aaron.ballman added a reviewer: aaron.ballman.
aaron.ballman added a comment.
This should also have Sema tests ensuring that it only applies to the correct
subjects, accepts no arguments, etc.
================
Comment at: clang/include/clang/Basic/Attr.td:1799
+ let Spellings = [Clang<"nomerge">];
+ let Subjects = SubjectList<[Function]>;
+ let Documentation = [NoMergeDocs];
----------------
zequanwu wrote:
> rnk wrote:
> > Clang supports many function-like things that are not functions, for
> > example, Objective C method declarations are not considered FunctionDecls
> > in the AST. Blocks are another function-like thing. I see below there is a
> > `FunctionLike` subject type. Lets use that here.
> >
> > I would like to make it possible to apply this attribute directly to call
> > expressions as well, but I don't see a good example of how to do that in
> > the existing attribute. I'd like to be able to do this, for example:
> >
> > ```
> > void __attribute__((noreturn)) bar();
> > void foo(bool cond) {
> > if (cond)
> > [[clang::nomerge]] bar();
> > else
> > [[clang::nomerge]] bar();
> > }
> > ```
> >
> > This gives the user fine-grained control. It allows them to call some
> > existing API, like perhaps RaiseException, of which they do not control the
> > declaration, and mark the calls as unmergeable.
> It seems like there is no exiting example of call site attributes.
> https://github.com/llvm/llvm-project/blob/master/clang/lib/CodeGen/CGCall.cpp#L4767.
> And the function `EmitCall` may not know existence of call site attributes.
> I would like to make it possible to apply this attribute directly to call
> expressions as well, but I don't see a good example of how to do that in the
> existing attribute.
You would have to use a statement attribute rather than a declaration attribute
for this, and we have a few of those but none that work on call expressions
specifically.
One question I have about that idea is whether attributes give you fine enough
levels of control (I don't know enough about `nomerge` to answer this myself).
e.g., `foo(bar(), bar()); // Do you want to nomerge the bar() calls, the foo()
call, or all three?` (You can only add the attribute to the statement
expression, not to individual expressions.)
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D79121/new/
https://reviews.llvm.org/D79121
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