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From: dfawcus+lists-tuhs@employees.org (Derek Fawcus)
Date: Sun, 14 May 2017 14:14:44 +0100
Subject: [TUHS] C declarations.
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On Sat, May 13, 2017 at 03:05:24PM -0400, Random832 wrote:
> On Sat, May 13, 2017, at 08:20, Michael Kjörling wrote:
> > Correct me if I am wrong, but _pass by value_ as opposed to _pass by
> > reference_ requires making a copy, no? That's the whole point, to
> > allow the callee to poke at the value it is given at will.
> 
> If that were the issue, the callee could simply automatically make the
> copy if-and-only-if it needs it.

I recall reading a proposed ABI for C on MIPS which would have done
something similar for passing structs by value,  namely pass a pointer
but allocate local storage space in the callee.  If the callee ever
assigned to the passed struct,  it was to copy the actual values,
then update its pointer.  I don't think that ABI was ever implemented.

DF