Implement two pass encoding

First pass:
 - collect information for numbers, registers and which instructions
   contain label references
 - encode all instructions that don't contain label references
 - Set (temporary) addresses for each instruction

Second pass:
 - Collect information about label references (address, offset, size)
 - encode all instructions that contain label references
 - Update (if necessary) addresses for each instruction

 The second pass is iterated 10 times or until no instructions change
 size, whichever comes first.

src/ast.h

@@ -5,6 +5,7 @@
 #include "error.h"
 #include "lexer.h"
 #include "tokenlist.h"
+#include <assert.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ -79,6 +80,22 @@ typedef struct opcode_encoding {
     size_t len;
 } opcode_encoding_t;
 
+typedef struct instruction {
+    bool has_reference;
+    opcode_encoding_t encoding;
+    int64_t address;
+} instruction_t;
+
+typedef struct reference {
+    int64_t offset;
+    int64_t address;
+    operand_size_t size;
+} reference_t;
+
+typedef struct {
+    int64_t address;
+} label_t;
+
 struct ast_node {
     node_id_t id;
     tokenlist_entry_t *token_entry;
@@ -89,22 +106,37 @@ struct ast_node {
     union {
         register_t reg;
         number_t number;
-        struct {
-            bool has_reference;
-            opcode_encoding_t encoding;
-            int64_t address;
-        } instruction;
-        struct {
-            int64_t offset;
-            int64_t address;
-            operand_size_t size;
-        } reference;
-        struct {
-            int64_t address;
-        } label;
+        instruction_t instruction;
+        reference_t reference;
+        label_t label;
     } value;
 };
 
+static inline register_t *ast_node_register_value(ast_node_t *node) {
+    assert(node->id == NODE_REGISTER);
+    return &node->value.reg;
+}
+
+static inline number_t *ast_node_number_value(ast_node_t *node) {
+    assert(node->id == NODE_NUMBER);
+    return &node->value.number;
+}
+
+static inline instruction_t *ast_node_instruction_value(ast_node_t *node) {
+    assert(node->id == NODE_INSTRUCTION);
+    return &node->value.instruction;
+}
+
+static inline reference_t *ast_node_reference_value(ast_node_t *node) {
+    assert(node->id == NODE_LABEL_REFERENCE);
+    return &node->value.reference;
+}
+
+static inline label_t *ast_node_label_value(ast_node_t *node) {
+    assert(node->id == NODE_LABEL);
+    return &node->value.label;
+}
+
 /**
  * @brief Allocates a new AST node
  *

src/encoder/encoder.c

@@ -269,7 +269,7 @@ bool is_operand_match(operand_info_t *info, ast_node_t *operand) {
     switch (info->kind) {
     case OPERAND_REGISTER:
         return operand->id == NODE_REGISTER &&
-               operand->value.reg.size == info->size;
+               ast_node_register_value(operand)->size == info->size;
     case OPERAND_MEMORY:
         return operand->id == NODE_MEMORY;
     case OPERAND_IMMEDIATE: {
@@ -278,7 +278,7 @@ bool is_operand_match(operand_info_t *info, ast_node_t *operand) {
         ast_node_t *child = operand->children[0];
 
         if (child->id == NODE_NUMBER)
-            return (child->value.number.size & info->size) > 0;
+            return (ast_node_number_value(child)->size & info->size) > 0;
         else if (child->id == NODE_LABEL_REFERENCE)
             return info->size == OPERAND_SIZE_32;
         // FIXME: first pass should give us information about the distance of
@@ -340,7 +340,7 @@ error_t *encode_one_register_in_opcode(encoder_t *encoder,
     (void)encoder;
     (void)opcode;
 
-    register_id_t id = operands->children[0]->value.reg.id;
+    register_id_t id = ast_node_register_value(operands->children[0])->id;
     encoding->buffer[encoding->len - 1] |= id & 0b111;
     if ((id & 0b1000) > 0) {
         *rex |= rex_prefix_r;
@@ -355,7 +355,7 @@ error_t *encode_one_register(encoder_t *encoder, opcode_data_t *opcode,
     assert(operands->len == 1);
     assert(operands->children[0]->id == NODE_REGISTER);
 
-    register_id_t id = operands->children[0]->value.reg.id;
+    register_id_t id = ast_node_register_value(operands->children[0])->id;
 
     uint8_t modrm = modrm_mod_register;
 
@@ -390,7 +390,7 @@ error_t *encode_one_immediate(encoder_t *encoder, opcode_data_t *opcode,
            immediate->id == NODE_LABEL_REFERENCE);
 
     if (immediate->id == NODE_NUMBER) {
-        uint64_t value = immediate->value.number.value;
+        uint64_t value = ast_node_number_value(immediate)->value;
         operand_size_t size = opcode->operands[0].size;
         error_t *err = nullptr;
         switch (size) {
@@ -483,7 +483,8 @@ error_t *encoder_encode_instruction(encoder_t *encoder,
         return err;
 
     // produce the actual encoding output in the NODE_INSTRUCTION value
-    uint8_t *output = instruction->value.instruction.encoding.buffer;
+    instruction_t *instruction_value = ast_node_instruction_value(instruction);
+    uint8_t *output = instruction_value->encoding.buffer;
     size_t output_len = 0;
 
     // Handle prefixes
@@ -502,11 +503,17 @@ error_t *encoder_encode_instruction(encoder_t *encoder,
     memcpy(output + output_len, encoding->buffer, encoding->len);
     output_len += encoding->len;
 
-    instruction->value.instruction.encoding.len = output_len;
+    instruction_value->encoding.len = output_len;
 
     return nullptr;
 }
 
+/**
+ * Initial guess for instruction size of instructions that contain a label
+ * reference
+ */
+constexpr size_t instruction_size_estimate = 10;
+
 /**
  * Perform the initial pass over the AST.
  *
@@ -518,7 +525,6 @@ error_t *encoder_encode_instruction(encoder_t *encoder,
  * - determine estimated addresses of each statement
  *
  */
-constexpr size_t instruction_size_estimate = 10;
 error_t *encoder_first_pass(encoder_t *encoder) {
     ast_node_t *root = encoder->ast;
     assert(root->id == NODE_PROGRAM);
@@ -532,19 +538,21 @@ error_t *encoder_first_pass(encoder_t *encoder) {
             return err;
 
         if (statement->id == NODE_INSTRUCTION &&
-            statement->value.instruction.has_reference == false) {
+            ast_node_instruction_value(statement)->has_reference == false) {
             err = encoder_encode_instruction(encoder, statement);
             if (err)
                 return err;
-            statement->value.instruction.address = address;
-            address += statement->value.instruction.encoding.len;
+            instruction_t *instruction = ast_node_instruction_value(statement);
+            instruction->address = address;
+            address += instruction->encoding.len;
         } else if (statement->id == NODE_INSTRUCTION) {
-            statement->value.instruction.encoding.len =
-                instruction_size_estimate;
-            statement->value.instruction.address = address;
+            instruction_t *instruction = ast_node_instruction_value(statement);
+            instruction->encoding.len = instruction_size_estimate;
+            instruction->address = address;
             address += instruction_size_estimate;
         } else if (statement->id == NODE_LABEL) {
-            statement->value.instruction.address = address;
+            label_t *label = ast_node_label_value(statement);
+            label->address = address;
         }
     }
 
@@ -567,18 +575,18 @@ operand_size_t signed_to_size_mask(int64_t value) {
 }
 
 int64_t statement_offset(ast_node_t *from, ast_node_t *to) {
-    assert(from->id == NODE_LABEL || from->id == NODE_INSTRUCTION);
-    assert(to->id == NODE_LABEL || to->id == NODE_INSTRUCTION);
+    assert(from->id == NODE_INSTRUCTION);
+    assert(to->id == NODE_LABEL);
 
-    int64_t from_addr =
-        from->value.instruction.address + from->value.instruction.encoding.len;
-    int64_t to_addr = to->value.instruction.address;
+    instruction_t *instruction = ast_node_instruction_value(from);
+    int64_t from_addr = instruction->address + instruction->encoding.len;
+    int64_t to_addr = ast_node_label_value(to)->address;
 
     return to_addr - from_addr;
 }
 
-error_t *encoder_collect_label_info(encoder_t *encoder, ast_node_t *node,
-                                    ast_node_t *statement) {
+error_t *encoder_collect_reference_info(encoder_t *encoder, ast_node_t *node,
+                                        ast_node_t *statement) {
     assert(statement->id == NODE_INSTRUCTION);
     if (node->id == NODE_LABEL_REFERENCE) {
         const char *name = node->token_entry->token.value;
@@ -587,7 +595,7 @@ error_t *encoder_collect_label_info(encoder_t *encoder, ast_node_t *node,
                symbol->statement->id == NODE_LABEL);
 
         int64_t offset = statement_offset(statement, symbol->statement);
-        int64_t absolute = symbol->statement->value.instruction.address;
+        int64_t absolute = ast_node_label_value(symbol->statement)->address;
         operand_size_t size = signed_to_size_mask(offset);
 
         node->value.reference.address = absolute;
@@ -598,6 +606,28 @@ error_t *encoder_collect_label_info(encoder_t *encoder, ast_node_t *node,
     return nullptr;
 }
 
+bool encoder_should_reencode(ast_node_t *statement) {
+    if (statement->id != NODE_INSTRUCTION)
+        return false;
+
+    instruction_t *instruction = ast_node_instruction_value(statement);
+    return instruction->has_reference == false;
+}
+
+void set_statement_address(ast_node_t *statement, int64_t address) {
+    if (statement->id == NODE_INSTRUCTION) {
+        ast_node_instruction_value(statement)->address = address;
+    } else if (statement->id == NODE_LABEL) {
+        ast_node_label_value(statement)->address = address;
+    }
+}
+
+size_t get_statement_length(ast_node_t *statement) {
+    if (statement->id != NODE_INSTRUCTION)
+        return 0;
+    return ast_node_instruction_value(statement)->encoding.len;
+}
+
 /**
  * Perform the second pass. Updates the label info and encodes all instructions
  * that have a label reference.that performs actual encoding.
@@ -610,28 +640,22 @@ error_t *encoder_second_pass(encoder_t *encoder, bool *did_update) {
     for (size_t i = 0; i < root->len; ++i) {
         ast_node_t *statement = root->children[i];
 
-        if (statement->id == NODE_INSTRUCTION &&
-            statement->value.instruction.has_reference) {
-            statement->value.instruction.address = address;
-            size_t before = statement->value.instruction.encoding.len;
+        set_statement_address(statement, address);
+        size_t before = get_statement_length(statement);
+
+        if (encoder_should_reencode(statement)) {
             error_t *err =
-                encoder_collect_label_info(encoder, statement, statement);
+                encoder_collect_reference_info(encoder, statement, statement);
             if (err)
                 return err;
             err = encoder_encode_instruction(encoder, statement);
             if (err)
                 return err;
-            size_t after = statement->value.instruction.encoding.len;
-            address += after;
-            *did_update = *did_update || (before != after);
-        } else if (statement->id == NODE_INSTRUCTION &&
-                   statement->value.instruction.has_reference) {
-            statement->value.instruction.address = address;
-            address += statement->value.instruction.encoding.len;
-        } else if (statement->id == NODE_LABEL) {
-            statement->value.label.address = address;
         }
-        address += statement->value.instruction.encoding.len;
+
+        size_t after = get_statement_length(statement);
+        *did_update = *did_update || (before != after);
+        address += after;
     }
     return nullptr;
 }