Re: [PATCH] Introduce in_inclusive_range, fix -Wtautological-compare warnings

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2017-10-30 11:57, John Baldwin wrote:
> On 10/30/17 2:32 PM, Simon Marchi wrote:
>> When compiling with clang or gcc 8, we see warnings like this:
>> 
>> /home/emaisin/src/binutils-gdb/gdb/arm-tdep.c:10013:13: error: 
>> comparison of 0 <= unsigned expression is always true 
>> [-Werror,-Wtautological-compare]
>>       if (0 <= insn_op1 && 3 >= insn_op1)
>>           ~ ^  ~~~~~~~~
>> /home/emaisin/src/binutils-gdb/gdb/arm-tdep.c:11722:20: error: 
>> comparison of unsigned expression >= 0 is always true 
>> [-Werror,-Wtautological-compare]
>>       else if (opB >= 0 && opB <= 2)
>>                ~~~ ^  ~
>> 
>> This is because an unsigned integer (opB in this case) will always be 
>> >=
>> 0.  It is still useful to keep both bounds of the range in the
>> expression, even if one is at the edge of the data type range.  This
>> patch introduces a utility function in_inclusive_range that gets rid 
>> of
>> the warning while conveying that we are checking for a range.
>> 
>> Tested by rebuilding.
>> 
>> gdb/ChangeLog:
>> 
>> 	* common/common-utils.h (in_inclusive_range): New function.
>> 	* arm-tdep.c (arm_record_extension_space): Use
>> 	in_inclusive_range.
>> 	* cris-tdep.c (cris_spec_reg_applicable): Use
>> 	in_inclusive_range.
>> ---
>>  gdb/arm-tdep.c            | 4 ++--
>>  gdb/common/common-utils.h | 9 +++++++++
>>  gdb/cris-tdep.c           | 4 ++--
>>  3 files changed, 13 insertions(+), 4 deletions(-)
>> 
>> diff --git a/gdb/cris-tdep.c b/gdb/cris-tdep.c
>> index d623eb6..209e29f 100644
>> --- a/gdb/cris-tdep.c
>> +++ b/gdb/cris-tdep.c
>> @@ -1434,7 +1434,7 @@ cris_spec_reg_applicable (struct gdbarch 
>> *gdbarch,
>>        /* Indeterminate/obsolete.  */
>>        return 0;
>>      case cris_ver_v0_3:
>> -      return (version >= 0 && version <= 3);
>> +      return in_inclusive_range (version, 0U, 3U);
>>      case cris_ver_v3p:
>>        return (version >= 3);
>>      case cris_ver_v8:
>> @@ -1442,7 +1442,7 @@ cris_spec_reg_applicable (struct gdbarch 
>> *gdbarch,
>>      case cris_ver_v8p:
>>        return (version >= 8);
>>      case cris_ver_v0_10:
>> -      return (version >= 0 && version <= 10);
>> +      return in_inclusive_range (version, 0U, 10U);
>>      case cris_ver_v3_10:
>>        return (version >= 3 && version <= 10);
>>      case cris_ver_v8_10:
> 
> I wonder if in this file it wouldn't be best to use the new function 
> throughout
> the various cases so that the style is more consistent?  LGTM 
> regardless.


Good point, I'll make that change.  I'll see if it's possible in 
arm-tdep.c too or if it's a too daunting task.

Simon