RFR: 8354887: Preserve runtime blobs in AOT code cache [v2]

[Ashutosh Mehra]

On Tue, 6 May 2025 14:11:54 GMT, Ashutosh Mehra <asmehra at openjdk.org> wrote:

> I can recreate this test locally. Looking into it.

Looks like the code for C2 blobs generated in assembly phase is not correct.
For example, code for new_instance blob is:


[0.141s][550409][aot,codecache,stubs] Decoding CodeBlob, name: C2 Runtime new_instance, at  [0x00007fed0f904260, 0x00007fed0f9042b8]  88 bytes
[0.141s][550409][aot,codecache,stubs]  ;; N1: # out( B1 ) <- in( B3 B2 )  Freq: 1
[0.141s][550409][aot,codecache,stubs]  ;; B1: # out( B3 B2 ) <- BLOCK HEAD IS JUNK  Freq: 1
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f904260:   sub    $0x8,%rsp
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f904267:   mov    %rbp,(%rsp)
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f90426b:   mov    %rsp,0x3e8(%r15)
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f904272:   mov    %rsi,%rdi
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f904275:   mov    %r15,%rsi
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f904278:   movabs $0x7fed28908982,%r10
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f904282:   call   *%r10
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f904285:   nopl   0x0(%rax,%rax,1)
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f90428d:   mov    %r12,0x3e8(%r15)
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f904294:   mov    %r12,0x3f0(%r15)
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f90429b:   mov    0x440(%r15),%rax
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f9042a2:   mov    %r12,0x440(%r15)
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f9042a9:   cmp    0x8(%r15),%r12
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f9042ad:   jne    0x00007fed0f9042b1
[0.141s][550409][aot,codecache,stubs]  ;; B2: # out( N1 ) <- in( B1 )  Freq: 0.999999
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f9042af:   pop    %rbp
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f9042b0:   ret    
[0.141s][550409][aot,codecache,stubs]  ;; B3: # out( N1 ) <- in( B1 )  Freq: 1e-06
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f9042b1:   pop    %rbp
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f9042b2:   jmp    Stub::forward_exception
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f9042b7:   hlt    

Look at the instructions generated after the call to runtime method:


[0.141s][550409][aot,codecache,stubs]   0x00007fed0f90428d:   mov    %r12,0x3e8(%r15)
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f904294:   mov    %r12,0x3f0(%r15)
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f90429b:   mov    0x440(%r15),%rax
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f9042a2:   mov    %r12,0x440(%r15)
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f9042a9:   cmp    0x8(%r15),%r12
[0.141s][550409][aot,codecache,stubs]   0x00007fed0f9042ad:   jne    0x00007fed0f9042b1


Comparing it with the case when AOT code cache is not used:

   0x7fffdef07c8d:	movq   $0x0,0x3e8(%r15)
   0x7fffdef07c98:	movq   $0x0,0x3f0(%r15)
   0x7fffdef07ca3:	mov    0x440(%r15),%rax
   0x7fffdef07caa:	movq   $0x0,0x440(%r15)
   0x7fffdef07cb5:	mov    0x8(%r15),%r10
   0x7fffdef07cb9:	test   %r10,%r10
   0x7fffdef07cbc:	jne    0x7fffdef07cc0


For some reason r12 is used instead of null (0x0). r12 is the CompressedOop::base address. 
C2 code that generates this is https://github.com/openjdk/jdk/blob/762423d64d10dcdb37800767d2b2f1b7757c804a/src/hotspot/share/opto/generateOptoStub.cpp#L222

I suspect I missed porting a change from premain. @adinn @vnkozlov any idea what that could be?

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PR Comment: https://git.openjdk.org/jdk/pull/25019#issuecomment-2856943220