[PATCH] D148381: [WIP][Clang] Add element_count attribute

[Nick Desaulniers via Phabricator via cfe-commits]

nickdesaulniers added a comment.

Cool!

How about some codegen tests?

This looks a lot like the EuroLLVM keynote: https://llvm.swoogo.com/2023eurollvm/agenda (Thursday `-fbounds-safety`). What's your plan for reconciling this with the authors of that? Have you reached out to them with this proposal?



================
Comment at: clang/include/clang/Basic/Attr.td:4167
+  let Documentation = [ElementCountDocs];
+  let LangOpts = [COnly];
+}
----------------
Does C++ not support VLAs?


================
Comment at: clang/include/clang/Basic/AttrDocs.td:6957
+  let Content = [{
+Clang supports the ``__element_count__`` attribute for flexible array members.
+  }];
----------------
Maybe worth noting that this the number of elements and not the number of bytes?


================
Comment at: clang/lib/CodeGen/CGExpr.cpp:951-952
+    if (auto *ME = dyn_cast<MemberExpr>(CE->getSubExpr())) {
+      if (ME->isFlexibleArrayMemberLike(CGF.getContext(),
+                                        StrictFlexArraysLevel, true)) {
+        if (auto *MD = dyn_cast<FieldDecl>(ME->getMemberDecl())) {
----------------
eventually, we may want to support non-FAMs:

```
struct foo {
  size_t count;
  char arr [PATH_MAX] __attribute((element_count("count")));
};

char *foo (size_t offset) {
  struct foo my_foo = {
    .count = sizeof("hello"),
    .arr = "hello",
  };
  return &my_foo.arr[offset];
}
```


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D148381/new/

https://reviews.llvm.org/D148381