[Bug c++/39089] New: -Wconversion is buggy with bitwise operators

[oleg dot smolsky at riverbed dot com]

g++ 4.3.3 emits warnings for every statement in the following function when the
code is built this way:

/gcc43/bin/g++ -c -Wall -Wconversion test.cpp

void func(unsigned char a, unsigned char b, unsigned char *out)
{
*out = a | b;
*out = out[0] & 0x20;
out[0] &= 0x20;
}

I'd expect bitwise operators to see/preserve argument widths...


-- 
   Summary: -Wconversion is buggy with bitwise operators
   Product: gcc
   Version: 4.3.3
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
    ReportedBy: oleg dot smolsky at riverbed dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39089

[Bug c++/39089] -Wconversion is buggy with bitwise operators

[oleg dot smolsky at riverbed dot com]

--- Comment #1 from oleg dot smolsky at riverbed dot com  2009-02-03 17:58 
---
Created an attachment (id=17238)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17238&action=view)
The test case


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39089

[Bug c++/39089] -Wconversion is buggy with bitwise operators

[oleg dot smolsky at riverbed dot com]

--- Comment #6 from oleg dot smolsky at riverbed dot com  2009-02-03 22:23 
---
Created an attachment (id=17239)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17239&action=view)
The fix from gcc4.4

This is the naive fix merged from the trunk. Fixes two out of three warnings in
C++ mode.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39089

[Bug c++/39089] -Wconversion is buggy with bitwise operators

[oleg dot smolsky at riverbed dot com]

--- Comment #5 from oleg dot smolsky at riverbed dot com  2009-02-03 21:13 
---
I've just built gcc 4.4 and it emits no warnings for the test case above. 

Is there any chance the fix could be back-ported into 4.3?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39089

[Bug c++/38522] g++ -Wconversion warnings

[oleg dot smolsky at riverbed dot com]

--- Comment #3 from oleg dot smolsky at riverbed dot com  2009-03-03 19:40 
---
I've just built gcc from the official SVN and it looks like this bug is not
fully fixed. The following code generates a warning when compiled with
-Wconversion:

#include 

#define M10xC0u
#define M20x20u

unsigned char test(unsigned char a1, unsigned char a2)
{
unsigned char local = (a1 & M1) | (a2 & M2);  // warn
return local;
}

Could someone re-open the bug please?


-- 

oleg dot smolsky at riverbed dot com changed:

   What|Removed |Added

 CC||gcc at gaul dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38522

[Bug c++/38522] g++ -Wconversion warnings

[oleg dot smolsky at riverbed dot com]

--- Comment #5 from oleg dot smolsky at riverbed dot com  2009-03-03 22:24 
---
BTW, my comment was about the C++ frontend. IE:
.../gcc44/bin/g++ -c -Wall -W -Wconversion test.cpp


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38522