re PR rtl-optimization/78559 (wrong code due to tree if-conversion?)

	PR rtl-optimization/78559
	* combine.c (try_combine): Discard REG_EQUAL and REG_EQUIV for
	other_insn in combine.

	gcc/testsuite
	PR rtl-optimization/78559
	* gcc.c-torture/execute/pr78559.c: New test.

From-SVN: r244979

gcc/ChangeLog

+2017-01-27  Bin Cheng  <bin.cheng@arm.com>
+
+	PR rtl-optimization/78559
+	* combine.c (try_combine): Discard REG_EQUAL and REG_EQUIV for
+	other_insn in combine.
+
 2017-01-27  Pekka Jääskeläinen  <pekka.jaaskelainen@parmance.com>
 
 	* builtin-types.def: Use unsigned_char_type_node for BT_UINT8.  Use

gcc/combine.c

@@ -4148,7 +4148,16 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
 				     PATTERN (undobuf.other_insn)))
 	      ||(REG_NOTE_KIND (note) == REG_UNUSED
 		 && !reg_set_p (XEXP (note, 0),
-				PATTERN (undobuf.other_insn))))
+				PATTERN (undobuf.other_insn)))
+	      /* Simply drop equal note since it may be no longer valid
+		 for other_insn.  It may be possible to record that CC
+		 register is changed and only discard those notes, but
+		 in practice it's unnecessary complication and doesn't
+		 give any meaningful improvement.
+
+		 See PR78559.  */
+	      || REG_NOTE_KIND (note) == REG_EQUAL
+	      || REG_NOTE_KIND (note) == REG_EQUIV)
 	    remove_note (undobuf.other_insn, note);
 	}
 

gcc/testsuite/ChangeLog

+2017-01-27  Bin Cheng  <bin.cheng@arm.com>
+
+	PR rtl-optimization/78559
+	* gcc.c-torture/execute/pr78559.c: New test.
+
 2017-01-27  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/79245

gcc/testsuite/gcc.c-torture/execute/pr78559.c

+/* PR rtl-optimization/78559 */
+
+int g = 20;
+int d = 0;
+
+short
+fn2 (int p1, int p2)
+{
+  return p2 >= 2 || 5 >> p2 ? p1 : p1 << p2;
+}
+
+int
+main ()
+{
+  int result = 0;
+lbl_2582:
+  if (g)
+    {
+      for (int c = -3; c; c++)
+        result = fn2 (1, g);
+    }
+  else
+    {
+      for (int i = 0; i < 2; i += 2)
+        if (d)
+          goto lbl_2582;
+    }
+  if (result != 1)
+    __builtin_abort ();
+  return 0;
+}
+
+
+