re PR tree-optimization/56125 (-O2 -ffast-math generates bad code when dividing…

re PR tree-optimization/56125 (-O2 -ffast-math generates bad code when dividing a double by the square of another double.)

	PR tree-optimization/56125
	* tree-ssa-math-opts.c (gimple_expand_builtin_pow): Don't optimize
	pow(x,c) into sqrt(x) * powi(x, n/2) or
	1.0 / (sqrt(x) * powi(x, abs(n/2))) if c is an integer or when
	optimizing for size.
	Don't optimize pow(x,c) into powi(x, n/3) * powi(cbrt(x), n%3) or
	1.0 / (powi(x, abs(n)/3) * powi(cbrt(x), abs(n)%3)) if 2c is an
	integer.

	* gcc.dg/pr56125.c: New test.

From-SVN: r195507

gcc/ChangeLog

 2013-01-28  Jakub Jelinek  <jakub@redhat.com>
 
+	PR tree-optimization/56125
+	* tree-ssa-math-opts.c (gimple_expand_builtin_pow): Don't optimize
+	pow(x,c) into sqrt(x) * powi(x, n/2) or
+	1.0 / (sqrt(x) * powi(x, abs(n/2))) if c is an integer or when
+	optimizing for size.
+	Don't optimize pow(x,c) into powi(x, n/3) * powi(cbrt(x), n%3) or
+	1.0 / (powi(x, abs(n)/3) * powi(cbrt(x), abs(n)%3)) if 2c is an
+	integer.
+
 	PR tree-optimization/56094
 	* gimplify.c (force_gimple_operand_1): Temporarily set input_location
 	to UNKNOWN_LOCATION while gimplifying expr.
@@ -22,7 +31,6 @@
 	* config.gcc (microblaze*-*-*): Rename microblaze*-*-elf, update
 	tm_file.
 
-
 2013-01-25  Naveen H.S  <Naveen.Hurugalawadi@caviumnetworks.com>
 
 	* config/aarch64/aarch64.c (TARGET_FIXED_CONDITION_CODE_REGS):

gcc/testsuite/ChangeLog

+2013-01-28  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/56125
+	* gcc.dg/pr56125.c: New test.
+
 2013-01-28  Tobias Burnus  <burnus@net-b.de>
 	    Mikael Morin  <mikael@gcc.gnu.org>
 

gcc/testsuite/gcc.dg/pr56125.c

+/* PR tree-optimization/56125 */
+/* { dg-do run } */
+/* { dg-options "-O2 -ffast-math" } */
+
+extern void abort (void);
+extern double fabs (double);
+
+__attribute__((cold)) double
+foo (double x, double n)
+{
+  double u = x / (n * n);
+  return u;
+}
+
+int
+main ()
+{
+  if (fabs (foo (29, 2) - 7.25) > 0.001)
+    abort ();
+  return 0;
+}

gcc/tree-ssa-math-opts.c

@@ -1110,7 +1110,7 @@ gimple_expand_builtin_pow (gimple_stmt_iterator *gsi, location_t loc,
   HOST_WIDE_INT n;
   tree type, sqrtfn, cbrtfn, sqrt_arg0, sqrt_sqrt, result, cbrt_x, powi_cbrt_x;
   enum machine_mode mode;
-  bool hw_sqrt_exists;
+  bool hw_sqrt_exists, c_is_int, c2_is_int;
 
   /* If the exponent isn't a constant, there's nothing of interest
      to be done.  */
@@ -1122,8 +1122,9 @@ gimple_expand_builtin_pow (gimple_stmt_iterator *gsi, location_t loc,
   c = TREE_REAL_CST (arg1);
   n = real_to_integer (&c);
   real_from_integer (&cint, VOIDmode, n, n < 0 ? -1 : 0, 0);
+  c_is_int = real_identical (&c, &cint);
 
-  if (real_identical (&c, &cint)
+  if (c_is_int
       && ((n >= -1 && n <= 2)
 	  || (flag_unsafe_math_optimizations
 	      && optimize_insn_for_speed_p ()
@@ -1221,7 +1222,8 @@ gimple_expand_builtin_pow (gimple_stmt_iterator *gsi, location_t loc,
       return build_and_insert_call (gsi, loc, cbrtfn, sqrt_arg0);
     }
 
-  /* Optimize pow(x,c), where n = 2c for some nonzero integer n, into
+  /* Optimize pow(x,c), where n = 2c for some nonzero integer n
+     and c not an integer, into
 
        sqrt(x) * powi(x, n/2),                n > 0;
        1.0 / (sqrt(x) * powi(x, abs(n/2))),   n < 0.
@@ -1230,10 +1232,13 @@ gimple_expand_builtin_pow (gimple_stmt_iterator *gsi, location_t loc,
   real_arithmetic (&c2, MULT_EXPR, &c, &dconst2);
   n = real_to_integer (&c2);
   real_from_integer (&cint, VOIDmode, n, n < 0 ? -1 : 0, 0);
+  c2_is_int = real_identical (&c2, &cint);
 
   if (flag_unsafe_math_optimizations
       && sqrtfn
-      && real_identical (&c2, &cint))
+      && c2_is_int
+      && !c_is_int
+      && optimize_function_for_speed_p (cfun))
     {
       tree powi_x_ndiv2 = NULL_TREE;
 
@@ -1286,6 +1291,7 @@ gimple_expand_builtin_pow (gimple_stmt_iterator *gsi, location_t loc,
       && cbrtfn
       && (gimple_val_nonnegative_real_p (arg0) || !HONOR_NANS (mode))
       && real_identical (&c2, &c)
+      && !c2_is_int
       && optimize_function_for_speed_p (cfun)
       && powi_cost (n / 3) <= POWI_MAX_MULTS)
     {