rnk added inline comments.
================ Comment at: clang/include/clang/Basic/Attr.td:1799 + let Spellings = [Clang<"nomerge">]; + let Subjects = SubjectList<[Function]>; + let Documentation = [NoMergeDocs]; ---------------- aaron.ballman wrote: > 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.) I guess what I really wanted was an expression attribute, so you can put it on the calls to `bar`. :) But given that that doesn't exist, I think it would be OK to do either one of the following: - Apply nomerge attribute to all call sites in the whole Stmt - Apply nomerge only to the first CallExpr found inside the Stmt I think the simplest implementation is to, in CodeGenFunction, set a flag (NoMerge) on CodeGenFunction when emitting such an attributed statement with this attribute. Then set it back on exit. Something like that. CHANGES SINCE LAST ACTION https://reviews.llvm.org/D79121/new/ https://reviews.llvm.org/D79121 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits