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Add return value support to C++ thunks. (#5976)

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Based on #5948. A couple of tricky parts:

* When generating the C++ side of the thunk, we are given a pointer to
the location to emplace the return value. The only mechanism C++
provides to perform this emplacement is using placement `operator new`,
which requires a library function in the `<new>` header. We handle this
by declaring that library function ourselves, and rely on Clang not
actually needing a definition for it (which the standard library owns).

* On the Carbon side of the thunk, we want to form an initializing
expression as the result of the call. We don't have a way of expressing
in SemIR that an initializing expression performs its initialization by
storing through a pointer, so this PR adds a new initializing
instruction, `InPlaceInit`, to model an initialization that's performed
opaquely in-place.
This commit is contained in:
Richard Smith
2025-08-26 02:23:38 +00:00
committed by GitHub
parent 1331ade57f
commit d37f1ae6b5
17 changed files with 1039 additions and 96 deletions
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toolchain/check/testdata/interop/cpp/function/struct.carbon
Vendored
+32 -6
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@@ -445,13 +445,30 @@ auto foo() -> S;
library "[[@TEST_NAME]]";
// TODO: We should only produce one error here.
// CHECK:STDERR: fail_import_decl_value_return_type.carbon:[[@LINE+12]]:10: in file included here [InCppInclude]
// CHECK:STDERR: ./decl_value_return_type.h:4:6: error: calling 'foo' with incomplete return type 'S' [CppInteropParseError]
// CHECK:STDERR: 4 | auto foo() -> S;
// CHECK:STDERR: | ^~~
// CHECK:STDERR: fail_import_decl_value_return_type.carbon:[[@LINE+8]]:10: in file included here [InCppInclude]
// CHECK:STDERR: ./decl_value_return_type.h:4:6: note: 'foo' declared here [CppInteropParseNote]
// CHECK:STDERR: 4 | auto foo() -> S;
// CHECK:STDERR: | ^
// CHECK:STDERR: fail_import_decl_value_return_type.carbon:[[@LINE+4]]:10: in file included here [InCppInclude]
// CHECK:STDERR: ./decl_value_return_type.h:2:8: note: forward declaration of 'S' [CppInteropParseNote]
// CHECK:STDERR: 2 | struct S;
// CHECK:STDERR: | ^
import Cpp library "decl_value_return_type.h";
fn F() {
// CHECK:STDERR: fail_import_decl_value_return_type.carbon:[[@LINE+13]]:3: note: in `Cpp` name lookup for `foo` [InCppNameLookup]
// CHECK:STDERR: Cpp.foo();
// CHECK:STDERR: ^~~~~~~
// CHECK:STDERR:
// CHECK:STDERR: fail_import_decl_value_return_type.carbon:[[@LINE+9]]:3: error: function returns incomplete type `Cpp.S` [IncompleteTypeInFunctionReturnType]
// CHECK:STDERR: Cpp.foo();
// CHECK:STDERR: ^~~~~~~~~
// CHECK:STDERR: fail_import_decl_value_return_type.carbon:[[@LINE-6]]:10: in file included here [InCppInclude]
// CHECK:STDERR: fail_import_decl_value_return_type.carbon:[[@LINE-10]]:10: in file included here [InCppInclude]
// CHECK:STDERR: ./decl_value_return_type.h:2:8: note: class was forward declared here [ClassForwardDeclaredHere]
// CHECK:STDERR: struct S;
// CHECK:STDERR: ^
@@ -1155,9 +1172,11 @@ fn F() {
// CHECK:STDOUT: %S: type = class_type @S [concrete]
// CHECK:STDOUT: %foo.type: type = fn_type @foo [concrete]
// CHECK:STDOUT: %foo: %foo.type = struct_value () [concrete]
// CHECK:STDOUT: %ptr.5c7: type = ptr_type %S [concrete]
// CHECK:STDOUT: %foo__carbon_thunk.type: type = fn_type @foo__carbon_thunk [concrete]
// CHECK:STDOUT: %foo__carbon_thunk: %foo__carbon_thunk.type = struct_value () [concrete]
// CHECK:STDOUT: %T.as.Destroy.impl.Op.type.642: type = fn_type @T.as.Destroy.impl.Op, @T.as.Destroy.impl(%S) [concrete]
// CHECK:STDOUT: %T.as.Destroy.impl.Op.ab5: %T.as.Destroy.impl.Op.type.642 = struct_value () [concrete]
// CHECK:STDOUT: %ptr.5c7: type = ptr_type %S [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
@@ -1170,6 +1189,11 @@ fn F() {
// CHECK:STDOUT: } {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: %foo__carbon_thunk.decl: %foo__carbon_thunk.type = fn_decl @foo__carbon_thunk [concrete = constants.%foo__carbon_thunk] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: } {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: fn @F() {
@@ -1177,13 +1201,15 @@ fn F() {
// CHECK:STDOUT: %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %foo.ref: %foo.type = name_ref foo, imports.%foo.decl [concrete = constants.%foo]
// CHECK:STDOUT: %.loc8_11.1: ref %S = temporary_storage
// CHECK:STDOUT: %foo.call: init %S = call %foo.ref() to %.loc8_11.1
// CHECK:STDOUT: %.loc8_11.2: ref %S = temporary %.loc8_11.1, %foo.call
// CHECK:STDOUT: %addr.loc8_11.1: %ptr.5c7 = addr_of %.loc8_11.1
// CHECK:STDOUT: %foo__carbon_thunk.call: init %empty_tuple.type = call imports.%foo__carbon_thunk.decl(%addr.loc8_11.1)
// CHECK:STDOUT: %.loc8_11.2: init %S = in_place_init %foo__carbon_thunk.call, %.loc8_11.1
// CHECK:STDOUT: %.loc8_11.3: ref %S = temporary %.loc8_11.1, %.loc8_11.2
// CHECK:STDOUT: %T.as.Destroy.impl.Op.bound: <bound method> = bound_method %.loc8_11.1, constants.%T.as.Destroy.impl.Op.ab5
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %bound_method: <bound method> = bound_method %.loc8_11.1, %T.as.Destroy.impl.Op.specific_fn
// CHECK:STDOUT: %addr: %ptr.5c7 = addr_of %.loc8_11.1
// CHECK:STDOUT: %T.as.Destroy.impl.Op.call: init %empty_tuple.type = call %bound_method(%addr)
// CHECK:STDOUT: %addr.loc8_11.2: %ptr.5c7 = addr_of %.loc8_11.1
// CHECK:STDOUT: %T.as.Destroy.impl.Op.call: init %empty_tuple.type = call %bound_method(%addr.loc8_11.2)
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }
// CHECK:STDOUT: