[MDEV-6305] UNINIT_VAR emits code in non-debug builds Created: 2014-06-05  Updated: 2014-08-27  Resolved: 2014-08-26

Status: Closed
Project: MariaDB Server
Component/s: None
Affects Version/s: 5.5.37, 10.0.11, 10.1.0
Fix Version/s: 10.1.1

Type: Bug Priority: Minor
Reporter: Sergey Vojtovich Assignee: Sergey Vojtovich
Resolution: Fixed Votes: 0
Labels: None

Issue Links:
Relates
relates to MDEV-6650 LINT_INIT emits code in non-debug builds Closed

 Description   

Leaving variables uninitialized in certain cases helps to achieve top-notch performance. Sometimes compiler thinks that variable may be used uninitialized (whereas it may not) and emits a warning.

To silence these warnings there is UNINIT_VAR() macro:

#if defined(_lint) || defined(FORCE_INIT_OF_VARS) || \
 
    defined(__cplusplus) || !defined(__GNUC__)
 
#define UNINIT_VAR(x) x= 0
 
#else
 
/* GCC specific self-initialization which inhibits the warning. */
 
#define UNINIT_VAR(x) x= x
 
#endif

There are a few problems with this macro:
1. It always emits "x= 0" for non-gcc
2. It always emits "x= 0" for C++ code

It means leaving variable uninitialized makes sense only in C code compiled by gcc.

Regarding __cplusplus: there is a reference to gcc bug which was fixed 3 years ago. Probably it is time to remove it?

 Comments   
Comment by Sergey Vojtovich [ 2014-06-24 ]

Sergei, please review fix for this bug.

Though I doubt it is a good idea to "Always enable -Wall for gnu C/C++" bypassing cmake maintainer mode (specifically FORCE_INIT_OF_VARS).
Now we get more warnings from LINT_INIT(). And there is also LINT_INIT_STRUCT() which didn't work before.

Comment by Sergei Golubchik [ 2014-08-25 ]

Ok to push.
let's handle LINT_INIT/etc warnings separately

Comment by Sergey Vojtovich [ 2014-08-26 ]

Fixed in 10.1.1:

commit bb11eb82d5dce664e151519577df173acb31ee91
 
Author: Sergey Vojtovich <svoj@mariadb.org>
 
Date:   Tue Aug 26 14:57:09 2014 +0400
 
 
 
    MDEV-6305 - UNINIT_VAR emits code in non-debug builds
 
 
 
    Reverted workaround for gcc bug, which was fixed 3 years ago:
 
    http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34772

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