[PATCH][RTL-ifcvt] PR rtl-optimization/68506: Fix emitting order of insns in IF-THEN-JOIN case

[Kyrill Tkachov]

Hi all,

In this PR we have an IF-THEN-JOIN formation i.e. no ELSE block and we have a 
situation
where the THEN block modifies a register used in emit_b, so emit_b must be 
emitted before
the THEN block. However the bug in the logic that performs these checks ends up 
to us
emitting emit_a+then_bb followed by emit_b+else_bb.

The fix is pretty simple and involves emitting emit_b (+ else_bb that is empty 
in this case)
if modified_a is true, even if emit_a is NULL. If emit_a is NULL noce_emit_bb 
will handle
it properly and not do anything bad, so we're safe.

Bootstrapped and tested on arm, aarch64, x86_64.

Ok for trunk?

Thanks,
Kyrill

2015-11-26  Kyrylo Tkachov  <kyrylo.tkac...@arm.com>

    PR rtl-optimization/68506
    * ifcvt.c (noce_try_cmove_arith): Try emitting the else basic block
    first if emit_a exists or then_bb modifies 'b'.

2015-11-26  Kyrylo Tkachov  <kyrylo.tkac...@arm.com>

    PR rtl-optimization/68506
    * gcc.c-torture/execute/pr68506.c: New test.

commit 08a371d20793bd57e9a68b85beaf2cab0804ed48
Author: Kyrylo Tkachov <kyrylo.tkac...@arm.com>
Date:   Tue Nov 24 11:49:30 2015 +0000

    PR rtl-optimization/68506: Fix emitting order of insns in IF-THEN-JOIN case

diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index af7a3b9..3e3dc8d 100644
--- a/gcc/ifcvt.c
+++ b/gcc/ifcvt.c
@@ -2220,7 +2220,7 @@ noce_try_cmove_arith (struct noce_if_info *if_info)
 	  }
 
     }
-    if (emit_a && modified_in_a)
+    if (emit_a || modified_in_a)
       {
 	modified_in_b = emit_b != NULL_RTX && modified_in_p (orig_a, emit_b);
 	if (tmp_b && else_bb)
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr68506.c b/gcc/testsuite/gcc.c-torture/execute/pr68506.c
new file mode 100644
index 0000000..15984ed
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr68506.c
@@ -0,0 +1,63 @@
+/* { dg-options "-fno-builtin-abort" } */
+
+int a, b, m, n, o, p, s, u, i;
+char c, q, y;
+short d;
+unsigned char e;
+static int f, h;
+static short g, r, v;
+unsigned t;
+
+extern void abort ();
+
+int
+fn1 (int p1)
+{
+  return a ? p1 : p1 + a;
+}
+
+unsigned char
+fn2 (unsigned char p1, int p2)
+{
+  return p2 >= 2 ? p1 : p1 >> p2;
+}
+
+static short
+fn3 ()
+{
+  int w, x = 0;
+  for (; p < 31; p++)
+    {
+      s = fn1 (c | ((1 && c) == c));
+      t = fn2 (s, x);
+      c = (unsigned) c > -(unsigned) ((o = (m = d = t) == p) <= 4UL) && n;
+      v = -c;
+      y = 1;
+      for (; y; y++)
+	e = v == 1;
+      d = 0;
+      for (; h != 2;)
+	{
+	  for (;;)
+	    {
+	      if (!m)
+		abort ();
+	      r = 7 - f;
+	      x = e = i | r;
+	      q = u * g;
+	      w = b == q;
+	      if (w)
+		break;
+	    }
+	  break;
+	}
+    }
+  return x;
+}
+
+int
+main ()
+{
+  fn3 ();
+  return 0;
+}