zig/src/codegen.cpp

/*
 * Copyright (c) 2015 Andrew Kelley
 *
 * This file is part of zig, which is MIT licensed.
 * See http://opensource.org/licenses/MIT
 */

#include "codegen.hpp"
#include "hash_map.hpp"
#include "zig_llvm.hpp"
#include "os.hpp"
#include "config.h"
#include "error.hpp"

#include "semantic_info.hpp"

#include <stdio.h>
#include <errno.h>

CodeGen *create_codegen(AstNode *root, Buf *in_full_path) {
    CodeGen *g = allocate<CodeGen>(1);
    g->root = root;
    g->fn_table.init(32);
    g->str_table.init(32);
    g->type_table.init(32);
    g->link_table.init(32);
    g->is_static = false;
    g->build_type = CodeGenBuildTypeDebug;
    g->strip_debug_symbols = false;
    g->out_name = nullptr;
    g->out_type = OutTypeUnknown;

    os_path_split(in_full_path, &g->in_dir, &g->in_file);
    return g;
}

void codegen_set_build_type(CodeGen *g, CodeGenBuildType build_type) {
    g->build_type = build_type;
}

void codegen_set_is_static(CodeGen *g, bool is_static) {
    g->is_static = is_static;
}

void codegen_set_strip(CodeGen *g, bool strip) {
    g->strip_debug_symbols = strip;
}

void codegen_set_out_type(CodeGen *g, OutType out_type) {
    g->out_type = out_type;
}

void codegen_set_out_name(CodeGen *g, Buf *out_name) {
    g->out_name = out_name;
}

static LLVMValueRef gen_expr(CodeGen *g, AstNode *expr_node);

static LLVMTypeRef to_llvm_type(AstNode *type_node) {
    assert(type_node->type == NodeTypeType);
    assert(type_node->codegen_node);
    assert(type_node->codegen_node->data.type_node.entry);

    return type_node->codegen_node->data.type_node.entry->type_ref;
}

static LLVMZigDIType *to_llvm_debug_type(AstNode *type_node) {
    assert(type_node->type == NodeTypeType);
    assert(type_node->codegen_node);
    assert(type_node->codegen_node->data.type_node.entry);

    return type_node->codegen_node->data.type_node.entry->di_type;
}

static bool type_is_unreachable(AstNode *type_node) {
    assert(type_node->type == NodeTypeType);
    assert(type_node->codegen_node);
    assert(type_node->codegen_node->data.type_node.entry);
    return type_node->codegen_node->data.type_node.entry->id == TypeIdUnreachable;
}

static void add_debug_source_node(CodeGen *g, AstNode *node) {
    LLVMZigSetCurrentDebugLocation(g->builder, node->line + 1, node->column + 1, g->block_scopes.last());
}

static LLVMValueRef find_or_create_string(CodeGen *g, Buf *str) {
    auto entry = g->str_table.maybe_get(str);
    if (entry) {
        return entry->value;
    }
    LLVMValueRef text = LLVMConstString(buf_ptr(str), buf_len(str), false);
    LLVMValueRef global_value = LLVMAddGlobal(g->module, LLVMTypeOf(text), "");
    LLVMSetLinkage(global_value, LLVMPrivateLinkage);
    LLVMSetInitializer(global_value, text);
    LLVMSetGlobalConstant(global_value, true);
    LLVMSetUnnamedAddr(global_value, true);
    g->str_table.put(str, global_value);

    return global_value;
}

static LLVMValueRef get_variable_value(CodeGen *g, Buf *name) {
    assert(g->cur_fn->proto_node->type == NodeTypeFnProto);
    int param_count = g->cur_fn->proto_node->data.fn_proto.params.length;
    for (int i = 0; i < param_count; i += 1) {
        AstNode *param_decl_node = g->cur_fn->proto_node->data.fn_proto.params.at(i);
        assert(param_decl_node->type == NodeTypeParamDecl);
        Buf *param_name = &param_decl_node->data.param_decl.name;
        if (buf_eql_buf(name, param_name)) {
            CodeGenNode *codegen_node = g->cur_fn->fn_def_node->codegen_node;
            assert(codegen_node);
            FnDefNode *codegen_fn_def = &codegen_node->data.fn_def_node;
            return codegen_fn_def->params[i];
        }
    }
    zig_unreachable();
}

static LLVMValueRef gen_fn_call_expr(CodeGen *g, AstNode *node) {
    assert(node->type == NodeTypeFnCallExpr);

    Buf *name = hack_get_fn_call_name(g, node->data.fn_call_expr.fn_ref_expr);

    FnTableEntry *fn_table_entry = g->fn_table.get(name);
    assert(fn_table_entry->proto_node->type == NodeTypeFnProto);
    int expected_param_count = fn_table_entry->proto_node->data.fn_proto.params.length;
    int actual_param_count = node->data.fn_call_expr.params.length;
    assert(expected_param_count == actual_param_count);

    LLVMValueRef *param_values = allocate<LLVMValueRef>(actual_param_count);
    for (int i = 0; i < actual_param_count; i += 1) {
        AstNode *expr_node = node->data.fn_call_expr.params.at(i);
        param_values[i] = gen_expr(g, expr_node);
    }

    add_debug_source_node(g, node);
    LLVMValueRef result = LLVMZigBuildCall(g->builder, fn_table_entry->fn_value,
            param_values, actual_param_count, fn_table_entry->calling_convention, "");

    if (type_is_unreachable(fn_table_entry->proto_node->data.fn_proto.return_type)) {
        return LLVMBuildUnreachable(g->builder);
    } else {
        return result;
    }
}

static LLVMValueRef gen_prefix_op_expr(CodeGen *g, AstNode *node) {
    assert(node->type == NodeTypePrefixOpExpr);
    assert(node->data.prefix_op_expr.primary_expr);

    LLVMValueRef expr = gen_expr(g, node->data.prefix_op_expr.primary_expr);

    switch (node->data.prefix_op_expr.prefix_op) {
        case PrefixOpNegation:
            add_debug_source_node(g, node);
            return LLVMBuildNeg(g->builder, expr, "");
        case PrefixOpBoolNot:
            {
                LLVMValueRef zero = LLVMConstNull(LLVMTypeOf(expr));
                add_debug_source_node(g, node);
                return LLVMBuildICmp(g->builder, LLVMIntEQ, expr, zero, "");
            }
        case PrefixOpBinNot:
            add_debug_source_node(g, node);
            return LLVMBuildNot(g->builder, expr, "");
        case PrefixOpInvalid:
            zig_unreachable();
    }
    zig_unreachable();
}

static LLVMValueRef gen_cast_expr(CodeGen *g, AstNode *node) {
    assert(node->type == NodeTypeCastExpr);

    LLVMValueRef expr = gen_expr(g, node->data.cast_expr.prefix_op_expr);

    if (!node->data.cast_expr.type)
        return expr;

    zig_panic("TODO cast expression");
}

static LLVMValueRef gen_arithmetic_bin_op_expr(CodeGen *g, AstNode *node) {
    assert(node->type == NodeTypeBinOpExpr);

    LLVMValueRef val1 = gen_expr(g, node->data.bin_op_expr.op1);
    LLVMValueRef val2 = gen_expr(g, node->data.bin_op_expr.op2);

    switch (node->data.bin_op_expr.bin_op) {
        case BinOpTypeBinOr:
            add_debug_source_node(g, node);
            return LLVMBuildOr(g->builder, val1, val2, "");
        case BinOpTypeBinXor:
            add_debug_source_node(g, node);
            return LLVMBuildXor(g->builder, val1, val2, "");
        case BinOpTypeBinAnd:
            add_debug_source_node(g, node);
            return LLVMBuildAnd(g->builder, val1, val2, "");
        case BinOpTypeBitShiftLeft:
            add_debug_source_node(g, node);
            return LLVMBuildShl(g->builder, val1, val2, "");
        case BinOpTypeBitShiftRight:
            // TODO implement type system so that we know whether to do
            // logical or arithmetic shifting here.
            // signed -> arithmetic, unsigned -> logical
            add_debug_source_node(g, node);
            return LLVMBuildLShr(g->builder, val1, val2, "");
        case BinOpTypeAdd:
            add_debug_source_node(g, node);
            return LLVMBuildAdd(g->builder, val1, val2, "");
        case BinOpTypeSub:
            add_debug_source_node(g, node);
            return LLVMBuildSub(g->builder, val1, val2, "");
        case BinOpTypeMult:
            // TODO types so we know float vs int
            add_debug_source_node(g, node);
            return LLVMBuildMul(g->builder, val1, val2, "");
        case BinOpTypeDiv:
            // TODO types so we know float vs int and signed vs unsigned
            add_debug_source_node(g, node);
            return LLVMBuildSDiv(g->builder, val1, val2, "");
        case BinOpTypeMod:
            // TODO types so we know float vs int and signed vs unsigned
            add_debug_source_node(g, node);
            return LLVMBuildSRem(g->builder, val1, val2, "");
        case BinOpTypeBoolOr:
        case BinOpTypeBoolAnd:
        case BinOpTypeCmpEq:
        case BinOpTypeCmpNotEq:
        case BinOpTypeCmpLessThan:
        case BinOpTypeCmpGreaterThan:
        case BinOpTypeCmpLessOrEq:
        case BinOpTypeCmpGreaterOrEq:
        case BinOpTypeInvalid:
            zig_unreachable();
    }
    zig_unreachable();
}

static LLVMIntPredicate cmp_op_to_int_predicate(BinOpType cmp_op, bool is_signed) {
    switch (cmp_op) {
        case BinOpTypeCmpEq:
            return LLVMIntEQ;
        case BinOpTypeCmpNotEq:
            return LLVMIntNE;
        case BinOpTypeCmpLessThan:
            return is_signed ? LLVMIntSLT : LLVMIntULT;
        case BinOpTypeCmpGreaterThan:
            return is_signed ? LLVMIntSGT : LLVMIntUGT;
        case BinOpTypeCmpLessOrEq:
            return is_signed ? LLVMIntSLE : LLVMIntULE;
        case BinOpTypeCmpGreaterOrEq:
            return is_signed ? LLVMIntSGE : LLVMIntUGE;
        default:
            zig_unreachable();
    }
}

static LLVMValueRef gen_cmp_expr(CodeGen *g, AstNode *node) {
    assert(node->type == NodeTypeBinOpExpr);

    LLVMValueRef val1 = gen_expr(g, node->data.bin_op_expr.op1);
    LLVMValueRef val2 = gen_expr(g, node->data.bin_op_expr.op2);

    // TODO implement type system so that we know whether to do signed or unsigned comparison here
    LLVMIntPredicate pred = cmp_op_to_int_predicate(node->data.bin_op_expr.bin_op, true);
    add_debug_source_node(g, node);
    return LLVMBuildICmp(g->builder, pred, val1, val2, "");
}

static LLVMValueRef gen_bool_and_expr(CodeGen *g, AstNode *node) {
    assert(node->type == NodeTypeBinOpExpr);

    LLVMValueRef val1 = gen_expr(g, node->data.bin_op_expr.op1);

    // block for when val1 == true
    LLVMBasicBlockRef true_block = LLVMAppendBasicBlock(g->cur_fn->fn_value, "BoolAndTrue");
    // block for when val1 == false (don't even evaluate the second part)
    LLVMBasicBlockRef false_block = LLVMAppendBasicBlock(g->cur_fn->fn_value, "BoolAndFalse");

    LLVMValueRef zero = LLVMConstNull(LLVMTypeOf(val1));
    add_debug_source_node(g, node);
    LLVMValueRef val1_i1 = LLVMBuildICmp(g->builder, LLVMIntEQ, val1, zero, "");
    LLVMBuildCondBr(g->builder, val1_i1, false_block, true_block);

    LLVMPositionBuilderAtEnd(g->builder, true_block);
    LLVMValueRef val2 = gen_expr(g, node->data.bin_op_expr.op2);
    add_debug_source_node(g, node);
    LLVMValueRef val2_i1 = LLVMBuildICmp(g->builder, LLVMIntEQ, val2, zero, "");

    LLVMPositionBuilderAtEnd(g->builder, false_block);
    add_debug_source_node(g, node);
    LLVMValueRef phi = LLVMBuildPhi(g->builder, LLVMInt1Type(), "");
    LLVMValueRef one_i1 = LLVMConstAllOnes(LLVMInt1Type());
    LLVMValueRef incoming_values[2] = {one_i1, val2_i1};
    LLVMBasicBlockRef incoming_blocks[2] = {LLVMGetInsertBlock(g->builder), true_block};
    LLVMAddIncoming(phi, incoming_values, incoming_blocks, 2);

    return phi;
}

static LLVMValueRef gen_bool_or_expr(CodeGen *g, AstNode *expr_node) {
    assert(expr_node->type == NodeTypeBinOpExpr);

    LLVMValueRef val1 = gen_expr(g, expr_node->data.bin_op_expr.op1);

    // block for when val1 == false
    LLVMBasicBlockRef false_block = LLVMAppendBasicBlock(g->cur_fn->fn_value, "BoolOrFalse");
    // block for when val1 == true (don't even evaluate the second part)
    LLVMBasicBlockRef true_block = LLVMAppendBasicBlock(g->cur_fn->fn_value, "BoolOrTrue");

    LLVMValueRef zero = LLVMConstNull(LLVMTypeOf(val1));
    add_debug_source_node(g, expr_node);
    LLVMValueRef val1_i1 = LLVMBuildICmp(g->builder, LLVMIntEQ, val1, zero, "");
    LLVMBuildCondBr(g->builder, val1_i1, false_block, true_block);

    LLVMPositionBuilderAtEnd(g->builder, false_block);
    LLVMValueRef val2 = gen_expr(g, expr_node->data.bin_op_expr.op2);
    add_debug_source_node(g, expr_node);
    LLVMValueRef val2_i1 = LLVMBuildICmp(g->builder, LLVMIntEQ, val2, zero, "");

    LLVMPositionBuilderAtEnd(g->builder, true_block);
    add_debug_source_node(g, expr_node);
    LLVMValueRef phi = LLVMBuildPhi(g->builder, LLVMInt1Type(), "");
    LLVMValueRef one_i1 = LLVMConstAllOnes(LLVMInt1Type());
    LLVMValueRef incoming_values[2] = {one_i1, val2_i1};
    LLVMBasicBlockRef incoming_blocks[2] = {LLVMGetInsertBlock(g->builder), false_block};
    LLVMAddIncoming(phi, incoming_values, incoming_blocks, 2);

    return phi;
}

static LLVMValueRef gen_bin_op_expr(CodeGen *g, AstNode *node) {
    switch (node->data.bin_op_expr.bin_op) {
        case BinOpTypeInvalid:
            zig_unreachable();
        case BinOpTypeBoolOr:
            return gen_bool_or_expr(g, node);
        case BinOpTypeBoolAnd:
            return gen_bool_and_expr(g, node);
        case BinOpTypeCmpEq:
        case BinOpTypeCmpNotEq:
        case BinOpTypeCmpLessThan:
        case BinOpTypeCmpGreaterThan:
        case BinOpTypeCmpLessOrEq:
        case BinOpTypeCmpGreaterOrEq:
            return gen_cmp_expr(g, node);
        case BinOpTypeBinOr:
        case BinOpTypeBinXor:
        case BinOpTypeBinAnd:
        case BinOpTypeBitShiftLeft:
        case BinOpTypeBitShiftRight:
        case BinOpTypeAdd:
        case BinOpTypeSub:
        case BinOpTypeMult:
        case BinOpTypeDiv:
        case BinOpTypeMod:
            return gen_arithmetic_bin_op_expr(g, node);
    }
    zig_unreachable();
}

static LLVMValueRef gen_return_expr(CodeGen *g, AstNode *node) {
    assert(node->type == NodeTypeReturnExpr);
    AstNode *param_node = node->data.return_expr.expr;
    if (param_node) {
        LLVMValueRef value = gen_expr(g, param_node);

        add_debug_source_node(g, node);
        return LLVMBuildRet(g->builder, value);
    } else {
        add_debug_source_node(g, node);
        return LLVMBuildRetVoid(g->builder);
    }
}
/*
Expression : BoolOrExpression | ReturnExpression
*/
static LLVMValueRef gen_expr(CodeGen *g, AstNode *node) {
    switch (node->type) {
        case NodeTypeBinOpExpr:
            return gen_bin_op_expr(g, node);
        case NodeTypeReturnExpr:
            return gen_return_expr(g, node);
        case NodeTypeCastExpr:
            return gen_cast_expr(g, node);
        case NodeTypePrefixOpExpr:
            return gen_prefix_op_expr(g, node);
        case NodeTypeFnCallExpr:
            return gen_fn_call_expr(g, node);
        case NodeTypeUnreachable:
            add_debug_source_node(g, node);
            return LLVMBuildUnreachable(g->builder);
        case NodeTypeNumberLiteral:
            {
                Buf *number_str = &node->data.number;
                LLVMTypeRef number_type = LLVMInt32Type();
                LLVMValueRef number_val = LLVMConstIntOfStringAndSize(number_type,
                        buf_ptr(number_str), buf_len(number_str), 10);
                return number_val;
            }
        case NodeTypeStringLiteral:
            {
                Buf *str = &node->data.string;
                LLVMValueRef str_val = find_or_create_string(g, str);
                LLVMValueRef indices[] = {
                    LLVMConstInt(LLVMInt32Type(), 0, false),
                    LLVMConstInt(LLVMInt32Type(), 0, false)
                };
                LLVMValueRef ptr_val = LLVMBuildInBoundsGEP(g->builder, str_val, indices, 2, "");
                return ptr_val;
            }
        case NodeTypeSymbol:
            {
                Buf *name = &node->data.symbol;
                return get_variable_value(g, name);
            }
        case NodeTypeRoot:
        case NodeTypeRootExportDecl:
        case NodeTypeFnProto:
        case NodeTypeFnDef:
        case NodeTypeFnDecl:
        case NodeTypeParamDecl:
        case NodeTypeType:
        case NodeTypeBlock:
        case NodeTypeExternBlock:
        case NodeTypeDirective:
            zig_unreachable();
    }
    zig_unreachable();
}

static void gen_block(CodeGen *g, AstNode *block_node, bool add_implicit_return) {
    assert(block_node->type == NodeTypeBlock);

    LLVMZigDILexicalBlock *di_block = LLVMZigCreateLexicalBlock(g->dbuilder, g->block_scopes.last(),
            g->di_file, block_node->line + 1, block_node->column + 1);
    g->block_scopes.append(LLVMZigLexicalBlockToScope(di_block));

    add_debug_source_node(g, block_node);

    for (int i = 0; i < block_node->data.block.statements.length; i += 1) {
        AstNode *statement_node = block_node->data.block.statements.at(i);
        gen_expr(g, statement_node);
    }

    if (add_implicit_return) {
        LLVMBuildRetVoid(g->builder);
    }

    g->block_scopes.pop();
}

static LLVMZigDISubroutineType *create_di_function_type(CodeGen *g, AstNodeFnProto *fn_proto,
        LLVMZigDIFile *di_file)
{
    LLVMZigDIType **types = allocate<LLVMZigDIType*>(1 + fn_proto->params.length);
    types[0] = to_llvm_debug_type(fn_proto->return_type);
    int types_len = fn_proto->params.length + 1;
    for (int i = 0; i < fn_proto->params.length; i += 1) {
        AstNode *param_node = fn_proto->params.at(i);
        assert(param_node->type == NodeTypeParamDecl);
        LLVMZigDIType *param_type = to_llvm_debug_type(param_node->data.param_decl.type);
        types[i + 1] = param_type;
    }
    return LLVMZigCreateSubroutineType(g->dbuilder, di_file, types, types_len, 0);
}

void code_gen(CodeGen *g) {
    assert(!g->errors.length);

    Buf *producer = buf_sprintf("zig %s", ZIG_VERSION_STRING);
    bool is_optimized = g->build_type == CodeGenBuildTypeRelease;
    const char *flags = "";
    unsigned runtime_version = 0;
    g->compile_unit = LLVMZigCreateCompileUnit(g->dbuilder, LLVMZigLang_DW_LANG_C99(),
            buf_ptr(&g->in_file), buf_ptr(&g->in_dir),
            buf_ptr(producer), is_optimized, flags, runtime_version,
            "", 0, !g->strip_debug_symbols);

    g->block_scopes.append(LLVMZigCompileUnitToScope(g->compile_unit));

    g->di_file = LLVMZigCreateFile(g->dbuilder, buf_ptr(&g->in_file), buf_ptr(&g->in_dir));


    // Generate function prototypes
    auto it = g->fn_table.entry_iterator();
    for (;;) {
        auto *entry = it.next();
        if (!entry)
            break;

        FnTableEntry *fn_table_entry = entry->value;

        AstNode *proto_node = fn_table_entry->proto_node;
        assert(proto_node->type == NodeTypeFnProto);
        AstNodeFnProto *fn_proto = &proto_node->data.fn_proto;

        LLVMTypeRef ret_type = to_llvm_type(fn_proto->return_type);
        LLVMTypeRef *param_types = allocate<LLVMTypeRef>(fn_proto->params.length);
        for (int param_decl_i = 0; param_decl_i < fn_proto->params.length; param_decl_i += 1) {
            AstNode *param_node = fn_proto->params.at(param_decl_i);
            assert(param_node->type == NodeTypeParamDecl);
            AstNode *type_node = param_node->data.param_decl.type;
            param_types[param_decl_i] = to_llvm_type(type_node);
        }
        LLVMTypeRef function_type = LLVMFunctionType(ret_type, param_types, fn_proto->params.length, 0);
        LLVMValueRef fn = LLVMAddFunction(g->module, buf_ptr(&fn_proto->name), function_type);

        LLVMSetLinkage(fn, fn_table_entry->internal_linkage ? LLVMInternalLinkage : LLVMExternalLinkage);

        if (type_is_unreachable(fn_proto->return_type)) {
            LLVMAddFunctionAttr(fn, LLVMNoReturnAttribute);
        }
        LLVMSetFunctionCallConv(fn, fn_table_entry->calling_convention);
        if (!fn_table_entry->is_extern) {
            LLVMAddFunctionAttr(fn, LLVMNoUnwindAttribute);
        }

        fn_table_entry->fn_value = fn;
    }

    // Generate function definitions.
    for (int i = 0; i < g->fn_defs.length; i += 1) {
        FnTableEntry *fn_table_entry = g->fn_defs.at(i);
        AstNode *fn_def_node = fn_table_entry->fn_def_node;
        LLVMValueRef fn = fn_table_entry->fn_value;
        g->cur_fn = fn_table_entry;

        AstNode *proto_node = fn_table_entry->proto_node;
        assert(proto_node->type == NodeTypeFnProto);
        AstNodeFnProto *fn_proto = &proto_node->data.fn_proto;

        // Add debug info.
        LLVMZigDIScope *fn_scope = LLVMZigFileToScope(g->di_file);
        unsigned line_number = fn_def_node->line + 1;
        unsigned scope_line = line_number;
        bool is_definition = true;
        unsigned flags = 0;
        LLVMZigDISubprogram *subprogram = LLVMZigCreateFunction(g->dbuilder,
            fn_scope, buf_ptr(&fn_proto->name), "", g->di_file, line_number,
            create_di_function_type(g, fn_proto, g->di_file), fn_table_entry->internal_linkage, 
            is_definition, scope_line, flags, is_optimized, fn);

        g->block_scopes.append(LLVMZigSubprogramToScope(subprogram));

        LLVMBasicBlockRef entry_block = LLVMAppendBasicBlock(fn, "entry");
        LLVMPositionBuilderAtEnd(g->builder, entry_block);

        CodeGenNode *codegen_node = fn_def_node->codegen_node;
        assert(codegen_node);

        FnDefNode *codegen_fn_def = &codegen_node->data.fn_def_node;
        codegen_fn_def->params = allocate<LLVMValueRef>(LLVMCountParams(fn));
        LLVMGetParams(fn, codegen_fn_def->params);

        bool add_implicit_return = codegen_fn_def->add_implicit_return;
        gen_block(g, fn_def_node->data.fn_def.body, add_implicit_return);

        g->block_scopes.pop();
    }
    assert(!g->errors.length);

    LLVMZigDIBuilderFinalize(g->dbuilder);

    LLVMDumpModule(g->module);

    // in release mode, we're sooooo confident that we've generated correct ir,
    // that we skip the verify module step in order to get better performance.
#ifndef NDEBUG
    char *error = nullptr;
    LLVMVerifyModule(g->module, LLVMAbortProcessAction, &error);
#endif
}

void code_gen_optimize(CodeGen *g) {
    LLVMZigOptimizeModule(g->target_machine, g->module);
    LLVMDumpModule(g->module);
}

ZigList<ErrorMsg> *codegen_error_messages(CodeGen *g) {
    return &g->errors;
}

static Buf *to_c_type(CodeGen *g, AstNode *type_node) {
    assert(type_node->type == NodeTypeType);
    assert(type_node->codegen_node);

    TypeTableEntry *type_entry = type_node->codegen_node->data.type_node.entry;
    assert(type_entry);

    switch (type_entry->id) {
        case TypeIdUserDefined:
            zig_panic("TODO");
            break;
        case TypeIdPointer:
            zig_panic("TODO");
            break;
        case TypeIdU8:
            g->c_stdint_used = true;
            return buf_create_from_str("uint8_t");
        case TypeIdI32:
            g->c_stdint_used = true;
            return buf_create_from_str("int32_t");
        case TypeIdVoid:
            zig_panic("TODO");
            break;
        case TypeIdUnreachable:
            zig_panic("TODO");
            break;
    }
    zig_unreachable();
}

static void generate_h_file(CodeGen *g) {
    Buf *h_file_out_path = buf_sprintf("%s.h", buf_ptr(g->out_name));
    FILE *out_h = fopen(buf_ptr(h_file_out_path), "wb");
    if (!out_h)
        zig_panic("unable to open %s: %s", buf_ptr(h_file_out_path), strerror(errno));

    Buf *export_macro = buf_sprintf("%s_EXPORT", buf_ptr(g->out_name));
    buf_upcase(export_macro);

    Buf *extern_c_macro = buf_sprintf("%s_EXTERN_C", buf_ptr(g->out_name));
    buf_upcase(extern_c_macro);

    Buf h_buf = BUF_INIT;
    buf_resize(&h_buf, 0);
    for (int fn_def_i = 0; fn_def_i < g->fn_defs.length; fn_def_i += 1) {
        FnTableEntry *fn_table_entry = g->fn_defs.at(fn_def_i);
        AstNode *proto_node = fn_table_entry->proto_node;
        assert(proto_node->type == NodeTypeFnProto);
        AstNodeFnProto *fn_proto = &proto_node->data.fn_proto;

        if (fn_proto->visib_mod != FnProtoVisibModExport)
            continue;

        buf_appendf(&h_buf, "%s %s %s(",
                buf_ptr(export_macro),
                buf_ptr(to_c_type(g, fn_proto->return_type)),
                buf_ptr(&fn_proto->name));

        if (fn_proto->params.length) {
            for (int param_i = 0; param_i < fn_proto->params.length; param_i += 1) {
                AstNode *param_decl_node = fn_proto->params.at(param_i);
                AstNode *param_type = param_decl_node->data.param_decl.type;
                buf_appendf(&h_buf, "%s %s",
                        buf_ptr(to_c_type(g, param_type)),
                        buf_ptr(&param_decl_node->data.param_decl.name));
                if (param_i < fn_proto->params.length - 1)
                    buf_appendf(&h_buf, ", ");
            }
            buf_appendf(&h_buf, ");\n");
        } else {
            buf_appendf(&h_buf, "void);\n");
        }
    }

    Buf *ifdef_dance_name = buf_sprintf("%s_%s_H", buf_ptr(g->out_name), buf_ptr(g->out_name));
    buf_upcase(ifdef_dance_name);

    fprintf(out_h, "#ifndef %s\n", buf_ptr(ifdef_dance_name));
    fprintf(out_h, "#define %s\n\n", buf_ptr(ifdef_dance_name));

    if (g->c_stdint_used)
        fprintf(out_h, "#include <stdint.h>\n");

    fprintf(out_h, "\n");

    fprintf(out_h, "#ifdef __cplusplus\n");
    fprintf(out_h, "#define %s extern \"C\"\n", buf_ptr(extern_c_macro));
    fprintf(out_h, "#else\n");
    fprintf(out_h, "#define %s\n", buf_ptr(extern_c_macro));
    fprintf(out_h, "#endif\n");
    fprintf(out_h, "\n");
    fprintf(out_h, "#if defined(_WIN32)\n");
    fprintf(out_h, "#define %s %s __declspec(dllimport)\n", buf_ptr(export_macro), buf_ptr(extern_c_macro));
    fprintf(out_h, "#else\n");
    fprintf(out_h, "#define %s %s __attribute__((visibility (\"default\")))\n",
            buf_ptr(export_macro), buf_ptr(extern_c_macro));
    fprintf(out_h, "#endif\n");
    fprintf(out_h, "\n");

    fprintf(out_h, "%s", buf_ptr(&h_buf));

    fprintf(out_h, "\n#endif\n");

    if (fclose(out_h))
        zig_panic("unable to close h file: %s", strerror(errno));
}

void code_gen_link(CodeGen *g, const char *out_file) {
    if (!out_file) {
        out_file = buf_ptr(g->out_name);
    }

    Buf out_file_o = BUF_INIT;
    buf_init_from_str(&out_file_o, out_file);

    if (g->out_type != OutTypeObj) {
        buf_append_str(&out_file_o, ".o");
    }

    char *err_msg = nullptr;
    if (LLVMTargetMachineEmitToFile(g->target_machine, g->module, buf_ptr(&out_file_o),
                LLVMObjectFile, &err_msg))
    {
        zig_panic("unable to write object file: %s", err_msg);
    }

    if (g->out_type == OutTypeObj) {
        return;
    }

    if (g->out_type == OutTypeLib && g->is_static) {
        // invoke `ar`
        // example:
        // # static link into libfoo.a
        // ar cq libfoo.a foo1.o foo2.o 
        zig_panic("TODO invoke ar");
        return;
    }

    // invoke `ld`
    ZigList<const char *> args = {0};
    if (g->is_static) {
        args.append("-static");
    }

    char *ZIG_NATIVE_DYNAMIC_LINKER = getenv("ZIG_NATIVE_DYNAMIC_LINKER");
    if (g->is_native_target && ZIG_NATIVE_DYNAMIC_LINKER) {
        if (ZIG_NATIVE_DYNAMIC_LINKER[0] != 0) {
            args.append("-dynamic-linker");
            args.append(ZIG_NATIVE_DYNAMIC_LINKER);
        }
    } else {
        args.append("-dynamic-linker");
        args.append(buf_ptr(get_dynamic_linker(g->target_machine)));
    }

    if (g->out_type == OutTypeLib) {
        Buf *out_lib_so = buf_sprintf("lib%s.so.%d.%d.%d",
                buf_ptr(g->out_name), g->version_major, g->version_minor, g->version_patch);
        Buf *soname = buf_sprintf("lib%s.so.%d", buf_ptr(g->out_name), g->version_major);
        args.append("-shared");
        args.append("-soname");
        args.append(buf_ptr(soname));
        out_file = buf_ptr(out_lib_so);
    }

    args.append("-o");
    args.append(out_file);

    args.append((const char *)buf_ptr(&out_file_o));

    auto it = g->link_table.entry_iterator();
    for (;;) {
        auto *entry = it.next();
        if (!entry)
            break;

        Buf *arg = buf_sprintf("-l%s", buf_ptr(entry->key));
        args.append(buf_ptr(arg));
    }

    os_spawn_process("ld", args, false);

    if (g->out_type == OutTypeLib) {
        generate_h_file(g);
    }
}