[Libre-soc-isa] [Bug 1048] OPF ISA External RFC ls011 - Fixed and Floating point LD/ST-with-update EXT2xx instructions

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=1048

--- Comment #32 from Jacob Lifshay <programmerjake at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #31)
> main point: without post-increment which is present in other ISAs
> such as 68000 and x86 it is necessary to pre-decrement outside of
> a loop. this is inappropriate in many scenarios.

post-increment is barely present in x86, it's only in the stack-popping
instructions (where they increment esp/rsp after reading) and
stringinstructions (the non-rep-prefixed form of which are rarely used
presumably because they're slow) and no where else iirc -- so not general
purpose enough to be used in loops like you want, gcc and clang generate
separate add/inc instructions.

68000 only has post-increment, no pre-increment.

I would use arm64 as the example, since it has both post and pre-increment and
is widely used.

https://gcc.godbolt.org/z/j11za7Pff

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