[patch,avr] Add support for devices with flash accessible by LD.

[Georg-Johann Lay]

Hi,

This patch adds support for devices that can access flash memory
by LD* instructions, hence there is no need to put .rodata in RAM.

The default linker script for the new multilib versions already
supports this feature, it's similar to avrtiny, cf.

https://sourceware.org/PR21472

This patch does the following:

* Add multilib variants avrxmega3 and avrxmega3/short-calls.

* Add new option -mshort-calls for multilib selection between
   devices with <= 8KiB flash and > 8KiB flash.

* Add specs handling for -mshort-calls:  The compiler knows
   if this option is needed or not appropriate (similar to -msp8).

* Add new ISA feature AVR_ISA_RCALL for multilib selection
   via -mshort-calls.

* Add a new row to architecture description that contains the
   start address of flash memory in the RAM address range.
   (The actual value is not needed).

* For devices with flash in RAM space, don't let .rodata
   objects trigger need for __do_copy_data.

* Add some devices.

* Add configure test for Binutils PR21472.

* Adjust documentation etc.

Even the smaller devices with flash <= 8KiB support JMP+CALL,
but we get better code by assuming RJMP+RCALL:  Jump tables
are more efficient and insn length computation is more exact
(CALL -> RCALL relaxation would need -mrelax and insn size
would still be 4 bytes).

Moreover, avr-libc uses __AVR_HAVE_JMP_CALL__ to determine
vector entry size, and libgcc uses that macro for flash size
estimation.


Ok for trunk?

Johann

	* config/avr/avr-arch.h (avr_arch_id) <ARCH_AVRXMEGA3>: New enum.
	(avr_mcu_t) <flash_pm_offset>: New field.
	(avr_device_specific_features) <AVR_ISA_RCALL>: New enum.
	* config/avr/avr.h (AVR_SHORT_CALLS): New define.
	(AVR_HAVE_JMP_CALL): Don't set if AVR_SHORT_CALLS.
	(AVR_TINY_PM_OFFSET): Remove macro.
	* config/avr/avr.opt (-mshort-calls): New option.
	* config/avr/gen-avr-mmcu-specs.c (print_mcu)
	[*self_spec]: Add / remove -mshort-calls depending on AVR_ISA_RCALL.
	* config/avr/avr-c.c (avr_cpu_cpp_builtins)
	<__AVR_SHORT_CALLS__>: Built-in define if AVR_SHORT_CALLS.
	<__AVR_HAVE_JMP_CALL__>: Use AVR_HAVE_JMP_CALL as condition
	instead of avr_arch->have_jmp_call.
	<__AVR_PM_BASE_ADDRESS__>: Built-in define if avr_arch->flash_pm_offset.
	[AVR_TINY] <__AVR_TINY_PM_BASE_ADDRESS__>: Use
	avr_arch->flash_pm_offset to define.
	* config/avr/avr-devices.c (avr_arch_types): Add initializers for
	new field flash_pm_offset.  Add entry for avrxmega3.
	(avr_texinfo): Add entry for avrxmega3.
	* avr-mcus.def: Add entries for: avrxmega3, attiny212, attiny214,
	attiny412, attiny414, attiny416, attiny417, attiny814,
	attiny816, attiny817, attiny1616, attiny1617, attiny3214,
	attiny3216, attiny3217.
	* config/avr/avr.c (avr_assemble_integer)[AVR_TINY]: Use
	avr_arch->flash_pm_offset instead of AVR_TINY_PM_OFFSET.
	(avr_print_operand_address) [AVR_TINY]: Same.
	(avr_asm_init_sections) <readonly_data_section>: Only patch
	callback if avr_arch->flash_pm_offset = 0.
	(avr_asm_named_section) <avr_need_copy_data_p>: Skip setting it
	for rodata if avr_arch->flash_pm_offset != 0.
	(avr_encode_section_info) [AVR_TINY]: Adjust comment.
	* config/avr/genmultilib.awk (dir_rcall, opt_rcall): New vars.
	(opts) [AVR_ISA_RCALL]: Append opt_rcall.
	(m_options): Append opt_rcall.
	(m_dirnames): Append dir_rcall.
	* config/avr/t-multilib: Regenerate.

	* configure.ac [target=avr]: Check whether avrxmega3 default
	linker description file works as needed.
	* configure: Regenerate.
	* doc/avr-mmcu.texi: Regenerate.
	* doc/invoke.texi (AVR Options) <-mshort-calls>: Document it.
	<__AVR_ARCH__>: Document avrxmega3 and 103.
	<__AVR_HAVE_JMP_CALL__>: Adjust documentation.
	<__AVR_SHORT_CALLS__>: Document it.
	<__AVR_PM_BASE_ADDRESS__>: Document it.
	* doc/extend.texi (AVR Options) <-mshort-calls>: Document it.
	(AVR Variable Attributes) <progmem>: Document this is
	not needed for avrxmega3.
	(AVR Named Address Spaces) <__flash>: Dito.

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