aaron.ballman added a comment.

In D63082#1560667 <https://reviews.llvm.org/D63082#1560667>, @xbolva00 wrote:

> I wanted to follow GCC’s behaviour -Wall but then dicussion moved to 
> “tautological compare group” - I was fine with that too..
>  I can again revert it to -Wall...
>  If this should be off by default even on -Wall, then all work was useless..


Personally, my feeling is that this new diagnostic group belongs under the 
tautological compare group. That group is currently off by default, but I'm 
wondering if we want it to be on by default (in a subsequent patch), or whether 
we're okay having parts of it on by default and parts off by default. I'm 
hoping @rsmith will voice an opinion here.

In D63082#1560684 <https://reviews.llvm.org/D63082#1560684>, @xbolva00 wrote:

> “Perhaps appending something about the resulting value always being 
> true|false would help most of these diagnostics be more obvious”
>
> I dont know, this could only diagnose constant multiplications (maybe this is 
> already handled by some “always true” check). Anyway, I have no motivation to 
> diagnose constant muls, sorry. My goal is to make this warning atleast as 
> good as GCC’s implementation.
>
> Okay, we could make it better and append “; did you mean “index * 3 != 0”?


I don't think that actually improves anything. I do not think we want a "did 
you mean" in this case because I'm not confident anyone can guess what a user 
was trying for in this situation. However, telling the user the result of the 
computation does give them very useful information -- it tells them the result 
will always be tautologically true or false (which is what the other 
tautological warnings do, as well). As it stands, the current diagnostic 
wording doesn't help the user understand what's wrong with their code. I'd like 
to correct that deficiency before we commit this.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D63082/new/

https://reviews.llvm.org/D63082



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