commit 33131f774705b936afc1a26c145e1214b388771f
Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com>
Date:   Fri Nov 13 15:01:47 2015 +0000

    [RTL-ree] PR rtl-optimization/68194: Restrict copy instruction in presence of conditional moves

diff --git a/gcc/ree.c b/gcc/ree.c
index b8436f2..e91d164 100644
--- a/gcc/ree.c
+++ b/gcc/ree.c
@@ -814,7 +814,30 @@ combine_reaching_defs (ext_cand *cand, const_rtx set_pat, ext_state *state)
 
       rtx tmp_reg = gen_rtx_REG (GET_MODE (SET_DEST (PATTERN (cand->insn))),
 				 REGNO (SET_DEST (*dest_sub_rtx)));
-      if (reg_overlap_mentioned_p (tmp_reg, SET_DEST (PATTERN (cand->insn))))
+
+      /* When transforming:
+	(set (reg1) (expression))
+	 ...
+	(set (reg2) (any_extend (reg1)))
+
+	into
+
+	(set (reg2) (any_extend (expression)))
+	(set (reg1) (reg2))
+	make sure that reg1 from the first set feeds directly into the extend.
+	This may not hold in a situation with an intermediate
+	conditional copy i.e.
+	I1: (set (reg3) (expression))
+	I2: (set (reg1) (cond ? reg3 : reg1))
+	I3: (set (reg2) (any_extend (reg1)))
+
+	where I3 is cand, I1 is def_insn and I2 is a conditional copy.
+	We want to avoid transforming that into:
+	(set (reg2) (any_extend (expression)))
+	(set (reg1) (reg2))
+	(set (reg1) (cond ? reg3 : reg1)).  */
+      if (reg_overlap_mentioned_p (tmp_reg, SET_DEST (PATTERN (cand->insn)))
+	  || !reg_overlap_mentioned_p (tmp_reg, SET_SRC (PATTERN (cand->insn))))
 	return false;
 
       /* The destination register of the extension insn must not be
diff --git a/gcc/testsuite/gcc.dg/pr68194.c b/gcc/testsuite/gcc.dg/pr68194.c
new file mode 100644
index 0000000..b4855ea
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr68194.c
@@ -0,0 +1,35 @@
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+int a, c, d, e, g, h;
+short f;
+
+short
+fn1 (void)
+{
+  int j[2];
+  for (; e; e++)
+    if (j[0])
+      for (;;)
+	;
+  if (!g)
+    return f;
+}
+
+int
+main (void)
+{
+  for (; a < 1; a++)
+    {
+      for (c = 0; c < 2; c++)
+	{
+	  d && (f = 0);
+	  h = fn1 ();
+	}
+      __builtin_printf ("%d\n", (char) f);
+   }
+
+ return 0;
+}
+
+/* { dg-output "0" } */