class AbstractCompiler : public CHeapObj<mtCompiler> {
...
  // Compiler type queries.
  const bool is_c1() { return _type == compiler_c1; }
  const bool is_c2() { return _type == compiler_c2; }
  const bool is_jvmci() { return _type == compiler_jvmci; }
  const CompilerType type() { return _type; }


it doesn't make any sense to return a const scalar in this case.
I think the original intention is to mark those member functions const.
  bool is_c1() const { return _type == compiler_c1; }