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Unused array of primitives: what does javac and the JIT compiler do?

Suppose I have a method that declares an array of primitives but does not use it:

public void frobnicate() {
    int[] pointless = new int[1000];
    System.out.println("bored");
}

What will happen to my array pointless? I think javac will save it (although I'm not sure). If so, what will the JIT compiler do? Will he completely get rid of this? Will it create an array but not reference it?

There is troubled waters. It is not quite the same as unused

int pointless = 23;

which can be easily removed. An instance of the object is created with the array, and it is also nullified. Can the JIT compiler overcome all this? Or will everything be done?

The motivation for this, by the way, is that I am writing a benchmark that examines the effect of different buffer sizes. I would like to remove the effect of allocating space for different buffer sizes. Internally, the buffer is equal to everything byte[]; therefore, the easiest way to remove the effect of memory allocation is to run the method by creating an unused array, so that the total amount allocated will be the same in each case. In other words, if the maximum buffer size that I will test is 4 MB, then when I test the buffer 1 MB, I start by creating an unused one byte[3*1024*1024], so the total allocation is still 4 MB. (I am willing to ignore a few bytes of extra overhead, which should be negligible.)

, , , JIT...

+4
2

Java- . - frobincate , javac (OpenJDK 7) ...

Compiled from "Frobincate.java"
public class Frobincate {
  public Frobincate();
    Code:
       0: aload_0       
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return        

  public static void frobincate();
    Code:
       0: sipush        1000
       3: newarray       int
       5: astore_0      
       6: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
       9: ldc           #3                  // String bored
      11: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
      14: return        
}

, ( ) jvm...

[Disassembling for mach='i386:x86-64']
[Entry Point]
[Verified Entry Point]
[Constants]
  # {method} 'frobincate' '()V' in 'Foo'
  #           [sp+0x20]  (sp of caller)
  0x00007fd335060aa0: mov    %eax,-0x14000(%rsp)
  0x00007fd335060aa7: push   %rbp
  0x00007fd335060aa8: sub    $0x10,%rsp         ;*synchronization entry
                                                ; - Foo::frobincate@-1 (line 4)
  0x00007fd335060aac: mov    0x60(%r15),%rdi
  0x00007fd335060ab0: mov    %rdi,%r10
  0x00007fd335060ab3: add    $0xfb0,%r10
  0x00007fd335060aba: cmp    0x70(%r15),%r10
  0x00007fd335060abe: jae    0x00007fd335060b18
  0x00007fd335060ac0: mov    %r10,0x60(%r15)
  0x00007fd335060ac4: prefetchnta 0xc0(%r10)
  0x00007fd335060acc: movq   $0x1,(%rdi)
  0x00007fd335060ad3: prefetchnta 0x100(%r10)
  0x00007fd335060adb: movl   $0xe7780204,0x8(%rdi)  ;   {oop({type array int})}
  0x00007fd335060ae2: prefetchnta 0x140(%r10)
  0x00007fd335060aea: movl   $0x3e8,0xc(%rdi)
  0x00007fd335060af1: prefetchnta 0x180(%r10)
  0x00007fd335060af9: add    $0x10,%rdi
  0x00007fd335060afd: mov    $0x1f4,%ecx
  0x00007fd335060b02: xor    %rax,%rax
  0x00007fd335060b05: shl    $0x3,%rcx
  0x00007fd335060b09: rex.W rep stos %al,%es:(%rdi)
  0x00007fd335060b0c: add    $0x10,%rsp
  0x00007fd335060b10: pop    %rbp
  0x00007fd335060b11: test   %eax,0xbb954e9(%rip)        # 0x00007fd340bf6000
                                                ;   {poll_return}
  0x00007fd335060b17: retq   
  0x00007fd335060b18: mov    $0x3e8,%edx
  0x00007fd335060b1d: mov    $0x73bc01020,%rsi  ;   {oop({type array int})}
  0x00007fd335060b27: callq  0x00007fd33505f260  ; OopMap{off=140}
                                                ;*newarray
                                                ; - Foo::frobincate@3 (line 4)
                                                ;   {runtime_call}
  0x00007fd335060b2c: jmp    0x00007fd335060b0c  ;*newarray
                                                ; - Foo::frobincate@3 (line 4)
  0x00007fd335060b2e: mov    %rax,%rsi
  0x00007fd335060b31: add    $0x10,%rsp
  0x00007fd335060b35: pop    %rbp
  0x00007fd335060b36: jmpq   0x00007fd335062160  ;   {runtime_call}
  0x00007fd335060b3b: hlt    
  0x00007fd335060b3c: hlt    
  0x00007fd335060b3d: hlt    
  0x00007fd335060b3e: hlt    
  0x00007fd335060b3f: hlt    
[Exception Handler]
[Stub Code]
  0x00007fd335060b40: jmpq   0x00007fd33505f3e0  ;   {no_reloc}
[Deopt Handler Code]
  0x00007fd335060b45: callq  0x00007fd335060b4a
  0x00007fd335060b4a: subq   $0x5,(%rsp)
  0x00007fd335060b4f: jmpq   0x00007fd335038f00  ;   {runtime_call}
  0x00007fd335060b54: hlt    
  0x00007fd335060b55: hlt    
  0x00007fd335060b56: hlt    
  0x00007fd335060b57: hlt

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