aaron.ballman added inline comments.
================
Comment at: clang/lib/Sema/SemaStmt.cpp:561-568
+ for (const auto *A : Attrs) {
+ if (A->getKind() == attr::MustTail) {
+ if (!checkMustTailAttr(SubStmt, *A)) {
+ return SubStmt;
+ }
+ setFunctionHasMustTail();
+ }
----------------
aaron.ballman wrote:
> haberman wrote:
> > aaron.ballman wrote:
> > > haberman wrote:
> > > > haberman wrote:
> > > > > aaron.ballman wrote:
> > > > > > haberman wrote:
> > > > > > > aaron.ballman wrote:
> > > > > > > > This functionality belongs in SemaStmtAttr.cpp, I think.
> > > > > > > That is where I had originally put it, but that didn't work for
> > > > > > > templates. The semantic checks can only be performed at
> > > > > > > instantiation time. `ActOnAttributedStmt` seems to be the right
> > > > > > > hook point where I can evaluate the semantic checks for both
> > > > > > > template and non-template functions (with template functions
> > > > > > > getting checked at instantiation time).
> > > > > > I disagree that `ActOnAttributedStmt()` is the correct place for
> > > > > > this checking -- template checking should occur when the template
> > > > > > is instantiated, same as happens for declaration attributes. I'd
> > > > > > like to see this functionality moved to SemaStmtAttr.cpp. Keeping
> > > > > > the attribute logic together and following the same patterns is
> > > > > > what allows us to tablegenerate more of the attribute logic.
> > > > > > Statement attributes are just starting to get more such automation.
> > > > > I tried commenting out this code and adding the following code into
> > > > > `handleMustTailAttr()` in `SemaStmtAttr.cpp`:
> > > > >
> > > > > ```
> > > > > if (!S.checkMustTailAttr(St, MTA))
> > > > > return nullptr;
> > > > > ```
> > > > >
> > > > > This caused my test cases related to templates to fail. It also
> > > > > seemed to break test cases related to `JumpDiagnostics`. My
> > > > > interpretation of this is that `handleMustTailAttr()` is called
> > > > > during parsing only, and cannot catch errors at template
> > > > > instantiation time or that require a more complete AST.
> > > > >
> > > > > What am I missing? Where in SemaStmtAttr.cpp are you suggesting that
> > > > > I put this check?
> > > > Scratch the part about `JumpDiagnostics`, that was me failing to call
> > > > `S.setFunctionHasMustTail()`. I added that and now the
> > > > `JumpDiagnostics` tests pass.
> > > >
> > > > But the template test cases still fail, and I can't find any hook point
> > > > in `SemaStmtAttr.cpp` that will let me evaluate these checks at
> > > > template instantiation time.
> > > I think there's a bit of an architectural mixup, but I'm curious if
> > > @rsmith agrees before anyone starts doing work to make changes.
> > >
> > > When transforming declarations, `RebuildWhatever()` calls the
> > > `ActOnWhatever()` function which calls `ProcessDeclAttributeList()` so
> > > that attributes are processed. `RebuildAttributedStmt()` similarly calls
> > > `ActOnAttributedStmt()`. However, `ActOnAttributedStmt()` doesn't call
> > > `ProcessStmtAttributes()` -- the logic is reversed so that
> > > `ProcessStmtAttributes()` is what calls `ActOnAttributedStmt()`.
> > >
> > > I think the correct answer is to switch the logic so that
> > > `ActOnAttributedStmt()` calls `ProcessStmtAttributes()`, then the
> > > template logic should automatically work.
> > > I think the correct answer is to switch the logic so that
> > > ActOnAttributedStmt() calls ProcessStmtAttributes()
> >
> > I think this would require `ProcessStmtAttributes()` to be split into two
> > separate functions. Currently that function is doing two separate things:
> >
> > 1. Translation of `ParsedAttr` into various subclasses of `Attr`.
> > 2. Validation that the attribute is semantically valid.
> >
> > The function signature for `ActOnAttributedStmt()` uses `Attr` (not
> > `ParsedAttr`), so (1) must happen during the parse, before
> > `ActOnAttributedStmt()` is called. But (2) must be deferred until template
> > instantiation time for some cases, like `musttail`.
> I don't think the signature for `ActOnAttributedStmt()` is correct to use
> `Attr` instead of `ParsedAttr`. I think it should be `StmtResult
> ActOnAttributedStmt(const ParsedAttributesViewWithRange &AttrList, Stmt
> *SubStmt);` -- this likely requires a fair bit of surgery to make work
> though, which is why I'd like to hear from @rsmith if he agrees with the
> approach. In the meantime, I'll play around with this idea locally in more
> depth.
I think my suggestion wasn't quite right, but close. I've got a patch in
progress that changes this the way I was thinking it should be changed, but it
won't call `ActOnAttributedStmt()` when doing template instantiation. Instead,
it will continue to instantiate attributes explicitly by calling
`TransformAttr()` and any additional instantiation time checks will require you
to add a `TreeTransfor::TransformWhateverAttr()` to do the actual instantiation
work (which is similar to how the declaration attributes work in
`Sema::InstantiateAttrs()`).
I hope to put up a patch for review for these changes today or tomorrow. It'd
be interesting to know whether they make your life easier or harder though, if
you don't mind taking a look and seeing how well (or poorly) they integrate
with your changes here.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D99517/new/
https://reviews.llvm.org/D99517
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
