diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 4d3a46fe6eade83fa8bde25bad4660604e4940fd..b0765b8676c7dae9dbe88d4b23b116437cc32b74 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,12 @@
+2012-01-17  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/51877
+	* tree-ssa-tail-merge.c (gimple_equal_p): Don't return true whenever
+	call arguments and fndecls compare equal, instead return false if they
+	don't.  Return true only if lhs1 and lhs2 are either both NULL, or
+	both SSA_NAMEs that are valueized the same, or they satisfy
+	operand_equal_p.
+
 2012-01-17  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
 	* configure.ac (gcc_cv_target_dl_iterate_phdr): Only check on
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index b6271c469ef6cba2973dcb9eb9c7d150f28773e3..e640e945613aae63b2603ce010567463e795ff27 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2012-01-17  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/51877
+	* gcc.c-torture/execute/pr51877.c: New test.
+
 2012-01-17  Michael Zolotukhin  <michael.v.zolotukhin@intel.com>
 
 	* gcc.dg/vect/no-section-anchors-vect-69.c: Change
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr51877.c b/gcc/testsuite/gcc.c-torture/execute/pr51877.c
new file mode 100644
index 0000000000000000000000000000000000000000..a2d65cfd9d830108dab0d8e689688ae7671c1058
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr51877.c
@@ -0,0 +1,50 @@
+/* PR tree-optimization/51877 */
+
+extern void abort (void);
+struct A { int a; char b[32]; } a, b;
+
+__attribute__((noinline, noclone))
+struct A
+bar (int x)
+{
+  struct A r;
+  static int n;
+  r.a = ++n;
+  __builtin_memset (r.b, 0, sizeof (r.b));
+  r.b[0] = x;
+  return r;
+}
+
+__attribute__((noinline, noclone))
+void
+baz (void)
+{
+  asm volatile ("" : : : "memory");
+}
+
+__attribute__((noinline, noclone))
+void
+foo (struct A *x, int y)
+{
+  if (y == 6)
+    a = bar (7);
+  else
+    *x = bar (7);
+  baz ();
+}
+
+int
+main ()
+{
+  a = bar (3);
+  b = bar (4);
+  if (a.a != 1 || a.b[0] != 3 || b.a != 2 || b.b[0] != 4)
+    abort ();
+  foo (&b, 0);
+  if (a.a != 1 || a.b[0] != 3 || b.a != 3 || b.b[0] != 7)
+    abort ();
+  foo (&b, 6);
+  if (a.a != 4 || a.b[0] != 7 || b.a != 3 || b.b[0] != 7)
+    abort ();
+  return 0;
+}
diff --git a/gcc/tree-ssa-tail-merge.c b/gcc/tree-ssa-tail-merge.c
index 7452266af2bdb6a2846b2dc84fd2a8f93408492c..47dc0a6ffc8d3b34ffe427ddb0cf6a5e3c12e3d8 100644
--- a/gcc/tree-ssa-tail-merge.c
+++ b/gcc/tree-ssa-tail-merge.c
@@ -1,5 +1,5 @@
 /* Tail merging for gimple.
-   Copyright (C) 2011 Free Software Foundation, Inc.
+   Copyright (C) 2011, 2012 Free Software Foundation, Inc.
    Contributed by Tom de Vries (tom@codesourcery.com)
 
 This file is part of GCC.
@@ -1071,14 +1071,18 @@ gimple_equal_p (same_succ same_succ, gimple s1, gimple s2)
 	  equal = false;
 	  break;
 	}
-      if (equal)
-	return true;
+      if (!equal)
+	return false;
 
       lhs1 = gimple_get_lhs (s1);
       lhs2 = gimple_get_lhs (s2);
-      return (lhs1 != NULL_TREE && lhs2 != NULL_TREE
-	      && TREE_CODE (lhs1) == SSA_NAME && TREE_CODE (lhs2) == SSA_NAME
-	      && vn_valueize (lhs1) == vn_valueize (lhs2));
+      if (lhs1 == NULL_TREE && lhs2 == NULL_TREE)
+	return true;
+      if (lhs1 == NULL_TREE || lhs2 == NULL_TREE)
+	return false;
+      if (TREE_CODE (lhs1) == SSA_NAME && TREE_CODE (lhs2) == SSA_NAME)
+	return vn_valueize (lhs1) == vn_valueize (lhs2);
+      return operand_equal_p (lhs1, lhs2, 0);
 
     case GIMPLE_ASSIGN:
       lhs1 = gimple_get_lhs (s1);