re PR rtl-optimization/71724 (ICE: Segmentation fault, deep recursion between…

re PR rtl-optimization/71724 (ICE: Segmentation fault, deep recursion between combine_simplify_rtx and subst)

	PR rtl-optimization/71724
	* combine.c (if_then_else_cond): Look for situations where it is
	beneficial to undo the work of one of the recursive calls.

From-SVN: r244817

gcc/ChangeLog

@@ -5,6 +5,10 @@
 	(TARGET_MAX_NOCE_IFCVT_SEQ_COST): Define.
 	* ifcvt.c (noce_try_cmove): Add missing cost check.
 
+	PR rtl-optimization/71724
+	* combine.c (if_then_else_cond): Look for situations where it is
+	beneficial to undo the work of one of the recursive calls.
+
 2017-01-23  Bin Cheng  <bin.cheng@arm.com>
 
 	PR tree-optimization/70754

gcc/combine.c

@@ -9044,11 +9044,31 @@ if_then_else_cond (rtx x, rtx *ptrue, rtx *pfalse)
      the same value, compute the new true and false values.  */
   else if (BINARY_P (x))
     {
-      cond0 = if_then_else_cond (XEXP (x, 0), &true0, &false0);
-      cond1 = if_then_else_cond (XEXP (x, 1), &true1, &false1);
+      rtx op0 = XEXP (x, 0);
+      rtx op1 = XEXP (x, 1);
+      cond0 = if_then_else_cond (op0, &true0, &false0);
+      cond1 = if_then_else_cond (op1, &true1, &false1);
+
+      if ((cond0 != 0 && cond1 != 0 && !rtx_equal_p (cond0, cond1))
+	  && (REG_P (op0) || REG_P (op1)))
+	{
+	  /* Try to enable a simplification by undoing work done by
+	     if_then_else_cond if it converted a REG into something more
+	     complex.  */
+	  if (REG_P (op0))
+	    {
+	      cond0 = 0;
+	      true0 = false0 = op0;
+	    }
+	  else
+	    {
+	      cond1 = 0;
+	      true1 = false1 = op1;
+	    }
+	}
 
       if ((cond0 != 0 || cond1 != 0)
-	  && ! (cond0 != 0 && cond1 != 0 && ! rtx_equal_p (cond0, cond1)))
+	  && ! (cond0 != 0 && cond1 != 0 && !rtx_equal_p (cond0, cond1)))
 	{
 	  /* If if_then_else_cond returned zero, then true/false are the
 	     same rtl.  We must copy one of them to prevent invalid rtl