Summary
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Obsolete the option -XX:+UseRDPCForConstantTableBase which optimizes code generation exclusively for SPARC. 

Problem
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This was a C2 internal optimization that was used for the SPARC CPUs, which support to load base of Constant table. Because the entire backend of Sparc has been removed, it is no longer in use now. Leaving it as a JVMOption may expose risk of stability. 

Solution
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The -XX:+UseRDPCForConstantTableBase option will be turned off by default and will issue an Obsolete message if used.

Specification
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Remove

  product(bool, UseRDPCForConstantTableBase, false,       
          "Use Sparc RDPC instruction for the constant table base.") 

and make it obsolete in JDK 16 and expired in JDK 17.