From: Richard Biener <rguenther@suse.de>
Date: Wed, 7 May 2014 07:59:26 +0000 (+0000)
Subject: backport: re PR tree-optimization/58246 (wrong code at -O1 and above)
X-Git-Tag: releases/gcc-4.7.4~114
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7a6547fc50c909fe39a6e8ff0df3213188fcd7d8;p=thirdparty%2Fgcc.git

backport: re PR tree-optimization/58246 (wrong code at -O1 and above)

2014-05-07  Richard Biener  <rguenther@suse.de>

	Backport from mainline
	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.

From-SVN: r210141
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 030f3ffcd74d..804f3231b4a3 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2014-05-07  Richard Biener  <rguenther@suse.de>
+
+	Backport from mainline
+	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.
+
 2014-05-06  Richard Biener  <rguenther@suse.de>
 
 	Backport from mainline
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 6b5f1f576203..811cff5c7204 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2014-05-07  Richard Biener  <rguenther@suse.de>
+
+	Backport from mainline
+	2013-08-29  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/58246
+	* gcc.dg/torture/pr58246.c: New testcase.
+
 2014-05-06  Richard Biener  <rguenther@suse.de>
 
 	Backport from mainline
diff --git a/gcc/testsuite/gcc.dg/torture/pr58246.c b/gcc/testsuite/gcc.dg/torture/pr58246.c
new file mode 100644
index 000000000000..5417abf913d5
--- /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 ace9ef9972d4..d99e77130d42 100644
--- a/gcc/tree-ssa-dce.c
+++ b/gcc/tree-ssa-dce.c
@@ -576,6 +576,11 @@ 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))