Find template types of std::map

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#1

Hi,

for a current project I'm required to get the types of the template arguments key and value for std::map<K,V>. I've noticed that the STL implementation used by Clang defines the type of the map as

     %"class.std::map" = type { %"class.std::_Rb_tree" }

which then is further defined and finally ends as

     %"struct.std::_Rb_tree_node_base" = type {
         i32,
         %"struct.std::_Rb_tree_node_base"*,
         %"struct.std::_Rb_tree_node_base"*
     }

However, indifferent what K and V are and how many different maps are instantiated, it always ends at this definition. But, I also noticed, that

     %"struct.std::pair" = type { i32, double }

is defined, which then provides the information I need.

Now the problem arises to connect %"class.std::map" to %"struct.std::pair" correctly. To solve this I looked at the IR and noticed, that the std::pair's are always defined in the reverse order of the definitions of std::map. So I think about using some index to find the correct std::pair.

From this idea two issues arise:

1. I feel that this approach is not that stable as it should be, for instance, I think that the ordering of instantiation I'm making use of may change.

2. I'm unable to retrieve all defined named types from the module. I know there is LLVMContextImpl but this class is a forward declaration and therefore I'm not able to access LLVMContextImpl::NamedStructTypes.

Thanks for any suggestions.

Best regards,
Sebastian

#2

Sebastian Dreßler wrote

Now the problem arises to connect %"class.std::map" to
%"struct.std::pair" correctly. To solve this I looked at the IR and
noticed, that the std::pair's are always defined in the reverse order of
the definitions of std::map. So I think about using some index to find
the correct std::pair.

I just thought again about this approach: this actually is the most
inelegant way I could come up with. The following might be better: I will
try to use the Clang library directly to convert the C++ type string, e. g.
std::string, int, ..., to a LLVM type.

However, any other suggestions are welcome. Maybe someone else already had
this sort of problem?

Best regards,
Sebastian

#3

Trying to dig template arguments out of LLVM IR types is a bad idea.
Try a C++ demangler on a related function name, or the debug
information.

-Eli

#4

Eli Friedman-2 wrote

Hi,

for a current project I'm required to get the types of the template
arguments key and value for std::map&lt;K,V&gt;. I've noticed that the
STL
implementation used by Clang defines the type of the map as

    %"class.std::map" = type { %"class.std::_Rb_tree" }

Trying to dig template arguments out of LLVM IR types is a bad idea.
Try a C++ demangler on a related function name, or the debug
information.

Thanks for the hint, I'll try that. However, when I successfully determined
the name of the template parameters, I'll have to find the LLVM IR std::pair
definition nevertheless. So, is there any function providing all names of
named structs from a module? When I dump the module, I'm able to see all
those structs, but I didn't find a function for e.g. iterating them.

Best,
Sebastian

#5

Sebastian Dreßler wrote

So, is there any function providing all names of named structs from a
module? When I dump the module, I'm able to see all those structs, but I
didn't find a function for e.g. iterating them.

Just realized, that there is llvm::TypeFinder, which I've never seen before,
but does exactly that what I want.

Thanks for the help,
Sebastian