[cfe-users] How to get code for a function template specialization

[Romulo via cfe-users]

Thanks, this solved my problem!

On Sun, Aug 4, 2019 at 11:07 PM Richard Smith <richard at metafoo.co.uk> wrote:

> On Fri, 2 Aug 2019 at 15:05, Romulo via cfe-users <
> cfe-users at lists.llvm.org> wrote:
>
>> Hello there, thanks for your time reading this :)
>>
>> I am trying to extract the code for a specialized template function, but
>> I have no idea on how to proceed. I know I can use SourceManager to get the
>> original 'pure template' code but I don't know how to access the
>> specialized functions (the SourceLocation for them points to the original
>> function in the AST). My idea is to allow users to write some sugar code
>> like:
>>
>> template <typename T>
>> T myAdd(T x, T y) {
>>   return x + y;
>> }
>>
>> myAdd< double >(5.5, 3.3);
>> or
>> myAdd(1, 2);
>>
>> and after parsing their source files, generate the specialized functions
>> with a different name in a separated utility file, replacing the
>> occurrences of of use (that's the easy part).
>> The utility file would look like:
>>
>> double _impl_double_myAdd(double x, double y) {
>>   return x + y;
>> }
>>
>> int _impl_int_myAdd(int x, int y) {
>>   return x + y;
>> }
>>
>> and the calls:
>>
>> _impl_double_myAdd(5.5, 3.3);
>> and
>> _impl_int_myAdd(1, 2);
>>
>> Can anyone point me in the right direction? I though about just replacing
>> the usage cases of 'T' but that seems really manual and error prone.
>>
>
> You can call clang::Decl::print
> <https://clang.llvm.org/doxygen/classclang_1_1Decl.html#a5bac5131c3f19c2f460c1437eedb051c>
> on the template specialization declaration to see what it looks like after
> substitution. We don't guarantee that the output will be valid C++ code in
> all cases (and in fact, there are some constructs that can be produced by
> template instantiation and cannot be written directly in C++, but they're
> generally very rare), but it usually will be.
>
> If you want a sample of what that looks like, try compiling your code with
> "-Xclang -ast-print -S -o -"
>
> For your original example (with the calls to myAdd moved to a function
> f()), I get this with clang trunk:
>
> template <typename T> T myAdd(T x, T y) {
>     return x + y;
> }
> template<> double myAdd<double>(double x, double y) {
>     return x + y;
> }
> template<> int myAdd<int>(int x, int y) {
>     return x + y;
> }
> void f() {
>     myAdd<double>(5.5, 3.2999999999999998);
>     myAdd(1, 2);
> }
>
> Example case where the output is not valid C++:
>
> template <typename T>
> void destroy(T &t) { t.~T(); }
> void f(int n) { destroy(n); }
>
> ... produces ...
>
> template <typename T> void destroy(T &t) {
>     t.~T();
> }
> template<> void destroy<int>(int &t) {
>     t.~int(); // this won't parse
> }
> void f(int n) {
>     destroy(n);
> }
>
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