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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/66916] [6 Regression] FAIL: gcc.target/arm/pr43920-2.c object-size text <= 54
Date: Wed, 22 Jul 2015 09:49:00 -0000	[thread overview]
Message-ID: <bug-66916-4-NsoblzusqG@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-66916-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66916

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
It's a combination of sign-changed compare and  X - Y CMP 0 to X CMP Y.  Bad
is

  <bb 4>:
  _9 = end_8 - start_6;
  length_10 = (size_t) _9;
  if (start_6 == end_8)

and I guess good was

  if (length_10 == 0)

where the sign-change actually didn't matter.  The single-use restriction
on the X - Y CMP 0 to X CMP Y doesn't help us because it has just a single
use - the conversion.  The sign-change and widen comparison optimization
has no such restriction though.  Adding that restriction avoids the above
transform and fixes the testcase.


  parent reply	other threads:[~2015-07-22  9:49 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-07-17 17:10 [Bug middle-end/66916] New: " ktkachov at gcc dot gnu.org
2015-07-17 17:11 ` [Bug middle-end/66916] " ktkachov at gcc dot gnu.org
2015-07-21  8:02 ` rguenth at gcc dot gnu.org
2015-07-22  9:49 ` rguenth at gcc dot gnu.org [this message]
2015-07-23  7:30 ` rguenth at gcc dot gnu.org
2015-07-23  7:30 ` rguenth at gcc dot gnu.org

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