Virtualizing CodeGenerator fails

[samasri]

Tasks

• [x] Remove OMR_API from PRs
• [x] Try to build it locally and fix issues by creating default implementations

Description of problem

The PR to virtualize CodeGenerator is failing. The main problem seems to be from virtualizing generateSwitchToInterpreterPrePrologue(TR::Instruction*, uint8_t, uint8_t). Error message:

../../libtestjit_base.a(OMRCodeGenerator.o):(.data.rel.ro._ZTVN3OMR3X865AMD6413CodeGeneratorE[_ZTVN3OMR3X865AMD6413CodeGeneratorE]+0x1d0): undefined reference to `OMR::X86::CodeGenerator::generateSwitchToInterpreterPrePrologue(TR::Instruction*, unsigned char, unsigned char)'

This function is declared in OMR::X86::CodeGenerator however it is not defined in the OMR project. It is, however, defined in J9::X86::CodeGenerator. Hence, when compiling the OMR project independently of OpenJ9 (as in Travis CI), the linker would not be able to find a definition for the virtual function which causes an error.

I tried adding = 0 to the end of the functions declaration making it pure virtual; since pure virtual functions are allowed not to have a declaration which caused another error:

../../compiler/compile/OMRCompilation.cpp:188:56: error: invalid new-expression of abstract class type ‘TR::CodeGenerator’
    return new (comp->trHeapMemory()) TR::CodeGenerator();

[samasri]

Proposed solution: add default implementation for such cases