[PATCH] D79121: Add nomerge function attribute to clang

[Reid Kleckner via Phabricator via cfe-commits]

rnk added inline comments.


================
Comment at: clang/include/clang/Basic/Attr.td:1799
+  let Spellings = [Clang<"nomerge">];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [NoMergeDocs];
----------------
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.


================
Comment at: clang/test/CodeGen/attr-nomerge.c:15
+// CHECK: attributes #1 = { nomerge {{.*}} }
+// CHECK: attributes #2 = { nomerge }
----------------
These numbers can be unstable. Generally the best practice is to do something like this:
  // CHECK: declare void @bar() #[[NOMERGEATTR:\d+]]
  // CHECK: attributes #[[NOMERGEATTR]] = { nomerge {{.*}} }

This makes the test more readable and more resilient in the case that the attribute set numbers change.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D79121/new/

https://reviews.llvm.org/D79121