[clang] [clang][Sema] Don't report pointer subtraction on a VLA as zero size (PR #217465)

[Aditya Medhane via cfe-commits]

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@@ -416,6 +416,11 @@ features cannot lower the translation-unit ABI level;
 - `-Wc++98-compat` now diagnoses explicit conversion functions in C++20 and
   later, matching the behavior in C++11 through C++17. (#GH161689)
 
+- `-Wpointer-arith` no longer reports subtraction of pointers to a variably
+  modified type, such as `int[n]`, as a subtraction of pointers to a type of
+  zero size. The size of such a type is not known statically and is modelled as
+  zero, which is not the same as the type being empty. (#GH28328)
+
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flash1729 wrote:

yeah, added a helper that walks the array dimensions and folds each variable bound as an ICE, so it only warns when the size really comes out to zero. struct Empty `vla[n]` and` int vla[n][0]` warn again now, both covered in empty1.c

https://github.com/llvm/llvm-project/pull/217465