commit ca25fa7000dd9d086b78bf9a02126f83fbab8073
Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com>
Date:   Mon Sep 7 14:58:01 2015 +0100

    [RTL-ifcvt] PR rtl-optimization/67465: Do not ifcvt complex blocks if the else block is empty

diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index d2f5b66..9adce60 100644
--- a/gcc/ifcvt.c
+++ b/gcc/ifcvt.c
@@ -1997,6 +1997,7 @@ noce_try_cmove_arith (struct noce_if_info *if_info)
   rtx a = if_info->a;
   rtx b = if_info->b;
   rtx x = if_info->x;
+  machine_mode x_mode = GET_MODE (x);
   rtx orig_a, orig_b;
   rtx_insn *insn_a, *insn_b;
   bool a_simple = if_info->then_simple;
@@ -2008,6 +2009,9 @@ noce_try_cmove_arith (struct noce_if_info *if_info)
   enum rtx_code code;
   rtx_insn *ifcvt_seq;
 
+  if (!can_conditionally_move_p (x_mode))
+    return FALSE;
+
   /* A conditional move from two memory sources is equivalent to a
      conditional on their addresses followed by a load.  Don't do this
      early because it'll screw alias analysis.  Note that we've
@@ -2079,13 +2083,32 @@ noce_try_cmove_arith (struct noce_if_info *if_info)
 	}
     }
 
-  if (!a_simple && then_bb && !b_simple && else_bb
+  if (then_bb && else_bb && !a_simple && !b_simple
       && (!bbs_ok_for_cmove_arith (then_bb, else_bb)
 	  || !bbs_ok_for_cmove_arith (else_bb, then_bb)))
     return FALSE;
 
   start_sequence ();
 
+  /* If one of the blocks is empty then the corresponding B or A value
+     came from the test block.  The non-empty complex block that we will
+     emit might clobber the register used by B or A, so move it to a pseudo
+     first.  */
+
+  if (b_simple || !else_bb)
+    {
+      rtx tmp_b = gen_reg_rtx (x_mode);
+      noce_emit_move_insn (tmp_b, b);
+      b = tmp_b;
+    }
+
+  if (a_simple || !then_bb)
+    {
+      rtx tmp_a = gen_reg_rtx (x_mode);
+      noce_emit_move_insn (tmp_a, a);
+      a = tmp_a;
+    }
+
   orig_a = a;
   orig_b = b;
 
diff --git a/gcc/testsuite/gcc.dg/pr67465.c b/gcc/testsuite/gcc.dg/pr67465.c
new file mode 100644
index 0000000..321fd38
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr67465.c
@@ -0,0 +1,53 @@
+/* { dg-do run } */
+/* { dg-options "-O3 -std=gnu99" } */
+
+int a, b, c, d, e, h;
+
+int
+fn1 (int p1)
+{
+  {
+    int g[2];
+    for (int i = 0; i < 1; i++)
+      g[i] = 0;
+    if (g[0] < c)
+      {
+	a = (unsigned) (1 ^ p1) % 2;
+	return 0;
+      }
+  }
+  return 0;
+}
+
+void
+fn2 ()
+{
+  for (h = 0; h < 1; h++)
+    {
+      for (int j = 0; j < 2; j++)
+	{
+	  for (b = 1; b; b = 0)
+	    a = 1;
+	  for (; b < 1; b++)
+	    ;
+	  if (e)
+	    continue;
+	  a = 2;
+	}
+      fn1 (h);
+      short k = -16;
+      d = k > a;
+    }
+}
+
+int
+main ()
+{
+  fn2 ();
+
+  if (a != 2)
+    __builtin_abort ();
+
+  return 0;
+}
+