llvm dev - Aug 2015 - Canonical representation for empty lists in debug info metadata

While checking for serialization/deserialization without using pointee
types, I've come across a few test cases that crash at head, without my
debugging assertions for accessing pointee types.

One of them is test/Transforms/StripSymbols/2010-06-30-StripDebug.ll

Its retainedTypes metadata points to a metadata array of a single null
element.

This crashes the dyn_cast (because it's not a dyn_cast_or_null)
Verifier.cpp:3785

Do you have a preferred/canonical representation intended in this case - an
extant, but zero-length list, or no list at all? I tend to prefer no list
at all, just because it simplifies reading of the debug info. Rather than
seeing a "retainedTypes" property, following it to the metadata, only
to
find it's zero-length?
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> On 2015-Aug-21, at 13:39, David Blaikie <dblaikie at gmail.com>
wrote:
> 
> While checking for serialization/deserialization without using pointee
types, I've come across a few test cases that crash at head, without my
debugging assertions for accessing pointee types.
> 
> One of them is test/Transforms/StripSymbols/2010-06-30-StripDebug.ll
> 
> Its retainedTypes metadata points to a metadata array of a single null
element.
> 
> This crashes the dyn_cast (because it's not a dyn_cast_or_null)
Verifier.cpp:3785
The Verifier should crash in any case, it should just fail.
> Do you have a preferred/canonical representation intended in this case - an
extant, but zero-length list, or no list at all? I tend to prefer no list at
all, just because it simplifies reading of the debug info. Rather than seeing a
"retainedTypes" property, following it to the metadata, only to find
it's zero-length?
I agree: no list at all is better.

On Fri, Aug 21, 2015 at 4:54 PM, Duncan P. N. Exon Smith <
dexonsmith at apple.com> wrote:
>
> > On 2015-Aug-21, at 13:39, David Blaikie <dblaikie at gmail.com>
wrote:
> >
> > While checking for serialization/deserialization without using pointee
> types, I've come across a few test cases that crash at head, without my
> debugging assertions for accessing pointee types.
> >
> > One of them is test/Transforms/StripSymbols/2010-06-30-StripDebug.ll
> >
> > Its retainedTypes metadata points to a metadata array of a single null
> element.
> >
> > This crashes the dyn_cast (because it's not a dyn_cast_or_null)
> Verifier.cpp:3785
>
> The Verifier should crash in any case, it should just fail.
>
r245795
> Do you have a preferred/canonical representation intended in this case -
> an extant, but zero-length list, or no list at all? I tend to prefer no
> list at all, just because it simplifies reading of the debug info. Rather
> than seeing a "retainedTypes" property, following it to the
metadata, only
> to find it's zero-length?
>
> I agree: no list at all is better.

r245796

Thanks!
- Dave
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