RFR: 8351965: [leyden] Skip installing C2 AOT code if C2 precompiled AOT code trapped
Aleksey Shipilev
shade at openjdk.org
Thu Mar 13 17:30:11 UTC 2025
On Thu, 13 Mar 2025 16:43:23 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:
> This is clearly visible in compilation logs:
>
>
> 43 W0.1 Q8.1 C0.0 293 AP 4 com.sun.tools.javac.util.StringNameTable::fromString (50 bytes)
> [0.049s][debug ][deoptimization] cid= 293 level=4 com.sun.tools.javac.util.StringNameTable::fromString(Ljava/lang/String;)Lcom/sun/tools/javac/util/Name; trap_bci=28 unloaded reinterpret pc=0x00007c6bd7e4e7ac relative_pc=0x000000000000068c
> 49 293 AP 4 com.sun.tools.javac.util.StringNameTable::fromString (50 bytes) made not entrant
> 49 W0.2 Q0.0 C0.3 1394 2 com.sun.tools.javac.util.StringNameTable::fromString (50 bytes)
> 90 1394 2 com.sun.tools.javac.util.StringNameTable::fromString (50 bytes) made not entrant
> 90 W0.0 Q0.0 C0.1 1867 A 4 com.sun.tools.javac.util.StringNameTable::fromString (50 bytes)
> [0.098s][debug ][deoptimization] cid=1867 level=4 com.sun.tools.javac.util.StringNameTable::fromString(Ljava/lang/String;)Lcom/sun/tools/javac/util/Name; trap_bci=28 unloaded reinterpret pc=0x00007c6bd7ebcb58 relative_pc=0x00000000000005d8
> 98 1867 A 4 com.sun.tools.javac.util.StringNameTable::fromString (50 bytes) made not entrant
> 104 W0.0 Q0.0 C0.3 1942 2 com.sun.tools.javac.util.StringNameTable::fromString (50 bytes)
> 130 1942 2 com.sun.tools.javac.util.StringNameTable::fromString (50 bytes) made not entrant
> 130 W1.0 Q0.7 C13.3 1968 4 com.sun.tools.javac.util.StringNameTable::fromString (50 bytes)
>
>
> So the AP4 method was preloaded, then it trapped and got replaced by T2 method, which eventually got to C2, at which point we loaded A4 method. That method trapped _at the same bci_, which is really expected, so we are back at T2, then then to real T4. So we have spent one deopt cycle unnecessarily, and the code was in T2 for twice as long.
>
> I don't think we would be able to fully tame uncommon traps from the preload code, so fixing this gap is valuable.
>
> `decompile_count()` is only updated by C2, so we can just check it directly.
>
> Additional testing:
> - [x] Ad-hoc benchmarks
> - [x] Linux x86_64 server fastdebug, `runtime/cds`
Here are the snippets of `AP4` and `A4` versions:
[0.051s][debug ][deoptimization] cid= 294 level=4 com.sun.tools.javac.util.StringNameTable::fromString(Ljava/lang/String;)Lcom/sun/tools/javac/util/Name; trap_bci=28 unloaded reinterpret pc=0x000070d873e3f4dc relative_pc=0x00000000000003bc
=== AP 4 code:
[Verified Entry Point]
0x000070d873e3f130: mov %eax,-0x14000(%rsp)
0x000070d873e3f137: push %rbp
0x000070d873e3f138: sub $0x40,%rsp
0x000070d873e3f13c: cmpl $0x0,0x20(%r15)
0x000070d873e3f144: jne 0x000070d873e3f8e3
0x000070d873e3f14a: mov %rsi,%rcx
0x000070d873e3f14d: mov 0x14(%rsi),%r10d
0x000070d873e3f151: mov 0x8(%r12,%r10,8),%r8d ; implicit exception: dispatches to 0x000070d873e3f888
0x000070d873e3f156: cmp $0x2ff628,%r8d ; {metadata('java/util/HashMap')}
0x000070d873e3f15d: jne 0x000070d873e3f5fc
0x000070d873e3f163: shl $0x3,%r10
0x000070d873e3f167: mov 0x24(%r10),%r11d
0x000070d873e3f16b: test %r11d,%r11d
0x000070d873e3f16e: je 0x000070d873e3f4b7 ; <--- branch to trap handler
...
0x000070d873e3f4b6: ret
0x000070d873e3f4b7: mov %rdx,%r10
0x000070d873e3f4ba: movzbl 0x10(%rcx),%r11d
0x000070d873e3f4bf: test %r11d,%r11d
0x000070d873e3f4c2: jne 0x000070d873e3f670
0x000070d873e3f4c8: mov $0x28,%esi
0x000070d873e3f4cd: mov %rcx,%rbp
0x000070d873e3f4d0: mov %r10,(%rsp)
0x000070d873e3f4d4: vzeroupper
0x000070d873e3f4d7: call 0x000070d873633340 ; ImmutableOopMap {rbp=Oop [0]=Oop }
;*new {reexecute=0 rethrow=0 return_oop=0}
; - com.sun.tools.javac.util.StringNameTable::fromString at 28 (line 70)
; {runtime_call UncommonTrapBlob}
=== A4 code:
Compiled method (c2) 97 1861 A 4 com.sun.tools.javac.util.StringNameTable::fromString (50 bytes)
106 W0.1 Q46.3 C0.0 1582 A [0.107s][debug ][deoptimization] cid=1861 level=4 com.sun.tools.javac.util.StringNameTable::fromString(Ljava/lang/String;)Lcom/sun/tools/javac/util/Name; trap_bci=28 unloaded reinterpret pc=0x000070d873e9d8e0 relative_pc=0x0000000000000360
[Verified Entry Point]
0x000070d873e9d590: mov %eax,-0x14000(%rsp)
0x000070d873e9d597: push %rbp
0x000070d873e9d598: sub $0x40,%rsp
0x000070d873e9d59c: cmpl $0x0,0x20(%r15)
0x000070d873e9d5a4: jne 0x000070d873e9dbd3
0x000070d873e9d5aa: mov %rsi,%r11
0x000070d873e9d5ad: mov 0x14(%rsi),%r8d
0x000070d873e9d5b1: mov 0x8(%r12,%r8,8),%r10d ; implicit exception: dispatches to 0x000070d873e9db78
0x000070d873e9d5b6: cmp $0x2ff628,%r10d ; {metadata('java/util/HashMap')}
0x000070d873e9d5bd: jne 0x000070d873e9d9de
0x000070d873e9d5c3: lea (%r12,%r8,8),%r10
0x000070d873e9d5c7: mov 0x24(%r10),%eax
0x000070d873e9d5cb: test %eax,%eax
0x000070d873e9d5cd: je 0x000070d873e9d8ba ; <--- branch to trap handler
...
0x000070d873e9d8b9: ret
0x000070d873e9d8ba: mov %rdx,%r10
0x000070d873e9d8bd: movzbl 0x10(%r11),%r8d
0x000070d873e9d8c2: test %r8d,%r8d
0x000070d873e9d8c5: jne 0x000070d873e9da24
0x000070d873e9d8cb: mov $0x28,%esi
0x000070d873e9d8d0: mov %r11,%rbp
0x000070d873e9d8d3: mov %r10,(%rsp)
0x000070d873e9d8d7: nop
0x000070d873e9d8d8: vzeroupper
0x000070d873e9d8db: call 0x000070d873633340 ; ImmutableOopMap {rbp=Oop [0]=Oop }
;*new {reexecute=0 rethrow=0 return_oop=0}
; - com.sun.tools.javac.util.StringNameTable::fromString at 28 (line 70)
; {runtime_call UncommonTrapBlob}
-------------
PR Comment: https://git.openjdk.org/leyden/pull/48#issuecomment-2722092964
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