Volatile MEMs in statement expressions and functions inlined as trees
Alexandre Oliva
aoliva@redhat.com
Fri Dec 14 10:28:00 GMT 2001
On Dec 14, 2001, Linus Torvalds <torvalds@transmeta.com> wrote:
> t3 = a; // reload 'a'
> t4 = c; // load 'c'
> r2 = t3 + t4; // rvalue of '(a += b) += c
> store r2 into a // stable side effect of whole expression
> See? We end up reloading 'a' - simply because on the left side of the
> assignment we have to use the lvalue.
Interesting. That's a very reasonable and consistent approach. But
``The behavior of an expression of the form E1 op= E2 is equivalent
to E1=E1 op E2 except that E1 is evaluated only once.'' [expr.ass]/7
seems to imply that:
(a += b) += c;
should be equivalent to
a = (a += b) + c;
but, according to my understanding of your interpretation, this
doesn't hold, because the latter would not load back from a after the
+= assignment, whereas the former would.
--
Alexandre Oliva Enjoy Guarana', see http://www.ic.unicamp.br/~oliva/
Red Hat GCC Developer aoliva@{cygnus.com, redhat.com}
CS PhD student at IC-Unicamp oliva@{lsd.ic.unicamp.br, gnu.org}
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