[all-commits] [llvm/llvm-project] e96cc9: [llvm][DebugInfo] Unwrap template parameters that ...

[Michael Buch via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: e96cc996875f58306aa7f28f2e47b51cadc180b7
      https://github.com/llvm/llvm-project/commit/e96cc996875f58306aa7f28f2e47b51cadc180b7
  Author: Michael Buch <michaelbuch12 at gmail.com>
  Date:   2025-11-20 (Thu, 20 Nov 2025)

  Changed paths:
    M cross-project-tests/debuginfo-tests/clang_llvm_roundtrip/simplified_template_names.test
    M llvm/include/llvm/DebugInfo/DWARF/DWARFTypePrinter.h

  Log Message:
  -----------
  [llvm][DebugInfo] Unwrap template parameters that are typedefs when reconstructing DIE names (#168734)

Depends on: 
* https://github.com/llvm/llvm-project/pull/168725

When compiling with `-glldb`, we repoint the `DW_AT_type` of a DIE to be
a typedef that refers to the `preferred_name`. I.e.,:
```
template <typename T> structure t7;
using t7i = t7<int>;
template <typename T> struct __attribute__((__preferred_name__(t7i))) t7 {};
template <typename... Ts> void f1()

int main() { f1<t7i>(); }
```
would produce following (minified) DWARF:
```
DW_TAG_subprogram
  DW_AT_name      ("_STN|f1|<t7<int> >")
  DW_TAG_template_type_parameter
    DW_AT_type  (0x0000299c "t7i")
...
DW_TAG_typedef
  DW_AT_type      (0x000029a7 "t7<int>")
  DW_AT_name      ("t7i")
```

Note how the `DW_AT_type` of the template parameter is a typedef itself
(instead of the canonical type). The `DWARFTypePrinter` would take the
`DW_AT_name` of this typedef when reconstructing the name of `f1`, so we
would end up with a verifier failure:
```
error: Simplified template DW_AT_name could not be reconstituted:
         original: f1<t7<int> >
    reconstituted: f1<t7i>
```

Fixing this allows us to un-XFAIL the `simplified-template-names.cpp`
test in `cross-project-tests`. Unfortunately this is only tested on
Darwin, where LLDB tuning is the default. AFAIK, there is no other case
where the template parameter type wouldn't be canonical.



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