On Mon, Nov 29, 2021 at 3:48 PM Richard Biener
<richard.guent...@gmail.com> wrote:
>
> On Mon, Nov 29, 2021 at 3:39 PM Jeff Law <jeffreya...@gmail.com> wrote:
> >
> >
> >
> > On 11/29/2021 7:00 AM, Aldy Hernandez via Gcc-patches wrote:
> > > As discussed in the PR. The code makes no difference, so whatever test
> > > we added this special case for has been fixed or is being papered over.
> > > I think we should fix any fall out upstream.
> > >
> > > [Unless Andrew can remember why we added this and it still applies.]
> > >
> > > Tested on x86-64 Linux.
> > >
> > > OK for trunk?
> > >
> > > PR 103451
> > >
> > > gcc/ChangeLog:
> > >
> > > * range-op.cc (operator_div::wi_fold): Remove
> > > can_throw_non_call_exceptions special case.
> > >
> > > gcc/testsuite/ChangeLog:
> > >
> > > * gcc.dg/pr103451.c: New test.
> > I'll defer to Andrew, but it seems wrong to me. The whole point is to
> > set the result to varying so that we don't know the result and never
> > remove the division which is critical for -fnon-call-exceptions.
>
> But that has nothing to do with computing the value range for
> the result which is only accessible when the stmt does _not_ throw ...
>
> That is, if we compute non-VARYING here and because of that
> remove the stmt then _that's_ the place to fix (IMO)
Ughh, I think you're both right.
We should fix this upstream AND we should test for the presence of the
division by 0 in the optimized dump.
Of course doing both opens a can of worms. The division by zero can
be cleaned up by (at least) DCE, DSE, and the code sinking passes.
I've fixed all 3 in the attached (untested) patch. Dunno what y'all
want to do at this point.
Aldy
From c521bd22d4a7360c7b01f864392eb5cf68cfc6f0 Mon Sep 17 00:00:00 2001
From: Aldy Hernandez <al...@redhat.com>
Date: Mon, 29 Nov 2021 12:52:45 +0100
Subject: [PATCH] Remove can_throw_non_call_exceptions special case from
operator_div::wi_fold.
PR 103451
gcc/ChangeLog:
* range-op.cc (operator_div::wi_fold): Remove
can_throw_non_call_exceptions special case.
* tree-ssa-dce.c (mark_stmt_if_obviously_necessary): Check for
can_throw_non_call_exceptions.
* tree-ssa-dse.c (pass_dse::execute): Same.
* tree-ssa-sink.c (sink_code_in_bb): Same.
gcc/testsuite/ChangeLog:
* gcc.dg/pr103451.c: New test.
---
gcc/range-op.cc | 7 -------
gcc/testsuite/gcc.dg/pr103451.c | 19 +++++++++++++++++++
gcc/tree-ssa-dce.c | 3 ++-
gcc/tree-ssa-dse.c | 3 ++-
gcc/tree-ssa-sink.c | 4 +++-
5 files changed, 26 insertions(+), 10 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/pr103451.c
diff --git a/gcc/range-op.cc b/gcc/range-op.cc
index bbf2924f815..6fe5f1cb4e0 100644
--- a/gcc/range-op.cc
+++ b/gcc/range-op.cc
@@ -1832,13 +1832,6 @@ operator_div::wi_fold (irange &r, tree type,
return;
}
- // If flag_non_call_exceptions, we must not eliminate a division by zero.
- if (cfun->can_throw_non_call_exceptions)
- {
- r.set_varying (type);
- return;
- }
-
// If we're definitely dividing by zero, there's nothing to do.
if (wi_zero_p (type, divisor_min, divisor_max))
{
diff --git a/gcc/testsuite/gcc.dg/pr103451.c b/gcc/testsuite/gcc.dg/pr103451.c
new file mode 100644
index 00000000000..90a584490ae
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr103451.c
@@ -0,0 +1,19 @@
+// { dg-do compile }
+// { dg-options "-O2 -w -fnon-call-exceptions -fdump-tree-optimized" }
+
+int func_10_ptr_12;
+
+void func_10(long li_8)
+{
+ long *ptr_9 = &li_8;
+ li_8 &= *ptr_9 / 0 ?: li_8;
+ for (;;)
+ func_10_ptr_12 &= 4 ? *ptr_9 : 4;
+}
+
+void func_9_s_8()
+{
+ func_10(func_9_s_8);
+}
+
+// { dg-final { scan-tree-dump " / 0" "optimized" } }
diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c
index 1f817b95fab..1c1a5cc0811 100644
--- a/gcc/tree-ssa-dce.c
+++ b/gcc/tree-ssa-dce.c
@@ -304,7 +304,8 @@ mark_stmt_if_obviously_necessary (gimple *stmt, bool aggressive)
/* If a statement could throw, it can be deemed necessary unless we
are allowed to remove dead EH. Test this after checking for
new/delete operators since we always elide their EH. */
- if (!cfun->can_delete_dead_exceptions
+ if ((!cfun->can_delete_dead_exceptions
+ || cfun->can_throw_non_call_exceptions)
&& stmt_could_throw_p (cfun, stmt))
{
mark_stmt_necessary (stmt, true);
diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
index 8717d654e5a..aa16565b429 100644
--- a/gcc/tree-ssa-dse.c
+++ b/gcc/tree-ssa-dse.c
@@ -1446,7 +1446,8 @@ pass_dse::execute (function *fun)
&& !gimple_has_side_effects (stmt)
&& !is_ctrl_altering_stmt (stmt)
&& (!stmt_could_throw_p (fun, stmt)
- || fun->can_delete_dead_exceptions))
+ || (fun->can_delete_dead_exceptions
+ && !cfun->can_throw_non_call_exceptions)))
{
if (dump_file && (dump_flags & TDF_DETAILS))
{
diff --git a/gcc/tree-ssa-sink.c b/gcc/tree-ssa-sink.c
index 92f444ec1c8..29299129cfa 100644
--- a/gcc/tree-ssa-sink.c
+++ b/gcc/tree-ssa-sink.c
@@ -696,7 +696,9 @@ sink_code_in_bb (basic_block bb)
/* If we face a dead stmt remove it as it possibly blocks
sinking of uses. */
if (zero_uses_p
- && ! gimple_vdef (stmt))
+ && !gimple_vdef (stmt)
+ && (cfun->can_delete_dead_exceptions
+ && !cfun->can_throw_non_call_exceptions))
{
gsi_remove (&saved, true);
release_defs (stmt);
--
2.31.1
