PR tree-optimization/84178 reports a couple of source files that ICE inside
ifcvt when compiled with -03 -fno-tree-forwprop (trunk and gcc 7).
Both cases involve problems with ifcvt's per-BB gimplified predicates.
Testcase 1 fails this assertion within release_bb_predicate during cleanup:
283 if (flag_checking)
284 for (gimple_stmt_iterator i = gsi_start (stmts);
285 !gsi_end_p (i); gsi_next (&i))
286 gcc_assert (! gimple_use_ops (gsi_stmt (i)));
The testcase contains a division in the loop, which leads to
if_convertible_loop_p returning false (due to gimple_could_trap_p being true
for the division). This happens *after* the per-BB gimplified predicates
have been created in predicate_bbs (loop).
Hence tree_if_conversion bails out to "cleanup", but the gimplified predicates
exist and make use of SSA names; for example this conjunction for two BB
conditions:
_4 = h4.1_112 != 0;
_175 = (signed char) _117;
_176 = _175 >= 0;
_174 = _4 & _176;
is using SSA names.
This assertion was added in r236498 (aka
c3deca2519d97c55876869c57cf11ae1e5c6cf8b):
2016-05-20 Richard Biener <rguent...@suse.de>
* tree-if-conv.c (add_bb_predicate_gimplified_stmts): Use
gimple_seq_add_seq_without_update.
(release_bb_predicate): Assert we have no operands to free.
(if_convertible_loop_p_1): Calculate post dominators later.
Do not free BB predicates here.
(combine_blocks): Do not recompute BB predicates.
(version_loop_for_if_conversion): Save BB predicates around
loop versioning.
* gcc.dg/tree-ssa/ifc-cd.c: Adjust.
The following patch fixes this by removing the assertion, and reinstating the
cleanup of the operands.
Testcase 2 segfaults inside update_ssa when called from
version_loop_for_if_conversion when a loop is versioned.
During loop_version, some blocks are duplicated, and this can duplicate
SSA names, leading to the duplicated SSA names being added to
tree-into-ssa.c's old_ssa_names.
For example, _117 is an SSA name defined in one of these to-be-duplicated
blocks, and hence is added to old_ssa_names when duplicated.
One of the BBs has this gimplified predicate (again, these stmts are *not*
yet in a BB):
_173 = h4.1_112 != 0;
_171 = (signed char) _117;
_172 = _171 >= 0;
_170 = ~_172;
_169 = _170 & _173;
Note the reference to SSA name _117 in the above.
When update_ssa runs later on in version_loop_for_if_conversion,
SSA name _117 is in the old_ssa_names bitmap, and thus has
prepare_use_sites_for called on it:
2771 /* If an old name is in NAMES_TO_RELEASE, we cannot remove it from
2772 OLD_SSA_NAMES, but we have to ignore its definition site. */
2773 EXECUTE_IF_SET_IN_BITMAP (old_ssa_names, 0, i, sbi)
2774 {
2775 if (names_to_release == NULL || !bitmap_bit_p (names_to_release,
i))
2776 prepare_def_site_for (ssa_name (i), insert_phi_p);
2777 prepare_use_sites_for (ssa_name (i), insert_phi_p);
2778 }
prepare_use_sites_for iterates over the immediate users, which includes
the:
_171 = (signed char) _117;
in the gimplified predicate.
This tried to call "mark_block_for_update" on the BB of this def_stmt,
leading to a read-through-NULL segfault, since this statement isn't in a
BB yet.
With the caveat that this is at the limit of my understanding of the
innards of gimple, I'm wondering how this ever works: we have gimplified
predicates that aren't in a BB yet, which typically refer to
SSA names in the CFG proper, and we're attempting non-trivial manipulations
of that CFG that can e.g. duplicate those SSA names.
The following patch fixes the 2nd ICE by inserting the gimplified predicates
earlier: immediately before the possible version_loop_for_if_conversion,
rather than within combine_blocks. That way they're in their BBs before
we attempt any further manipulation of the CFG.
This fixes the ICE, though it introduces a regression of
gcc.target/i386/avx2-vec-mask-bit-not.c
which no longer vectorizes for some reason (I haven't investigated
why yet).
Successfully bootstrapped®rtested on x86_64-pc-linux-gnu.
Thoughts? Does this analysis sound sane?
Dave
gcc/ChangeLog:
PR tree-optimization/84178
* tree-if-conv.c (release_bb_predicate): Reinstate the
free_stmt_operands loop removed in r236498, removing
the assertion that the stmts have NULL use_ops.
(combine_blocks): Move the call to insert_gimplified_predicates...
(tree_if_conversion): ...to here, immediately before attempting
to version the loop.
gcc/testsuite/ChangeLog:
PR tree-optimization/84178
* gcc.c-torture/compile/pr84178-1.c: New test.
* gcc.c-torture/compile/pr84178-2.c: New test.
---
gcc/testsuite/gcc.c-torture/compile/pr84178-1.c | 18 ++++++++++++++++++
gcc/testsuite/gcc.c-torture/compile/pr84178-2.c | 18 ++++++++++++++++++
gcc/tree-if-conv.c | 15 +++++++++------
3 files changed, 45 insertions(+), 6 deletions(-)
create mode 100644 gcc/testsuite/gcc.c-torture/compile/pr84178-1.c
create mode 100644 gcc/testsuite/gcc.c-torture/compile/pr84178-2.c
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr84178-1.c
b/gcc/testsuite/gcc.c-torture/compile/pr84178-1.c
new file mode 100644
index 0000000..49f2c89
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr84178-1.c
@@ -0,0 +1,18 @@
+/* { dg-options "-fno-tree-forwprop" } */
+
+int zy, h4;
+
+void
+r8 (long int mu, int *jr, int *fi, short int dv)
+{
+ do
+ {
+ int tx;
+
+ tx = !!h4 ? (zy / h4) : 1;
+ mu = tx;
+ *jr = (((unsigned char) mu > (254 >> dv)) ? 0 : (unsigned char) tx) +
*fi;
+ } while (*jr == 0);
+
+ r8 (mu, jr, fi, 1);
+}
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr84178-2.c
b/gcc/testsuite/gcc.c-torture/compile/pr84178-2.c
new file mode 100644
index 0000000..b2548e9
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr84178-2.c
@@ -0,0 +1,18 @@
+/* { dg-options "-fno-tree-forwprop" } */
+
+int zy, h4;
+
+void
+r8 (long int mu, int *jr, int *fi, short int dv)
+{
+ do
+ {
+ int tx;
+
+ tx = !!h4 ? (zy + h4) : 1;
+ mu = tx;
+ *jr = (((unsigned char) mu > (254 >> dv)) ? 0 : (unsigned char) tx) +
*fi;
+ } while (*jr == 0);
+
+ r8 (mu, jr, fi, 1);
+}
diff --git a/gcc/tree-if-conv.c b/gcc/tree-if-conv.c
index cac3fd7..3edfc70 100644
--- a/gcc/tree-if-conv.c
+++ b/gcc/tree-if-conv.c
@@ -280,11 +280,9 @@ release_bb_predicate (basic_block bb)
gimple_seq stmts = bb_predicate_gimplified_stmts (bb);
if (stmts)
{
- if (flag_checking)
- for (gimple_stmt_iterator i = gsi_start (stmts);
- !gsi_end_p (i); gsi_next (&i))
- gcc_assert (! gimple_use_ops (gsi_stmt (i)));
-
+ gimple_stmt_iterator i;
+ for (i = gsi_start (stmts); !gsi_end_p (i); gsi_next (&i))
+ free_stmt_operands (cfun, gsi_stmt (i));
set_bb_predicate_gimplified_stmts (bb, NULL);
}
}
@@ -2369,7 +2367,6 @@ combine_blocks (struct loop *loop)
edge_iterator ei;
remove_conditions_and_labels (loop);
- insert_gimplified_predicates (loop);
predicate_all_scalar_phis (loop);
if (any_pred_load_store)
@@ -2839,6 +2836,12 @@ tree_if_conversion (struct loop *loop)
|| loop->dont_vectorize))
goto cleanup;
+ /* We've generated gimplified predicates, but they aren't in their BBs
+ yet. Put them there now, in case version_loop_for_if_conversion
+ needs to duplicate the SSA names for the gimplified predicates
+ (at which point they need to be in BBs; PR 84178). */
+ insert_gimplified_predicates (loop);
+
/* Since we have no cost model, always version loops unless the user
specified -ftree-loop-if-convert or unless versioning is required.
Either version this loop, or if the pattern is right for outer-loop
--
1.8.5.3
