re PR tree-optimization/69556 (forwprop4/match.pd undoing work from recip)

2016-02-01  Richard Biener  <rguenther@suse.de>

	PR middle-end/69556
	* match.pd: Guard (C1/X)*C2 -> (C1*C2)/X with single_use.

	* gcc.dg/tree-ssa/recip-8.c: New testcase.

From-SVN: r233040

gcc/ChangeLog

 2016-02-01  Richard Biener  <rguenther@suse.de>
 
+	PR middle-end/69556
+	* match.pd: Guard (C1/X)*C2 -> (C1*C2)/X with single_use.
+
+2016-02-01  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/69574
 	* tree-chrec.c (hide_evolution_in_other_loops_than_loop): Instead
 	of asserting return chrec_dont_know.

gcc/match.pd

@@ -445,8 +445,9 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 
 /* Fold (C1/X)*C2 into (C1*C2)/X.  */
 (simplify
- (mult (rdiv:s REAL_CST@0 @1) REAL_CST@2)
-  (if (flag_associative_math)
+ (mult (rdiv@3 REAL_CST@0 @1) REAL_CST@2)
+  (if (flag_associative_math
+       && single_use (@3))
    (with
     { tree tem = const_binop (MULT_EXPR, type, @0, @2); }
     (if (tem)

gcc/testsuite/ChangeLog

 2016-02-01  Richard Biener  <rguenther@suse.de>
 
+	PR middle-end/69556
+	* gcc.dg/tree-ssa/recip-8.c: New testcase.
+
+2016-02-01  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/69574
 	* gcc.dg/torture/pr69574.c: New testcase.
 

gcc/testsuite/gcc.dg/tree-ssa/recip-8.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -ffast-math -fdump-tree-optimized" } */
+
+double bar (double, double, double, double, double);
+
+double
+foo (double a)
+{
+  return bar (1.0/a, 2.0/a, 4.0/a, 8.0/a, 16.0/a);
+}
+
+/* { dg-final { scan-tree-dump-times "/" 1 "optimized"  } } */