PR71026: Canonicalize negates in division

Canonicalize x / (- y) into (-x) / y.

This moves negates out of the RHS of a division in order to
allow further simplifications and potentially more reciprocal CSEs.

2017-11-07  Wilco Dijkstra  <wdijkstr@arm.com>
	    Jackson Woodruff  <jackson.woodruff@arm.com>

    gcc/
	PR tree-optimization/71026
	* match.pd: Canonicalize negate in division.

    testsuite/
	PR 71026/tree-optimization/71026
	* gcc.dg/div_neg: New test.

From-SVN: r254497

gcc/ChangeLog

+2017-11-07  Wilco Dijkstra  <wdijkstr@arm.com>
+	    Jackson Woodruff  <jackson.woodruff@arm.com>
+
+	PR tree-optimization/71026
+	* match.pd: Canonicalize negate in division.
+
 2017-11-07  Sudakshina Das  <sudi.das@arm.com>
 
 	PR middle-end/80131

gcc/match.pd

@@ -354,6 +354,11 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
   (rdiv @0 (rdiv:s @1 @2))
    (mult (rdiv @0 @1) @2)))
 
+/* Simplify x / (- y) to -x / y.  */
+(simplify
+ (rdiv @0 (negate @1))
+ (rdiv (negate @0) @1))
+
 /* Optimize (X & (-A)) / A where A is a power of 2, to X >> log2(A) */
 (for div (trunc_div ceil_div floor_div round_div exact_div)
  (simplify

gcc/testsuite/ChangeLog

+2017-10-17  Wilco Dijkstra  <wdijkstr@arm.com>
+	    Jackson Woodruff  <jackson.woodruff@arm.com>
+
+	PR tree-optimization/71026
+	* gcc.dg/div_neg: New test.
+
 2017-11-07  Sudakshina Das  <sudi.das@arm.com>
 
 	PR middle-end/80131
-	* testsuite/gcc.dg/pr80131-1.c: New Test.
+	* gcc.dg/pr80131-1.c: New Test.
 
 2017-11-07  Marc Glisse  <marc.glisse@inria.fr>
 

gcc/testsuite/gcc.dg/div_neg.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+float
+div_neg (float x, float y)
+{
+  return (-x / y) * (x / -y);
+}
+
+/* { dg-final { scan-tree-dump-times " / " 1 "optimized" } } */