Bug 49848

Summary: False positive warning triggered by -Wmaybe-uninitialized
Product: gcc Reporter: Arnaud Lacombe <lacombar>
Component: middle-endAssignee: Not yet assigned to anyone <unassigned>
Status: RESOLVED DUPLICATE    
Severity: normal CC: jeffreyalaw, Laurent.Rineau__gcc, manu
Priority: P3    
Version: 4.5.1   
Target Milestone: ---   
Host: Target:
Build: Known to work:
Known to fail: Last reconfirmed: 2012-10-25 00:00:00
Bug Depends on:    
Bug Blocks: 24639    
Attachments: reduced testcase

Description Arnaud Lacombe 2011-07-26 01:29:35 UTC 
Considering the attached reduced-testcase, gcc will trigger the following warning:

% gcc -m32 -Wall -Os -c -S -o /dev/null foo.c                                                                  
foo.c: In function 'foo':
foo.c:9:12: warning: 'b' may be used uninitialized in this function

Affected gcc is:

% gcc -v                                     
Using built-in specs.
[...]
Thread model: posix
gcc version 4.5.1 20100924 (Red Hat 4.5.1-4) (GCC)

however, gcc from trunk (as of 20110609) also produces the warning:

/src/x86-64/obj/destdir/bin/x86_64-none-linux-gcc -m32 -Wall -Os -c -S -o /dev/null foo.c
foo.c: In function 'foo':
foo.c:14:21: warning: 'b' may be used uninitialized in this function [-Wmaybe-uninitialized]

This warning only shows up at -Os.

Mailing list reference: http://gcc.gnu.org/ml/gcc-help/2011-07/msg00243.html
Comment 1 Arnaud Lacombe 2011-07-26 01:31:07 UTC 
Created attachment 24834 [details]
reduced testcase
Comment 2 Andrew Pinski 2011-07-26 02:15:38 UTC 
This is a semi standard issue with uninitialized variable warnings.
Comment 3 Manuel López-Ibáñez 2012-10-25 00:12:34 UTC 
Still present in GCC 4.8.0pr49848.c: In function ‘foo’:
pr49848.c:14:21: warning: ‘b’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  if (a != NULL && b != NULL)
                     ^
Comment 4 Jeffrey A. Law 2013-11-20 01:12:56 UTC 
Another case where throttling optimizations inhibits accurate warnings.

*** This bug has been marked as a duplicate of bug 42145 ***