On Thu, Jan 30, 2020 at 11:49 AM Prathamesh Kulkarni
<prathamesh.kulka...@linaro.org> wrote:
>
> On Wed, 29 Jan 2020 at 14:38, Richard Biener <richard.guent...@gmail.com>
> wrote:
> >
> > On Tue, Jan 28, 2020 at 1:02 PM Jakub Jelinek <ja...@redhat.com> wrote:
> > >
> > > On Tue, Jan 28, 2020 at 05:09:36PM +0530, Prathamesh Kulkarni wrote:
> > > > On Tue, 28 Jan 2020 at 17:00, Jakub Jelinek <ja...@redhat.com> wrote:
> > > > >
> > > > > On Tue, Jan 28, 2020 at 04:56:59PM +0530, Prathamesh Kulkarni wrote:
> > > > > > Thanks for the suggestions. In the attached patch I bumped up value
> > > > > > of
> > > > > > ERF_RETURNS_ARG_MASK
> > > > > > to UINT_MAX >> 2, and use highest two bits for ERF_NOALIAS and
> > > > > > ERF_RETURNS_ARG.
> > > > > > And use fn spec "Z<argnum>" to store the argument number in fn-spec
> > > > > > format.
> > > > > > Does that look OK ?
> > > > >
> > > > > No.
> > > > >
> > > > > +#define ERF_RETURN_ARG_MASK (UINT_MAX >> 2)
> > > > >
> > > > > /* Nonzero if the return value is equal to the argument number
> > > > > flags & ERF_RETURN_ARG_MASK. */
> > > > > -#define ERF_RETURNS_ARG (1 << 2)
> > > > > +#define ERF_RETURNS_ARG (1 << (BITS_PER_WORD - 2))
> > > > >
> > > > > How is size of host int related to BITS_PER_WORD? Not to mention that
> > > > > if BITS_PER_WORD is 64 and host int is 32-bit, 1 << (64 - 2) is UB.
> > > > Oops sorry. I should have used HOST_BITS_PER_INT.
> > > > I assume that'd be correct ?
> > >
> > > It still wouldn't, 1 << (HOST_BITS_PER_INT - 1) is negative number, you'd
> > > need either 1U and verify all ERF_* flags uses, or avoid using the sign
> > > bit.
> > > The patch has other issues, you don't verify that the argnum fits into
> > > the bits (doesn't overflow into the other ERF_* bits), in
> > > + char *s = (char *) xmalloc (sizeof (char) * BITS_PER_WORD);
> > > + s[0] = 'Z';
> > > + sprintf (s + 1, "%lu", argnum);
> > > 1) sizeof (char) is 1 by definition
> > > 2) it is pointless to allocate it and then deallocate (just use automatic
> > > array)
> > > 3) it is unclear how is BITS_PER_WORD related to the length of decimal
> > > encoded string + Z char + terminating '\0'. The usual way is for unsigned
> > > numbers to estimate number of digits by counting 3 digits per each 8 bits,
> > > in your case of course + 2.
> > >
> > > More importantly, the "fn spec" attribute isn't used just in
> > > gimple_call_return_flags, but also in e.g. gimple_call_arg_flags which
> > > assumes that the return stuff in there is a single char and the reaming
> > > chars are for argument descriptions, or in decl_return_flags which you
> > > haven't modified.
> > >
> > > I must say I fail to see the point in trying to glue this together into
> > > the
> > > "fn spec" argument so incompatibly, why can't we handle the fn spec with
> > > its
> > > 1-4 returns_arg and returns_arg attribute with arbitrary position
> > > side-by-side?
> >
> > Yeah, I wouldn't have added "fn spec" for "returns_arg" but kept the
> > query interface thus access it via gimple_call_return_flags and use
> > ERF_*. For the flags adjustment just up the maximum argument
> > to 1<<15 then the argument number is also nicely aligned, no need
> > to do fancy limiting that depends on the host. For too large
> > argument numbers just warn the attribute is ignored. I'd say even
> > a max of 255 is sane just the existing limit is a bit too low.
> Hi,
> Thanks for the suggestions. In the attached patch, I use TREE_VALUE
> (attr) to store/retrieve
> arbitrary argument position, and have bumped ERF_RETURNS_ARG_MASK to 0x3fff.
> Does it look OK ?
+ warning_at (DECL_SOURCE_LOCATION (decl), OPT_Wattributes,
+ "%qE attribute ignored on a function returning %qT.",
+ name, rettype);
no punctuation in diagnostics (trailing '.'), also elsewhere in the patch.
+ tree fndecl = gimple_call_fndecl (stmt);
+ attr = lookup_attribute ("returns_arg", DECL_ATTRIBUTES (fndecl));
+ if (attr)
+ {
+ unsigned argnum = tree_to_uhwi (TREE_VALUE (TREE_VALUE (attr)));
+ return ERF_RETURNS_ARG | argnum;
please verify argnum against ERF_ARG_MASK.
+ tree attr = lookup_attribute ("returns_arg", DECL_ATTRIBUTES (decl));
+ if (attr)
+ TREE_VALUE (attr) = build_int_cst (unsigned_type_node, argnum);
+ else
+ DECL_ATTRIBUTES (decl)
+ = tree_cons (get_identifier ("returns_arg"),
+ build_int_cst (unsigned_type_node, argnum),
+ DECL_ATTRIBUTES (decl));
+ return NULL_TREE;
what's this for? for *no_add_attrs = false you get the attribute
added by the caller.
Also other positional_argument callers overwrite TREE_VALUE with the result
from the function.
> Thanks,
> Prathamesh
> >
> > Richard.
> >
> > > Jakub
> > >
