-- argRegs is the set of regs which are read for an n-argument call to C.
-- For archs which pass all args on the stack (x86), is empty.
-- Sparc passes up to the first 6 args in regs.
--- Dunno about Alpha.
argRegs :: RegNo -> [Reg]
argRegs _ = panic "MachRegs.argRegs(x86): should not be used!"
{-
AMD x86_64 architecture:
-- Registers 0-16 have 32-bit counterparts (eax, ebx etc.)
-- Registers 0-7 have 16-bit counterparts (ax, bx etc.)
-- Registers 0-3 have 8 bit counterparts (ah, bh etc.)
-
+- All 16 integer registers are addressable as 8, 16, 32 and 64-bit values:
+
+ 8 16 32 64
+ ---------------------
+ al ax eax rax
+ bl bx ebx rbx
+ cl cx ecx rcx
+ dl dx edx rdx
+ sil si esi rsi
+ dil si edi rdi
+ bpl bp ebp rbp
+ spl sp esp rsp
+ r10b r10w r10d r10
+ r11b r11w r11d r11
+ r12b r12w r12d r12
+ r13b r13w r13d r13
+ r14b r14w r14d r14
+ r15b r15w r15d r15
-}
rax, rbx, rcx, rdx, rsp, rbp, rsi, rdi,