Andrew Haley wrote:
Roberto COSTA writes:
> Andrew Haley wrote:
> > Chris Jefferson writes:
> >
> > > One thing which comes up regularly in various C and C++
> > > messageboards is that statements like "f() + g()" and "a(f(), g())"
> > > do not declare which order f() and g() will be executed in.
> > >
> > > How hard would it be to fix the order of execution in gcc/g++?
> > > Could someone point me to the piece of code which must change, or
> > > if it is only a very small change, the actual change required? I
> > > would very much like to be able to benchmark this, as I can find no
> > > previous case where someone has tried fixing the order of execution
> > > to see if it actually makes any measureable difference.
> >
> > The easiest way is during gimplification: you'd walk over the arglist
> > from left to right, calling
> >
> > gimplify_expr (&arg, pre_p, post_p,
> > is_gimple_formal_tmp_var, fb_rvalue);
> >
> > on each arg.
>
> But would it be sufficient?
I think so.
> I guess you would also have to make sure that further passes (i.e.
> out-of-ssa) do not revert what you have just done.
If any arg had side-effects that would be a bug.
Actually, I was thinking about the case "g(a(), b());".
Let's imagine the gimplified code (because of your change) looks like:
t1 = a();
t2 = b();
g(t1, t2);
Are we always sure that t1 and t2 will not be pushed again in the
CALL_EXPR by further transformations?
Roberto
