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Unify "needs thunk" logic. (#6277)

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Remove duplication between determining whether a parameter needs custom
thunk mapping and whether a function needs a thunk. Now a function needs
a thunk if any parameter or the return type does.

This fixes some inconsistencies; previously:
- We would not require a thunk when passing an `unsigned int`, but if we
  had a thunk we'd pass `unsigned int` indirectly.
- We would always require a thunk for an enum parameter, even though
  we'd actually pass it directly if its underlying type is a 32- or
  64-bit integer.
- We would require a thunk for a nullable pointer, even though
  we arrange for all pointer types to have the same ABI in Carbon and
  C++, including nullable pointers / Optional(T*).

This also causes us to use a thunk for rvalue reference return types,
which we used to miscompile.

Depends on #6276.
This commit is contained in:
Richard Smith
2025-10-27 22:49:29 +00:00
committed by GitHub
parent f022e91e45
commit a1a35c207e
7 changed files with 181 additions and 229 deletions
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toolchain/check/testdata/interop/cpp/function/decayed_param.carbon
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+4 -4
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@@ -117,8 +117,8 @@ fn F() {
// CHECK:STDOUT: %OptionalStorage.impl_witness.01b: <witness> = impl_witness imports.%OptionalStorage.impl_witness_table.377, @ptr.as.OptionalStorage.impl(%i32) [concrete]
// CHECK:STDOUT: %OptionalStorage.facet: %OptionalStorage.type = facet_value %ptr.235, (%OptionalStorage.impl_witness.01b) [concrete]
// CHECK:STDOUT: %Optional.8fd: type = class_type @Optional, @Optional(%OptionalStorage.facet) [concrete]
// CHECK:STDOUT: %TakesArray__carbon_thunk.type: type = fn_type @TakesArray__carbon_thunk [concrete]
// CHECK:STDOUT: %TakesArray__carbon_thunk: %TakesArray__carbon_thunk.type = struct_value () [concrete]
// CHECK:STDOUT: %TakesArray.type: type = fn_type @TakesArray [concrete]
// CHECK:STDOUT: %TakesArray: %TakesArray.type = struct_value () [concrete]
// CHECK:STDOUT: %ImplicitAs.type.6cc: type = facet_type <@ImplicitAs, @ImplicitAs(%Optional.8fd)> [concrete]
// CHECK:STDOUT: %ImplicitAs.Convert.type.770: type = fn_type @ImplicitAs.Convert, @ImplicitAs(%Optional.8fd) [concrete]
// CHECK:STDOUT: %T.binding.as_type.as.ImplicitAs.impl.Convert.type.6f7: type = fn_type @T.binding.as_type.as.ImplicitAs.impl.Convert.2, @T.binding.as_type.as.ImplicitAs.impl.3a5(%T.76d) [symbolic]
@@ -153,7 +153,7 @@ fn F() {
// CHECK:STDOUT: %Core.import_ref.6db = import_ref Core//prelude/types/optional, loc{{\d+_\d+}}, unloaded
// CHECK:STDOUT: %Core.import_ref.5a7 = import_ref Core//prelude/types/optional, loc{{\d+_\d+}}, unloaded
// CHECK:STDOUT: %OptionalStorage.impl_witness_table.377 = impl_witness_table (%Core.import_ref.8c0, %Core.import_ref.566, %Core.import_ref.637, %Core.import_ref.6db, %Core.import_ref.5a7), @ptr.as.OptionalStorage.impl [concrete]
// CHECK:STDOUT: %TakesArray__carbon_thunk.decl: %TakesArray__carbon_thunk.type = fn_decl @TakesArray__carbon_thunk [concrete = constants.%TakesArray__carbon_thunk] {
// CHECK:STDOUT: %TakesArray.decl: %TakesArray.type = fn_decl @TakesArray [concrete = constants.%TakesArray] {
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: } {
// CHECK:STDOUT: <elided>
@@ -207,7 +207,7 @@ fn F() {
// CHECK:STDOUT: %.loc11_18.2: init %Optional.8fd = converted %addr.loc11_18.1, %T.binding.as_type.as.ImplicitAs.impl.Convert.call
// CHECK:STDOUT: %.loc11_18.3: ref %Optional.8fd = temporary %.loc11_18.1, %.loc11_18.2
// CHECK:STDOUT: %.loc11_18.4: %Optional.8fd = bind_value %.loc11_18.3
// CHECK:STDOUT: %TakesArray__carbon_thunk.call: init %empty_tuple.type = call imports.%TakesArray__carbon_thunk.decl(%.loc11_18.4)
// CHECK:STDOUT: %TakesArray.call: init %empty_tuple.type = call imports.%TakesArray.decl(%.loc11_18.4)
// CHECK:STDOUT: %DestroyT.binding.as_type.as.Destroy.impl.Op.bound.loc11: <bound method> = bound_method %.loc11_18.3, constants.%DestroyT.binding.as_type.as.Destroy.impl.Op.af3
// CHECK:STDOUT: <elided>
// CHECK:STDOUT: %bound_method.loc11_18.3: <bound method> = bound_method %.loc11_18.3, %DestroyT.binding.as_type.as.Destroy.impl.Op.specific_fn.1