On Thu, Feb 9, 2023 at 12:07 AM Richard Biener via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Wed, Feb 8, 2023 at 8:14 PM Andrew Pinski via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > In simple_dce_from_worklist, we were removing an inline-asm which had a vdef
> > (due to clobbering memory) but not unlinking the statement's vdef.
> > This fixes that oversight. This was a latent bug exposed recently
> > by both VRP and removal of stores to static starting to use
> > simple_dce_from_worklist.
> >
> > OK for trunk (and for GCC 12 after a week)?
> > Bootstrapped and tested on x86_64-linux-gnu with no regressions.
>
> I think this is actually wrong-code - we cannot remove memory side-effects
> of a stmt and the
>
> /* The defining statement needs to be defining only this name.
> ASM is the only statement that can define more than one
> (non-virtual) name. */
> if (is_a<gasm *>(t)
> && !single_ssa_def_operand (t, SSA_OP_DEF))
> continue;
>
> should use SSA_OP_ALL_DEFS instead.
Yes there is definitely wrong code. Will implement this change and add
a testcase which was being definitely being miscompiled (I put the
testcase in the bug report already).
Thanks,
Andrew Pinski
>
> OK with that change.
>
> Richard.
>
> > PR tree-optimization/108684
> >
> > gcc/ChangeLog:
> >
> > * tree-ssa-dce.cc (simple_dce_from_worklist):
> > Call unlink_stmt_vdef on the statement before
> > removing it.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * gcc.c-torture/compile/dce-inline-asm-1.c: New test.
> > * gcc.c-torture/compile/dce-inline-asm-2.c: New test.
> >
> > co-authored-by: Andrew Macleod <amacl...@redhat.com>
> > ---
> > .../gcc.c-torture/compile/dce-inline-asm-1.c | 15 +++++++++++++++
> > .../gcc.c-torture/compile/dce-inline-asm-2.c | 16 ++++++++++++++++
> > gcc/tree-ssa-dce.cc | 1 +
> > 3 files changed, 32 insertions(+)
> > create mode 100644 gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-1.c
> > create mode 100644 gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-2.c
> >
> > diff --git a/gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-1.c
> > b/gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-1.c
> > new file mode 100644
> > index 00000000000..a9f02e44bd7
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-1.c
> > @@ -0,0 +1,15 @@
> > +/* PR tree-optimization/108684 */
> > +/* This used to ICE as when we remove the store to
> > + `t`, we also would remove the inline-asm which
> > + had a VDEF on it but we didn't update the
> > + VUSE that was later on. */
> > +static int t;
> > +
> > +int f (int *a)
> > +{
> > + int t1;
> > + asm (" " : "=X" (t1) : : "memory");
> > + t = t1;
> > + return *a;
> > +}
> > +
> > diff --git a/gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-2.c
> > b/gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-2.c
> > new file mode 100644
> > index 00000000000..a41b16e4bd0
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.c-torture/compile/dce-inline-asm-2.c
> > @@ -0,0 +1,16 @@
> > +/* PR tree-optimization/108684 */
> > +/* This used to ICE as when we removed the
> > + __builtin_unreachable in VRP, as we
> > + would also remove the branch and the
> > + inline-asm. The inline-asm had a VDEF on it,
> > + which we didn't update further along and
> > + not have the VDEF on the return statement
> > + updated. */
> > +
> > +int f (int a)
> > +{
> > + asm (" " : "=X" (a) : : "memory");
> > + if (a)
> > + return 0;
> > + __builtin_unreachable();
> > +}
> > diff --git a/gcc/tree-ssa-dce.cc b/gcc/tree-ssa-dce.cc
> > index b2fe9f4f55e..752785541e4 100644
> > --- a/gcc/tree-ssa-dce.cc
> > +++ b/gcc/tree-ssa-dce.cc
> > @@ -2140,6 +2140,7 @@ simple_dce_from_worklist (bitmap worklist)
> > remove_phi_node (&gsi, true);
> > else
> > {
> > + unlink_stmt_vdef (t);
> > gsi_remove (&gsi, true);
> > release_defs (t);
> > }
> > --
> > 2.31.1
> >
