dexonsmith 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}}
----------------
jfb wrote:
> 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.
> It would be easy to diagnose non-trivially-copyable types differently in this
> circumstance.
Good point.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D80055/new/
https://reviews.llvm.org/D80055
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