[Patch] Disable -Wtaulological-compare for substituted template types

Richard Trieu rtrieu at google.com
Thu Oct 31 16:12:23 PDT 2013

On Thu, Oct 31, 2013 at 2:44 PM, Richard Trieu <rtrieu at google.com> wrote:

> On Thu, Oct 31, 2013 at 10:35 AM, David Blaikie <dblaikie at gmail.com>wrote:
>> Looks pretty reasonable - but are these two separate code changes, or do
>> they interrelate in some way? If they're separate changes that can have
>> separate test cases, it'd be nice to commit them each in their on commit
>> just for clarity.
> Yes, I can separate them into two pieces when I submit them.
>> Have you considered/plan to look at non-type template parameters?
>> template<int Num>
>> bool greater(unsigned Val) {
>>   return Val >= Num;
>> }
>> ... greater<0>(42); ...
>> I'm not sure if this tickles the same kind of problem or not - but might
>> be worth checking.
>> I haven't seen this case yet, but I would say it is good to include this
> test case too.   I think changing the check to an instantiation dependency
> check would allow it to catch this case as well.

I spoke too soon.  The information about non-template types doesn't persist
up the AST tree so it isn't as easily retrievable as the substituted
template types.  For a simple case like your example, it would be simple to
check for a substituted expression in the operand.  For a more complicated
constant expression, an AST visitor would be needed, or the function that
computes the constant value would need to pass this information back.  I'll
stick with template types for now.

>> On Wed, Oct 30, 2013 at 8:17 PM, Richard Trieu <rtrieu at google.com> wrote:
>>> This patch turns off the tautological compare warnings when one of the
>>> operands is a template parameter type.  There's not an easy way to correct
>>> the code or silence this warning so this way seemed to be the best
>>> solution.  Anyone have any thoughts on altering the behavior of this
>>> warning?
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