Fix handling of stores in modref_summary::useful_p

[Szabolcs Nagy]

The 10/05/2020 17:28, Szabolcs Nagy via Gcc-patches wrote:
> The 10/05/2020 12:52, Vaseeharan Vinayagamoorthy wrote:
> > Hi,
> > 
> > After this patch, I am noticing that some glibc crypto tests get stuck in scanf which goes into busy loop.
> > 
> > My build/host/target setup is:
> > Build: aarch64-none-linux-gnu
> > Host: aarch64-none-linux-gnu
> > Target: aarch64-none-linux-gnu
> 
> i can reproduce this on aarch64, i'm looking at it:
> 
> if i compile glibc with gcc trunk after this commit i see
> 
> $ ./testrun.sh crypt/cert < $glibcsrc/crypt/cert.input
>  K: 0000000000000000 P: 0000000000000000 C: 0000000000000000 Encrypt FAIL
>  K: 0000000000000000 P: 0000000000000000 C: 0000000000000000 Encrypt FAIL
>  K: 0000000000000000 P: 0000000000000000 C: 0000000000000000 Encrypt FAIL
>  K: 0000000000000000 P: 0000000000000000 C: 0000000000000000 Encrypt FAIL
>  K: 0000000000000000 P: 0000000000000000 C: 0000000000000000 Encrypt FAIL
>  K: 0000000000000000 P: 0000000000000000 C: 0000000000000000 Encrypt FAIL
> ...
> 
> it just keeps printing this.
> 
> same test binary with glibc code compiled with an
> older gcc works, so something in glibc gets miscompiled.
> 
> i will have to do more digging to figure out what.

minimal reproducer:

#include <stdio.h>
int main()
{
        int r,t;
        r = sscanf("01", "%2x", &t);
        printf("scanf: %d  %02x\n", r, t);
        return 0;
}

should print

scanf: 1  01

but when glibc is compiled with gcc trunk on aarch64 it prints

scanf: 0  00

i will continute the debugging from here tomorrow.


> > On 27/09/2020, 22:46, "Gcc-patches on behalf of Jan Hubicka" <gcc-patches-bounces@gcc.gnu.org on behalf of hubicka@ucw.cz> wrote:
> > 
> >     Hi,
> >     this patch fixes a pasto in modref_summary::useful_p that made
> >     ipa-modref to give up on tracking stores when all load info got lost.
> > 
> >     Bootstrapped/regtested x86_64-linux, comitted.
> > 
> >     gcc/ChangeLog:
> > 
> >     2020-09-27  Jan Hubicka  <hubicka@ucw.cz>
> > 
> >     * ipa-modref.c (modref_summary::useful_p): Fix testing of stores.
> > 
> >     diff --git a/gcc/ipa-modref.c b/gcc/ipa-modref.c
> >     index 728c6c1523d..6225552e41a 100644
> >     --- a/gcc/ipa-modref.c
> >     +++ b/gcc/ipa-modref.c
> >     @@ -135,7 +135,7 @@ modref_summary::useful_p (int ecf_flags)
> >          return true;
> >        if (ecf_flags & ECF_PURE)
> >          return false;
> >     -  return stores && !loads->every_base;
> >     +  return stores && !stores->every_base;
> >      }
> > 
> >      /* Dump A to OUT.  */
> >