From dea1c177cd3592cc24fd15ad446a676da2e4da28 Mon Sep 17 00:00:00 2001
From: Eugen Wissner <belka@caraus.de>
Date: Sat, 25 Jul 2026 23:33:22 +0200
Subject: Support #offset trait at compile time

---
 boot/evaluator.cc | 232 +++++++++++++++++++++++++++++-------------------------
 1 file changed, 126 insertions(+), 106 deletions(-)

(limited to 'boot')

diff --git a/boot/evaluator.cc b/boot/evaluator.cc
index 40a6533..bb50bd3 100644
--- a/boot/evaluator.cc
+++ b/boot/evaluator.cc
@@ -18,12 +18,115 @@ along with GCC; see the file COPYING3.  If not see
 #include "elna/boot/evaluator.h"
 #include "elna/boot/ast.h"
 
-#include <numeric>
 #include <algorithm>
 #include <limits>
+#include <ranges>
 
 namespace elna::boot
 {
+    std::optional<type_properties> get_type_properties(const type& subject, const target_info& target)
+    {
+        auto resolved = resolve_underlying_type(subject);
+
+        if (is_primitive_type(resolved, "Int")
+                || resolved.get<enumeration_type>() != nullptr)
+        {
+            return target.int_properties;
+        }
+        else if (is_primitive_type(resolved, "Word"))
+        {
+            return target.word_properties;
+        }
+        else if (is_primitive_type(resolved, "Char"))
+        {
+            return target.char_properties;
+        }
+        else if (is_primitive_type(resolved, "Float"))
+        {
+            return target.float_properties;
+        }
+        else if (is_primitive_type(resolved, "Bool"))
+        {
+            return target.bool_properties;
+        }
+        else if (resolved.get<slice_type>() != nullptr)
+        {
+            return type_properties{
+                .size = target.pointer_properties.size + target.word_properties.size,
+                .alignment = target.pointer_properties.alignment
+            };
+        }
+        else if (is_any_pointer_type(resolved))
+        {
+            return target.pointer_properties;
+        }
+        else if (auto array = resolved.get<array_type>())
+        {
+            if (auto element = get_type_properties(array->base, target))
+            {
+                return type_properties{
+                    .size = array->size * element->size,
+                    .alignment = element->alignment
+                };
+            }
+        }
+        else if (auto record = resolved.get<record_type>())
+        {
+            auto record_layout = layout_record(record, target);
+            if (record_layout.has_value())
+            {
+                return type_properties{
+                    .size = record_layout.value().size,
+                    .alignment = record_layout.value().alignment
+                };
+            }
+        }
+        return std::nullopt;
+    }
+
+    std::optional<record_properties> layout_record(const std::shared_ptr<record_type>& subject,
+            const target_info& target)
+    {
+        std::size_t current_offset{ 0 };
+        std::size_t size{ 0 };
+        std::size_t alignment{ 1 };
+        ordered_map<std::size_t> result_map;
+        std::vector<const record_type *> chain;
+
+        for (auto current_record = subject; current_record != nullptr;)
+        {
+            chain.push_back(current_record.get());
+            if (current_record->base.empty())
+            {
+                break;
+            }
+            current_record = resolve_underlying_type(current_record->base).get<record_type>();
+        }
+        for (auto const *current_record : std::views::reverse(chain))
+        {
+            for (auto const& field : current_record->fields)
+            {
+                auto props = get_type_properties(field.second, target);
+                if (!props.has_value())
+                {
+                    return std::nullopt;
+                }
+                size = (size + props->alignment - 1) & ~(props->alignment - 1);
+                size += props->size;
+                alignment = std::max(alignment, props->alignment);
+                current_offset = (current_offset + props->alignment - 1) & ~(props->alignment - 1);
+
+                result_map.insert(field.first, current_offset);
+                current_offset += props->size;
+            }
+        }
+        return record_properties{
+            .offset_map = std::move(result_map),
+            .size = (size + alignment - 1) & ~(alignment - 1),
+            .alignment = alignment
+        };
+    }
+
     evaluator::evaluator(symbol_bag& bag, const target_info& target,
             const std::map<std::string, expression*>& evaluated_initializers)
         : bag(bag), target(target), evaluated_initializers(evaluated_initializers)
@@ -434,114 +537,14 @@ namespace elna::boot
 
     std::optional<std::size_t> evaluator::evaluate_traits_size(const type& subject)
     {
-        type const resolved = resolve_underlying_type(subject);
-
-        if (is_primitive_type(resolved, "Int")
-                || resolved.get<enumeration_type>() != nullptr)
-        {
-            return target.int_size;
-        }
-        else if (is_primitive_type(resolved, "Word"))
-        {
-            return target.word_size;
-        }
-        else if (is_primitive_type(resolved, "Char"))
-        {
-            return target.char_size;
-        }
-        else if (is_primitive_type(resolved, "Float"))
-        {
-            return target.float_size;
-        }
-        else if (is_primitive_type(resolved, "Bool"))
-        {
-            return target.bool_size;
-        }
-        else if (resolved.get<slice_type>() != nullptr)
-        {
-            return target.pointer_size + target.word_size;
-        }
-        else if (is_primitive_type(resolved, "Pointer")
-                || resolved.get<pointer_type>() != nullptr)
-        {
-            return target.pointer_size;
-        }
-        else if (auto array = resolved.get<array_type>())
-        {
-            if (auto element_size = evaluate_traits_size(array->base))
-            {
-                return array->size * element_size.value();
-            }
-        }
-        return std::nullopt;
+        auto props = get_type_properties(subject, this->target);
+        return props ? std::optional{ props->size } : std::nullopt;
     }
 
     std::optional<std::size_t> evaluator::evaluate_traits_alignment(const type& subject)
     {
-        type const resolved = resolve_underlying_type(subject);
-
-        if (is_primitive_type(resolved, "Int"))
-        {
-            return target.int_alignment;
-        }
-        if (is_primitive_type(resolved, "Word"))
-        {
-            return target.word_alignment;
-        }
-        if (is_primitive_type(resolved, "Char"))
-        {
-            return target.char_alignment;
-        }
-        if (is_primitive_type(resolved, "Float"))
-        {
-            return target.float_alignment;
-        }
-        if (is_primitive_type(resolved, "Pointer"))
-        {
-            return target.pointer_alignment;
-        }
-        if (resolved.get<pointer_type>() != nullptr)
-        {
-            return target.pointer_alignment;
-        }
-        if (auto array = resolved.get<array_type>())
-        {
-            // The alignment of the array equals that of its element.
-            return evaluate_traits_alignment(array->base);
-        }
-        if (auto record = resolved.get<record_type>())
-        {
-            // An empty record has alignment 1.
-            std::optional<std::size_t> by_field_alignment = std::accumulate(
-                std::begin(record->fields), std::end(record->fields), std::make_optional<std::size_t>(1),
-                [this](std::optional<std::size_t> max_alignment, auto& field) {
-                    std::optional<std::size_t> field_alignment = evaluate_traits_alignment(field.second);
-
-                    return field_alignment.has_value() && max_alignment.has_value()
-                        ? std::make_optional(std::max(field_alignment.value(), max_alignment.value()))
-                        : std::nullopt;
-                }
-            );
-            if (!by_field_alignment.has_value())
-            {
-                return by_field_alignment;
-            }
-            std::size_t max_alignment = by_field_alignment.value();
-
-            if (!record->base.empty())
-            {
-                if (auto base_alignment = evaluate_traits_alignment(record->base))
-                {
-                    max_alignment = std::max(base_alignment.value(), max_alignment);
-                }
-                else
-                {
-                    return std::nullopt;
-                }
-            }
-            return max_alignment;
-        }
-        return std::nullopt;
+        auto props = get_type_properties(subject, this->target);
+        return props ? std::optional{ props->alignment } : std::nullopt;
     }
 
     std::optional<constant_value> evaluator::evaluate_traits(traits_expression& subject)
@@ -622,7 +625,24 @@ namespace elna::boot
                 return constant_value{ static_cast<std::int32_t>(enumeration->members.size()) };
             }
         }
-        // #offset(T, field) stays in codegen - needs GCC record layout.
+        else if (subject.name.name() == "offset")
+        {
+            auto *field = subject.arguments.at(1)->is_named();
+            auto record = resolve_underlying_type(subject.types.front()).get<record_type>();
+            if (field == nullptr || record == nullptr)
+            {
+                return std::nullopt;
+            }
+            if (auto record_layout = layout_record(record, this->target))
+            {
+                auto field_search = record_layout.value().offset_map.find(field->name);
+
+                if (field_search != std::cend(record_layout.value().offset_map))
+                {
+                    return constant_value{ static_cast<std::uint32_t>(field_search->second) };
+                }
+            }
+        }
         return std::nullopt;
     }
 }
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