JDK-8211518 : C2 should optimize if diamonds that feed into Phis merging the same value
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: compiler
  • Affected Version: 12,20
  • Priority: P4
  • Status: Open
  • Resolution: Unresolved
  • Submitted: 2018-10-03
  • Updated: 2025-03-27
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Other
tbdUnresolved
Related Reports
Blocks :  
JDK-8302137 - Speed up compiler/codegen/TestTrichotomyExpressions.java
Relates :  
JDK-8210215 - C2 should optimize trichotomy calculations
Relates :  
JDK-8275202 - C2: optimize out more redundant conditions
Description
C2 should optimize the following code shape:

       If
      /  \
   Proj  Proj
     \    /  [...]
      \  /   /
      Region1
       |
       |  x x  y
        \ | | /
          Phi 

This optimization was added with JDK-8210215 for regions with 2 and 3 inputs but should be extended/replaced for the general case. See discussion in:
http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2018-October/030834.html