[Libre-soc-bugs] [Bug 238] POWER Compressed Formal Standard writeup

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Thu Nov 19 03:17:10 GMT 2020


--- Comment #41 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
i had a go at creating some ld/st r1 imm opcodes.  the imm range is reduced by
1 bit so as to fit the 4x combination of ld/st + d/w into only the 1 Cmaj

i took out addis and crammed cmpw/d into one Cmaj.m to get the full Cmaj to do

i have no idea what impact, statistically,  that will have on C.cmp, it would
be necessary to see some of the values of immediates used.

however, coming back to ld/st r1: the immediate range is 0-127 even with 1 bit
shared, which for doubles (ldi, stdi) is x8 so 0 to (1024-8) and for words
(lwi, stwi) is x4 so 0 to (512-4)

which given it's primarily intended for stack usage seems pretty damn enormous
if you ask me :)

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