On Thu, 26 Sep 2024, Richard Biener wrote:
> When path isolation performs CFG manipulations (block splitting) it
> fails to update post-dominators it computes on-demand. That both
> runs into dominance verification issues when we compute post-dominators
> again and possibly accessing missing or broken post-dominance data
> when checking is disabled. The following attempts to get rid of
> post-dominator use by approximating always-executed with dominating
> function exit instead of post-dominating function entry. For this to
> work we have to add fake exit edges.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>
> I'll push this later if nobody has comments.
On a second thought using dominators isn't an equivalent thing. The
following avoids the issue by delaying splitting of blocks (instead
of implementing post-dominator update for split_block).
Bootstrap & regtest in progress on x86_64-unknown-linux-gnu.
Richard.
>From d1d900b32bfbb146b010dcdc7cc3fdf442fb12d1 Mon Sep 17 00:00:00 2001
From: Richard Biener <rguent...@suse.de>
Date: Thu, 26 Sep 2024 15:41:59 +0200
Subject: [PATCH] tree-optimization/116850 - corrupt post-dom info
To: gcc-patches@gcc.gnu.org
Path isolation computes post-dominators on demand but can end up
splitting blocks after that, wrecking it. We can delay splitting
of blocks until we no longer need the post-dom info which is what
the following patch does to solve the issue.
PR tree-optimization/116850
* gimple-ssa-isolate-paths.cc (bb_split_points): New global.
(insert_trap): Delay BB splitting if post-doms are computed.
(find_explicit_erroneous_behavior): Process delayed BB
splitting after releasing post dominators.
(gimple_ssa_isolate_erroneous_paths): Do not free post-dom
info here.
* gcc.dg/pr116850.c: New testcase.
---
gcc/gimple-ssa-isolate-paths.cc | 23 ++++++++++++++++++++---
gcc/testsuite/gcc.dg/pr116850.c | 12 ++++++++++++
2 files changed, 32 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/pr116850.c
diff --git a/gcc/gimple-ssa-isolate-paths.cc b/gcc/gimple-ssa-isolate-paths.cc
index fae18db0c1d..55a516987db 100644
--- a/gcc/gimple-ssa-isolate-paths.cc
+++ b/gcc/gimple-ssa-isolate-paths.cc
@@ -62,6 +62,8 @@ check_loadstore (gimple *stmt, tree op, tree, void *data)
return false;
}
+static vec<gimple *> *bb_split_points;
+
/* Insert a trap after SI and split the block after the trap. */
static void
@@ -104,14 +106,20 @@ insert_trap (gimple_stmt_iterator *si_p, tree op)
gsi_insert_after (si_p, seq, GSI_NEW_STMT);
if (stmt_ends_bb_p (stmt))
{
- split_block (gimple_bb (stmt), stmt);
+ if (dom_info_available_p (CDI_POST_DOMINATORS))
+ bb_split_points->safe_push (stmt);
+ else
+ split_block (gimple_bb (stmt), stmt);
return;
}
}
else
gsi_insert_before (si_p, seq, GSI_NEW_STMT);
- split_block (gimple_bb (new_stmt), new_stmt);
+ if (dom_info_available_p (CDI_POST_DOMINATORS))
+ bb_split_points->safe_push (new_stmt);
+ else
+ split_block (gimple_bb (new_stmt), new_stmt);
*si_p = gsi_for_stmt (stmt);
}
@@ -842,6 +850,8 @@ static void
find_explicit_erroneous_behavior (void)
{
basic_block bb;
+ auto_vec<gimple *> local_bb_split_points;
+ bb_split_points = &local_bb_split_points;
FOR_EACH_BB_FN (bb, cfun)
{
@@ -883,6 +893,14 @@ find_explicit_erroneous_behavior (void)
warn_return_addr_local (bb, return_stmt);
}
}
+
+ free_dominance_info (CDI_POST_DOMINATORS);
+
+ /* Perform delayed splitting of blocks. */
+ for (gimple *stmt : local_bb_split_points)
+ split_block (gimple_bb (stmt), stmt);
+
+ bb_split_points = NULL;
}
/* Search the function for statements which, if executed, would cause
@@ -939,7 +957,6 @@ gimple_ssa_isolate_erroneous_paths (void)
/* We scramble the CFG and loop structures a bit, clean up
appropriately. We really should incrementally update the
loop structures, in theory it shouldn't be that hard. */
- free_dominance_info (CDI_POST_DOMINATORS);
if (cfg_altered)
{
free_dominance_info (CDI_DOMINATORS);
diff --git a/gcc/testsuite/gcc.dg/pr116850.c b/gcc/testsuite/gcc.dg/pr116850.c
new file mode 100644
index 00000000000..7ab5da1848b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr116850.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-Os -w" } */
+
+int a, b;
+int *c()
+{
+ int d, *e = 0, *f = &d, *g = &a;
+ if (b)
+ g = 0;
+ *e = *g;
+ return f;
+}
--
2.43.0
