Chandler CarruthandChristopher Di Bella 8a59f2a76b Fix mangling collision for C++ class template specializations (#7269) ...

Carbon-side thunks (for example the `Copy`/`Destroy` witness thunks
generated for imported C++ types) are mangled by Carbon, and their names
incorporate a fingerprint of the involved types. The instruction
fingerprinter identifies a class only by its name and parent scope,
which is sufficient for Carbon classes but not for imported C++ classes:
different specializations of one class template (and other cases such as
types in anonymous namespaces) share a Carbon name and parent scope. As
a result, the thunks for two distinct specializations could mangle to
the same name, producing a single LLVM function with two definitions and
failing `verifyModule` during lowering.

When fingerprinting a class imported from C++, also include the Clang
mangled name of its type.

Test: toolchain/lower/testdata/interop/cpp/thunks.carbon gains a split
with two specializations of one class template, each requiring a thunk;
their thunks now get distinct mangled names instead of colliding.

Assisted-by: Claude Code

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Co-authored-by: Christopher Di Bella <cjdb.ns@gmail.com>

2026-05-30 08:13:00 +00:00

..

dynamic.carbon

Fix mangling collision for C++ class template specializations (#7269)

2026-05-30 08:13:00 +00:00