https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95635
Bug ID: 95635
Summary: -Warray-bounds falsely claims out-of-bounds access
Product: gcc
Version: 10.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: gccbugs at dima dot secretsauce.net
Target Milestone: ---
Created attachment 48716
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48716&action=edit
Bug demo
Hi. I'm running gcc-10 from Debian:
dima@shorty:~$ gcc-10 --version
gcc-10 (Debian 10.1.0-3) 10.1.0
I'm building the attached source like this:
gcc-10 -Warray-bounds -O2 -c -o /dev/null tst.c
And I get this:
tst.c: In function 'a':
tst.c:12:27: warning: array subscript <unknown> is outside array bounds of
'int[0]' [-Warray-bounds]
12 | if(L[i] > 0 && arr[L[i]] )
| ~~~^~~~~~
tst.c:8:9: note: while referencing 'arr'
8 | int arr[0];
| ^~~
tst.c:12:27: warning: array subscript <unknown> is outside array bounds of
'int[0]' [-Warray-bounds]
12 | if(L[i] > 0 && arr[L[i]] )
| ~~~^~~~~~
tst.c:8:9: note: while referencing 'arr'
8 | int arr[0];
The array arr[] has 0 elements, and gcc is telling me I'm accessing outside of
those bounds. But L[i]>0 is always false, so we'll never actually look at
arr[anything]. gcc knows this most of the time. If I remove the -O2 or the b()
call or lots of little unrelated-looking things, the issue goes away. Thanks.
