[avr-gcc-list] Using progmem on the reduced Tiny core?

[Georg-Johann Lay]

Currently progmem attribute works the same way on the reduced core (no LPM, 16 
GPRs) and on the ordinary cores (with LPM, 32 GPRs).

As we have a linearized memory model on reduced core and flash memory is 
visible in the RAM address range (starting at 0x4000), it would make sense if 
the compiler added that offset.

Attached is a tentative patch that adds this feature to avr-gcc together with a 
small test program that demonstrates some use cases.

If this does not break anything (e.g. because the current practice is to use 
progmem together with hand-crafted offsets and / or inline assembly) and the 
feedback is positive, I would propose the change to gcc-patches.

Johann

gcc/
        * doc/extend.texi (AVR Variable Attributes) [progmem]: Add
        documentation how it works on reduced Tiny cores.
        * avr.c (AVR_SYMBOL_FLAG_TINY_PM): New macro.
        (avr_address_tiny_pm_p): New static function.
        (avr_print_operand_address) [AVR_TINY]: Add AVR_TINY_PM_OFFSET
        if the address is in progmem.
        (avr_assemble_integer): Same.
        (avr_encode_section_info) [AVR_TINY]: Set AVR_SYMBOL_FLAG_TINY_PM
        for symbol_ref in progmem.
        * avr.h (AVR_TINY_PM_OFFSET): New macro.
        * avr-c.c (avr_cpu_cpp_builtins): Use it instead of magic 0x4000
        when built-in def'ing __AVR_TINY_PM_BASE_ADDRESS__.

tiny-progmem.diff
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ptiny.c
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