Sorry, I probably shouldn't have used HTML for that message. Converted to plain
text.
-------- Original message --------
15.12.2017, 18:01, "xgsa" <x...@yandex.ru>:
Hi,
I am working on issue that in C++ program for some complex cases with templates
showing dynamic type based on RTTI in lldb doesn't work properly. Consider the
following example:
enum class TagType : bool
{
Tag1
};
struct I
{
virtual ~I() = default;
};
template <TagType Tag>
struct Impl : public I
{
private:
int v = 123;
};
int main(int argc, const char * argv[]) {
Impl<TagType::Tag1> impl;
I& i = impl;
return 0;
}
For this example clang generates type name "Impl<TagType::Tag1>" in DWARF and
"__ZTS4ImplIL7TagType0EE" when mangling symbols (which lldb demangles to
Impl<(TagType)0>). Thus when in
ItaniumABILanguageRuntime::GetTypeInfoFromVTableAddress() lldb tries to resolve
the type, it is unable to find it. More cases and the detailed description why
lldb fails here can be found in this clang review, which tries to fix this in
clang [1].
However, during the discussion around this review [2], it was pointed out that
DWARF names are expected to be close to sources, which clang does perfectly,
whereas mangling algorithm is strictly defined. Thus matching them on equality
could sometimes fail. The suggested idea in [2] was to implement more
semantically aware matching. There is enough information in the DWARF to
semantically match "Impl<(TagType)0>)" with "Impl<TagType::Tag1>", as enum
TagType is in the DWARF, and the enumerator Tag1 is present with its value 0. I
have some concerns about the performance of such solution, but I'd like to know
your opinion about this idea in general. In case it is approved, I'm going to
work on implementing it.
So what do you think about type names inequality and the suggested solution?
[1] - https://reviews.llvm.org/D39622
[2] -
http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20171211/212859.html
Thank you,
Anton.
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