stage2: introduce CacheMode

The two CacheMode values are `whole` and `incremental`.
`incremental` is what we had before; `whole` is new.
Whole cache mode uses everything as inputs to the cache hash;
and when a hit occurs it skips everything including linking.
This is ideal for when source files change rarely and for backends that
do not have good incremental compilation support, for example
compiler-rt or libc compiled with LLVM with optimizations on.
This is the main motivation for the additional mode, so that we can have
LLVM-optimized compiler-rt/libc builds, without waiting for the LLVM
backend every single time Zig is invoked.

Incremental cache mode hashes only the input file path and a few target
options, intentionally relying on collisions to locate already-existing
build artifacts which can then be incrementally updated.

The bespoke logic for caching stage1 backend build artifacts
is removed since we now have a global caching mechanism for
when we want to cache the entire compilation, *including* linking.
Previously we had to get "creative" with libs.txt and a special
byte in the hash id to communicate flags, so that when the cached
artifacts were re-linked, we had this information from stage1
even though we didn't actually run it. Now that `CacheMode.whole`
includes linking, this extra information does not need to be
preserved for cache hits. So although this changeset introduces
complexity, it also removes complexity.

The main trickiness here comes from the inherent differences between the
two modes: `incremental` wants a directory immediately to operate on,
while `whole` doesn't know the output directory until the compilation is
complete. This commit deals with this problem mostly inside `update()`,
where, on a cache miss, it replaces `zig_cache_artifact_directory` with a
temporary directory, and then renames it into place once the compilation is
complete.

Items remaining before this branch can be merged:

* [ ] make sure these things make it into the cache manifest:
  - @import files
  - @embedFile files
  - we already add dep files from c but make sure the main .c files make
    it in there too, not just the included files

* [ ] double check that the emit paths of other things besides the binary
  are working correctly.

* [ ] test `-fno-emit-bin` + `-fstage1`
* [ ] test `-femit-bin=foo` + `-fstage1`

* [ ] implib emit directory copies bin_file_emit directory in create() and needs
  to be adjusted to be overridden as well.

* [ ] make sure emit-h is handled correctly in the cache hash
* [ ] Cache: detect duplicate files added to the manifest

Some preliminary performance measurements of wall clock time and
peak RSS used:

stage1 behavior (1077 tests), llvm backend, release build:
 * cold global cache: 4.6s, 1.1 GiB
 * warm global cache: 3.4s, 980 MiB

stage2 master branch behavior (575 tests), llvm backend, release build:
 * cold global cache: 0.62s, 191 MiB
 * warm global cache: 0.40s, 128 MiB

stage2 this branch behavior (575 tests), llvm backend, release build:
 * cold global cache: 0.62s, 179 MiB
 * warm global cache: 0.27s, 90 MiB

14 files changed, 401 insertions, 218 deletions

diff --git a/src/Compilation.zig b/src/Compilation.zig
index cd4794554e..8afb373699 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -41,8 +41,8 @@ gpa: Allocator,
 arena_state: std.heap.ArenaAllocator.State,
 bin_file: *link.File,
 c_object_table: std.AutoArrayHashMapUnmanaged(*CObject, void) = .{},
-stage1_lock: ?Cache.Lock = null,
-stage1_cache_manifest: *Cache.Manifest = undefined,
+/// This is a pointer to a local variable inside `update()`.
+whole_cache_manifest: ?*Cache.Manifest = null,
 
 link_error_flags: link.File.ErrorFlags = .{},
 
@@ -98,6 +98,9 @@ clang_argv: []const []const u8,
 cache_parent: *Cache,
 /// Path to own executable for invoking `zig clang`.
 self_exe_path: ?[]const u8,
+/// null means -fno-emit-bin. Contains the basename of the
+/// outputted binary file in case we don't know the directory yet.
+whole_bin_basename: ?[]const u8,
 zig_lib_directory: Directory,
 local_cache_directory: Directory,
 global_cache_directory: Directory,
@@ -612,6 +615,15 @@ pub const Directory = struct {
             return std.fs.path.joinZ(allocator, paths);
         }
     }
+
+    /// Whether or not the handle should be closed, or the path should be freed
+    /// is determined by usage, however this function is provided for convenience
+    /// if it happens to be what the caller needs.
+    pub fn closeAndFree(self: *Directory, gpa: Allocator) void {
+        self.handle.close();
+        if (self.path) |p| gpa.free(p);
+        self.* = undefined;
+    }
 };
 
 pub const EmitLoc = struct {
@@ -631,6 +643,7 @@ pub const ClangPreprocessorMode = enum {
 };
 
 pub const SystemLib = link.SystemLib;
+pub const CacheMode = link.CacheMode;
 
 pub const InitOptions = struct {
     zig_lib_directory: Directory,
@@ -668,6 +681,7 @@ pub const InitOptions = struct {
     /// is externally modified - essentially anything other than zig-cache - then
     /// this flag would be set to disable this machinery to avoid false positives.
     disable_lld_caching: bool = false,
+    cache_mode: CacheMode = .incremental,
     object_format: ?std.Target.ObjectFormat = null,
     optimize_mode: std.builtin.Mode = .Debug,
     keep_source_files_loaded: bool = false,
@@ -885,6 +899,8 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             break :blk build_options.is_stage1;
         };
 
+        const cache_mode = if (use_stage1) CacheMode.whole else options.cache_mode;
+
         // Make a decision on whether to use LLVM or our own backend.
         const use_llvm = build_options.have_llvm and blk: {
             if (options.use_llvm) |explicit|
@@ -1219,18 +1235,26 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             // modified between incremental updates.
             var hash = cache.hash;
 
-            // Here we put the root source file path name, but *not* with addFile. We want the
-            // hash to be the same regardless of the contents of the source file, because
-            // incremental compilation will handle it, but we do want to namespace different
-            // source file names because they are likely different compilations and therefore this
-            // would be likely to cause cache hits.
-            hash.addBytes(main_pkg.root_src_path);
-            hash.addOptionalBytes(main_pkg.root_src_directory.path);
-            {
-                var local_arena = std.heap.ArenaAllocator.init(gpa);
-                defer local_arena.deinit();
-                var seen_table = std.AutoHashMap(*Package, void).init(local_arena.allocator());
-                try addPackageTableToCacheHash(&hash, &local_arena, main_pkg.table, &seen_table, .path_bytes);
+            switch (cache_mode) {
+                .incremental => {
+                    // Here we put the root source file path name, but *not* with addFile.
+                    // We want the hash to be the same regardless of the contents of the
+                    // source file, because incremental compilation will handle it, but we
+                    // do want to namespace different source file names because they are
+                    // likely different compilations and therefore this would be likely to
+                    // cause cache hits.
+                    hash.addBytes(main_pkg.root_src_path);
+                    hash.addOptionalBytes(main_pkg.root_src_directory.path);
+                    {
+                        var seen_table = std.AutoHashMap(*Package, void).init(arena);
+                        try addPackageTableToCacheHash(&hash, &arena_allocator, main_pkg.table, &seen_table, .path_bytes);
+                    }
+                },
+                .whole => {
+                    // In this case, we postpone adding the input source file until
+                    // we create the cache manifest, in update(), because we want to
+                    // track it and packages as files.
+                },
             }
             hash.add(valgrind);
             hash.add(single_threaded);
@@ -1238,9 +1262,35 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             hash.add(use_llvm);
             hash.add(dll_export_fns);
             hash.add(options.is_test);
+            hash.add(options.test_evented_io);
+            hash.addOptionalBytes(options.test_filter);
+            hash.addOptionalBytes(options.test_name_prefix);
             hash.add(options.skip_linker_dependencies);
             hash.add(options.parent_compilation_link_libc);
 
+            // In the case of incremental cache mode, this `zig_cache_artifact_directory`
+            // is computed based on a hash of non-linker inputs, and it is where all
+            // build artifacts are stored (even while in-progress).
+            //
+            // For whole cache mode, it is still used for builtin.zig so that the file
+            // path to builtin.zig can remain consistent during a debugging session at
+            // runtime. However, we don't know where to put outputs from the linker
+            // or stage1 backend object files until the final cache hash, which is available
+            // after the compilation is complete.
+            //
+            // Therefore, in whole cache mode, we additionally create a temporary cache
+            // directory for these two kinds of build artifacts, and then rename it
+            // into place after the final hash is known. However, we don't want
+            // to create the temporary directory here, because in the case of a cache hit,
+            // this would have been wasted syscalls to make the directory and then not
+            // use it (or delete it).
+            //
+            // In summary, for whole cache mode, we simulate `-fno-emit-bin` in this
+            // function, and `zig_cache_artifact_directory` is *wrong* except for builtin.zig,
+            // and then at the beginning of `update()` when we find out whether we need
+            // a temporary directory, we patch up all the places that the incorrect
+            // `zig_cache_artifact_directory` was passed to various components of the compiler.
+
             const digest = hash.final();
             const artifact_sub_dir = try std.fs.path.join(arena, &[_][]const u8{ "o", &digest });
             var artifact_dir = try options.local_cache_directory.handle.makeOpenPath(artifact_sub_dir, .{});
@@ -1374,6 +1424,11 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
                 };
             }
 
+            switch (cache_mode) {
+                .whole => break :blk null,
+                .incremental => {},
+            }
+
             if (module) |zm| {
                 break :blk link.Emit{
                     .directory = zm.zig_cache_artifact_directory,
@@ -1425,6 +1480,18 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             };
         };
 
+        // This is so that when doing `CacheMode.whole`, the mechanism in update()
+        // can use it for communicating the result directory via `bin_file.emit`.
+        // This is used to distinguish between -fno-emit-bin and -femit-bin
+        // for `CacheMode.whole`.
+        const whole_bin_basename: ?[]const u8 = if (options.emit_bin) |x|
+            if (x.directory == null)
+                x.basename
+            else
+                null
+        else
+            null;
+
         var system_libs: std.StringArrayHashMapUnmanaged(SystemLib) = .{};
         errdefer system_libs.deinit(gpa);
         try system_libs.ensureTotalCapacity(gpa, options.system_lib_names.len);
@@ -1512,7 +1579,8 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             .skip_linker_dependencies = options.skip_linker_dependencies,
             .parent_compilation_link_libc = options.parent_compilation_link_libc,
             .each_lib_rpath = options.each_lib_rpath orelse options.is_native_os,
-            .disable_lld_caching = options.disable_lld_caching,
+            .cache_mode = cache_mode,
+            .disable_lld_caching = options.disable_lld_caching or cache_mode == .whole,
             .subsystem = options.subsystem,
             .is_test = options.is_test,
             .wasi_exec_model = wasi_exec_model,
@@ -1529,6 +1597,7 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
             .local_cache_directory = options.local_cache_directory,
             .global_cache_directory = options.global_cache_directory,
             .bin_file = bin_file,
+            .whole_bin_basename = whole_bin_basename,
             .emit_asm = options.emit_asm,
             .emit_llvm_ir = options.emit_llvm_ir,
             .emit_llvm_bc = options.emit_llvm_bc,
@@ -1725,20 +1794,11 @@ pub fn create(gpa: Allocator, options: InitOptions) !*Compilation {
     return comp;
 }
 
-fn releaseStage1Lock(comp: *Compilation) void {
-    if (comp.stage1_lock) |*lock| {
-        lock.release();
-        comp.stage1_lock = null;
-    }
-}
-
 pub fn destroy(self: *Compilation) void {
     const optional_module = self.bin_file.options.module;
     self.bin_file.destroy();
     if (optional_module) |module| module.deinit();
 
-    self.releaseStage1Lock();
-
     const gpa = self.gpa;
     self.work_queue.deinit();
     self.anon_work_queue.deinit();
@@ -1815,22 +1875,135 @@ pub fn getTarget(self: Compilation) Target {
     return self.bin_file.options.target;
 }
 
+fn restorePrevZigCacheArtifactDirectory(comp: *Compilation, directory: *Directory) void {
+    if (directory.path) |p| comp.gpa.free(p);
+
+    // Restore the Module's previous zig_cache_artifact_directory
+    // This is only for cleanup purposes; Module.deinit calls close
+    // on the handle of zig_cache_artifact_directory.
+    if (comp.bin_file.options.module) |module| {
+        const builtin_pkg = module.main_pkg.table.get("builtin").?;
+        module.zig_cache_artifact_directory = builtin_pkg.root_src_directory;
+    }
+}
+
+fn cleanupTmpArtifactDirectory(
+    comp: *Compilation,
+    tmp_artifact_directory: *?Directory,
+    tmp_dir_sub_path: []const u8,
+) void {
+    comp.gpa.free(tmp_dir_sub_path);
+    if (tmp_artifact_directory.*) |*directory| {
+        directory.handle.close();
+        restorePrevZigCacheArtifactDirectory(comp, directory);
+    }
+}
+
 /// Detect changes to source files, perform semantic analysis, and update the output files.
-pub fn update(self: *Compilation) !void {
+pub fn update(comp: *Compilation) !void {
     const tracy_trace = trace(@src());
     defer tracy_trace.end();
 
-    self.clearMiscFailures();
+    comp.clearMiscFailures();
+
+    var man: Cache.Manifest = undefined;
+    defer if (comp.whole_cache_manifest != null) man.deinit();
+
+    var tmp_dir_sub_path: []const u8 = &.{};
+    var tmp_artifact_directory: ?Directory = null;
+    defer cleanupTmpArtifactDirectory(comp, &tmp_artifact_directory, tmp_dir_sub_path);
+
+    // If using the whole caching strategy, we check for *everything* up front, including
+    // C source files.
+    if (comp.bin_file.options.cache_mode == .whole) {
+        // We are about to obtain this lock, so here we give other processes a chance first.
+        comp.bin_file.releaseLock();
+
+        man = comp.cache_parent.obtain();
+        try comp.addNonIncrementalStuffToCacheManifest(&man);
+
+        const is_hit = man.hit() catch |err| {
+            // TODO properly bubble these up instead of emitting a warning
+            const i = man.failed_file_index orelse return err;
+            const file_path = man.files.items[i].path orelse return err;
+            std.log.warn("{s}: {s}", .{ @errorName(err), file_path });
+            return err;
+        };
+        if (is_hit) {
+            const digest = man.final();
+
+            // Communicate the output binary location to parent Compilations.
+            if (comp.whole_bin_basename) |basename| {
+                const new_sub_path = try std.fs.path.join(comp.gpa, &.{
+                    "o", &digest, basename,
+                });
+                if (comp.bin_file.options.emit) |emit| {
+                    comp.gpa.free(emit.sub_path);
+                }
+                comp.bin_file.options.emit = .{
+                    .directory = comp.local_cache_directory,
+                    .sub_path = new_sub_path,
+                };
+            }
+
+            comp.emitOthers();
+
+            assert(comp.bin_file.lock == null);
+            comp.bin_file.lock = man.toOwnedLock();
+            return;
+        }
+        comp.whole_cache_manifest = &man;
+
+        // Initialize `bin_file.emit` with a temporary Directory so that compilation can
+        // continue on the same path as incremental, using the temporary Directory.
+        tmp_artifact_directory = d: {
+            const s = std.fs.path.sep_str;
+            const rand_int = std.crypto.random.int(u64);
+
+            tmp_dir_sub_path = try std.fmt.allocPrint(comp.gpa, "tmp" ++ s ++ "{x}", .{rand_int});
+
+            const path = try comp.local_cache_directory.join(comp.gpa, &.{tmp_dir_sub_path});
+            errdefer comp.gpa.free(path);
+
+            const handle = try comp.local_cache_directory.handle.makeOpenPath(tmp_dir_sub_path, .{});
+            errdefer handle.close();
+
+            break :d .{
+                .path = path,
+                .handle = handle,
+            };
+        };
+
+        // This updates the output directory for stage1 backend and linker outputs.
+        if (comp.bin_file.options.module) |module| {
+            module.zig_cache_artifact_directory = tmp_artifact_directory.?;
+        }
+
+        // This resets the link.File to operate as if we called openPath() in create()
+        // instead of simulating -fno-emit-bin.
+        var options = comp.bin_file.options;
+        if (comp.whole_bin_basename) |basename| {
+            if (options.emit) |emit| {
+                comp.gpa.free(emit.sub_path);
+            }
+            options.emit = .{
+                .directory = tmp_artifact_directory.?,
+                .sub_path = basename,
+            };
+        }
+        comp.bin_file.destroy();
+        comp.bin_file = try link.File.openPath(comp.gpa, options);
+    }
 
     // For compiling C objects, we rely on the cache hash system to avoid duplicating work.
     // Add a Job for each C object.
-    try self.c_object_work_queue.ensureUnusedCapacity(self.c_object_table.count());
-    for (self.c_object_table.keys()) |key| {
-        self.c_object_work_queue.writeItemAssumeCapacity(key);
+    try comp.c_object_work_queue.ensureUnusedCapacity(comp.c_object_table.count());
+    for (comp.c_object_table.keys()) |key| {
+        comp.c_object_work_queue.writeItemAssumeCapacity(key);
     }
 
-    const use_stage1 = build_options.is_stage1 and self.bin_file.options.use_stage1;
-    if (self.bin_file.options.module) |module| {
+    const use_stage1 = build_options.is_stage1 and comp.bin_file.options.use_stage1;
+    if (comp.bin_file.options.module) |module| {
         module.compile_log_text.shrinkAndFree(module.gpa, 0);
         module.generation += 1;
 
@@ -1845,7 +2018,7 @@ pub fn update(self: *Compilation) !void {
         // import_table here.
         // Likewise, in the case of `zig test`, the test runner is the root source file,
         // and so there is nothing to import the main file.
-        if (use_stage1 or self.bin_file.options.is_test) {
+        if (use_stage1 or comp.bin_file.options.is_test) {
             _ = try module.importPkg(module.main_pkg);
         }
 
@@ -1854,34 +2027,34 @@ pub fn update(self: *Compilation) !void {
         // to update it.
         // We still want AstGen work items for stage1 so that we expose compile errors
         // that are implemented in stage2 but not stage1.
-        try self.astgen_work_queue.ensureUnusedCapacity(module.import_table.count());
+        try comp.astgen_work_queue.ensureUnusedCapacity(module.import_table.count());
         for (module.import_table.values()) |value| {
-            self.astgen_work_queue.writeItemAssumeCapacity(value);
+            comp.astgen_work_queue.writeItemAssumeCapacity(value);
         }
 
         if (!use_stage1) {
             // Put a work item in for checking if any files used with `@embedFile` changed.
             {
-                try self.embed_file_work_queue.ensureUnusedCapacity(module.embed_table.count());
+                try comp.embed_file_work_queue.ensureUnusedCapacity(module.embed_table.count());
                 var it = module.embed_table.iterator();
                 while (it.next()) |entry| {
                     const embed_file = entry.value_ptr.*;
-                    self.embed_file_work_queue.writeItemAssumeCapacity(embed_file);
+                    comp.embed_file_work_queue.writeItemAssumeCapacity(embed_file);
                 }
             }
 
-            try self.work_queue.writeItem(.{ .analyze_pkg = std_pkg });
-            if (self.bin_file.options.is_test) {
-                try self.work_queue.writeItem(.{ .analyze_pkg = module.main_pkg });
+            try comp.work_queue.writeItem(.{ .analyze_pkg = std_pkg });
+            if (comp.bin_file.options.is_test) {
+                try comp.work_queue.writeItem(.{ .analyze_pkg = module.main_pkg });
             }
         }
     }
 
-    try self.performAllTheWork();
+    try comp.performAllTheWork();
 
     if (!use_stage1) {
-        if (self.bin_file.options.module) |module| {
-            if (self.bin_file.options.is_test and self.totalErrorCount() == 0) {
+        if (comp.bin_file.options.module) |module| {
+            if (comp.bin_file.options.is_test and comp.totalErrorCount() == 0) {
                 // The `test_functions` decl has been intentionally postponed until now,
                 // at which point we must populate it with the list of test functions that
                 // have been discovered and not filtered out.
@@ -1910,39 +2083,184 @@ pub fn update(self: *Compilation) !void {
         }
     }
 
-    if (self.totalErrorCount() != 0) {
+    if (comp.totalErrorCount() != 0) {
         // Skip flushing.
-        self.link_error_flags = .{};
+        comp.link_error_flags = .{};
         return;
     }
 
     // This is needed before reading the error flags.
-    try self.bin_file.flush(self);
-    self.link_error_flags = self.bin_file.errorFlags();
+    try comp.bin_file.flush(comp);
+    comp.link_error_flags = comp.bin_file.errorFlags();
 
     if (!use_stage1) {
-        if (self.bin_file.options.module) |module| {
+        if (comp.bin_file.options.module) |module| {
             try link.File.C.flushEmitH(module);
         }
     }
 
     // Flush takes care of -femit-bin, but we still have -femit-llvm-ir, -femit-llvm-bc, and
     // -femit-asm to handle, in the case of C objects.
-    self.emitOthers();
+    comp.emitOthers();
 
     // If there are any errors, we anticipate the source files being loaded
     // to report error messages. Otherwise we unload all source files to save memory.
     // The ZIR needs to stay loaded in memory because (1) Decl objects contain references
     // to it, and (2) generic instantiations, comptime calls, inline calls will need
     // to reference the ZIR.
-    if (self.totalErrorCount() == 0 and !self.keep_source_files_loaded) {
-        if (self.bin_file.options.module) |module| {
+    if (!comp.keep_source_files_loaded) {
+        if (comp.bin_file.options.module) |module| {
             for (module.import_table.values()) |file| {
-                file.unloadTree(self.gpa);
-                file.unloadSource(self.gpa);
+                file.unloadTree(comp.gpa);
+                file.unloadSource(comp.gpa);
+            }
+        }
+    }
+
+    if (comp.whole_cache_manifest != null) {
+        const digest = man.final();
+
+        // Rename the temporary directory into place.
+        var directory = tmp_artifact_directory.?;
+        tmp_artifact_directory = null;
+
+        directory.handle.close();
+        defer restorePrevZigCacheArtifactDirectory(comp, &directory);
+
+        const o_sub_path = try std.fs.path.join(comp.gpa, &[_][]const u8{ "o", &digest });
+        defer comp.gpa.free(o_sub_path);
+
+        try std.fs.rename(
+            comp.local_cache_directory.handle,
+            tmp_dir_sub_path,
+            comp.local_cache_directory.handle,
+            o_sub_path,
+        );
+
+        // Failure here only means an unnecessary cache miss.
+        man.writeManifest() catch |err| {
+            log.warn("failed to write cache manifest: {s}", .{@errorName(err)});
+        };
+
+        // Communicate the output binary location to parent Compilations.
+        if (comp.whole_bin_basename) |basename| {
+            comp.bin_file.options.emit = .{
+                .directory = comp.local_cache_directory,
+                .sub_path = try std.fs.path.join(comp.gpa, &.{ "o", &digest, basename }),
+            };
+        }
+
+        assert(comp.bin_file.lock == null);
+        comp.bin_file.lock = man.toOwnedLock();
+        return;
+    }
+}
+
+/// This is only observed at compile-time and used to emit a compile error
+/// to remind the programmer to update multiple related pieces of code that
+/// are in different locations. Bump this number when adding or deleting
+/// anything from the link cache manifest.
+pub const link_hash_implementation_version = 1;
+
+fn addNonIncrementalStuffToCacheManifest(comp: *Compilation, man: *Cache.Manifest) !void {
+    const gpa = comp.gpa;
+    const target = comp.getTarget();
+
+    var arena_allocator = std.heap.ArenaAllocator.init(gpa);
+    errdefer arena_allocator.deinit();
+    const arena = arena_allocator.allocator();
+
+    comptime assert(link_hash_implementation_version == 1);
+
+    if (comp.bin_file.options.module) |mod| {
+        const main_zig_file = try mod.main_pkg.root_src_directory.join(arena, &[_][]const u8{
+            mod.main_pkg.root_src_path,
+        });
+        _ = try man.addFile(main_zig_file, null);
+        {
+            var seen_table = std.AutoHashMap(*Package, void).init(arena);
+
+            // Skip builtin.zig; it is useless as an input, and we don't want to have to
+            // write it before checking for a cache hit.
+            const builtin_pkg = mod.main_pkg.table.get("builtin").?;
+            try seen_table.put(builtin_pkg, {});
+
+            try addPackageTableToCacheHash(&man.hash, &arena_allocator, mod.main_pkg.table, &seen_table, .{ .files = man });
+        }
+    }
+
+    try man.addOptionalFile(comp.bin_file.options.linker_script);
+    try man.addOptionalFile(comp.bin_file.options.version_script);
+    try man.addListOfFiles(comp.bin_file.options.objects);
+
+    for (comp.c_object_table.keys()) |key| {
+        _ = try man.addFile(key.src.src_path, null);
+        man.hash.addListOfBytes(key.src.extra_flags);
+    }
+
+    man.hash.addOptionalEmitLoc(comp.emit_asm);
+    man.hash.addOptionalEmitLoc(comp.emit_llvm_ir);
+    man.hash.addOptionalEmitLoc(comp.emit_llvm_bc);
+    man.hash.addOptionalEmitLoc(comp.emit_analysis);
+    man.hash.addOptionalEmitLoc(comp.emit_docs);
+
+    man.hash.addListOfBytes(comp.clang_argv);
+
+    man.hash.addOptional(comp.bin_file.options.stack_size_override);
+    man.hash.addOptional(comp.bin_file.options.image_base_override);
+    man.hash.addOptional(comp.bin_file.options.gc_sections);
+    man.hash.add(comp.bin_file.options.eh_frame_hdr);
+    man.hash.add(comp.bin_file.options.emit_relocs);
+    man.hash.add(comp.bin_file.options.rdynamic);
+    man.hash.addListOfBytes(comp.bin_file.options.lib_dirs);
+    man.hash.addListOfBytes(comp.bin_file.options.rpath_list);
+    man.hash.add(comp.bin_file.options.each_lib_rpath);
+    man.hash.add(comp.bin_file.options.skip_linker_dependencies);
+    man.hash.add(comp.bin_file.options.z_nodelete);
+    man.hash.add(comp.bin_file.options.z_notext);
+    man.hash.add(comp.bin_file.options.z_defs);
+    man.hash.add(comp.bin_file.options.z_origin);
+    man.hash.add(comp.bin_file.options.z_noexecstack);
+    man.hash.add(comp.bin_file.options.z_now);
+    man.hash.add(comp.bin_file.options.z_relro);
+    man.hash.add(comp.bin_file.options.include_compiler_rt);
+    if (comp.bin_file.options.link_libc) {
+        man.hash.add(comp.bin_file.options.libc_installation != null);
+        if (comp.bin_file.options.libc_installation) |libc_installation| {
+            man.hash.addBytes(libc_installation.crt_dir.?);
+            if (target.abi == .msvc) {
+                man.hash.addBytes(libc_installation.msvc_lib_dir.?);
+                man.hash.addBytes(libc_installation.kernel32_lib_dir.?);
             }
         }
+        man.hash.addOptionalBytes(comp.bin_file.options.dynamic_linker);
     }
+    man.hash.addOptionalBytes(comp.bin_file.options.soname);
+    man.hash.addOptional(comp.bin_file.options.version);
+    link.hashAddSystemLibs(&man.hash, comp.bin_file.options.system_libs);
+    man.hash.addOptional(comp.bin_file.options.allow_shlib_undefined);
+    man.hash.add(comp.bin_file.options.bind_global_refs_locally);
+    man.hash.add(comp.bin_file.options.tsan);
+    man.hash.addOptionalBytes(comp.bin_file.options.sysroot);
+    man.hash.add(comp.bin_file.options.linker_optimization);
+
+    // WASM specific stuff
+    man.hash.add(comp.bin_file.options.import_memory);
+    man.hash.addOptional(comp.bin_file.options.initial_memory);
+    man.hash.addOptional(comp.bin_file.options.max_memory);
+    man.hash.addOptional(comp.bin_file.options.global_base);
+
+    // Mach-O specific stuff
+    man.hash.addListOfBytes(comp.bin_file.options.framework_dirs);
+    man.hash.addListOfBytes(comp.bin_file.options.frameworks);
+
+    // COFF specific stuff
+    man.hash.addOptional(comp.bin_file.options.subsystem);
+    man.hash.add(comp.bin_file.options.tsaware);
+    man.hash.add(comp.bin_file.options.nxcompat);
+    man.hash.add(comp.bin_file.options.dynamicbase);
+    man.hash.addOptional(comp.bin_file.options.major_subsystem_version);
+    man.hash.addOptional(comp.bin_file.options.minor_subsystem_version);
 }
 
 fn emitOthers(comp: *Compilation) void {
@@ -2988,7 +3306,9 @@ pub fn cImport(comp: *Compilation, c_src: []const u8) !CImportResult {
 
         const dep_basename = std.fs.path.basename(out_dep_path);
         try man.addDepFilePost(zig_cache_tmp_dir, dep_basename);
-        if (build_options.is_stage1 and comp.bin_file.options.use_stage1) try comp.stage1_cache_manifest.addDepFilePost(zig_cache_tmp_dir, dep_basename);
+        if (comp.whole_cache_manifest) |whole_cache_manifest| {
+            try whole_cache_manifest.addDepFilePost(zig_cache_tmp_dir, dep_basename);
+        }
 
         const digest = man.final();
         const o_sub_path = try std.fs.path.join(arena, &[_][]const u8{ "o", &digest });
@@ -3351,13 +3671,13 @@ fn updateCObject(comp: *Compilation, c_object: *CObject, c_obj_prog_node: *std.P
     };
 }
 
-pub fn tmpFilePath(comp: *Compilation, arena: Allocator, suffix: []const u8) error{OutOfMemory}![]const u8 {
+pub fn tmpFilePath(comp: *Compilation, ally: Allocator, suffix: []const u8) error{OutOfMemory}![]const u8 {
     const s = std.fs.path.sep_str;
     const rand_int = std.crypto.random.int(u64);
     if (comp.local_cache_directory.path) |p| {
-        return std.fmt.allocPrint(arena, "{s}" ++ s ++ "tmp" ++ s ++ "{x}-{s}", .{ p, rand_int, suffix });
+        return std.fmt.allocPrint(ally, "{s}" ++ s ++ "tmp" ++ s ++ "{x}-{s}", .{ p, rand_int, suffix });
     } else {
-        return std.fmt.allocPrint(arena, "tmp" ++ s ++ "{x}-{s}", .{ rand_int, suffix });
+        return std.fmt.allocPrint(ally, "tmp" ++ s ++ "{x}-{s}", .{ rand_int, suffix });
     }
 }
 
@@ -4424,6 +4744,7 @@ fn buildOutputFromZig(
         .global_cache_directory = comp.global_cache_directory,
         .local_cache_directory = comp.global_cache_directory,
         .zig_lib_directory = comp.zig_lib_directory,
+        .cache_mode = .whole,
         .target = target,
         .root_name = root_name,
         .main_pkg = &main_pkg,
@@ -4501,10 +4822,7 @@ fn updateStage1Module(comp: *Compilation, main_progress_node: *std.Progress.Node
         mod.main_pkg.root_src_path,
     });
     const zig_lib_dir = comp.zig_lib_directory.path.?;
-    const builtin_zig_path = try directory.join(arena, &[_][]const u8{"builtin.zig"});
     const target = comp.getTarget();
-    const id_symlink_basename = "stage1.id";
-    const libs_txt_basename = "libs.txt";
 
     // The include_compiler_rt stored in the bin file options here means that we need
     // compiler-rt symbols *somehow*. However, in the context of using the stage1 backend
@@ -4516,115 +4834,6 @@ fn updateStage1Module(comp: *Compilation, main_progress_node: *std.Progress.Node
     const include_compiler_rt = comp.bin_file.options.output_mode == .Obj and
         comp.bin_file.options.include_compiler_rt;
 
-    // We are about to obtain this lock, so here we give other processes a chance first.
-    comp.releaseStage1Lock();
-
-    // Unlike with the self-hosted Zig module, stage1 does not support incremental compilation,
-    // so we input all the zig source files into the cache hash system. We're going to keep
-    // the artifact directory the same, however, so we take the same strategy as linking
-    // does where we have a file which specifies the hash of the output directory so that we can
-    // skip the expensive compilation step if the hash matches.
-    var man = comp.cache_parent.obtain();
-    defer man.deinit();
-
-    _ = try man.addFile(main_zig_file, null);
-    {
-        var seen_table = std.AutoHashMap(*Package, void).init(arena_allocator.allocator());
-        try addPackageTableToCacheHash(&man.hash, &arena_allocator, mod.main_pkg.table, &seen_table, .{ .files = &man });
-    }
-    man.hash.add(comp.bin_file.options.valgrind);
-    man.hash.add(comp.bin_file.options.single_threaded);
-    man.hash.add(target.os.getVersionRange());
-    man.hash.add(comp.bin_file.options.dll_export_fns);
-    man.hash.add(comp.bin_file.options.function_sections);
-    man.hash.add(include_compiler_rt);
-    man.hash.add(comp.bin_file.options.is_test);
-    man.hash.add(comp.bin_file.options.emit != null);
-    man.hash.add(mod.emit_h != null);
-    if (mod.emit_h) |emit_h| {
-        man.hash.addEmitLoc(emit_h.loc);
-    }
-    man.hash.addOptionalEmitLoc(comp.emit_asm);
-    man.hash.addOptionalEmitLoc(comp.emit_llvm_ir);
-    man.hash.addOptionalEmitLoc(comp.emit_llvm_bc);
-    man.hash.addOptionalEmitLoc(comp.emit_analysis);
-    man.hash.addOptionalEmitLoc(comp.emit_docs);
-    man.hash.add(comp.test_evented_io);
-    man.hash.addOptionalBytes(comp.test_filter);
-    man.hash.addOptionalBytes(comp.test_name_prefix);
-    man.hash.addListOfBytes(comp.clang_argv);
-
-    // Capture the state in case we come back from this branch where the hash doesn't match.
-    const prev_hash_state = man.hash.peekBin();
-    const input_file_count = man.files.items.len;
-
-    const hit = man.hit() catch |err| {
-        const i = man.failed_file_index orelse return err;
-        const file_path = man.files.items[i].path orelse return err;
-        fatal("unable to build stage1 zig object: {s}: {s}", .{ @errorName(err), file_path });
-    };
-    if (hit) {
-        const digest = man.final();
-
-        // We use an extra hex-encoded byte here to store some flags.
-        var prev_digest_buf: [digest.len + 2]u8 = undefined;
-        const prev_digest: []u8 = Cache.readSmallFile(
-            directory.handle,
-            id_symlink_basename,
-            &prev_digest_buf,
-        ) catch |err| blk: {
-            log.debug("stage1 {s} new_digest={s} error: {s}", .{
-                mod.main_pkg.root_src_path,
-                std.fmt.fmtSliceHexLower(&digest),
-                @errorName(err),
-            });
-            // Handle this as a cache miss.
-            break :blk prev_digest_buf[0..0];
-        };
-        if (prev_digest.len >= digest.len + 2) hit: {
-            if (!mem.eql(u8, prev_digest[0..digest.len], &digest))
-                break :hit;
-
-            log.debug("stage1 {s} digest={s} match - skipping invocation", .{
-                mod.main_pkg.root_src_path,
-                std.fmt.fmtSliceHexLower(&digest),
-            });
-            var flags_bytes: [1]u8 = undefined;
-            _ = std.fmt.hexToBytes(&flags_bytes, prev_digest[digest.len..]) catch {
-                log.warn("bad cache stage1 digest: '{s}'", .{std.fmt.fmtSliceHexLower(prev_digest)});
-                break :hit;
-            };
-
-            if (directory.handle.readFileAlloc(comp.gpa, libs_txt_basename, 10 * 1024 * 1024)) |libs_txt| {
-                var it = mem.tokenize(u8, libs_txt, "\n");
-                while (it.next()) |lib_name| {
-                    try comp.stage1AddLinkLib(lib_name);
-                }
-            } else |err| switch (err) {
-                error.FileNotFound => {}, // That's OK, it just means 0 libs.
-                else => {
-                    log.warn("unable to read cached list of link libs: {s}", .{@errorName(err)});
-                    break :hit;
-                },
-            }
-            comp.stage1_lock = man.toOwnedLock();
-            mod.stage1_flags = @bitCast(@TypeOf(mod.stage1_flags), flags_bytes[0]);
-            return;
-        }
-        log.debug("stage1 {s} prev_digest={s} new_digest={s}", .{
-            mod.main_pkg.root_src_path,
-            std.fmt.fmtSliceHexLower(prev_digest),
-            std.fmt.fmtSliceHexLower(&digest),
-        });
-        man.unhit(prev_hash_state, input_file_count);
-    }
-
-    // We are about to change the output file to be different, so we invalidate the build hash now.
-    directory.handle.deleteFile(id_symlink_basename) catch |err| switch (err) {
-        error.FileNotFound => {},
-        else => |e| return e,
-    };
-
     const stage2_target = try arena.create(stage1.Stage2Target);
     stage2_target.* = .{
         .arch = @enumToInt(target.cpu.arch) + 1, // skip over ZigLLVM_UnknownArch
@@ -4637,9 +4846,9 @@ fn updateStage1Module(comp: *Compilation, main_progress_node: *std.Progress.Node
         .llvm_target_abi = if (target_util.llvmMachineAbi(target)) |s| s.ptr else null,
     };
 
-    comp.stage1_cache_manifest = &man;
-
     const main_pkg_path = mod.main_pkg.root_src_directory.path orelse "";
+    const builtin_pkg = mod.main_pkg.table.get("builtin").?;
+    const builtin_zig_path = try builtin_pkg.root_src_directory.join(arena, &.{builtin_pkg.root_src_path});
 
     const stage1_module = stage1.create(
         @enumToInt(comp.bin_file.options.optimize_mode),
@@ -4740,19 +4949,8 @@ fn updateStage1Module(comp: *Compilation, main_progress_node: *std.Progress.Node
         .have_dllmain_crt_startup = false,
     };
 
-    const inferred_lib_start_index = comp.bin_file.options.system_libs.count();
     stage1_module.build_object();
 
-    if (comp.bin_file.options.system_libs.count() > inferred_lib_start_index) {
-        // We need to save the inferred link libs to the cache, otherwise if we get a cache hit
-        // next time we will be missing these libs.
-        var libs_txt = std.ArrayList(u8).init(arena);
-        for (comp.bin_file.options.system_libs.keys()[inferred_lib_start_index..]) |key| {
-            try libs_txt.writer().print("{s}\n", .{key});
-        }
-        try directory.handle.writeFile(libs_txt_basename, libs_txt.items);
-    }
-
     mod.stage1_flags = .{
         .have_c_main = stage1_module.have_c_main,
         .have_winmain = stage1_module.have_winmain,
@@ -4763,34 +4961,6 @@ fn updateStage1Module(comp: *Compilation, main_progress_node: *std.Progress.Node
     };
 
     stage1_module.destroy();
-
-    const digest = man.final();
-
-    // Update the small file with the digest. If it fails we can continue; it only
-    // means that the next invocation will have an unnecessary cache miss.
-    const stage1_flags_byte = @bitCast(u8, mod.stage1_flags);
-    log.debug("stage1 {s} final digest={s} flags={x}", .{
-        mod.main_pkg.root_src_path, std.fmt.fmtSliceHexLower(&digest), stage1_flags_byte,
-    });
-    var digest_plus_flags: [digest.len + 2]u8 = undefined;
-    digest_plus_flags[0..digest.len].* = digest;
-    assert(std.fmt.formatIntBuf(digest_plus_flags[digest.len..], stage1_flags_byte, 16, .lower, .{
-        .width = 2,
-        .fill = '0',
-    }) == 2);
-    log.debug("saved digest + flags: '{s}' (byte = {}) have_winmain_crt_startup={}", .{
-        digest_plus_flags, stage1_flags_byte, mod.stage1_flags.have_winmain_crt_startup,
-    });
-    Cache.writeSmallFile(directory.handle, id_symlink_basename, &digest_plus_flags) catch |err| {
-        log.warn("failed to save stage1 hash digest file: {s}", .{@errorName(err)});
-    };
-    // Failure here only means an unnecessary cache miss.
-    man.writeManifest() catch |err| {
-        log.warn("failed to write cache manifest when linking: {s}", .{@errorName(err)});
-    };
-    // We hang on to this lock so that the output file path can be used without
-    // other processes clobbering it.
-    comp.stage1_lock = man.toOwnedLock();
 }
 
 fn stage1LocPath(arena: Allocator, opt_loc: ?EmitLoc, cache_directory: Directory) ![]const u8 {
@@ -4862,6 +5032,7 @@ pub fn build_crt_file(
         .local_cache_directory = comp.global_cache_directory,
         .global_cache_directory = comp.global_cache_directory,
         .zig_lib_directory = comp.zig_lib_directory,
+        .cache_mode = .whole,
         .target = target,
         .root_name = root_name,
         .main_pkg = null,
diff --git a/src/Module.zig b/src/Module.zig
index ef01aa2c54..fa79783c6a 100644
--- a/src/Module.zig
+++ b/src/Module.zig
@@ -33,7 +33,7 @@ const build_options = @import("build_options");
 gpa: Allocator,
 comp: *Compilation,
 
-/// Where our incremental compilation metadata serialization will go.
+/// Where build artifacts and incremental compilation metadata serialization go.
 zig_cache_artifact_directory: Compilation.Directory,
 /// Pointer to externally managed resource.
 root_pkg: *Package,
diff --git a/src/glibc.zig b/src/glibc.zig
index e9c0651fdc..4424cb9b90 100644
--- a/src/glibc.zig
+++ b/src/glibc.zig
@@ -1062,6 +1062,7 @@ fn buildSharedLib(
         .local_cache_directory = zig_cache_directory,
         .global_cache_directory = comp.global_cache_directory,
         .zig_lib_directory = comp.zig_lib_directory,
+        .cache_mode = .whole,
         .target = comp.getTarget(),
         .root_name = lib.name,
         .main_pkg = null,
diff --git a/src/libcxx.zig b/src/libcxx.zig
index fe96207c48..42ac1bf6ad 100644
--- a/src/libcxx.zig
+++ b/src/libcxx.zig
@@ -177,6 +177,7 @@ pub fn buildLibCXX(comp: *Compilation) !void {
         .local_cache_directory = comp.global_cache_directory,
         .global_cache_directory = comp.global_cache_directory,
         .zig_lib_directory = comp.zig_lib_directory,
+        .cache_mode = .whole,
         .target = target,
         .root_name = root_name,
         .main_pkg = null,
@@ -309,6 +310,7 @@ pub fn buildLibCXXABI(comp: *Compilation) !void {
         .local_cache_directory = comp.global_cache_directory,
         .global_cache_directory = comp.global_cache_directory,
         .zig_lib_directory = comp.zig_lib_directory,
+        .cache_mode = .whole,
         .target = target,
         .root_name = root_name,
         .main_pkg = null,
diff --git a/src/libtsan.zig b/src/libtsan.zig
index 0f05957387..c7f288e76f 100644
--- a/src/libtsan.zig
+++ b/src/libtsan.zig
@@ -199,6 +199,7 @@ pub fn buildTsan(comp: *Compilation) !void {
         .local_cache_directory = comp.global_cache_directory,
         .global_cache_directory = comp.global_cache_directory,
         .zig_lib_directory = comp.zig_lib_directory,
+        .cache_mode = .whole,
         .target = target,
         .root_name = root_name,
         .main_pkg = null,
diff --git a/src/libunwind.zig b/src/libunwind.zig
index 95c58936fa..101ca6c8d4 100644
--- a/src/libunwind.zig
+++ b/src/libunwind.zig
@@ -101,6 +101,7 @@ pub fn buildStaticLib(comp: *Compilation) !void {
         .local_cache_directory = comp.global_cache_directory,
         .global_cache_directory = comp.global_cache_directory,
         .zig_lib_directory = comp.zig_lib_directory,
+        .cache_mode = .whole,
         .target = target,
         .root_name = root_name,
         .main_pkg = null,
diff --git a/src/link.zig b/src/link.zig
index 464d96ddac..215d24adca 100644
--- a/src/link.zig
+++ b/src/link.zig
@@ -22,6 +22,8 @@ pub const SystemLib = struct {
     needed: bool = false,
 };
 
+pub const CacheMode = enum { incremental, whole };
+
 pub fn hashAddSystemLibs(
     hh: *Cache.HashHelper,
     hm: std.StringArrayHashMapUnmanaged(SystemLib),
@@ -44,10 +46,9 @@ pub const Emit = struct {
 };
 
 pub const Options = struct {
-    /// This is `null` when -fno-emit-bin is used. When `openPath` or `flush` is called,
-    /// it will have already been null-checked.
+    /// This is `null` when `-fno-emit-bin` is used.
     emit: ?Emit,
-    /// This is `null` not building a Windows DLL, or when -fno-emit-implib is used.
+    /// This is `null` not building a Windows DLL, or when `-fno-emit-implib` is used.
     implib_emit: ?Emit,
     target: std.Target,
     output_mode: std.builtin.OutputMode,
@@ -70,6 +71,7 @@ pub const Options = struct {
     entry_addr: ?u64 = null,
     stack_size_override: ?u64,
     image_base_override: ?u64,
+    cache_mode: CacheMode,
     include_compiler_rt: bool,
     /// Set to `true` to omit debug info.
     strip: bool,
diff --git a/src/link/Coff.zig b/src/link/Coff.zig
index 2445b11caf..e6788120a0 100644
--- a/src/link/Coff.zig
+++ b/src/link/Coff.zig
@@ -920,6 +920,8 @@ fn linkWithLLD(self: *Coff, comp: *Compilation) !void {
         man = comp.cache_parent.obtain();
         self.base.releaseLock();
 
+        comptime assert(Compilation.link_hash_implementation_version == 1);
+
         try man.addListOfFiles(self.base.options.objects);
         for (comp.c_object_table.keys()) |key| {
             _ = try man.addFile(key.status.success.object_path, null);
diff --git a/src/link/Elf.zig b/src/link/Elf.zig
index 992332be36..5f3771a3cb 100644
--- a/src/link/Elf.zig
+++ b/src/link/Elf.zig
@@ -1357,6 +1357,8 @@ fn linkWithLLD(self: *Elf, comp: *Compilation) !void {
         // We are about to obtain this lock, so here we give other processes a chance first.
         self.base.releaseLock();
 
+        comptime assert(Compilation.link_hash_implementation_version == 1);
+
         try man.addOptionalFile(self.base.options.linker_script);
         try man.addOptionalFile(self.base.options.version_script);
         try man.addListOfFiles(self.base.options.objects);
diff --git a/src/link/MachO.zig b/src/link/MachO.zig
index 7dc6c52372..f970ffb5f2 100644
--- a/src/link/MachO.zig
+++ b/src/link/MachO.zig
@@ -466,6 +466,8 @@ pub fn flushModule(self: *MachO, comp: *Compilation) !void {
         // We are about to obtain this lock, so here we give other processes a chance first.
         self.base.releaseLock();
 
+        comptime assert(Compilation.link_hash_implementation_version == 1);
+
         try man.addListOfFiles(self.base.options.objects);
         for (comp.c_object_table.keys()) |key| {
             _ = try man.addFile(key.status.success.object_path, null);
diff --git a/src/link/Wasm.zig b/src/link/Wasm.zig
index 1ae50e8e33..5f8f48d1b1 100644
--- a/src/link/Wasm.zig
+++ b/src/link/Wasm.zig
@@ -1094,6 +1094,8 @@ fn linkWithLLD(self: *Wasm, comp: *Compilation) !void {
         // We are about to obtain this lock, so here we give other processes a chance first.
         self.base.releaseLock();
 
+        comptime assert(Compilation.link_hash_implementation_version == 1);
+
         try man.addListOfFiles(self.base.options.objects);
         for (comp.c_object_table.keys()) |key| {
             _ = try man.addFile(key.status.success.object_path, null);
diff --git a/src/main.zig b/src/main.zig
index 3f2dbd0cc7..53e7df3520 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -2578,10 +2578,6 @@ fn buildOutputType(
     };
     try comp.makeBinFileExecutable();
 
-    if (build_options.is_stage1 and comp.stage1_lock != null and watch) {
-        warn("--watch is not recommended with the stage1 backend; it leaks memory and is not capable of incremental compilation", .{});
-    }
-
     if (test_exec_args.items.len == 0 and object_format == .c) default_exec_args: {
         // Default to using `zig run` to execute the produced .c code from `zig test`.
         const c_code_loc = emit_bin_loc orelse break :default_exec_args;
diff --git a/src/musl.zig b/src/musl.zig
index d15d691a9c..c576dbec84 100644
--- a/src/musl.zig
+++ b/src/musl.zig
@@ -203,6 +203,7 @@ pub fn buildCRTFile(comp: *Compilation, crt_file: CRTFile) !void {
             const sub_compilation = try Compilation.create(comp.gpa, .{
                 .local_cache_directory = comp.global_cache_directory,
                 .global_cache_directory = comp.global_cache_directory,
+                .cache_mode = .whole,
                 .zig_lib_directory = comp.zig_lib_directory,
                 .target = target,
                 .root_name = "c",
diff --git a/src/stage1.zig b/src/stage1.zig
index 8263427fbe..a5be1b78fe 100644
--- a/src/stage1.zig
+++ b/src/stage1.zig
@@ -458,7 +458,7 @@ export fn stage2_fetch_file(
     const comp = @intToPtr(*Compilation, stage1.userdata);
     const file_path = path_ptr[0..path_len];
     const max_file_size = std.math.maxInt(u32);
-    const contents = comp.stage1_cache_manifest.addFilePostFetch(file_path, max_file_size) catch return null;
+    const contents = comp.whole_cache_manifest.?.addFilePostFetch(file_path, max_file_size) catch return null;
     result_len.* = contents.len;
     // TODO https://github.com/ziglang/zig/issues/3328#issuecomment-716749475
     if (contents.len == 0) return @intToPtr(?[*]const u8, 0x1);