[llvm-commits] dwarf regnum for the x86 subregisters

[Rafael Avila de Espindola]

I started working on PR9826. To fix it I need tblgen to produce a 
mapping from dwarf register number to llvm register number.

I now know that this mapping cannot be unique because of cases like 
xmm0/ymm0. I will have to pick one (maybe the first one in the file?).

Even ignoring cases like xmm0/ymm0, we still declare many duplicated 
dwarf numbers:

   def AH : Register<"ah">, DwarfRegNum<[0, 0, 0]>;
   def AL : Register<"al">, DwarfRegNum<[0, 0, 0]>;
   def AX : RegisterWithSubRegs<"ax", [AL,AH]>, DwarfRegNum<[0, 0, 0]>;
...

Are we doing the right thing in here? On the other end the debugger is 
going to map 0 to eax (or rax if in 64 bit mode). Should we refer to 
subregisters like AH with a DW_OP_bit_piece of EAX (or RAX if in 64 bit 
mode)?

Cheers,
Rafael