop index) 1 0 (result) 5 array.length 2 - 6 array 3 - 7 -

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@rrafols Loops – foreachII static long loopForeachArray(int[] array) { long result = 0; for(int v : array) { result += v; } return result; } 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 array 4 0 (loop index) 1 0 (result) 5 array.length 2 - 6 array 3 - 7 -

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@rrafols Loops – foreachII static long loopForeachArray(int[] array) { long result = 0; for(int v : array) { result += v; } return result; } 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 array 4 0 (loop index) 1 0 (result) 5 array.length 2 - 6 array 3 array[index] 7 -

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@rrafols Loops – foreachII static long loopForeachArray(int[] array) { long result = 0; for(int v : array) { result += v; } return result; } 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 array 4 0 (loop index) 1 0 + array[index] 5 array.length 2 - 6 array 3 array[index] 7 -

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@rrafols Loops – foreachII static long loopForeachArray(int[] array) { long result = 0; for(int v : array) { result += v; } return result; } 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 array 4 0 (loop index) + 1 1 0 + array[index] 5 array.length 2 - 6 array 3 array[index] 7 -

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@rrafols

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@rrafols

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@rrafols Loops Use arrays insteadof lists

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

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@rrafols Manual bytecode optimization Worthit?

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@rrafols Loops – foreachII 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

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@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 - - -

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@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 array.length 1 - 4 - 2 - 5 - Stack - - -

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@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 array.length 1 0 (index) 4 - 2 - 5 - Stack - - -

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@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 array.length 1 0 (index) 4 - 2 - 5 - Stack 0 (result) - -

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@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 array.length 1 0 (index) 4 - 2 - 5 - Stack 0 (result) array[index] -

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@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 array.length 1 0 (index) 4 - 2 - 5 - Stack 0 + array[index] - -

131.
@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 array.length 1 0 (index) + 1 4 - 2 - 5 - Stack 0 + array[index] - -

132.
@rrafols *reduced dataset

133.
@rrafols Worth it? Only invery specific, unique, peculiar cases. Too much effort involved.

134.
@rrafols Calling a method Isthere an overhead?

135.
@rrafols Overhead of callinga method for(int i = 0; i < N; i++) { setVal(getVal() + 1); } for(int i = 0; i < N; i++) { val = val + 1; } vs

136.
@rrafols

137.
@rrafols String concatenation The evil+ sign

138.
@rrafols String concatenation String str= ""; for(int i = 0; i < N; i++) { str += OTHER_STR; }

139.
@rrafols String concatenation String str= ""; for(int i = 0; i < N; i++) { str += OTHER_STR; } 0: ldc #13 // String 2: astore_1 3: iconst_0 4: istore_2 5: iload_2 6: sipush N 9: if_icmpge 40 12: new #14 // class java/lang/StringBuilder 15: dup 16: invokespecial #15 // Method java/lang/StringBuilder."<init>":()V 19: aload_1 20: invokevirtual #16 // Method java/lang/StringBuilder.append:(Ljava/lang/S 23: aload_0 24: getfield #3 // Field OTHER_STR:Ljava/lang/String; 27: invokevirtual #16 // Method java/lang/StringBuilder.append:(Ljava/lang/S 30: invokevirtual #17 // Method java/lang/StringBuilder.toString:()Ljava/lan 33: astore_1 34: iinc 2, 1 37: goto 5

140.

141.

142.

143.

144.

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

146.
@rrafols String concatenation Object creation: Stringstr = ""; for(int i = 0; i < N; i++) { StringBuilder sb = new StringBuilder(); sb.append(str); sb.append(OTHER_STR); str = sb.toString(); }

147.
@rrafols String concatenation alternatives

148.
@rrafols String.concat() • Concat costis O(N) + O(M) • Concat returns a new String Object. String str = ""; for(int i = 0; i < N; i++) { str = str.concat(OTHER_STR); }

149.
@rrafols String.concat() Object creation: String str= ""; for(int i = 0; i < N; i++) { str = str.concat(OTHER_STR); }

150.
@rrafols StringBuilder • StringBuilder.append costis 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();

151.
@rrafols StringBuilder StringBuilder sb =new StringBuilder() for(int i = 0; i < N; i++) { sb.append(OTHER_STR); } str = sb.toString(); 0: ldc #13 // String 2: astore_1 3: new #14 // class java/lang/StringBuilder 6: dup 7: invokespecial #15 // Method java/lang/StringBuilder."<i 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 #3 // Field OTHER_STR:Ljava/lang/String; 25: invokevirtual #16 // Method java/lang/StringBuilder.ap 28: pop 29: iinc 3, 1 32: goto 13

152.
@rrafols StringBuilder StringBuilder sb =new StringBuilder() for(int i = 0; i < N; i++) { sb.append(OTHER_STR); } str = sb.toString(); 0: ldc #13 // String 2: astore_1 3: new #14 // class java/lang/StringBuilder 6: dup 7: invokespecial #15 // Method java/lang/StringBuilder."<i 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 #3 // Field OTHER_STR:Ljava/lang/String; 25: invokevirtual #16 // Method java/lang/StringBuilder.ap 28: pop 29: iinc 3, 1 32: goto 13

153.
@rrafols StringBuilder Object creation: StringBuilder sb= new StringBuilder(); for(int i = 0; i < N; i++) { sb.append(OTHER_STR); } str = sb.toString();

154.
@rrafols String concatenation Use StringBuilder(properly) as much as possible. StringBuffer is the thread safe implementation.

155.
@rrafols Strings in casestatements

156.
@rrafols public void taskStateMachine(Stringstatus) { switch(status) { case "PENDING": System.out.println("Status pending"); break; case "EXECUTING": System.out.println("Status executing"); break; } }

157.
@rrafols

158.
@rrafols

159.
@rrafols Tooling

160.
@rrafols Tooling - Disassembler Java •javap -c <classfile> Android: •Dexdump -d <dexfile>

161.
@rrafols Tooling - Assembler Krakatau https://github.com/Storyyeller/Krakatau

162.
@rrafols Tooling – Disassembler- ART adb pull /data/dalvik- cache/arm/data@app@<package>-1@base apk@classes.dex gobjdump -D <file>

163.
@rrafols Tooling – Disassembler- ART adb shell oatdump --oat-file=/data/dalvik- cache/arm/data@app@<package>-1@base. apk@classes.dex

164.
@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 [CON3808] http://alblue.bandlem.com/2016/09/javaone-hotspot.html

165.
@rrafols Always measure example -yuv2rgb optimization

166.
@rrafols Source: Wikipedia

167.
@rrafols

168.
@rrafols Slightly optimized version precalctables, fixed point operations, 2 pixels per loop…

169.
@rrafols

170.
@rrafols

171.
@rrafols Lets compare: Normal, minified,minified with optimizations & jack Minified = obfuscated using Proguard

172.
@rrafols Normal Minified Minified& optimized Jack 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 non-optimized optimized

173.
@rrafols Performance measurements Avoid doingmultiple tests in one run JIT might be evil!

174.
@rrafols Thank you! http://blog.rafols.org @rrafols https://es.linkedin.com/in/raimonrafols

The bytecode hocus pocus - JavaOne 2016

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The bytecode hocus pocus - JavaOne 2016