JDK-8349930 : C2: verify memory liveness invariants after scheduling
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: compiler
  • Affected Version: 25
  • Priority: P4
  • Status: In Progress
  • Resolution: Unresolved
  • Submitted: 2025-02-12
  • Updated: 2025-04-29
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Other
tbdUnresolved
Related Reports
Relates :  
JDK-8351468 - C2: array fill optimization assigns wrong type to intrinsic call
Relates :  
JDK-8255763 - C2: OSR miscompilation caused by invalid memory instruction placement
Relates :  
JDK-8258894 - C2: Forbid GCM to move stores into loops
Relates :  
JDK-8355891 - [Umbrella] Stabilization of C2's Memory Representation
Relates :  
JDK-8288975 - Incorrect result with C2 compiled code
Relates :  
JDK-8298951 - Umbrella: improve CCP and IGVN verification
Relates :  
JDK-8350864 - C2: verify structural invariants of the Ideal graph
Relates :  
JDK-8333393 - PhaseCFG::insert_anti_dependences can fail to raise LCAs and to add necessary anti-dependence edges
Description
Violation of memory liveness invariants can lead to subtle miscompilation issues such as JDK-8333393, JDK-8255763, and JDK-8288975. This RFE proposes adding debug-only verification code after scheduling (GCM and LCM) that computes liveness information for the memory subgraph and checks that certain invariants hold.

Examples of candidate invariants to be explored are that "all-memory" (<Bot> in the notation given in memnode.cpp) definitions do not interfere, or that a MergeMem definition using a certain memory state does not interfere with that particular memory state later on.