Currently, SDCC omits integer promotion of explictly typecast arguments
passed as variable arguments. This is done only when the selected
standard dialect is an SDCC variant, and the target is not a pdk port
(see section 3.5.15 of the manual).
The feature allows to save a byte of stack space (and some code size /
speed if pushing an 8-bit value is simpler than pushing a 16-bit one)
when passing a char, bool or _BitInt as variable argument.
I'd like to remove support for this langauge extension from the stm8
port, f8 port, the z80-related ports, hc08 and s08.
Rationale:
* The main benefit of the feature is saving a little bit of stack space.
But stm8, f8, the z80-related ports, hc08, s08, and mcs51 (for the large
and huge memory model) have a large stack (with the exception of some
stm8 devices, the whole RAM can be used as stack).
* Omitting the integer promotion violates the C standard, and could thus
result in surprising behavior for the user. After all that cast is not
necessarily explicitly written with intent to omit the promotion, the
cast might come e.g. from a macro expansion.
* The omission makes code compiled with the SDCC dialect incompatible
with code compiled without the dialect. This results in silent breakage
when there are calls between such code that pass explicitly cast
variable arguments (AFAIK even if that happens within the same file, and
there is a #pragma std_sdccXX / #pragma std_cXX in between).
* stm8, f8, the z80-related ports, hc08, s08 do have instructions to
efficiently push a 16-bit value onto the stack, so there is not much
benefit in code size and speed.
* For the z80-related ports, we do not have instructions to efficiently
put a single 8-bit value on the stack, we instead need to push a 16-bit
register or value, then adjust the stack pointer, so there typically is
no or even a negative benenefit in code size and speed.
Philipp
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