re PR tree-optimization/85466 (Performance is slow when doing 'branchless' conditional style math operations)

	PR libstdc++/85466
	* real.h (real_nextafter): Declare.
	* real.c (real_nextafter): New function.
	* fold-const-call.c (fold_const_nextafter): New function.
	(fold_const_call_sss): Call it for CASE_CFN_NEXTAFTER and
	CASE_CFN_NEXTTOWARD.
	(fold_const_call_1): For CASE_CFN_NEXTTOWARD call fold_const_call_sss
	even when arg1_mode is different from arg0_mode.

	* gcc.dg/nextafter-1.c: New test.
	* gcc.dg/nextafter-2.c: New test.
	* gcc.dg/nextafter-3.c: New test.
	* gcc.dg/nextafter-4.c: New test.

From-SVN: r259921

1 files changed, 62 insertions, 3 deletions

diff --git a/gcc/fold-const-call.c b/gcc/fold-const-call.c
index fcf4a14..4969492 100644
--- a/gcc/fold-const-call.c
+++ b/gcc/fold-const-call.c
@@ -529,6 +529,48 @@ fold_const_pow (real_value *result, const real_value *arg0,
 
 /* Try to evaluate:
 
+      *RESULT = nextafter (*ARG0, *ARG1)
+
+   or
+
+      *RESULT = nexttoward (*ARG0, *ARG1)
+
+   in format FORMAT.  Return true on success.  */
+
+static bool
+fold_const_nextafter (real_value *result, const real_value *arg0,
+		      const real_value *arg1, const real_format *format)
+{
+  if (REAL_VALUE_ISSIGNALING_NAN (*arg0)
+      || REAL_VALUE_ISSIGNALING_NAN (*arg1))
+    return false;
+
+  /* Don't handle composite modes, nor decimal, nor modes without
+     inf or denorm at least for now.  */
+  if (format->pnan < format->p
+      || format->b == 10
+      || !format->has_inf
+      || !format->has_denorm)
+    return false;
+
+  if (real_nextafter (result, format, arg0, arg1)
+      /* If raising underflow or overflow and setting errno to ERANGE,
+	 fail if we care about those side-effects.  */
+      && (flag_trapping_math || flag_errno_math))
+    return false;
+  /* Similarly for nextafter (0, 1) raising underflow.  */
+  else if (flag_trapping_math
+	   && arg0->cl == rvc_zero
+	   && result->cl != rvc_zero)
+    return false;
+
+  real_convert (result, format, result);
+
+  return true;
+}
+
+/* Try to evaluate:
+
       *RESULT = ldexp (*ARG0, ARG1)
 
    in format FORMAT.  Return true on success.  */
@@ -1260,6 +1302,10 @@ fold_const_call_sss (real_value *result, combined_fn fn,
     CASE_CFN_POW:
       return fold_const_pow (result, arg0, arg1, format);
 
+    CASE_CFN_NEXTAFTER:
+    CASE_CFN_NEXTTOWARD:
+      return fold_const_nextafter (result, arg0, arg1, format);
+
     default:
       return false;
     }
@@ -1365,20 +1411,33 @@ fold_const_call_1 (combined_fn fn, tree type, tree arg0, tree arg1)
   machine_mode arg0_mode = TYPE_MODE (TREE_TYPE (arg0));
   machine_mode arg1_mode = TYPE_MODE (TREE_TYPE (arg1));
 
-  if (arg0_mode == arg1_mode
+  if (mode == arg0_mode
       && real_cst_p (arg0)
       && real_cst_p (arg1))
     {
       gcc_checking_assert (SCALAR_FLOAT_MODE_P (arg0_mode));
-      if (mode == arg0_mode)
+      REAL_VALUE_TYPE result;
+      if (arg0_mode == arg1_mode)
 	{
 	  /* real, real -> real.  */
-	  REAL_VALUE_TYPE result;
 	  if (fold_const_call_sss (&result, fn, TREE_REAL_CST_PTR (arg0),
 				   TREE_REAL_CST_PTR (arg1),
 				   REAL_MODE_FORMAT (mode)))
 	    return build_real (type, result);
 	}
+      else if (arg1_mode == TYPE_MODE (long_double_type_node))
+	switch (fn)
+	  {
+	  CASE_CFN_NEXTTOWARD:
+	    /* real, long double -> real.  */
+	    if (fold_const_call_sss (&result, fn, TREE_REAL_CST_PTR (arg0),
+				     TREE_REAL_CST_PTR (arg1),
+				     REAL_MODE_FORMAT (mode)))
+	      return build_real (type, result);
+	    break;
+	  default:
+	    break;
+	  }
       return NULL_TREE;
     }