[HLSL] Add checks to the SPIRVInstructionSelector's `selectExtInst` functions for SPIR-V extended instruction set availability

[Icohedron]

Certain SPIR-V instructions are supported only with the OpenCL extended instruction set but not the GLSL extended instruction set, and vice-versa.

For example, the reflect instruction is supported in GLSL, but not OpenCL. Without adding a check that the extended instruction set is usable by the current SPIR-V target, the compiler will simply crash when attempting to select G_INTRINSIC intrinsic(@llvm.spv.reflect) in an OpenCL SPIR-V target.

#122992 implements the check as follows in llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp:

bool SPIRVInstructionSelector::selectExtInst(Register ResVReg,
                                             const SPIRVType *ResType,
                                             MachineInstr &I,
                                             GL::GLSLExtInst GLInst) const {
  if (!STI.canUseExtInstSet(
          SPIRV::InstructionSet::InstructionSet::GLSL_std_450)) {
    std::string DiagMsg;
    raw_string_ostream OS(DiagMsg);
    I.print(OS, true, false, false, false);
    DiagMsg += " is only supported with the GLSL extended instruction set.\n";
    report_fatal_error(DiagMsg.c_str(), false);
  }
  return selectExtInst(ResVReg, ResType, I,
                       {{SPIRV::InstructionSet::GLSL_std_450, GLInst}});
}

There should be similar checks made for the other overloaded versions of the selectExtInst to keep things consistent.

  bool selectExtInst(Register ResVReg, const SPIRVType *ResType,
                     MachineInstr &I, CL::OpenCLExtInst CLInst) const;
  bool selectExtInst(Register ResVReg, const SPIRVType *ResType,
                     MachineInstr &I, CL::OpenCLExtInst CLInst,
                     GL::GLSLExtInst GLInst) const;
  bool selectExtInst(Register ResVReg, const SPIRVType *ResType,
                     MachineInstr &I, const ExtInstList &ExtInsts) const;

A non-exhaustive list of OpenCL-only instructions:

• vstoren
• vloadn
• shuffle

(Note: AFAIK, these OpenCL-only instructions do not have corresponding HLSL intrinsics. I am not sure if there are any OpenCL-only instructions that have a direct HLSL intrinsic equivalent.)

A non-exhaustive list of GLSL-only instructions:

• Reflect
• Refract
• FaceForward

A full list of exclusive instructions may be constructed by comparing the OpenCL extended instruction set and GLSL extended instruction set specifications.

[bogner]

As mentioned in my comment here I don't think report_fatal_error is the right kind of error handling here. We should rework these functions so that they can use LLVMContext::diagnose to bubble errors up to the driver.