This adds a match.pd rule that drops the bitwwise nots when both arguments to a
subtract is inverted. i.e. for:
float g(float a, float b)
{
return ~(int)a - ~(int)b;
}
we instead generate
float g(float a, float b)
{
return (int)b - (int)a;
}
We already do a limited version of this from the fold_binary fold functions but
this makes a more general version in match.pd that applies more often.
gcc/ChangeLog:
* match.pd: New bit_not rule.
gcc/testsuite/ChangeLog:
* gcc.dg/subnot.c: New test.
(simplify
(bit_not (plus:c (bit_not @0) @1))
(minus @0 @1))
+/* (~X - ~Y) -> Y - X. */
+(simplify
+ (minus (bit_not @0) (bit_not @1))
+ (with { tree utype = unsigned_type_for (type); }
+ (convert (minus (convert:utype @1) (convert:utype @0)))))
/* ~(X - Y) -> ~X + Y. */
(simplify
--- /dev/null
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-optimized" } */
+
+float g(float a, float b)
+{
+ return ~(int)a - ~(int)b;
+}
+
+/* { dg-final { scan-tree-dump-not "~" "optimized" } } */