On 23 Nov 11:44, Richard Biener wrote:
> On Mon, Nov 23, 2015 at 11:10 AM, Ilya Enkovich <enkovich....@gmail.com>
> wrote:
> > On 23 Nov 10:39, Richard Biener wrote:
> >> On Fri, Nov 20, 2015 at 3:30 PM, Ilya Enkovich <enkovich....@gmail.com>
> >> wrote:
> >> > On 20 Nov 14:54, Richard Biener wrote:
> >> >>
> >> >> I don't think you can in any way rely on the pointer type of the src
> >> >> argument
> >> >> as all pointer conversions are useless and memcpy and friends take void
> >> >> *
> >> >> anyway.
> >> >
> >> > This check is looking for cases when we have type information indicating
> >> > no pointers are copied. In case of 'void *' we have to assume pointers
> >> > are copied and inlining is undesired. Test pr68337-2.c checks pointer
> >> > type allows to enable inlining. Looks like this check misses
> >> > || !COMPLETE_TYPE_P(TREE_TYPE (TREE_TYPE (src)))?
> >>
> >> As said there is no information in the pointer / pointed-to type in GIMPLE.
> >
> > What does it mean? We do have TREE_TYPE for used pointer and nested
> > TREE_TYPE
> > holding pointed-to type. Is it some random invalid type?
>
> Yes, it can be a "random" type. Like for
>
> void foo (float *f)
> {
> memcpy ((void *)f, ...);
> }
> int main()
> {
> int **a[10];
> foo (a);
> }
>
> which tries to copy to an array of int * but the GIMPLE IL for foo
> will call memcpy with a float * typed argument.
I see. But it should still be OK to check type in case of strict aliasing,
right?
Thanks,
Ilya
>
> >>
> >> >>
> >> >> Note that you also disable memmove to memcpy simplification with this
> >> >> early check.
> >> >
> >> > Doesn't matter for MPX which uses the same implementation for both cases.
> >> >
> >> >>
> >> >> Where is pointer transfer handled for MPX? I suppose it's not done
> >> >> transparently
> >> >> for all memory move instructions but explicitely by instrumented block
> >> >> copy
> >> >> routines in libmpx? In which case how does that identify pointers vs.
> >> >> non-pointers?
> >> >
> >> > It is handled by instrumentation pass. Compiler checks type of stored
> >> > data to
> >> > find pointer stores. Each pointer store is instrumented with bndstx
> >> > call.
> >>
> >> How does it identify "pointer store"? With -fno-strict-aliasing you can
> >> store
> >> pointers using an integer type. You can also always store pointers using
> >> a character type like
> >>
> >> void foo (int *p, int **dest)
> >> {
> >> ((char *)*dest)[0] = (((char *)&p)[0];
> >> ((char *)*dest)[1] = (((char *)&p)[1];
> >> ((char *)*dest)[2] = (((char *)&p)[2];
> >> ((char *)*dest)[3] = (((char *)&p)[3];
> >> }
> >
> > Pointer store is identified using type information. When pointer is casted
> > to
> > a non-pointer type its bounds are lost.
> >
> > Ilya
> >
> >>
> >> > MPX versions of memcpy, memmove etc. don't make any assumptions about
> >> > type of copied data and just copy whole chunk of bounds metadata
> >> > corresponding
> >> > to copied block.
> >>
> >> So it handles copying a pointer in two pieces with two memcpy calls
> >> correctly. Good.
> >>
> >> Richard.
> >>
> >> > Thanks,
> >> > Ilya
> >> >
> >> >>
> >> >> Richard.
> >> >>
