Re: Adding -Wshadow=local to gcc build rules

[Bernd Edlinger <bernd.edlinger@hotmail.de>]

On 9/19/19 12:19 PM, Richard Biener wrote:
> On Wed, Sep 18, 2019 at 3:09 PM Bernd Edlinger
> <bernd.edlinger@hotmail.de> wrote:
>>
>> Hi,
>>
>> I'm currently trying to add -Wshadow=local to the gcc build rules.
>> I started with -Wshadow, but gave up that idea immediately.
>>
>> As you could expect the current code base has plenty of shadowed
>> local variables.  Most are trivial to resolve, some are less trivial.
>> I am not finished yet, but it is clear that it will be a rather big
>> patch.
>>
>> I would like to ask you if you agree that would be a desirable step,
>> in improving code quality in the gcc tree.
> 
> I wonder if -Wshadow=compatible-local is easier to achieve?
> 

I tried that and it does not make a big difference, while
it misses for instance:

* gcc/c-family/c-ada-spec.c (dump_ada_macros)
unsigned char *s, shadowed by const unsigned char *s. :-/

On the other hand, -Wshadow=global is a lot more difficult,
because we have lots of globals, for instance:

context.h:
/* The global singleton context aka "g".
   (the name is chosen to be easy to type in a debugger).  */
extern gcc::context *g;

But unfortunately Wshadow=local does not find class members
shadowed by local variable, which happens for instance in
wide-int

With -Wshadow, I had to change this in wide-int.h:

Index: gcc/wide-int.h
===================================================================
--- gcc/wide-int.h      (revision 275545)
+++ gcc/wide-int.h      (working copy)
@@ -648,9 +648,9 @@ namespace wi
     storage_ref () {}
     storage_ref (const HOST_WIDE_INT *, unsigned int, unsigned int);

-    const HOST_WIDE_INT *val;
-    unsigned int len;
-    unsigned int precision;
+    const HOST_WIDE_INT *m_val;
+    unsigned int m_len;
+    unsigned int m_precision;


So this change was not necessary for -Wshadow=local, although
I would think that, shadowing class members is not much different from
shadowing a local scope.

Not sure if shadowing class members should be part of -Wshadow=local
instead of -Wshadow=global.


Bernd.