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Chandler CarruthandChristopher Di Bella
8a59f2a76b
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>