[Bug c/44376] New: optimiser destroys possibility of detecting overflow

[geoff at dyalog dot com]

optimiser generates SSE instructions that add 32 bit quantities when the field
being referenced is actually 21 bits wide. This disables the possibility of
testing the overflow of the additions.


-- 
   Summary: optimiser destroys possibility of detecting overflow
   Product: gcc
   Version: unknown
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: geoff at dyalog dot com
 GCC build triplet: x86_64-linux-gnu
  GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44376

[Bug c/44376] optimiser destroys possibility of detecting overflow

[geoff at dyalog dot com]

--- Comment #1 from geoff at dyalog dot com  2010-06-02 11:09 ---
Created an attachment (id=20807)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=20807&action=view)
example code to demonstrate bug

extract code using "cpio -i http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44376

[Bug tree-optimization/44376] optimiser destroys possibility of detecting overflow

[geoff at dyalog dot com]

--- Comment #3 from geoff at dyalog dot com  2010-06-02 11:36 ---
Subject: Re:  optimiser destroys possibility
 of detecting overflow

On 02/06/10 12:17, rguenth at gcc dot gnu dot org wrote:
> --- Comment #2 from rguenth at gcc dot gnu dot org  2010-06-02 11:17 
> ---
> Please specify the GCC version you see this bug.  I think it has been fixed
> with GCC 4.5.0.
>
> gcc-4.4 -o t main.c slave.c -O3
>> ./t
> overflow assigning 12524191771
> total returned = 27
>
> gcc-4.5 -o t main.c slave.c -O3
>> ./t
> total returned = 27
>
>

Yes I am using 4.4.3.

Thankyou for the stunning response.

Geoff


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44376