> > Hi,
> > the alias-2.c testcase fails on targets with anchors. The reason is that
> > the variable itself is anchored while the alias is not and they point to the
> > same location. I folllowed the docs of SYMBOL_REF claiming that
> > SYMBOL_REF_DECL if the symbol is label and tought it is safe to disambiguate
> > them.
>
> What kind of distinction do you mean between "label" and non-label here?
>
> I don't think !SYMBOL_REF_DECL tells us anything useful about the
> symbol. I think it's more a case of: if SYMBOF_REF_DECL is present,
> we can assume that what it says is accurate. If it isn't present we
> can't assume anything.
>
> So was it...
>
> Jan Hubicka <hubi...@ucw.cz> writes:
> > @@ -2323,26 +2367,14 @@
> >
> > if (GET_CODE (x) == SYMBOL_REF && GET_CODE (y) == SYMBOL_REF)
> > {
> > - tree x_decl = SYMBOL_REF_DECL (x);
> > - tree y_decl = SYMBOL_REF_DECL (y);
> > - int cmp;
> > + int cmp = compare_base_symbol_refs (x,y);
> >
> > - if (!x_decl || !y_decl)
> > - {
> > - /* Label and normal symbol are never the same. */
> > - if (x_decl != y_decl)
> > - return 0;
> > - return offset_overlap_p (c, xsize, ysize);
>
> ...this part of the code that was causing the problem? That doesn't
> seem valid even without the anchor stuff. I think the starting position
Yep, I misread the docs assuming that SYMBOL_REF_DECL == NULL only
for code labels. It is always safe to disambiguate these as they access
readonly memory anyway.
> should be that we can only use offset_overlap_p if XSTR (x) == XSTR (y)
> and need to assume a conflict otherwise. E.g. I think in principle it's
> valid for a target to create symbol_refs for different parts of a single
> artificial object.
The code original was:
if (rtx_equal_for_memref_p (x, y))
{
return offset_overlap_p (c, xsize, ysize);
}
and
rtx_equal_for_memref_p (const_rtx x, const_rtx y)
{
...
case SYMBOL_REF:
return XSTR (x, 0) == XSTR (y, 0);
So it assumed base+offset check for all labels with same XSTR. My patch
makes this strictly weaker: it is possible that the same variable is
accessed via its own symbol or via offset from variable anchor.
>
> I agree there are other refinements you can do on top of that,
> e.g. that two block symbols in different blocks can never conflict.
> But the patch seems to be treating anchors as an exception to the rule,
> whereas I think they're just one instance of the rule.
Can you think of some testcase?
Doing XSTR==XSTR test and assuming a conflict otherwise will cause a conflict
between
every external variable read/write and static variable read/write as one will
be anchored
and other not.
Honza
>
> Thanks,
> Richard
