Re: [PATCH] match.pd: Add bitwise and pattern [PR106243]

[Richard Biener <richard.guenther@gmail.com>]

On Thu, Aug 4, 2022 at 12:40 AM Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
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> 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
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