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Date: Wed, 25 Jan 2017 10:58:00 -0000
From: Richard Biener <rguenther@suse.de>
To: Yuri Gribov <tetra2005@gmail.com>
cc: GCC Patches <gcc-patches@gcc.gnu.org>, amodra@gmail.com,     rguenth@gcc.gnu.org
Subject: Re: [PATCH][PR 67328] Improve bitfield testing
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On Wed, 25 Jan 2017, Yuri Gribov wrote:

> Hi all,
> 
> This fixes inefficient bitfield code reported in
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67328
> 
> Bootstrapped and regtested on x86_64.
> 
> Ok for trunk?

This isn't a regression fix and thus not appropriate at this stage.

Some comments on the patch:

+/* A & (2**N - 1) <= 2**K - 1 -> ~(A & (2**N - 2**K)
+   A & (2**N - 1) <  2**K     -> ~(A & (2**N - 2**K)
+   A & (2**N - 1) >= 2**K     -> A & (2**N - 2**K)
+   A & (2**N - 1) >  2**K - 1 -> A & (2**N - 2**K)
+ */

you miss the != 0/== 0 in the result (and the ~ is redundant then).

Note that A & (2**N - 1) >= 2**K should already have been simplified
to A & (2**N - 1) >  2**K - 1 (we canonicalize to smaller constants).

+  (if (TYPE_UNSIGNED (TREE_TYPE (@0)) && tree_fits_uhwi_p (@2) && 
tree_fits_uhwi_p (@3))
+   (with
+    {

I think you should restrict this to INTEGRAL_TYPE_P types.

Please use wide-ints so you do not restrict yourself to fits_uhwi_p
values.

Thanks,
Richard.