JDK-8031752 : Failed speculative optimizations should be reattempted when root of compilation is different
  • Type: Bug
  • Component: hotspot
  • Sub-Component: compiler
  • Affected Version: hs25
  • Priority: P3
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2014-01-15
  • Updated: 2014-07-29
  • Resolved: 2014-02-25
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8u20Fixed 9 b04Fixed
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When C2 optimizes the code based on type profiling, it emits a guard. If the guard fails, the code "traps" and the location of the trap (method, bci) and cause (class check) are recorded. When C2 generates code for that method again, it doesn't perform any optimization of that type (class check) at that location (bci).

Let's say the trap occurs at (m, bci) when m is inlined in m1. When m2 that inlines m is compiled, no class check optimization is performed at (m, bci) because of the trap triggered in m1. With type speculation, type information is flowing from many profiling points in the application code. So in the example above, the profile data used at (m, bci) may come from m1 when the compiled method is m1 and it may be come from m2 when the compiled method is m2. And so the trap at (m,bci) in compiled method m1 doesn't say much about the validity of a speculative optimization at (m,bci) when the compiled method is m2.

When a trap occurs from a speculative optimization, the trap should record: (method, bci, compiled method) so that in the example above: erroneous optimization at (m, bci) is not reattempted if m1 is re-compiled but is attempted when m2 is compiled.