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Import non-const rvalue references as var parameters. (#7125)

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When importing a C++ function with an rvalue reference parameter, we
previously produced a Carbon value parameter. This would lead to the
toolchain believing it could pass the address of a non-expiring object
to the function, which would lead to a use-after-move.

Instead, we now map non-const rvalue reference parameters to Carbon
`var` parameters. This forces the object passed into C++ to be unique
and owned by the call. While that's not an exact match for C++ rvalue
reference parameters, given that it provides "always move" not
"conditionally move", it's the closest match we have at the moment.
This commit is contained in:
Richard Smith
2026-04-29 00:28:00 +00:00
committed by GitHub
parent ab0aff91b8
commit 0124aae041
23 changed files with 412 additions and 411 deletions
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toolchain/check/testdata/interop/cpp/function/import/reference.carbon
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+5 -8
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@@ -532,7 +532,6 @@ fn F() {
// CHECK:STDOUT: %ptr.5c7: type = ptr_type %S [concrete]
// CHECK:STDOUT: %TakesRValue__carbon_thunk.type: type = fn_type @TakesRValue__carbon_thunk [concrete]
// CHECK:STDOUT: %TakesRValue__carbon_thunk: %TakesRValue__carbon_thunk.type = struct_value () [concrete]
// CHECK:STDOUT: %.6ef: ref %S = temporary invalid, %S.val [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
@@ -557,13 +556,11 @@ fn F() {
// CHECK:STDOUT: %.loc8_20.1: %empty_struct_type = struct_literal () [concrete = constants.%empty_struct]
// CHECK:STDOUT: %Cpp.ref.loc8_25: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
// CHECK:STDOUT: %S.ref: type = name_ref S, imports.%S.decl [concrete = constants.%S]
// CHECK:STDOUT: %.loc8_20.2: ref %S = temporary_storage
// CHECK:STDOUT: %.loc8_20.3: init %S to %.loc8_20.2 = class_init () [concrete = constants.%S.val]
// CHECK:STDOUT: %.loc8_22.1: init %S = converted %.loc8_20.1, %.loc8_20.3 [concrete = constants.%S.val]
// CHECK:STDOUT: %.loc8_22.2: ref %S = temporary %.loc8_20.2, %.loc8_22.1 [concrete = constants.%.6ef]
// CHECK:STDOUT: %.loc8_22.3: %S = acquire_value %.loc8_22.2 [concrete = constants.%S.val]
// CHECK:STDOUT: %.loc8_22.4: ref %S = value_as_ref %.loc8_22.3
// CHECK:STDOUT: %addr: %ptr.5c7 = addr_of %.loc8_22.4
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %.loc8_20.2: init %S to %_.var = class_init () [concrete = constants.%S.val]
// CHECK:STDOUT: %.loc8_22: init %S = converted %.loc8_20.1, %.loc8_20.2 [concrete = constants.%S.val]
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %addr: %ptr.5c7 = addr_of %_.var
// CHECK:STDOUT: %TakesRValue__carbon_thunk.call: init %empty_tuple.type = call imports.%TakesRValue__carbon_thunk.decl(%addr)
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: }