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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/115005] [gcc-13] bogus -Warray-bounds warning
Date: Thu, 09 May 2024 16:29:34 +0000	[thread overview]
Message-ID: <bug-115005-4-CKOMilIViz@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-115005-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115005

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Folding statement: _336 = cmd_8bits[numbits_181];
Folded into: _336 = cmd_8bits[4294967295];


Which comes from:

                uint32 d = get_bits(in, numbits+1, &bb);

                if (d >= cmd_8bits[numbits]) {

get_bits:
static uint32 get_bits(HIO_HANDLE *f, int n, struct bit_buffer *bb)
{
        uint32 bits;

        if (n == 0) {
                return 0;
        }

There is a jump threading there handling n==0 (aka numbits==-1u) and that is
causing the warning. Now if I understand it numbits can't be more than 128 (or
even 16 in the 16bit case).

Adding `if (numbits >= 128) __builtin_unreachable();` right before the git_bits
gets rid of the warning and seems like would produce better code.

The reason why using smaller types works is well (numbits+1) can never be 0.

  parent reply	other threads:[~2024-05-09 16:29 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-05-09 10:10 [Bug c/115005] New: " sezeroz at gmail dot com
2024-05-09 10:17 ` [Bug c/115005] " sezeroz at gmail dot com
2024-05-09 16:29 ` pinskia at gcc dot gnu.org [this message]
2024-05-09 17:33 ` [Bug tree-optimization/115005] " sezeroz at gmail dot com
2024-05-09 23:02 ` sezeroz at gmail dot com
2024-05-09 23:03 ` sezeroz at gmail dot com

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