[Libre-soc-bugs] [Bug 1177] revert unauthorized change to pseudocode language

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Mon Oct 2 00:48:09 BST 2023


--- Comment #1 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
ok i took a look at power isa 3.0 using vex_flags and yes it looks
like vex_flags is a "gate" to disable writing to RT.

it is therefore reasonable to "special-case" vex_flags just like
the use of "overflow" in ISACaller to stop RT from being written,
rather than poison the language by adding extraneous external
"guidance" in the markdown.

the language is supposed to be self-describing and self-contained.

the other way to do this is:

    GPR(RT) <- val

but that gets quite involved and is a bit more work, especially when
doing vectorisation and element-width overrides, so it is better to
add a hack to detect vex_flags as the "write-gate" just like overflow
is the write-gate to XER.OV/SO.

please please for goodness sake start describing your intentions when
thinking up these types of changes as there are implications of the
hacks that you come up with which are just not thought through, and
although they appear to "get the job done" in fact cause a lot of damage.

for future work please use branches only so that there is an opportunity
for a full review.

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