[PATCH] Handle GIMPLE_ASSIGNs with different vuse in gimple_equal_p

[Tom de Vries <Tom_deVries at mentor dot com>]

Richard,

Consider the test-case test.c:
...
int z;
int x;

void
f (int c, int d)
{
  if (c)
    z = 5;
  else
    {
      if (d)
	x = 4;
      z = 5;
    }
}
...

Atm, we don't tail-merge the 'z = 5' blocks, because gimple_equal_p returns 
false for the 'z = 5' statements. The relevant code is this:
...
      if (TREE_CODE (lhs1) != SSA_NAME
          && TREE_CODE (lhs2) != SSA_NAME)
        return (vn_valueize (gimple_vdef (s1))
                == vn_valueize (gimple_vdef (s2)));
...
The vdefs of the 'z = 5' statements are different, because the incoming vuses 
are different.

This patch handles GIMPLE_ASSIGNs with different vuse in gimple_equal_p, by 
doing a structural comparison.

Bootstrapped and regtested on x86_64.

OK for trunk?

Thanks,
- Tom

2013-11-06  Tom de Vries  <tom@codesourcery.com>

	* tree-ssa-tail-merge.c (gimple_equal_p): Add test for structural
	equality for GIMPLE_ASSIGN.

	* gcc.dg/tail-merge-store.c: New test.

diff --git a/gcc/testsuite/gcc.dg/tail-merge-store.c b/gcc/testsuite/gcc.dg/tail-merge-store.c
new file mode 100644
index 0000000..1aefbdc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tail-merge-store.c
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -ftree-tail-merge -fdump-tree-pre" } */
+
+int z;
+int x;
+
+void
+f (int c, int d)
+{
+  if (c)
+    z = 5;
+  else
+    {
+      if (d)
+	x = 4;
+      z = 5;
+    }
+}
+
+/* { dg-final { scan-tree-dump-times "duplicate of" 1 "pre"} } */
+/* { dg-final { scan-tree-dump-times "z = 5" 1 "pre"} } */
+/* { dg-final { cleanup-tree-dump "pre" } } */
diff --git a/gcc/tree-ssa-tail-merge.c b/gcc/tree-ssa-tail-merge.c
index 98b5882..43516a7 100644
--- a/gcc/tree-ssa-tail-merge.c
+++ b/gcc/tree-ssa-tail-merge.c
@@ -1173,8 +1173,47 @@ gimple_equal_p (same_succ same_succ, gimple s1, gimple s2)
       lhs2 = gimple_get_lhs (s2);
       if (TREE_CODE (lhs1) != SSA_NAME
 	  && TREE_CODE (lhs2) != SSA_NAME)
-	return (vn_valueize (gimple_vdef (s1))
-		== vn_valueize (gimple_vdef (s2)));
+	{
+	  /* If the vdef is the same, it's the same statement.  */
+	  if (vn_valueize (gimple_vdef (s1))
+	      == vn_valueize (gimple_vdef (s2)))
+	    return true;
+
+	  /* If the vdef is not the same but the vuse is the same, it's not the
+	     same stmt.  */
+	  if (vn_valueize (gimple_vuse (s1))
+	      == vn_valueize (gimple_vuse (s2)))
+	    return false;
+	  /* If the vdef is not the same and the vuse is not the same, it might be
+	     same stmt.  */
+
+	  /* Test for structural equality.  */
+	  if (gimple_assign_rhs_code (s1) != gimple_assign_rhs_code (s1)
+	      || (gimple_assign_nontemporal_move_p (s1)
+		  != gimple_assign_nontemporal_move_p (s2)))
+	    return false;
+
+	  if (!operand_equal_p (lhs1, lhs2, 0))
+	    return false;
+
+	  t1 = gimple_assign_rhs1 (s1);
+	  t2 = gimple_assign_rhs1 (s2);
+	  if (!gimple_operand_equal_value_p (t1, t2))
+	    return false;
+
+	  t1 = gimple_assign_rhs2 (s1);
+	  t2 = gimple_assign_rhs2 (s2);
+	  if (!gimple_operand_equal_value_p (t1, t2))
+	    return false;
+
+	  t1 = gimple_assign_rhs3 (s1);
+	  t2 = gimple_assign_rhs3 (s2);
+	  if (!gimple_operand_equal_value_p (t1, t2))
+	    return false;
+
+	  /* Same structure.  */
+	  return true;
+	}
       else if (TREE_CODE (lhs1) == SSA_NAME
 	       && TREE_CODE (lhs2) == SSA_NAME)
 	return vn_valueize (lhs1) == vn_valueize (lhs2);