rnk added a comment.
The purpose of the attribute is really limited to preserving source location
information on instructions, and this isn't really a supported usage. The BPF
backend and verifier needs to learn to tolerate valid LLVM transforms if it
wants to be a real LLVM backend. Of course, you can do what you like.
Considered in the context of the original use case, I think it's reasonable to
allow the attribute on function pointers for the same reasons we allow it on
function declarations. It makes it easy to work the attribute onto the direct
call sites of the function without modifying tons of source code. However, I'd
like to see clearer documentation on the limitations.
================
Comment at: clang/include/clang/Basic/AttrDocs.td:551-555
calls to the specified function from merging. It has no effect on indirect
calls.
+
+``nomerge`` attribute can be specified for pointers to functions, all
+calls done through such pointer would be protected from merging.
----------------
This statement of the attribute having "no effect on indirect calls" is
slightly confusing now that we talk about function pointers immediately
afterward. Can you please rework this a bit, and clarify that when applied to
function pointers, the attribute only takes effect when the call target is
directly the variable which carries the attribute? For example, this has no
effect:
```
void (*fp)() __attribute__((nomerge));
void callit() {
auto tmp = fp;
tmp();
(*fp)(); // I think TargetDecl will be null in the code, tell me if I'm wrong
}
```
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D152986/new/
https://reviews.llvm.org/D152986
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