[Libre-soc-bugs] [Bug 558] gcc SV intrinsics concept

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=558

--- Comment #26 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
(In reply to Jacob Lifshay from comment #24)

> I'm inclined to define two different ABIs where one has VL be clobbered by
> calls and the other has it be saved by calls, though I'm not sure which
> should be default.

the generally-accepted industry-standard wisdom here is that making function
calls *at all* from inside a vectorised loop (unless they are static inline) is
simply too hard a problem to consider let alone write an ABI for.

if this wisdom is accepted then the problem entirely disappears.  VL does not
need saving (except by traps / contextswitching which is not the program's
responsibility)

remember that this is a Sub-Program-Counter we are talking about.

the idea of letting the compiler "loose" on VL is one that us effectively
equivalent to allowing "gotos" within a sub-function.  it's a similar level of
insanity.

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