aaron.ballman added inline comments.
================
Comment at: clang/test/Sema/warn-vla.c:8-12
+void test2(int n, int v[n]) { // c99 no-warning
+#if __STDC_VERSION__ < 199901L
+// expected-warning@-2{{variable length arrays are a C99 feature}}
+#endif
}
----------------
inclyc wrote:
> aaron.ballman wrote:
> > The diagnostic there is rather unfortunate because we're not using a
> > variable-length array in this case.
> Emm, I'm not clear about whether we should consider this a VLA, and generates
> `-Wvla-extensions`. Is `v[n]` literally a variable-length array? (in source
> code) So it seems to me that we should still report c89 incompatibility
> warnings?
>
C89's grammar only allowed for an integer constant expression to (optionally)
appear as the array extent in an array declarator, so there is a compatibility
warning needed for that. But I don't think we should issue a warning about this
being a VLA in C99 or later. The array *is* a VLA in terms of the form written
in the source, but C adjusts the parameter to be a pointer parameter, so as far
as the function's type is concerned, it's not a VLA (it's just a
self-documenting interface).
Because self-documenting code is nice and because people are worried about
accidental use of VLAs that cause stack allocations (which this does not), I
think we don't want to scare people off from this construct. But I'm curious
what others think as well.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D132952/new/
https://reviews.llvm.org/D132952
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