2013-08-29 Richard Biener <rguenther@suse.de>

	PR tree-optimization/58246
	* tree-ssa-dce.c (mark_aliased_reaching_defs_necessary_1): Properly
	handle the dominance check inside a basic-block.

	* gcc.dg/torture/pr58246.c: New testcase.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@202071 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index ad77502..30caf6e 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,11 @@
 2013-08-29  Richard Biener  <rguenther@suse.de>
 
+       PR tree-optimization/58246
+       * tree-ssa-dce.c (mark_aliased_reaching_defs_necessary_1): Properly
+       handle the dominance check inside a basic-block.
+
+2013-08-29  Richard Biener  <rguenther@suse.de>
+
        PR middle-end/57287
        * tree-ssa-copy.c (may_propagate_copy): Allow propagating
        of default defs that appear in abnormal PHI nodes.

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 3d54682..1f34c2d 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2013-08-29  Richard Biener  <rguenther@suse.de>
+
+       PR tree-optimization/58246
+       * gcc.dg/torture/pr58246.c: New testcase.
+
 2013-08-29  Thomas Koenig  <tkoenig@gcc.gnu.org>
 
        PR fortran/52243

diff --git a/gcc/testsuite/gcc.dg/torture/pr58246.c b/gcc/testsuite/gcc.dg/torture/pr58246.c
new file mode 100644 (file)
index 0000000..5417abf
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr58246.c
@@ -0,0 +1,21 @@
+/* { dg-do run } */
+
+extern void abort (void);
+
+int a, b; 
+
+int main ()
+{
+  int t[2] = {1,1};
+
+  for (a = 0; a < 2; a++)
+    {
+      b ^= t[a];
+      t[a] = t[1] = 0;
+    }
+
+  if (b != 1)
+    abort ();
+
+  return 0;
+}

diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c
index 4fd3cd8..22ae50b 100644 (file)
--- a/gcc/tree-ssa-dce.c
+++ b/gcc/tree-ssa-dce.c
@@ -574,6 +574,11 @@ mark_aliased_reaching_defs_necessary_1 (ao_ref *ref, tree vdef, void *data)
                      in the references (gcc.c-torture/execute/pr42142.c).
                      The simplest way is to check if the kill dominates
                      the use.  */
+                  /* But when both are in the same block we cannot
+                     easily tell whether we came from a backedge
+                     unless we decide to compute stmt UIDs
+                     (see PR58246).  */
+                  && (basic_block) data != gimple_bb (def_stmt)
                   && dominated_by_p (CDI_DOMINATORS, (basic_block) data,
                                      gimple_bb (def_stmt))
                   && operand_equal_p (ref->ref, lhs, 0))