On Thu, Aug 4, 2022 at 12:40 AM Jeff Law via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > > > On 8/3/2022 2:44 PM, Prathamesh Kulkarni via Gcc-patches wrote: > > On Thu, 4 Aug 2022 at 00:41, Sam Feifer via Gcc-patches > > <gcc-patches@gcc.gnu.org> wrote: > >> This patch adds a new optimization to match.pd. The pattern, -x & 1, > >> now gets simplified to x & 1, reducing the number of instructions > >> produced. > > Hi Sam, > > No comments on patch, but wondering if we can similarly add another pattern > > to > > simplify abs(x) & 1 -> x & 1 ? > > Currently we don't appear to do it on GIMPLE: > > > > __attribute__((noipa)) > > int f1 (int x) > > { > > return __builtin_abs (x) & 1; > > } > > > > .optimized dump shows: > > _1 = ABS_EXPR <x_2(D)>; > > _3 = _1 & 1; > > return _3; > > > > altho combine simplifies it to x & 1 on RTL, resulting in code-gen: > > f1: > > and w0, w0, 1 > > ret > Doesn't the abs(x) & mask simplify to x & mask for any mask where the > sign bit of x is off -- including cases where mask isn't necessarily a > compile-time constant, but we have range data which allows us to know > that x's sign bit is off in mask.
You can use tree_expr_nonnegative_p but then that does simplify abs(x) to x already. But sure, handling abs() like negate sounds it should work. Richard, > jeff > > >