re PR middle-end/84309 (Wrong-code with -ffast-math)

	PR middle-end/84309
	* match.pd (pow(C,x) -> exp(log(C)*x)): Use exp2s and log2s instead
	of exps and logs in the use_exp2 case.

	* gcc.dg/pr84309-2.c: New test.

From-SVN: r257634

gcc/ChangeLog

+2018-02-13  Jakub Jelinek  <jakub@redhat.com>
+
+	PR middle-end/84309
+	* match.pd (pow(C,x) -> exp(log(C)*x)): Use exp2s and log2s instead
+	of exps and logs in the use_exp2 case.
+
 2018-02-13  Jeff Law  <law@redhat.com>
 
  	* config/rl/rl78.c (rl78_attribute_table): Fix terminator and

gcc/match.pd

@@ -4021,7 +4021,7 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
       /* As libmvec doesn't have a vectorized exp2, defer optimizing
 	 this until after vectorization.  */
       (if (canonicalize_math_after_vectorization_p ())
-	(exps (mult (logs @0) @1))))))))
+	(exp2s (mult (log2s @0) @1))))))))
 
  (for sqrts (SQRT)
       cbrts (CBRT)

gcc/testsuite/ChangeLog

+2018-02-13  Jakub Jelinek  <jakub@redhat.com>
+
+	PR middle-end/84309
+	* gcc.dg/pr84309-2.c: New test.
+
 2018-02-12  Richard Sandiford  <richard.sandiford@linaro.org>
 
 	PR tree-optimization/84321

gcc/testsuite/gcc.dg/pr84309-2.c

+/* PR middle-end/84309 */
+/* { dg-do compile } */
+/* { dg-options "-Ofast -fdump-tree-optimized" } */
+
+double
+foo (double x)
+{
+  return __builtin_pow (2.0, x);
+}
+
+/* { dg-final { scan-tree-dump "__builtin_exp2 " "optimized" { target *-*-linux* *-*-gnu* } } } */