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

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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

---------

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

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This commit is contained in:

Chandler Carruth

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

committed by GitHub

co-authored by Christopher Di Bella

parent 3ef128ac91

commit 8a59f2a76b

64 changed files with 4762 additions and 4330 deletions

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toolchain/check/testdata/interop/cpp/function/import/pointer.carbon

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