arphaman added inline comments.
================
Comment at: lib/Lex/FilterToIncludes.cpp:628
+ First = Id.Last;
+ auto Kind = llvm::StringSwitch<TokenKind>(Id.Name)
+ .Case("include", pp_include)
----------------
arphaman wrote:
> arphaman wrote:
> > ddunbar wrote:
> > > What is our feeling w.r.t. _Pragma, which can in theory influence the
> > > preprocessor. I'm not sure this model can sanely support it?
> > We need to look into that. In the worst case we can always avoid minimizing
> > the file if it has a _Pragma anywhere in it.
> We also have to handle cases like this one:
>
> foo.h:
> ```
> #define PP _Pragma
> ```
>
> bar.h:
> ```
> PP ("foo")
> ```
>
> Unfortunately this can't be handled by just disabling minimization for
> `foo.h` as PP will be stripped out from `bar.h`. Furthermore, this pattern is
> quite reasonable, so we should expect it in the code we receive. Right now I
> can't think of a reasonable solution for this problem.
>
> There's also a more "evil" case:
>
> ```
> #define P(A, B) A##B
>
> P(_Pra,gma)("foo")
> ```
>
> It would be reasonable to introduce a warning for the use of `_Pragma` token
> that was created using PP token concatenation and just hope that our users
> won't use this pattern.
One possible solution to the first issue is to simply fallback to the regular
-Eonly invocation if we detect an include of a file that has a macro with a
`_Pragma` in it. Then we could emit a remark to the user saying that their
build could be faster if they rewrite their code so that this pattern no longer
occurs.
Repository:
rC Clang
https://reviews.llvm.org/D53354
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