This patch implements some of the optimizations discussed in
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71026.
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.
OK for commit?
ChangeLog
2017-10-17 Wilco Dijkstra <wdijk...@arm.com>
Jackson Woodruff <jackson.woodr...@arm.com>
gcc/
PR 71026/tree-optimization
* match.pd: Canonicalize negate in division.
gcc/testsuite/
PR 71026/tree-optimization
* gcc.dg/div_neg: New test.
--
diff --git a/gcc/match.pd b/gcc/match.pd
index
cb48f079b4a310272e49cc319a1b3b0ff2023ba4..ade851f78fb9ac6ce03b752f63e03f3b5a19cda9
100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -352,6 +352,11 @@ 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))
+
(if (flag_unsafe_math_optimizations)
/* Simplify (C / x op 0.0) to x op 0.0 for C > 0. */
(for op (lt le gt ge)
diff --git a/gcc/testsuite/gcc.dg/div_neg.c b/gcc/testsuite/gcc.dg/div_neg.c
new file mode 100644
index
0000000000000000000000000000000000000000..da499cda2fba6c943ec99c55cae2ea389f9e1cca
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/div_neg.c
@@ -0,0 +1,10 @@
+/* { 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" } } */
