https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107561
--- Comment #17 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #16)
> (In reply to Richard Biener from comment #15)
> > The compiler doesn't know that the allocation function cannot clobber *this.
> > The C++ frontend tries to communicate this by making 'this' restrict
> > qualified
> > and we make use of that info, but for calls we do not know how to use the
> > info.
> >
> > Maybe we can special-case directly the actual parameter case and compute
> > the restrictness info for the call arguments. The canonical example is
> >
> > void bar (void);
> > struct X {
> > X (int);
> > int i;
> > int j;
> > };
> >
> > X::X(int k)
> > {
> > i = k;
> > bar ();
> > j = i != k;
> > }
> >
> > where if I understand you correctly, bar () is not allowed to modify *this
> > (unless I pass it an argument to it, of course), even if *this is for
> > example
>
> Why? Because it is a constructor and the object isn't fully constructed yet
> at that point? For normal methods I certainly don't see anything that would
> preclude such modifications.
The canonical C example would be
void bar (void);
void foo (struct X * restrict this, int k)
{
this->i = k;
bar ();
this->j = i != k;
}
where as I understand bar () cannot modify what *this points to since it
cannot build a proper derived access from 'this' (unless I pass it to bar).
The C++ frontend annotates 'this' with restrict. For my example I get
void X::X (struct X * const this, int k)
{
# PT = { D.2806 } (nonlocal, restrict)
struct X * const this_5(D) = this;
int k_7(D) = k;
int _1;
bool _2;
int _3;
<bb 2> :
MEM[(struct X *)this_5(D) clique 1 base 1] ={v} {CLOBBER};
MEM[(struct X *)this_5(D) clique 1 base 1].i = k_7(D);
# USE = nonlocal escaped
# CLB = nonlocal escaped
bar ();
_1 = MEM[(struct X *)this_5(D) clique 1 base 1].i;
_2 = _1 != k_7(D);
# RANGE [irange] int [0, 1] NONZERO 0x1
_3 = (int) _2;
MEM[(struct X *)this_5(D) clique 1 base 1].j = _3;
return;
}
