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From: "matthijsvanduin at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/100801] Aggressive loop optimizations cause incorrect warning
Date: Sat, 31 Jul 2021 00:41:45 +0000	[thread overview]
Message-ID: <bug-100801-4-oG7dRQBeGT@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-100801-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100801

Matthijs van Duin <matthijsvanduin at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |matthijsvanduin at gmail dot com

--- Comment #3 from Matthijs van Duin <matthijsvanduin at gmail dot com> ---
Simpler testcase:

/* compiler flags required to trigger warning: -O1 -ftree-vrp  */

static void foo(int *x, long n)
{
        long i = 0;
        for (; i + 4 <= n; i += 4) {
        }
        for (; i < n; i++) {
                x[i]++;
        }
}

void bar(int *x)
{
        foo(x, 128);
}


A workaround with no runtime overhead is adding the following check between the
loops:

if (__builtin_constant_p(n % 4 == 0) && n % 4 == 0)
        return;

  parent reply	other threads:[~2021-07-31  0:41 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-27 14:03 [Bug ipa/100801] New: " jl_gccbugs at conductive dot de
2021-05-28 10:54 ` [Bug tree-optimization/100801] " rguenth at gcc dot gnu.org
2021-05-28 12:45 ` jl_gccbugs at conductive dot de
2021-07-31  0:41 ` matthijsvanduin at gmail dot com [this message]
2021-12-20  0:55 ` [Bug tree-optimization/100801] [9/10/11/12 Regression] " pinskia at gcc dot gnu.org
2022-01-05 14:29 ` rguenth at gcc dot gnu.org
2022-05-27  9:45 ` [Bug tree-optimization/100801] [10/11/12/13 " rguenth at gcc dot gnu.org
2022-06-28 10:45 ` jakub at gcc dot gnu.org
2023-07-07 10:40 ` [Bug tree-optimization/100801] [11/12/13/14 " rguenth at gcc dot gnu.org
2024-03-11  3:42 ` [Bug tree-optimization/100801] [11/12 " law at gcc dot gnu.org

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