Assembly output optimisations (was: PR 51094 - fprint_w() in output_addr_const() reinstated)

[Dimitrios Apostolou <jimis at gmx dot net>]

Hello list,

these clean-ups and minor speedups complete some TODOs and semi-finished 
changes I have gathered in the ELF backend. In a nutshell:

Fixed comment style, used INT_BITS_STRLEN_BOUND from gnulib to be future 
proof on integer representation string length, replaced long arguments in 
fast printing functions with HOST_WIDE_INT that is always a larger type 
(also asserted that), converted some never-negative ints to unsigned. 
Guarded the output.h:default_elf_asm_output_* declarations, mimicking 
varasm.c (I'm not exactly sure why this is guarded in the first place). 
Changed default_elf_asm_output_* to be clearer and faster, they now 
fwrite() line by line instead of putting char by char. Implemented fast 
octal output in default_elf_asm_output_*, this should give a good boost to 
-flto, but I haven't measured a big testcase for this one.

All in all I get a speed-up of ~30 M instr out of ~2 G instr, for -g3 
compilation of reload.c. Actually saving all the putc() calls gives more 
significant gain, but I lost a tiny bit because of converting [sf]print_* 
functions to HOST_WIDE_INT from long, for PR 51094. So on i586 which has 
HOST_WIDE_INT 8 byte wide, I can see slow calls to __u{div,mod}di3 taking 
place. I don't know whether there is a meaning in writing LEB128 values 
greater than 2^31 but I could change all that to HOST_WIDEST_FAST_INT if 
you think so.

Time savings are minor too, about 10 ms out of 0.85 s. Memory usage is the 
same. Bootstrapped on x86, no regressions for C,C++ testsuite.


Thanks Andreas, hp, Mike, for your comments. Mike I'd appreciate if you 
elaborated on how to speed-up sprint_uw_rev(), I don't think I understood 
what you have in mind.

Thanks,
Dimitris

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