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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>
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/template/class_template.carbon
Vendored
+9 -9
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@@ -36,7 +36,7 @@ var a: Cpp.A = Cpp.X(Cpp.A, Cpp.B).f({} as Cpp.B);
// CHECK:STDOUT: %A: type = class_type @A [concrete]
// CHECK:STDOUT: %empty_struct_type: type = struct_type {} [concrete]
// CHECK:STDOUT: %empty_tuple.type: type = tuple_type () [concrete]
// CHECK:STDOUT: %pattern_type.b54: type = pattern_type %A [concrete]
// CHECK:STDOUT: %pattern_type.aa6: type = pattern_type %A [concrete]
// CHECK:STDOUT: %X.type: type = cpp_type_template_type X [concrete]
// CHECK:STDOUT: %X.template: %X.type = struct_value () [concrete]
// CHECK:STDOUT: %B: type = class_type @B [concrete]
@@ -44,11 +44,11 @@ var a: Cpp.A = Cpp.X(Cpp.A, Cpp.B).f({} as Cpp.B);
// CHECK:STDOUT: %X.f.cpp_overload_set.value: %X.f.cpp_overload_set.type = cpp_overload_set_value @X.f.cpp_overload_set [concrete]
// CHECK:STDOUT: %empty_struct: %empty_struct_type = struct_value () [concrete]
// CHECK:STDOUT: %B.val: %B = struct_value () [concrete]
// CHECK:STDOUT: %ptr.13d: type = ptr_type %B [concrete]
// CHECK:STDOUT: %ptr.bce: type = ptr_type %A [concrete]
// CHECK:STDOUT: %ptr.fab: type = ptr_type %B [concrete]
// CHECK:STDOUT: %ptr.9f7: type = ptr_type %A [concrete]
// CHECK:STDOUT: %f__carbon_thunk.type: type = fn_type @f__carbon_thunk [concrete]
// CHECK:STDOUT: %f__carbon_thunk: %f__carbon_thunk.type = struct_value () [concrete]
// CHECK:STDOUT: %.dae: ref %B = temporary invalid, %B.val [concrete]
// CHECK:STDOUT: %.f11: ref %B = temporary invalid, %B.val [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
@@ -71,8 +71,8 @@ var a: Cpp.A = Cpp.X(Cpp.A, Cpp.B).f({} as Cpp.B);
// CHECK:STDOUT:
// CHECK:STDOUT: file {
// CHECK:STDOUT: name_binding_decl {
// CHECK:STDOUT: %a.patt: %pattern_type.b54 = ref_binding_pattern a [concrete]
// CHECK:STDOUT: %a.var_patt: %pattern_type.b54 = var_pattern %a.patt [concrete]
// CHECK:STDOUT: %a.patt: %pattern_type.aa6 = ref_binding_pattern a [concrete]
// CHECK:STDOUT: %a.var_patt: %pattern_type.aa6 = var_pattern %a.patt [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT: %a.var: ref %A = var %a.var_patt [concrete]
// CHECK:STDOUT: %.loc7: type = splice_block %A.ref [concrete = constants.%A] {
@@ -98,11 +98,11 @@ var a: Cpp.A = Cpp.X(Cpp.A, Cpp.B).f({} as Cpp.B);
// CHECK:STDOUT: %.loc7_39.3: init %B to %.loc7_39.2 = class_init () [concrete = constants.%B.val]
// CHECK:STDOUT: %.loc7_41.1: init %B = converted %.loc7_39.1, %.loc7_39.3 [concrete = constants.%B.val]
// CHECK:STDOUT: %.loc7_1: ref %A = splice_block file.%a.var [concrete = file.%a.var] {}
// CHECK:STDOUT: %.loc7_41.2: ref %B = temporary %.loc7_39.2, %.loc7_41.1 [concrete = constants.%.dae]
// CHECK:STDOUT: %.loc7_41.2: ref %B = temporary %.loc7_39.2, %.loc7_41.1 [concrete = constants.%.f11]
// CHECK:STDOUT: %.loc7_41.3: %B = acquire_value %.loc7_41.2 [concrete = constants.%B.val]
// CHECK:STDOUT: %.loc7_41.4: ref %B = value_as_ref %.loc7_41.3
// CHECK:STDOUT: %addr.loc7_49.1: %ptr.13d = addr_of %.loc7_41.4
// CHECK:STDOUT: %addr.loc7_49.2: %ptr.bce = addr_of %.loc7_1
// CHECK:STDOUT: %addr.loc7_49.1: %ptr.fab = addr_of %.loc7_41.4
// CHECK:STDOUT: %addr.loc7_49.2: %ptr.9f7 = addr_of %.loc7_1
// CHECK:STDOUT: %f__carbon_thunk.call: init %empty_tuple.type = call imports.%f__carbon_thunk.decl(%addr.loc7_49.1, %addr.loc7_49.2)
// CHECK:STDOUT: %.loc7_49: init %A to %.loc7_1 = mark_in_place_init %f__carbon_thunk.call
// CHECK:STDOUT: assign file.%a.var, %.loc7_49