wasm: store File.Index on the Atom

Also, consolidate the creation of Atoms so they all use `createAtom`.

src/link/Wasm.zig

@@ -569,6 +569,7 @@ pub fn createEmpty(
         if (!use_llvm) {
             const index: File.Index = @enumFromInt(wasm.files.len);
             var zig_object: ZigObject = .{
+                .index = index,
                 .path = try std.fmt.allocPrint(gpa, "{s}.o", .{std.fs.path.stem(zcu.main_mod.root_src_path)}),
                 .stack_pointer_sym = undefined,
             };
@@ -663,12 +664,11 @@ fn parseObjectFile(wasm: *Wasm, path: []const u8) !bool {
 }
 
 /// Creates a new empty `Atom` and returns its `Atom.Index`
-pub fn createAtom(wasm: *Wasm, sym_index: u32) !Atom.Index {
+pub fn createAtom(wasm: *Wasm, sym_index: u32, file_index: File.Index) !Atom.Index {
     const gpa = wasm.base.comp.gpa;
     const index: Atom.Index = @intCast(wasm.managed_atoms.items.len);
     const atom = try wasm.managed_atoms.addOne(gpa);
-    atom.* = Atom.empty;
-    atom.sym_index = sym_index;
+    atom.* = .{ .file_index = file_index, .sym_index = sym_index };
     try wasm.symbol_atom.putNoClobber(gpa, .{ .file = null, .index = sym_index }, index);
 
     return index;
@@ -1825,20 +1825,11 @@ fn createSyntheticFunction(
     symbol.index = func_index;
 
     // create the atom that will be output into the final binary
-    const atom_index = @as(Atom.Index, @intCast(wasm.managed_atoms.items.len));
-    const atom = try wasm.managed_atoms.addOne(gpa);
-    atom.* = .{
-        .size = @as(u32, @intCast(function_body.items.len)),
-        .offset = 0,
-        .sym_index = loc.index,
-        .file = null,
-        .alignment = .@"1",
-        .prev = null,
-        .code = function_body.moveToUnmanaged(),
-        .original_offset = 0,
-    };
+    const atom_index = try wasm.createAtom(loc.index, .null);
+    const atom = wasm.getAtomPtr(atom_index);
+    atom.code = function_body.moveToUnmanaged();
+    atom.size = @intCast(function_body.items.len);
     try wasm.appendAtomAtIndex(wasm.code_section_index.?, atom_index);
-    try wasm.symbol_atom.putNoClobber(gpa, loc, atom_index);
 }
 
 /// Unlike `createSyntheticFunction` this function is to be called by
@@ -1856,19 +1847,11 @@ pub fn createFunction(
     const gpa = wasm.base.comp.gpa;
     const loc = try wasm.createSyntheticSymbol(symbol_name, .function);
 
-    const atom_index: Atom.Index = @intCast(wasm.managed_atoms.items.len);
-    const atom = try wasm.managed_atoms.addOne(gpa);
-    atom.* = .{
-        .size = @intCast(function_body.items.len),
-        .offset = 0,
-        .sym_index = loc.index,
-        .file = null,
-        .alignment = .@"1",
-        .prev = null,
-        .code = function_body.moveToUnmanaged(),
-        .relocs = relocations.moveToUnmanaged(),
-        .original_offset = 0,
-    };
+    const atom_index = try wasm.createAtom(loc.index, wasm.zig_object_index);
+    const atom = wasm.getAtomPtr(atom_index);
+    atom.code = function_body.moveToUnmanaged();
+    atom.relocs = relocations.moveToUnmanaged();
+    atom.size = @intCast(function_body.items.len);
     const symbol = loc.getSymbol(wasm);
     symbol.setFlag(.WASM_SYM_VISIBILITY_HIDDEN); // ensure function does not get exported
 
@@ -1878,7 +1861,6 @@ pub fn createFunction(
         break :idx index;
     };
     try wasm.appendAtomAtIndex(section_index, atom_index);
-    try wasm.symbol_atom.putNoClobber(gpa, loc, atom_index);
     try wasm.zigObjectPtr().?.atom_types.put(
         gpa,
         atom_index,

src/link/Wasm/Atom.zig

@@ -1,55 +1,36 @@
-const Atom = @This();
-
-const std = @import("std");
-const types = @import("types.zig");
-const Wasm = @import("../Wasm.zig");
-const Symbol = @import("Symbol.zig");
-
-const leb = std.leb;
-const log = std.log.scoped(.link);
-const mem = std.mem;
-const Allocator = mem.Allocator;
-
+/// Represents the index of the file this atom was generated from.
+/// This is 'null' when the atom was generated by a synthetic linker symbol.
+file: FileIndex,
 /// symbol index of the symbol representing this atom
 sym_index: u32,
 /// Size of the atom, used to calculate section sizes in the final binary
-size: u32,
+size: u32 = 0,
 /// List of relocations belonging to this atom
 relocs: std.ArrayListUnmanaged(types.Relocation) = .{},
 /// Contains the binary data of an atom, which can be non-relocated
 code: std.ArrayListUnmanaged(u8) = .{},
 /// For code this is 1, for data this is set to the highest value of all segments
-alignment: Wasm.Alignment,
+alignment: Wasm.Alignment = .@"1",
 /// Offset into the section where the atom lives, this already accounts
 /// for alignment.
-offset: u32,
+offset: u32 = 0,
 /// The original offset within the object file. This value is substracted from
 /// relocation offsets to determine where in the `data` to rewrite the value
-original_offset: u32,
-/// Represents the index of the file this atom was generated from.
-/// This is 'null' when the atom was generated by a Decl from Zig code.
-file: ?u16,
+original_offset: u32 = 0,
+/// Next atom in relation to this atom.
+/// When null, this atom is the last atom
+next: ?Atom.Index = null,
 /// Previous atom in relation to this atom.
 /// is null when this atom is the first in its order
-prev: ?Atom.Index,
+prev: ?Atom.Index = null,
 /// Contains atoms local to a decl, all managed by this `Atom`.
 /// When the parent atom is being freed, it will also do so for all local atoms.
 locals: std.ArrayListUnmanaged(Atom.Index) = .{},
 
-/// Alias to an unsigned 32-bit integer
+/// Alias to an unsigned 32-bit integer.
+// TODO: Make this a non-exhaustive enum.
 pub const Index = u32;
 
-/// Represents a default empty wasm `Atom`
-pub const empty: Atom = .{
-    .alignment = .@"1",
-    .file = null,
-    .offset = 0,
-    .prev = null,
-    .size = 0,
-    .sym_index = 0,
-    .original_offset = 0,
-};
-
 /// Frees all resources owned by this `Atom`.
 pub fn deinit(atom: *Atom, gpa: std.mem.Allocator) void {
     atom.relocs.deinit(gpa);
@@ -217,3 +198,14 @@ fn thombstone(atom: Atom, wasm: *const Wasm) ?i64 {
     }
     return null;
 }
+const leb = std.leb;
+const log = std.log.scoped(.link);
+const mem = std.mem;
+const std = @import("std");
+const types = @import("types.zig");
+
+const Allocator = mem.Allocator;
+const Atom = @This();
+const FileIndex = @import("file.zig").File.Index;
+const Symbol = @import("Symbol.zig");
+const Wasm = @import("../Wasm.zig");

src/link/Wasm/ZigObject.zig

@@ -4,6 +4,8 @@
 //! Think about this as fake in-memory Object file for the Zig module.
 
 path: []const u8,
+/// Index within the list of relocatable objects of the linker driver.
+index: File.Index,
 /// List of all `Decl` that are currently alive.
 /// Each index maps to the corresponding `Atom.Index`.
 decls: std.AutoHashMapUnmanaged(InternPool.DeclIndex, Atom.Index) = .{},
@@ -292,7 +294,7 @@ pub fn getOrCreateAtomForDecl(zig_object: *ZigObject, wasm_file: *Wasm, decl_ind
     const gop = try zig_object.decls.getOrPut(gpa, decl_index);
     if (!gop.found_existing) {
         const sym_index = try zig_object.allocateSymbol(gpa);
-        gop.value_ptr.* = try wasm_file.createAtom(sym_index);
+        gop.value_ptr.* = try wasm_file.createAtom(sym_index, zig_object.index);
         const mod = wasm_file.base.comp.module.?;
         const decl = mod.declPtr(decl_index);
         const full_name = mod.intern_pool.stringToSlice(try decl.getFullyQualifiedName(mod));
@@ -379,7 +381,7 @@ fn lowerConst(zig_object: *ZigObject, wasm_file: *Wasm, name: []const u8, tv: Ty
 
     // Create and initialize a new local symbol and atom
     const sym_index = try zig_object.allocateSymbol(gpa);
-    const atom_index = try wasm_file.createAtom(sym_index);
+    const atom_index = try wasm_file.createAtom(sym_index, zig_object.index);
     var value_bytes = std.ArrayList(u8).init(gpa);
     defer value_bytes.deinit();
 
@@ -432,7 +434,7 @@ pub fn getErrorTableSymbol(zig_object: *ZigObject, wasm_file: *Wasm) !u32 {
     // during `flush` when we know all possible error names.
     const gpa = wasm_file.base.comp.gpa;
     const sym_index = try zig_object.allocateSymbol(gpa);
-    const atom_index = try wasm_file.createAtom(sym_index);
+    const atom_index = try wasm_file.createAtom(sym_index, zig_object.index);
     const atom = wasm_file.getAtomPtr(atom_index);
     const slice_ty = Type.slice_const_u8_sentinel_0;
     const mod = wasm_file.base.comp.module.?;
@@ -468,7 +470,7 @@ fn populateErrorNameTable(zig_object: *ZigObject, wasm_file: *Wasm) !void {
     // we create a symbol for the entire region of error names. We then calculate
     // the pointers into the list using addends which are appended to the relocation.
     const names_sym_index = try zig_object.allocateSymbol(gpa);
-    const names_atom_index = try wasm_file.createAtom(names_sym_index);
+    const names_atom_index = try wasm_file.createAtom(names_sym_index, zig_object.index);
     const names_atom = wasm_file.getAtomPtr(names_atom_index);
     names_atom.alignment = .@"1";
     const sym_name = try zig_object.string_table.insert(gpa, "__zig_err_names");
@@ -1087,7 +1089,7 @@ pub fn createDebugSectionForIndex(zig_object: *ZigObject, wasm_file: *Wasm, inde
     try zig_object.appendDummySegment();
 
     const sym_index = try zig_object.allocateSymbol(gpa);
-    const atom_index = try wasm_file.createAtom(sym_index);
+    const atom_index = try wasm_file.createAtom(sym_index, zig_object.index);
     const atom = wasm_file.getAtomPtr(atom_index);
     zig_object.symbols.items[sym_index] = .{
         .tag = .section,
@@ -1161,6 +1163,7 @@ const types = @import("types.zig");
 const Air = @import("../../Air.zig");
 const Atom = @import("Atom.zig");
 const Dwarf = @import("../Dwarf.zig");
+const File = @import("file.zig").File;
 const InternPool = @import("../../InternPool.zig");
 const Liveness = @import("../../Liveness.zig");
 const Module = @import("../../Module.zig");