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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
Download Patch File Download Diff File Expand all files Collapse all files
toolchain/check/thunk.cpp
+26 -10
View File
@@ -125,10 +125,27 @@ static auto ClonePattern(Context& context, SemIR::SpecificId specific_id,
new_pattern_id = CloneBindingPattern(context, pattern_id, *binding,
get_type(pattern_id));
} else if (auto return_slot = pattern.TryAs<SemIR::ReturnSlotPattern>()) {
auto new_subpattern_id = RebuildPatternInst<SemIR::OutParamPattern>(
context, return_slot->subpattern_id,
{.type_id = get_type(return_slot->subpattern_id),
.pretty_name_id = SemIR::NameId::ReturnSlot});
auto new_subpattern_id = SemIR::InstId::None;
auto subpattern = context.insts().Get(return_slot->subpattern_id);
CARBON_KIND_SWITCH(subpattern) {
case SemIR::OutParamPattern::Kind:
case SemIR::RefReturnPattern::Kind:
case SemIR::ValueReturnPattern::Kind:
// These are leaf insts, so we can reuse their contents after updating
// the type.
subpattern.SetType(get_type(return_slot->subpattern_id));
new_subpattern_id =
RebuildPatternInst(context, return_slot->subpattern_id, subpattern);
break;
case SemIR::ErrorInst::Kind:
subpattern.SetType(SemIR::ErrorInst::TypeId);
new_subpattern_id = SemIR::ErrorInst::InstId;
break;
default:
CARBON_FATAL("Unexpected kind for return slot subpattern {0}",
subpattern);
}
new_pattern_id = RebuildPatternInst<SemIR::ReturnSlotPattern>(
context, pattern_id,
{.type_id = get_type(pattern_id),
@@ -200,8 +217,8 @@ static auto CloneFunctionDecl(Context& context, SemIR::LocId loc_id,
context, signature_specific_id, signature.implicit_param_patterns_id);
auto param_patterns_id = ClonePatternBlock(context, signature_specific_id,
signature.param_patterns_id);
auto return_patterns_id = ClonePatternBlock(context, signature_specific_id,
signature.return_patterns_id);
auto return_pattern_id =
ClonePattern(context, signature_specific_id, signature.return_pattern_id);
auto return_type_inst_id = CloneTypeInstId(context, signature_specific_id,
signature.return_type_inst_id);
auto return_form_inst_id = CloneInstId(context, signature_specific_id,
@@ -211,9 +228,8 @@ static auto CloneFunctionDecl(Context& context, SemIR::LocId loc_id,
// Perform callee-side pattern matching to rebuild the parameter list.
context.inst_block_stack().Push();
auto match_results =
CalleePatternMatch(context, implicit_param_patterns_id, param_patterns_id,
return_patterns_id);
auto match_results = CalleePatternMatch(context, implicit_param_patterns_id,
param_patterns_id, return_pattern_id);
auto decl_block_id = context.inst_block_stack().Pop();
// Create the `FunctionDecl` instruction.
@@ -244,7 +260,7 @@ static auto CloneFunctionDecl(Context& context, SemIR::LocId loc_id,
.call_param_ranges = match_results.param_ranges,
.return_type_inst_id = return_type_inst_id,
.return_form_inst_id = return_form_inst_id,
.return_patterns_id = return_patterns_id,
.return_pattern_id = return_pattern_id,
.virtual_modifier = callee.virtual_modifier,
.virtual_index = callee.virtual_index,
.evaluation_mode = signature.evaluation_mode,