我在Mac OS X上使用Java 8编译了一个简单的Java文件以进行汇编。这是Test.java：
public class Test {
static volatile int a = 1;
public static void main(String[] args) {
a++;
}
}
我使用以下命令输出汇编代码：
java -server -Xcomp -XX:+UnlockDiagnosticVMOptions -XX:-Inline -XX:CompileCommand=print,*Test.main Test>Test.asm
这是Test.asm的输出：
CompilerOracle: print *Test.main
Compiled method (c1) 1733 1750 3 Test::main (9 bytes)
total in heap [0x0000000111848650,0x0000000111848970] = 800
relocation [0x0000000111848778,0x00000001118487a0] = 40
main code [0x00000001118487a0,0x0000000111848860] = 192
stub code [0x0000000111848860,0x00000001118488f0] = 144
oops [0x00000001118488f0,0x00000001118488f8] = 8
metadata [0x00000001118488f8,0x0000000111848900] = 8
scopes data [0x0000000111848900,0x0000000111848918] = 24
scopes pcs [0x0000000111848918,0x0000000111848968] = 80
dependencies [0x0000000111848968,0x0000000111848970] = 8
Loaded disassembler from /Library/Java/JavaVirtualMachines/jdk1.8.0_112.jdk/Contents/Home/jre/lib/hsdis-amd64.dylib
Decoding compiled method 0x0000000111848650:
Code:
[Disassembling for mach='i386:x86-64']
[Entry Point]
[Verified Entry Point]
[Constants]
# {method} {0x000000010e40e240} 'main' '([Ljava/lang/String;)V' in 'Test'
# parm0: rsi:rsi = '[Ljava/lang/String;'
# [sp+0x40] (sp of caller)
0x00000001118487a0: mov %eax,-0x14000(%rsp)
0x00000001118487a7: push %rbp
0x00000001118487a8: sub $0x30,%rsp
0x00000001118487ac: movabs $0x10e40e4d0,%rdi ; {metadata(method data for {method} {0x000000010e40e240} 'main' '([Ljava/lang/String;)V' in 'Test')}
0x00000001118487b6: mov 0xdc(%rdi),%ebx
0x00000001118487bc: add $0x8,%ebx
0x00000001118487bf: mov %ebx,0xdc(%rdi)
0x00000001118487c5: movabs $0x10e40e240,%rdi ; {metadata({method} {0x000000010e40e240} 'main' '([Ljava/lang/String;)V' in 'Test')}
0x00000001118487cf: and $0x0,%ebx
0x00000001118487d2: cmp $0x0,%ebx
0x00000001118487d5: je 0x00000001118487fe
0x00000001118487db: movabs $0x7955fd1e8,%rsi ; {oop(a 'java/lang/Class' = 'Test')}
0x00000001118487e5: mov 0x68(%rsi),%edi ;*getstatic a
; - Test::main@0 (line 6)
0x00000001118487e8: inc %edi
0x00000001118487ea: mov %edi,0x68(%rsi)
0x00000001118487ed: lock addl $0x0,(%rsp) ;*putstatic a
; - Test::main@5 (line 6)
0x00000001118487f2: add $0x30,%rsp
0x00000001118487f6: pop %rbp
0x00000001118487f7: test %eax,-0x5f7f6fd(%rip) # 0x000000010b8c9100
; {poll_return}
0x00000001118487fd: retq
0x00000001118487fe: mov %rdi,0x8(%rsp)
0x0000000111848803: movq $0xffffffffffffffff,(%rsp)
0x000000011184880b: callq 0x0000000111543f60 ; OopMap{rsi=Oop off=112}
;*synchronization entry
; - Test::main@-1 (line 6)
; {runtime_call}
0x0000000111848810: jmp 0x00000001118487db
0x0000000111848812: nop
0x0000000111848813: nop
0x0000000111848814: mov 0x2a8(%r15),%rax
0x000000011184881b: movabs $0x0,%r10
0x0000000111848825: mov %r10,0x2a8(%r15)
0x000000011184882c: movabs $0x0,%r10
0x0000000111848836: mov %r10,0x2b0(%r15)
0x000000011184883d: add $0x30,%rsp
0x0000000111848841: pop %rbp
0x0000000111848842: jmpq 0x00000001114b24a0 ; {runtime_call}
0x0000000111848847: hlt
0x0000000111848848: hlt
0x0000000111848849: hlt
0x000000011184884a: hlt
0x000000011184884b: hlt
0x000000011184884c: hlt
0x000000011184884d: hlt
0x000000011184884e: hlt
0x000000011184884f: hlt
0x0000000111848850: hlt
0x0000000111848851: hlt
0x0000000111848852: hlt
0x0000000111848853: hlt
0x0000000111848854: hlt
0x0000000111848855: hlt
0x0000000111848856: hlt
0x0000000111848857: hlt
0x0000000111848858: hlt
0x0000000111848859: hlt
0x000000011184885a: hlt
0x000000011184885b: hlt
0x000000011184885c: hlt
0x000000011184885d: hlt
0x000000011184885e: hlt
0x000000011184885f: hlt
[Exception Handler]
[Stub Code]
0x0000000111848860: callq 0x00000001115418e0 ; {no_reloc}
0x0000000111848865: mov %rsp,-0x28(%rsp)
0x000000011184886a: sub $0x80,%rsp
0x0000000111848871: mov %rax,0x78(%rsp)
0x0000000111848876: mov %rcx,0x70(%rsp)
0x000000011184887b: mov %rdx,0x68(%rsp)
0x0000000111848880: mov %rbx,0x60(%rsp)
0x0000000111848885: mov %rbp,0x50(%rsp)
0x000000011184888a: mov %rsi,0x48(%rsp)
0x000000011184888f: mov %rdi,0x40(%rsp)
0x0000000111848894: mov %r8,0x38(%rsp)
0x0000000111848899: mov %r9,0x30(%rsp)
0x000000011184889e: mov %r10,0x28(%rsp)
0x00000001118488a3: mov %r11,0x20(%rsp)
0x00000001118488a8: mov %r12,0x18(%rsp)
0x00000001118488ad: mov %r13,0x10(%rsp)
0x00000001118488b2: mov %r14,0x8(%rsp)
0x00000001118488b7: mov %r15,(%rsp)
0x00000001118488bb: movabs $0x10c7d8060,%rdi ; {external_word}
0x00000001118488c5: movabs $0x111848865,%rsi ; {internal_word}
0x00000001118488cf: mov %rsp,%rdx
0x00000001118488d2: and $0xfffffffffffffff0,%rsp
0x00000001118488d6: callq 0x000000010c60361a ; {runtime_call}
0x00000001118488db: hlt
[Deopt Handler Code]
0x00000001118488dc: movabs $0x1118488dc,%r10 ; {section_word}
0x00000001118488e6: push %r10
0x00000001118488e8: jmpq 0x000000011148d3c0 ; {runtime_call}
0x00000001118488ed: hlt
0x00000001118488ee: hlt
0x00000001118488ef: hlt
OopMapSet contains 1 OopMaps
#0
OopMap{rsi=Oop off=112}
Compiled method (c1) 1747 1751 1 Test::main (9 bytes)
total in heap [0x0000000111847250,0x0000000111847518] = 712
relocation [0x0000000111847378,0x00000001118473a0] = 40
main code [0x00000001118473a0,0x0000000111847420] = 128
stub code [0x0000000111847420,0x00000001118474b0] = 144
oops [0x00000001118474b0,0x00000001118474b8] = 8
metadata [0x00000001118474b8,0x00000001118474c0] = 8
scopes data [0x00000001118474c0,0x00000001118474d0] = 16
scopes pcs [0x00000001118474d0,0x0000000111847510] = 64
dependencies [0x0000000111847510,0x0000000111847518] = 8
Decoding compiled method 0x0000000111847250:
Code:
[Entry Point]
[Verified Entry Point]
[Constants]
# {method} {0x000000010e40e240} 'main' '([Ljava/lang/String;)V' in 'Test'
# parm0: rsi:rsi = '[Ljava/lang/String;'
# [sp+0x40] (sp of caller)
0x00000001118473a0: mov %eax,-0x14000(%rsp)
0x00000001118473a7: push %rbp
0x00000001118473a8: sub $0x30,%rsp
0x00000001118473ac: movabs $0x7955fd1e8,%rsi ; {oop(a 'java/lang/Class' = 'Test')}
0x00000001118473b6: mov 0x68(%rsi),%edi ;*getstatic a
; - Test::main@0 (line 6)
0x00000001118473b9: inc %edi
0x00000001118473bb: mov %edi,0x68(%rsi)
0x00000001118473be: lock addl $0x0,(%rsp) ;*putstatic a
; - Test::main@5 (line 6)
0x00000001118473c3: add $0x30,%rsp
0x00000001118473c7: pop %rbp
0x00000001118473c8: test %eax,-0x5f7e2ce(%rip) # 0x000000010b8c9100
; {poll_return}
0x00000001118473ce: retq
0x00000001118473cf: nop
0x00000001118473d0: nop
0x00000001118473d1: mov 0x2a8(%r15),%rax
0x00000001118473d8: movabs $0x0,%r10
0x00000001118473e2: mov %r10,0x2a8(%r15)
0x00000001118473e9: movabs $0x0,%r10
0x00000001118473f3: mov %r10,0x2b0(%r15)
0x00000001118473fa: add $0x30,%rsp
0x00000001118473fe: pop %rbp
0x00000001118473ff: jmpq 0x00000001114b24a0 ; {runtime_call}
0x0000000111847404: hlt
0x0000000111847405: hlt
0x0000000111847406: hlt
0x0000000111847407: hlt
0x0000000111847408: hlt
0x0000000111847409: hlt
0x000000011184740a: hlt
0x000000011184740b: hlt
0x000000011184740c: hlt
0x000000011184740d: hlt
0x000000011184740e: hlt
0x000000011184740f: hlt
0x0000000111847410: hlt
0x0000000111847411: hlt
0x0000000111847412: hlt
0x0000000111847413: hlt
0x0000000111847414: hlt
0x0000000111847415: hlt
0x0000000111847416: hlt
0x0000000111847417: hlt
0x0000000111847418: hlt
0x0000000111847419: hlt
0x000000011184741a: hlt
0x000000011184741b: hlt
0x000000011184741c: hlt
0x000000011184741d: hlt
0x000000011184741e: hlt
0x000000011184741f: hlt
[Exception Handler]
[Stub Code]
0x0000000111847420: callq 0x00000001115418e0 ; {no_reloc}
0x0000000111847425: mov %rsp,-0x28(%rsp)
0x000000011184742a: sub $0x80,%rsp
0x0000000111847431: mov %rax,0x78(%rsp)
0x0000000111847436: mov %rcx,0x70(%rsp)
0x000000011184743b: mov %rdx,0x68(%rsp)
0x0000000111847440: mov %rbx,0x60(%rsp)
0x0000000111847445: mov %rbp,0x50(%rsp)
0x000000011184744a: mov %rsi,0x48(%rsp)
0x000000011184744f: mov %rdi,0x40(%rsp)
0x0000000111847454: mov %r8,0x38(%rsp)
0x0000000111847459: mov %r9,0x30(%rsp)
0x000000011184745e: mov %r10,0x28(%rsp)
0x0000000111847463: mov %r11,0x20(%rsp)
0x0000000111847468: mov %r12,0x18(%rsp)
0x000000011184746d: mov %r13,0x10(%rsp)
0x0000000111847472: mov %r14,0x8(%rsp)
0x0000000111847477: mov %r15,(%rsp)
0x000000011184747b: movabs $0x10c7d8060,%rdi ; {external_word}
0x0000000111847485: movabs $0x111847425,%rsi ; {internal_word}
0x000000011184748f: mov %rsp,%rdx
0x0000000111847492: and $0xfffffffffffffff0,%rsp
0x0000000111847496: callq 0x000000010c60361a ; {runtime_call}
0x000000011184749b: hlt
[Deopt Handler Code]
0x000000011184749c: movabs $0x11184749c,%r10 ; {section_word}
0x00000001118474a6: push %r10
0x00000001118474a8: jmpq 0x000000011148d3c0 ; {runtime_call}
0x00000001118474ad: hlt
0x00000001118474ae: hlt
0x00000001118474af: hlt
OopMapSet contains 0 OopMaps
问题是：为什么生成的汇编代码有两个主要方法，我如何使其只有一个？
答案 0 :(得分：3)
为什么生成的汇编代码有两个主要方法？
程序集包含C1编译器在不同的compilation levels处的工作结果：
C1 / Level 3
C1 / Level 1
Test.asm输出中包含适当的信息：
Compiled method (c1) 1733 1750 3 Test::main (9 bytes)
Compiled method (c1) 1747 1751 1 Test::main (9 bytes)
为了消除额外的编译开销，您可以设置-XX:TieredStopAtLevel=1-选中answer以获得更多详细信息。