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

[John Baldwin <jhb at FreeBSD dot org>]

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.

-- 
John Baldwin