jfb marked an inline comment as done.
jfb added inline comments.
================
Comment at: clang/test/CodeGen/union-tail-padding.c:28-36
+union Front {
+ int i;
+ long long ll;
+};
+
+union Front front1;
+union Front front2 = {}; // expected-warning {{Initializing union
'Front' field 'i' only initializes the first 4 of 8 bytes, leaving the
remaining 4 bytes undefined}}
----------------
dexonsmith wrote:
> jfb wrote:
> > dexonsmith wrote:
> > > Are these warnings actionable? What should users do when they see this
> > > warning?
> > Good point!
> >
> > I was thinking about this, and was wondering if I should add a fixit which
> > suggests using the first wider member of the union. The problem is to offer
> > the same object representation... that's tricky on its own (there isn't
> > always an exact match), and then we have to deal with type punning (in C++,
> > not in C).
> >
> > So I'd love ideas, because I'm not sure what to do. That being said, I
> > wrote this partly because D68115 was surprising to folks, and partly
> > because developers would like to opt-in to this diagnostic to find places
> > where initialization isn't doing what they think.
> >
> > Maybe instead we should suggest to leave uninitialized, and use an
> > assignment, or `memset`?
> > Maybe instead we should suggest to leave uninitialized, and use an
> > assignment, or `memset`?
>
> It's not clear to me that those are better. For example, `memset` doesn't
> seem right for non-PODs in C++. I'm not sure what to suggest though.
I'd argue that non-PODs in unions don't seem right either ;-)
It would be easy to diagnose non-trivially-copyable types differently in this
circumstance.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D80055/new/
https://reviews.llvm.org/D80055
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