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Re: [Patch match.pd] Add a simplify rule for x * copysign (1.0, y);
- From: Jakub Jelinek <jakub at redhat dot com>
- To: James Greenhalgh <james dot greenhalgh at arm dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Thu, 1 Oct 2015 20:36:43 +0200
- Subject: Re: [Patch match.pd] Add a simplify rule for x * copysign (1.0, y);
- Authentication-results: sourceware.org; auth=none
- References: <1443707835-6888-1-git-send-email-james dot greenhalgh at arm dot com>
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
On Thu, Oct 01, 2015 at 02:57:15PM +0100, James Greenhalgh wrote:
> 2015-10-01 James Greenhalgh <james.greenhalgh@arm.com>
>
> * match.pd (mult (COPYSIGN:s real_onep @0) @1): New simplifier.
Also, please note that
+ wide_int m = wi::min_value (TYPE_PRECISION (type), SIGNED);
+ tree tt
+ = build_nonstandard_integer_type (TYPE_PRECISION (type),
+ false);
+ tree mask = wide_int_to_tree (tt, m);
is really not a reliable way to determine which bit to change.
In some floating format it is not possible at all, in others it might not
be the topmost bit of the precision, or might depend on
FLOAT_WORDS_BIG_ENDIAN etc., see expand_copysign_bit and expand_copysign
for details (e.g. one has to look at fmt->signbit_rw etc.).
So, I probably agree with Andrew that it would be better optimized during
expansion. One issue for that though is that TER stops at calls, we'd need
to special case this case.
Jakub