diff mbox series

[1/2] Avoid random stmt order result in pass_waccess::use_after_inval_p

Message ID 20230315104904.40D373858C66@sourceware.org
State New
Headers
Series [1/2] Avoid random stmt order result in pass_waccess::use_after_inval_p |

Commit Message

Richard Biener March 15, 2023, 10:48 a.m. UTC 
  use_after_inval_p uses stmt UIDs to speed up repeated dominance
checks within a basic-block but it fails to assign UIDs to PHIs
which means compares with PHIs in the same block get a random
result.

The following factors renumber_gimple_stmt_uids to expose a new
renumber_gimple_stmt_uids_in_block we can share.

This XFAILs the conditional loop case in gcc.dg/Wuse-after-free-2.c

Bootstrap and regtest running on x86_64-unknown-linux-gnu.  This
makes 2/2 a net positive on the testsuite (the early waccess
would not run into this bug)

OK if testing succeeds?  (we could also special-case PHIs somehow
and assert we never get to compare two PHIs here)

	* tree-dfa.h (renumber_gimple_stmt_uids_in_block): New.
	* tree-dfa.cc (renumber_gimple_stmt_uids_in_block): Split
	out from ...
	(renumber_gimple_stmt_uids): ... here and
	(renumber_gimple_stmt_uids_in_blocks): ... here.
	* gimple-ssa-warn-access.cc (pass_waccess::use_after_inval_p):
	Use renumber_gimple_stmt_uids_in_block to also assign UIDs
	to PHIs.

	* gcc.dg/Wuse-after-free-2.c: XFAIL conditional loop case.
---
 gcc/gimple-ssa-warn-access.cc            |  8 +---
 gcc/testsuite/gcc.dg/Wuse-after-free-2.c |  4 +-
 gcc/tree-dfa.cc                          | 48 +++++++++++-------------
 gcc/tree-dfa.h                           |  1 +
 4 files changed, 25 insertions(+), 36 deletions(-)
diff mbox series

Patch

diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
index 8b1c1cc019e..a8ad7a6df65 100644
--- a/gcc/gimple-ssa-warn-access.cc
+++ b/gcc/gimple-ssa-warn-access.cc
@@ -3862,13 +3862,7 @@  pass_waccess::use_after_inval_p (gimple *inval_stmt, gimple *use_stmt,
        to consecutive statements in it.  Use the ids to determine which
        precedes which.  This avoids the linear traversal on subsequent
        visits to the same block.  */
-    for (auto si = gsi_start_bb (inval_bb); !gsi_end_p (si);
-	 gsi_next_nondebug (&si))
-      {
-	gimple *stmt = gsi_stmt (si);
-	unsigned uid = inc_gimple_stmt_max_uid (m_func);
-	gimple_set_uid (stmt, uid);
-      }
+    renumber_gimple_stmt_uids_in_block (m_func, inval_bb);
 
   return gimple_uid (inval_stmt) < gimple_uid (use_stmt);
 }
diff --git a/gcc/testsuite/gcc.dg/Wuse-after-free-2.c b/gcc/testsuite/gcc.dg/Wuse-after-free-2.c
index ebc051690db..cd5c43c0fa3 100644
--- a/gcc/testsuite/gcc.dg/Wuse-after-free-2.c
+++ b/gcc/testsuite/gcc.dg/Wuse-after-free-2.c
@@ -113,6 +113,6 @@  int warn_cond_loop (char *p)
   while (*q)
     ++q;
 
-  free (p);         // { dg-message "call to 'free'" }
-  return *q;        // { dg-warning "pointer 'q' used after 'free'" }
+  free (p);         // dg-message "call to 'free'"
+  return *q;        // { dg-warning "pointer 'q' used after 'free'" "" { xfail *-*-* } }
 }
diff --git a/gcc/tree-dfa.cc b/gcc/tree-dfa.cc
index ec8df0d6401..82803a8ccb1 100644
--- a/gcc/tree-dfa.cc
+++ b/gcc/tree-dfa.cc
@@ -59,6 +59,25 @@  static void collect_dfa_stats (struct dfa_stats_d *);
 			Dataflow analysis (DFA) routines
 ---------------------------------------------------------------------------*/
 
+/* Renumber the gimple stmt uids in one block.  The caller is responsible
+   of calling set_gimple_stmt_max_uid (fun, 0) at some point.  */
+
+void
+renumber_gimple_stmt_uids_in_block (struct function *fun, basic_block bb)
+{
+  gimple_stmt_iterator bsi;
+  for (bsi = gsi_start_phis (bb); !gsi_end_p (bsi); gsi_next (&bsi))
+    {
+      gimple *stmt = gsi_stmt (bsi);
+      gimple_set_uid (stmt, inc_gimple_stmt_max_uid (fun));
+    }
+  for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi))
+    {
+      gimple *stmt = gsi_stmt (bsi);
+      gimple_set_uid (stmt, inc_gimple_stmt_max_uid (fun));
+    }
+}
+
 /* Renumber all of the gimple stmt uids.  */
 
 void
@@ -68,19 +87,7 @@  renumber_gimple_stmt_uids (struct function *fun)
 
   set_gimple_stmt_max_uid (fun, 0);
   FOR_ALL_BB_FN (bb, fun)
-    {
-      gimple_stmt_iterator bsi;
-      for (bsi = gsi_start_phis (bb); !gsi_end_p (bsi); gsi_next (&bsi))
-	{
-	  gimple *stmt = gsi_stmt (bsi);
-	  gimple_set_uid (stmt, inc_gimple_stmt_max_uid (fun));
-	}
-      for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi))
-	{
-	  gimple *stmt = gsi_stmt (bsi);
-	  gimple_set_uid (stmt, inc_gimple_stmt_max_uid (fun));
-	}
-    }
+    renumber_gimple_stmt_uids_in_block (fun, bb);
 }
 
 /* Like renumber_gimple_stmt_uids, but only do work on the basic blocks
@@ -93,20 +100,7 @@  renumber_gimple_stmt_uids_in_blocks (basic_block *blocks, int n_blocks)
 
   set_gimple_stmt_max_uid (cfun, 0);
   for (i = 0; i < n_blocks; i++)
-    {
-      basic_block bb = blocks[i];
-      gimple_stmt_iterator bsi;
-      for (bsi = gsi_start_phis (bb); !gsi_end_p (bsi); gsi_next (&bsi))
-	{
-	  gimple *stmt = gsi_stmt (bsi);
-	  gimple_set_uid (stmt, inc_gimple_stmt_max_uid (cfun));
-	}
-      for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi))
-	{
-	  gimple *stmt = gsi_stmt (bsi);
-	  gimple_set_uid (stmt, inc_gimple_stmt_max_uid (cfun));
-	}
-    }
+    renumber_gimple_stmt_uids_in_block (cfun, blocks[i]);
 }
 
 
diff --git a/gcc/tree-dfa.h b/gcc/tree-dfa.h
index 1632487c3ed..074a4da3a6c 100644
--- a/gcc/tree-dfa.h
+++ b/gcc/tree-dfa.h
@@ -20,6 +20,7 @@  along with GCC; see the file COPYING3.  If not see
 #ifndef GCC_TREE_DFA_H
 #define GCC_TREE_DFA_H
 
+extern void renumber_gimple_stmt_uids_in_block (struct function *, basic_block);
 extern void renumber_gimple_stmt_uids (struct function *);
 extern void renumber_gimple_stmt_uids_in_blocks (basic_block *, int);
 extern void dump_variable (FILE *, tree);