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
}
----------------
aaron.ballman wrote:
> 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.
> But I'm curious what others think as well.
(Specifically, I'm wondering if others agree that the only warning that should
be issued there is a C89 compatibility warning under `-Wvla-extensions` when in
C89 mode and via a new `CPre99Compat` diagnostic group when enabled in C99 and
later modes.)
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D132952/new/
https://reviews.llvm.org/D132952
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