RFR: 8351965: [leyden] Skip installing C2 AOT code if C2 precompiled AOT code trapped

[Aleksey Shipilev]

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`

-------------

Commit messages:
 - Cleanup
 - Fix

Changes: https://git.openjdk.org/leyden/pull/48/files
  Webrev: https://webrevs.openjdk.org/?repo=leyden&pr=48&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351965
  Stats: 8 lines in 1 file changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/leyden/pull/48.diff
  Fetch: git fetch https://git.openjdk.org/leyden.git pull/48/head:pull/48

PR: https://git.openjdk.org/leyden/pull/48