haberman 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:
> > 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`.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D99517/new/
https://reviews.llvm.org/D99517
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