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Restructure return declaration handling (#7076)

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- A function with a return declaration always has exactly one
`ReturnSlotPattern`, representing the whole return declaration (whereas
previously that was omitted for value and reference returns).
- The `ReturnSlotPattern` always has a subpattern with the same form.
`OutParamPattern` already plays that role for initializing forms, and
`TuplePattern` will play that role for tuple forms. This change
introduces `ValueReturnPattern` and `RefReturnPattern` to represent
value and reference return forms.
- As before, the `ReturnSlotPattern` has a corresponding `ReturnSlot`
that represents the output that is initialized by a `return` statement.
Its structure parallels the structure of the `ReturnSlotPattern`, so we
need `ValueReturn` and `RefReturn` insts that correspond to
`ValueReturnPattern` and `RefReturnPattern`.

This is a step toward supporting generic return forms, where the
`ReturnSlotPattern`'s subpattern may be an action: this change ensures
that evaluating the action for a specific form produces the same SemIR
as if the form were concrete to begin with. More speculatively, this
should simplify the implementation of `return` statements with compound
return forms.

---------

Co-authored-by: Chandler Carruth <chandlerc@gmail.com>
This commit is contained in:
Geoff Romer
2026-04-22 23:38:21 +00:00
committed by GitHub
co-authored by Chandler Carruth
parent 3abc334c42
commit 49c7288619
40 changed files with 598 additions and 390 deletions
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toolchain/check/testdata/function/declaration/ref.carbon
Vendored
+7 -2
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@@ -29,11 +29,11 @@ fn G() {
// CHECK:STDOUT: %Int.generic: %Int.type = struct_value () [concrete]
// CHECK:STDOUT: %i32: type = class_type @Int, @Int(%int_32) [concrete]
// CHECK:STDOUT: %.1da: Core.Form = ref_form %i32 [concrete]
// CHECK:STDOUT: %pattern_type.7ce: type = pattern_type %i32 [concrete]
// CHECK:STDOUT: %F.type: type = fn_type @F [concrete]
// CHECK:STDOUT: %F: %F.type = struct_value () [concrete]
// CHECK:STDOUT: %G.type: type = fn_type @G [concrete]
// CHECK:STDOUT: %G: %G.type = struct_value () [concrete]
// CHECK:STDOUT: %pattern_type.7ce: type = pattern_type %i32 [concrete]
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: imports {
@@ -52,10 +52,15 @@ fn G() {
// CHECK:STDOUT: .G = %G.decl
// CHECK:STDOUT: }
// CHECK:STDOUT: %Core.import = import Core
// CHECK:STDOUT: %F.decl: %F.type = fn_decl @F [concrete = constants.%F] {} {
// CHECK:STDOUT: %F.decl: %F.type = fn_decl @F [concrete = constants.%F] {
// CHECK:STDOUT: %.loc4_8.1: %pattern_type.7ce = ref_return_pattern [concrete]
// CHECK:STDOUT: %return.patt: %pattern_type.7ce = return_slot_pattern %.loc4_8.1, %i32 [concrete]
// CHECK:STDOUT: } {
// CHECK:STDOUT: %i32: type = type_literal constants.%i32 [concrete = constants.%i32]
// CHECK:STDOUT: %.loc4_11.1: type = ref_tag %i32
// CHECK:STDOUT: %.loc4_11.2: Core.Form = ref_form %i32 [concrete = constants.%.1da]
// CHECK:STDOUT: %.loc4_8.2: ref %i32 = ref_return
// CHECK:STDOUT: %return: ref %i32 = return_slot %.loc4_8.2
// CHECK:STDOUT: }
// CHECK:STDOUT: %G.decl: %G.type = fn_decl @G [concrete = constants.%G] {} {}
// CHECK:STDOUT: }