12 Mar
2023
12 Mar
'23
5:40 p.m.
On Sun, Mar 12, 2023, 3:39 AM Anthony Martin <ality(a)pbrane.org> wrote:
Dan Cross <crossd(a)gmail.com> once said:
Indeed. I typo-ed but meant caller-save; it wouldn't be very svelte if it
were the other way around. ;-)
Waserror works well except for one small issue
I'm told that the plan9 C compilers were
callee-save in part to keep
these state labels svelte.
The Plan 9 compilers are caller-save. That means the labels only have
to contain pc and sp. involving whether or not the compiler decides to store
a value to a
non-volatile, non-pointer variable when the value would not be used
after a function call. As in:
int a;
a = 1;
if(waserror()){ /* ... */ }
a = 2;
a = foo(a);
The waserror branch may see a == 1 if foo errors.
Ken's compilers are great, though. They don't engage in antisocial
optimizations based on dubious notions of undefined behavior. I'd
prefer my compiler to not elide explicit null checks or loads and
stores from a pointer.
It is certainly a shame that modern compiler writers have become
essentially hostile to programmers in their pursuit of ever more aggressive
optimizations based on rigid readings of the standard, common sense be
damned.
As for the plan9 C _language_, in the late 80s, it was arguably an
improvement over what ANSI put out. Nowadays, however, I think the inverse
is true. *Shrug*
- Dan C.