Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
On Nov 7, 2013, at 5:13 PM, Mingjie Xing mingjie.x...@gmail.com wrote: Well, it is my understanding that the warning should be emitted for a volatile variable only if it is not accessed. Initialization means accessing, even though it is not used anywhere. Let me try. A warning is useful, if there is no way a conforming program can tell that the variable exists or not. So, the question is, how can you notice the variable? Answer, there is no way, so, there is no utility in having the variable. The warning is to tell the user to remove the dead variable.
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
On Fri, Nov 8, 2013 at 5:03 PM, Mike Stump mikest...@comcast.net wrote: On Nov 7, 2013, at 5:13 PM, Mingjie Xing mingjie.x...@gmail.com wrote: Well, it is my understanding that the warning should be emitted for a volatile variable only if it is not accessed. Initialization means accessing, even though it is not used anywhere. Let me try. A warning is useful, if there is no way a conforming program can tell that the variable exists or not. So, the question is, how can you notice the variable? Answer, there is no way, so, there is no utility in having the variable. The warning is to tell the user to remove the dead variable. I am sort of lost. The bug is straightforward and it suggests the volatile variable is actually used if it is declared with an initialization, and GCC should not emit warning message for it. The patch is fixing this, right? Any explanation? Thanks, bin -- Best Regards.
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
On Nov 8, 2013, at 1:32 AM, Bin.Cheng amker.ch...@gmail.com wrote: On Fri, Nov 8, 2013 at 5:03 PM, Mike Stump mikest...@comcast.net wrote: On Nov 7, 2013, at 5:13 PM, Mingjie Xing mingjie.x...@gmail.com wrote: Well, it is my understanding that the warning should be emitted for a volatile variable only if it is not accessed. Initialization means accessing, even though it is not used anywhere. Let me try. A warning is useful, if there is no way a conforming program can tell that the variable exists or not. So, the question is, how can you notice the variable? Answer, there is no way, so, there is no utility in having the variable. The warning is to tell the user to remove the dead variable. I am sort of lost. I can try again. Begin your sentence, the important utility of this construct is demonstrated by the following code: See if you can complete it. If not, then, then there is no utility. The warning says, there is no utility. This isn't a theoretic thing, it is an engineering thing.
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
On Fri, Nov 8, 2013 at 10:39 AM, Mike Stump mikest...@comcast.net wrote: On Nov 8, 2013, at 1:32 AM, Bin.Cheng amker.ch...@gmail.com wrote: On Fri, Nov 8, 2013 at 5:03 PM, Mike Stump mikest...@comcast.net wrote: On Nov 7, 2013, at 5:13 PM, Mingjie Xing mingjie.x...@gmail.com wrote: Well, it is my understanding that the warning should be emitted for a volatile variable only if it is not accessed. Initialization means accessing, even though it is not used anywhere. Let me try. A warning is useful, if there is no way a conforming program can tell that the variable exists or not. So, the question is, how can you notice the variable? Answer, there is no way, so, there is no utility in having the variable. The warning is to tell the user to remove the dead variable. I am sort of lost. I can try again. Begin your sentence, the important utility of this construct is demonstrated by the following code: See if you can complete it. If not, then, then there is no utility. The warning says, there is no utility. This isn't a theoretic thing, it is an engineering thing. Yeah, and as opposed to the non-volatile case removing the volatile set-but-unused variable even reduces code size! Richard.
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
On Fri, Nov 8, 2013 at 5:39 PM, Mike Stump mikest...@comcast.net wrote: On Nov 8, 2013, at 1:32 AM, Bin.Cheng amker.ch...@gmail.com wrote: On Fri, Nov 8, 2013 at 5:03 PM, Mike Stump mikest...@comcast.net wrote: On Nov 7, 2013, at 5:13 PM, Mingjie Xing mingjie.x...@gmail.com wrote: Well, it is my understanding that the warning should be emitted for a volatile variable only if it is not accessed. Initialization means accessing, even though it is not used anywhere. Let me try. A warning is useful, if there is no way a conforming program can tell that the variable exists or not. So, the question is, how can you notice the variable? Answer, there is no way, so, there is no utility in having the variable. The warning is to tell the user to remove the dead variable. I am sort of lost. I can try again. Begin your sentence, the important utility of this construct is demonstrated by the following code: See if you can complete it. If not, then, then there is no utility. The warning says, there is no utility. This isn't a theoretic thing, it is an engineering thing. Thanks for elaborating. The warning message is actually for no-use of variable, and it has few things to do with whether it's accessed or not. Thanks, bin -- Best Regards.
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
Oops, if it is not a bug, please close the report http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57258 Thanks, Mingjie 2013/11/8 Richard Biener richard.guent...@gmail.com: On Fri, Nov 8, 2013 at 10:39 AM, Mike Stump mikest...@comcast.net wrote: On Nov 8, 2013, at 1:32 AM, Bin.Cheng amker.ch...@gmail.com wrote: On Fri, Nov 8, 2013 at 5:03 PM, Mike Stump mikest...@comcast.net wrote: On Nov 7, 2013, at 5:13 PM, Mingjie Xing mingjie.x...@gmail.com wrote: Well, it is my understanding that the warning should be emitted for a volatile variable only if it is not accessed. Initialization means accessing, even though it is not used anywhere. Let me try. A warning is useful, if there is no way a conforming program can tell that the variable exists or not. So, the question is, how can you notice the variable? Answer, there is no way, so, there is no utility in having the variable. The warning is to tell the user to remove the dead variable. I am sort of lost. I can try again. Begin your sentence, the important utility of this construct is demonstrated by the following code: See if you can complete it. If not, then, then there is no utility. The warning says, there is no utility. This isn't a theoretic thing, it is an engineering thing. Yeah, and as opposed to the non-volatile case removing the volatile set-but-unused variable even reduces code size! Richard.
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
On Nov 8, 2013, at 2:25 AM, Bin.Cheng amker.ch...@gmail.com wrote: Thanks for elaborating. The warning message is actually for no-use of variable, and it has few things to do with whether it's accessed or not. I disagree. If you examine why the warning was put in, you realize it was put in so that lazy programmers can find dead things. Why do they want to do that, to remove the dead things. This construct is a dead thing. If you disagree, you'd have to say why the warning was produced.
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
On Nov 8, 2013, at 2:35 AM, Mingjie Xing mingjie.x...@gmail.com wrote: Oops, if it is not a bug, please close the report http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57258 Well, I've stated my position. I can be swayed by a good argument, if someone has one. I'd give people a chance to weigh in if they can think of one. A global variable with linkage is completely different, as the linker can grab it, dlsym can grab it, and who knows… while a cleaver (Ian type of cleaver) person could grab an automatic variable, the difficulty is enormous and doing that would be exceedingly odd. I don't know of any coding style where people do that sort of thing. Reflection comes the closest; dynamic bindings (a la lisp) I guess comes second; shudder. I'd make them mark it with the used attribute, since they're really weird.
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
- warning_at (DECL_SOURCE_LOCATION (p),
- OPT_Wunused_but_set_variable,
- variable %qD set but not used, p);
+ {
+if (!TREE_THIS_VOLATILE (p))
+ warning_at (DECL_SOURCE_LOCATION (p),
+OPT_Wunused_but_set_variable,
+variable %qD set but not used, p);
+ }
I'd prefer
else if (DECL_CONTEXT (p) == current_function_decl
!TREE_THIS_VOLATILE (p))
which concises the logic and avoids indent change
Thanks,
Joey
On Thu, Nov 7, 2013 at 3:37 PM, Bin.Cheng amker.ch...@gmail.com wrote:
On Thu, Nov 7, 2013 at 11:53 AM, Mingjie Xing mingjie.x...@gmail.com wrote:
2013/11/6 Richard Biener richard.guent...@gmail.com:
You miss a testcase.
Also why should the warning be omitted for unused automatic
volatile variables? They cannot be used in any way.
Richard.
Thanks. I've updated the patch with a test case.
c/ChangeLog
PR 57258
Should be:
PR c/57258
Thanks,
bin
* c-decl.c (pop_scope): Don't emit unused variable warnings for
accessed volatile variables.
testsuite/ChangeLog
* gcc.dg/Wunused-var-4.c: New test.
Mingjie
--
Best Regards.
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
On Thu, 7 Nov 2013, Mingjie Xing wrote: 2013/11/6 Richard Biener richard.guent...@gmail.com: You miss a testcase. Also why should the warning be omitted for unused automatic volatile variables? They cannot be used in any way. Richard. Thanks. I've updated the patch with a test case. You don't seem to have answered Richard's question about why the change is desirable in the first place. -- Joseph S. Myers jos...@codesourcery.com
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
2013/11/7 Joseph S. Myers jos...@codesourcery.com: On Thu, 7 Nov 2013, Mingjie Xing wrote: 2013/11/6 Richard Biener richard.guent...@gmail.com: You miss a testcase. Also why should the warning be omitted for unused automatic volatile variables? They cannot be used in any way. Richard. Thanks. I've updated the patch with a test case. You don't seem to have answered Richard's question about why the change is desirable in the first place. Well, it is my understanding that the warning should be emitted for a volatile variable only if it is not accessed. Initialization means accessing, even though it is not used anywhere. Mingjie
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
On Wed, Nov 6, 2013 at 8:40 AM, Mingjie Xing mingjie.x...@gmail.com wrote: Hi, Changes: * c/c-decl.c (pop_scope): Skip volatile variables while emit warnings for unused variables. Tested on i686-pc-linux-gnu. OK? You miss a testcase. Also why should the warning be omitted for unused automatic volatile variables? They cannot be used in any way. Richard. Mingjie
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
On Wed, 6 Nov 2013, Mingjie Xing wrote: * c/c-decl.c (pop_scope): Skip volatile variables while emit warnings for unused variables. c/ has its own ChangeLog, so no c/ in the ChangeLog entries. This patch doesn't include a testsuite addition. -- Joseph S. Myers jos...@codesourcery.com
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
2013/11/6 Richard Biener richard.guent...@gmail.com:
You miss a testcase.
Also why should the warning be omitted for unused automatic
volatile variables? They cannot be used in any way.
Richard.
Thanks. I've updated the patch with a test case.
c/ChangeLog
PR 57258
* c-decl.c (pop_scope): Don't emit unused variable warnings for
accessed volatile variables.
testsuite/ChangeLog
* gcc.dg/Wunused-var-4.c: New test.
Mingjie
Index: c/c-decl.c
===
--- c/c-decl.c (revision 204285)
+++ c/c-decl.c (working copy)
@@ -1187,11 +1187,17 @@ pop_scope (void)
scope != external_scope)
{
if (!TREE_USED (p))
- warning (OPT_Wunused_variable, unused variable %q+D, p);
+ {
+ if (!TREE_THIS_VOLATILE (p) || !DECL_INITIAL (p))
+ warning (OPT_Wunused_variable, unused variable %q+D, p);
+ }
else if (DECL_CONTEXT (p) == current_function_decl)
- warning_at (DECL_SOURCE_LOCATION (p),
- OPT_Wunused_but_set_variable,
- variable %qD set but not used, p);
+ {
+ if (!TREE_THIS_VOLATILE (p))
+ warning_at (DECL_SOURCE_LOCATION (p),
+OPT_Wunused_but_set_variable,
+variable %qD set but not used, p);
+ }
}
if (b-inner_comp)
/* Test -Wunused. Bug 57258. */
/* { dg-do compile } */
/* { dg-options -Wunused } */
void
f (void)
{
volatile int a = 0;
volatile int b; /* { dg-warning unused variable } */
volatile int c;
int d; /* { dg-warning set but not used } */
c = 0;
d = 0;
}
Re: [C] Fix PR57258: unused variable warning is emitted for volatile variables
On Thu, Nov 7, 2013 at 11:53 AM, Mingjie Xing mingjie.x...@gmail.com wrote: 2013/11/6 Richard Biener richard.guent...@gmail.com: You miss a testcase. Also why should the warning be omitted for unused automatic volatile variables? They cannot be used in any way. Richard. Thanks. I've updated the patch with a test case. c/ChangeLog PR 57258 Should be: PR c/57258 Thanks, bin * c-decl.c (pop_scope): Don't emit unused variable warnings for accessed volatile variables. testsuite/ChangeLog * gcc.dg/Wunused-var-4.c: New test. Mingjie -- Best Regards.
[C] Fix PR57258: unused variable warning is emitted for volatile variables
Hi,
Changes:
* c/c-decl.c (pop_scope): Skip volatile variables while emit
warnings for unused variables.
Tested on i686-pc-linux-gnu.
OK?
Mingjie
Index: gcc/c/c-decl.c
===
--- gcc/c/c-decl.c (revision 204285)
+++ gcc/c/c-decl.c (working copy)
@@ -1183,6 +1183,8 @@ pop_scope (void)
!DECL_IN_SYSTEM_HEADER (p)
DECL_NAME (p)
!DECL_ARTIFICIAL (p)
+ /* A volatile variable might be used in some non-obvious way. */
+ !TREE_THIS_VOLATILE (p)
scope != file_scope
scope != external_scope)
{
