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Reduce stack usage of some type switch cases

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gingerBill
2023-02-17 16:51:57 +00:00
parent c08809e29d
commit 7d4e9497eb
1 changed files with 66 additions and 6 deletions
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72
src/llvm_backend_stmt.cpp
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@@ -1397,6 +1397,52 @@ gb_internal void lb_build_type_switch_stmt(lbProcedure *p, AstTypeSwitchStmt *ss
switch_instr = LLVMBuildSwitch(p->builder, tag.value, else_block->block, cast(unsigned)num_cases);
}
bool all_by_reference = false;
for (Ast *clause : body->stmts) {
ast_node(cc, CaseClause, clause);
if (cc->list.count != 1) {
continue;
}
Entity *case_entity = implicit_entity_of_node(clause);
all_by_reference |= (case_entity->flags & EntityFlag_Value) == 0;
break;
}
// NOTE(bill, 2023-02-17): In the case of a pass by value, the value does need to be copied
// to prevent errors such as these:
//
// switch v in some_union {
// case i32:
// fmt.println(v) // 'i32'
// some_union = f32(123)
// fmt.println(v) // if `v` is an implicit reference, then the data is now completely corrupted
// case f32:
// fmt.println(v)
// }
//
lbAddr backing_data = {};
if (!all_by_reference) {
bool variants_found = false;
i64 max_size = 0;
i64 max_align = 1;
for (Ast *clause : body->stmts) {
ast_node(cc, CaseClause, clause);
if (cc->list.count != 1) {
continue;
}
Entity *case_entity = implicit_entity_of_node(clause);
max_size = gb_max(max_size, type_size_of(case_entity->type));
max_align = gb_max(max_align, type_align_of(case_entity->type));
variants_found = true;
}
if (variants_found) {
Type *t = alloc_type_array(t_u8, max_size);
backing_data = lb_add_local(p, t, nullptr, false, true);
GB_ASSERT(lb_try_update_alignment(backing_data.addr, cast(unsigned)max_align));
}
}
lbValue backing_ptr = backing_data.addr;
for (Ast *clause : body->stmts) {
ast_node(cc, CaseClause, clause);
lb_open_scope(p, cc->scope);
@@ -1427,8 +1473,6 @@ gb_internal void lb_build_type_switch_stmt(lbProcedure *p, AstTypeSwitchStmt *ss
Entity *case_entity = implicit_entity_of_node(clause);
lbValue value = parent_value;
lb_start_block(p, body);
bool by_reference = (case_entity->flags & EntityFlag_Value) == 0;
@@ -1444,13 +1488,29 @@ gb_internal void lb_build_type_switch_stmt(lbProcedure *p, AstTypeSwitchStmt *ss
Type *ct = case_entity->type;
Type *ct_ptr = alloc_type_pointer(ct);
value = lb_emit_conv(p, data, ct_ptr);
if (!by_reference) {
value = lb_emit_load(p, value);
lbValue ptr = {};
if (backing_data.addr.value) { // by value
GB_ASSERT(!by_reference);
// make a copy of the case value
lb_mem_copy_non_overlapping(p,
backing_ptr, // dst
data, // src
lb_const_int(p->module, t_int, type_size_of(case_entity->type)));
ptr = lb_emit_conv(p, backing_ptr, ct_ptr);
} else { // by reference
GB_ASSERT(by_reference);
ptr = lb_emit_conv(p, data, ct_ptr);
}
GB_ASSERT(are_types_identical(case_entity->type, type_deref(ptr.type)));
lb_add_entity(p->module, case_entity, ptr);
lb_add_debug_local_variable(p, ptr.value, case_entity->type, case_entity->token);
} else {
// TODO(bill): is the correct expected behaviour?
lb_store_type_case_implicit(p, clause, parent_value);
}
lb_store_type_case_implicit(p, clause, value);
lb_type_case_body(p, ss->label, clause, body, done);
}