From: Alan Lawrence <alan.lawrence@arm.com>
To: Sebastian Pop <sebpop@gmail.com>
Cc: Richard Biener <richard.guenther@gmail.com>,
Jeff Law <law@redhat.com>, Abe Skolnik <a.skolnik@samsung.com>,
"gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
Subject: Re: fix PR46029: reimplement if conversion of loads and stores
Date: Fri, 26 Jun 2015 12:35:00 -0000 [thread overview]
Message-ID: <558D43C2.5000201@arm.com> (raw)
In-Reply-To: <CAFk3UF9O9PK8+ctcAB49sMduW7wDmM4R4=TgdYiFxS5pBH6V4w@mail.gmail.com>
Sebastian Pop wrote:
> On Thu, Jun 25, 2015 at 4:43 AM, Richard Biener
> <richard.guenther@gmail.com> wrote:
>> when the new scheme triggers vectorization cannot succeed on the
>> result as we get
>>
>> if (cond)
>> *p = val;
>>
>> if-converted to
>>
>> tem = cond ? p : &scratch;
>> *tem = val;
>
> That's correct.
>
>> and
>>
>> if (cond)
>> val = *p;
>>
>> if-converted to
>>
>> scatch = val;
>> tem = cond ? p : &scratch;
>> val = *tem;
>
> The patch does this slightly differently:
>
> tem = cond ? p : &scratch;
> val = cond ? *tem : val;
>
> I think I like your version better as it has only one cond_expr.
Another slight concern...by reusing scratchpad's, are we at risk of creating
lots of false dependencies here, that restrict instruction scheduling / other
opts later?
>> [...]
>> and thus the store and loads appear as scather/gather ones to
>> the vectorizer (if-conversion could directly generate masked
>> load/stores of course and not use a scratch-pad at all in that case).
Thank you Richard for much better expressing what I was thinking here too :)
> Abe also suggested to continue optimizing the other way in cases
> where we know to write or load from the same location on all branches:
>
> if (c)
> A[i] = ...
> else
> A[i] = ...
The store here really should be commoned, yes.
(Related but different?: BZ 56625.)
I might add, I find this code much easier to follow than the old (removed) code
about data references, memrefs_read_unconditionally, and
write_memrefs_written_at_least-once...
Thanks, Alan
next prev parent reply other threads:[~2015-06-26 12:21 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-12 21:05 Abe Skolnik
2015-06-22 16:31 ` Alan Lawrence
2015-06-24 17:11 ` Jeff Law
2015-06-25 9:48 ` Richard Biener
2015-06-25 14:28 ` Sebastian Pop
2015-06-26 12:35 ` Alan Lawrence [this message]
2015-06-26 15:10 ` Richard Biener
2015-06-26 21:29 ` Jeff Law
2015-07-06 20:46 ` Jeff Law
2015-06-24 16:51 ` Ramana Radhakrishnan
2015-06-24 17:02 ` Jeff Law
[not found] <001301d0ae99$0f015800$2d040800$@samsung.com>
[not found] ` <682387955.453848.1435166632115.JavaMail.yahoo@mail.yahoo.com>
[not found] ` <680180205.479081.1435168382362.JavaMail.yahoo@mail.yahoo.com>
2015-06-30 9:36 ` Alan Lawrence
2015-07-07 21:23 Abe
2015-07-08 9:14 ` Alan Lawrence
2015-07-08 15:52 ` Abe
2015-07-08 9:56 ` Richard Biener
2015-07-08 16:27 ` Abe
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