JDK-8370137 : C2: Ensure dependent memory accesses can't float past ReachabilityFence
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: compiler
  • Affected Version: 26
  • Priority: P4
  • Status: Open
  • Resolution: Unresolved
  • Submitted: 2025-10-17
  • Updated: 2025-10-17
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tbdUnresolved
Related Reports
Relates :  
JDK-8290892 - C2: Intrinsify Reference.reachabilityFence
Description
If a memory access (either load or store) dependent on a referent of a ReachabilityFence node floats past the corresponding ReachabilityFence node, it may break a ReachabilityFence guarantee if it then floats past a safepoint (those aren't classified as interfering by JDK-8290892).

If ReachabilityFence is represented as a memory barrier, it would guarantee such scheduling is impossible, but MemBar IR representation is prohibitively expensive (from performance POV). 

One way to address it is to make interfering safepoint enumeration algorithm in  JDK-8290892 more conservative and consider any safepoints reachable from referent control as interfering.