[PATCH] D83211: Factor out call to EXTRACTOR in generateCC1CommandLine

[Jan Svoboda via Phabricator via cfe-commits]

jansvoboda11 added inline comments.


================
Comment at: clang/lib/Frontend/CompilerInvocation.cpp:4062
+  if ((FLAGS)&options::CC1Option) {                                            \
+    const auto &Extracted = EXTRACTOR(this->KEYPATH);                          \
+    if (ALWAYS_EMIT || Extracted != (DEFAULT_VALUE))                           \
----------------
dexonsmith wrote:
> IIUC, then we can do this more simply as:
> ```
> bool Extracted = EXTRACTOR(this->KEYPATH);
> ```
> That might clarify why we don't have lifetime extension concerns here.
Yes, we could simplify this for booleans.


================
Comment at: clang/lib/Frontend/CompilerInvocation.cpp:3938
+  if ((FLAGS)&options::CC1Option) {                                            \
+    const auto &Extracted = EXTRACTOR(this->KEYPATH);                          \
+    if (ALWAYS_EMIT || Extracted != DEFAULT_VALUE)                             \
----------------
dexonsmith wrote:
> dexonsmith wrote:
> > jansvoboda11 wrote:
> > > Bigcheese wrote:
> > > > Will this ever have an issue with lifetime? I can see various values for `EXTRACTOR` causing issues here. https://abseil.io/tips/107
> > > > 
> > > > 
> > > > It would be good to at least document somewhere the restrictions on `EXTRACTOR`.
> > > Mentioned the reference lifetime extension in a comment near extractor definitions.
> > It might be safer to refactor as:
> > ```
> > // Capture the extracted value as a lambda argument to avoid potential
> > // lifetime extension issues.
> > [&](const auto &Extracted) {
> >   if (ALWAYS_EMIT || Extracted != (DEFAULT_VALUE))
> >     DENORMALIZER(Args, SPELLING, SA, TABLE_INDEX, Extracted);
> > }(EXTRACTOR(this->KEYPATH));
> > ```
> > 
> Might be even better to avoid the generic lambda:
> ```
> // Capture the extracted value as a lambda argument to avoid potential
> // lifetime extension issues.
> using ExtractedType =
>     std::remove_const_t<std::remove_reference_t<
>         decltype(EXTRACTOR(this->KEYPATH))>>
> [&](const ExtractedType &Extracted) {
>   if (ALWAYS_EMIT || Extracted != (DEFAULT_VALUE))
>     DENORMALIZER(Args, SPELLING, SA, TABLE_INDEX, Extracted);
> }(EXTRACTOR(this->KEYPATH));
> ```
> (since generic vs. non-generic could affect compile-time of CompilerInvocation.cpp given how many instances there will be).
Thanks for the suggestions @dexonsmith. I'm having trouble writing a test case where the lambda workaround produces a different result than `const auto &` variable.
@Bigcheese, could you show a concrete example of an extractor that causes issues so I can test it out?


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  https://reviews.llvm.org/D83211/new/

https://reviews.llvm.org/D83211