From: Joern Rennecke <joern.rennecke@embecosm.com>
To: Richard Biener <rguenther@suse.de>
Cc: gcc@gcc.gnu.org
Subject: ssa-pre-21.c / PRE for truncated indices
Date: Thu, 15 Aug 2013 11:56:00 -0000 [thread overview]
Message-ID: <20130815073557.i2u9oatlskw84k8s-nzlynne@webmail.spamcop.net> (raw)
[-- Attachment #1: Type: text/plain, Size: 469 bytes --]
I see that gcc.dg/tree-ssa/ssa-pre-21.c fails for avr.
The computation of k + 1L is done as unsigned int (16 bit),
but later ++k is performed as unsigned long (32 bit), and thus
array[k+1] is not re-used.
Is this to be considered a big in the optimizers for not
optimizing this, or in the testsuite for insisting that it
should be?
FWIW, equivalent behaviour can be seen natively on
i686-pc-linux-gnu by replacing "long" with "long long",
as shown in the attachment.
[-- Attachment #2: ssa-pre-21-ll.c --]
[-- Type: text/x-chdr, Size: 356 bytes --]
/* { dg-do compile } */
/* { dg-options "-O2 -fdump-tree-pre" } */
long long
NumSift (long long *array, unsigned long long k)
{
if (array[k] < array[k + 1LL])
++k;
return array[k];
}
/* There should be only two loads left. */
/* { dg-final { scan-tree-dump-times "= \\\*\[^\n;\]*;" 2 "pre" } } */
/* { dg-final { cleanup-tree-dump "pre" } } */
next reply other threads:[~2013-08-15 11:36 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-15 11:56 Joern Rennecke [this message]
2013-08-15 18:06 ` Richard Biener
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