On Sun, Aug 22, 2021 at 11:47 PM H.J. Lu via Gcc-patches <
gcc-patches@gcc.gnu.org> wrote:
> On Sun, Aug 22, 2021 at 10:32 AM Jan Hubicka <hubi...@ucw.cz> wrote:
> >
> > > Thanks for looking into this bug - it is interesting that ipa-pta
> > > requires !EAF_NOCLOBBER when function is called...
> > >
> > > I have some work done on teaching ipa-modref (and other propagation
> > > passes) to use ipa-devirt info when the full set of callees is known.
> > > This goes oposite way.
> > >
> > > You can drop flags only when callee == NAME and you can just frop
> > > EAF_NOCLOBBER. For example in testcase
> > >
> > > struct a {
> > > void (*foo)();
> > > void *bar;
> > > }
> > >
> > > void wrap (struct a *a)
> > > {
> > > a->foo ();
> > > }
> > >
> > > will prevent us from figuring out that bar can not be modified when you
> > > pass non-ecaping instance of struct a to wrap.
> > >
> >
> > I am testing this updated patch which implements that. I am not very
> > happy about this (it punishes -fno-ipa-pta path for not very good
> > reason), but we need bugfix for release branch.
> >
> > It is very easy now to add now EAF flags at modref side
> > so we can track EAF_NOT_CALLED.
> > tree-ssa-structalias side is always bit anoying wrt new EAF flags
> > because it has three copies of the code building constraints for call
> > (for normal, pure and const).
> >
> > Modref is already tracking if function can read/modify global memory. I
> > plan to add flags for NRC and link chain and then we can represent
> > effect of ECF_CONST and PURE by simply adding flags. I would thus would
> > like to merge that code. We do various optimizations to reduce amount
> > of constriants produced, but hopefully this is not very important (or
> > can be implemented by special casing in unified code).
> >
> > Honza
> >
> > gcc/ChangeLog:
> >
> > 2021-08-22 Jan Hubicka <hubi...@ucw.cz>
> > Martin Liska <mli...@suse.cz>
> >
> > * ipa-modref.c (analyze_ssa_name_flags): Indirect call implies
> > ~EAF_NOCLOBBER.
> >
> > gcc/testsuite/ChangeLog:
> >
> > 2021-08-22 Jan Hubicka <hubi...@ucw.cz>
> > Martin Liska <mli...@suse.cz>
> >
> > * gcc.dg/lto/pr101949_0.c: New test.
> > * gcc.dg/lto/pr101949_1.c: New test.
> >
> > diff --git a/gcc/ipa-modref.c b/gcc/ipa-modref.c
> > index fafd804d4ba..549153865b8 100644
> > --- a/gcc/ipa-modref.c
> > +++ b/gcc/ipa-modref.c
> > @@ -1700,6 +1700,15 @@ analyze_ssa_name_flags (tree name,
> vec<modref_lattice> &lattice, int depth,
> > else if (gcall *call = dyn_cast <gcall *> (use_stmt))
> > {
> > tree callee = gimple_call_fndecl (call);
> > +
> > + /* IPA PTA internally it treats calling a function as
> "writing" to
> > + the argument space of all functions the function pointer
> points to
> > + (PR101949). We can not drop EAF_NOCLOBBER only when ipa-pta
> > + is on since that would allow propagation of this from
> -fno-ipa-pta
> > + to -fipa-pta functions. */
> > + if (gimple_call_fn (use_stmt) == name)
> > + lattice[index].merge (~EAF_NOCLOBBER);
> > +
> > /* Return slot optimization would require bit of propagation;
> > give up for now. */
> > if (gimple_call_return_slot_opt_p (call)
> > diff --git a/gcc/testsuite/gcc.dg/lto/pr101949_0.c
> b/gcc/testsuite/gcc.dg/lto/pr101949_0.c
> > new file mode 100644
> > index 00000000000..142dffe8780
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/lto/pr101949_0.c
> > @@ -0,0 +1,20 @@
> > +/* { dg-lto-do run } */
> > +/* { dg-lto-options { "-O2 -fipa-pta -flto -flto-partition=1to1" } } */
> > +
> > +extern int bar (int (*)(int *), int *);
> > +
> > +static int x;
> > +
> > +static int __attribute__ ((noinline)) foo (int *p)
> > +{
> > + *p = 1;
> > + x = 0;
> > + return *p;
> > +}
> > +
> > +int main ()
> > +{
> > + if (bar (foo, &x) != 0)
> > + __builtin_abort ();
> > + return 0;
> > +}
> > diff --git a/gcc/testsuite/gcc.dg/lto/pr101949_1.c
> b/gcc/testsuite/gcc.dg/lto/pr101949_1.c
> > new file mode 100644
> > index 00000000000..871d15c9bfb
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/lto/pr101949_1.c
> > @@ -0,0 +1,4 @@
> > +int __attribute__((noinline,noclone)) bar (int (*fn)(int *), int *p)
> > +{
> > + return fn (p);
> > +}
>
> On Linux/x86-64 with -m32, I got
>
> FAIL: gcc.dg/lto/pr101949 c_lto_pr101949_0.o-c_lto_pr101949_1.o
> execute -O2 -fipa-pta -flto -flto-partition=1to1
>
>
It fails on aarch64 and arm too.
>
> --
> H.J.
>
