From 0d841e827ac120725eef1100b79f1807a2bc04bd Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Fri, 29 Sep 2023 16:02:00 -0700
Subject: [PATCH] C backend: remove unneeded ordering mechanism

This logic to lower snippets of C code in a dependency order is no
longer needed. Simplify the logic by deleting the mechanism.
---
 src/link/C.zig | 33 ++++++---------------------------
 1 file changed, 6 insertions(+), 27 deletions(-)

diff --git a/src/link/C.zig b/src/link/C.zig
index 8ffe33bb09..5f4d767f90 100644
--- a/src/link/C.zig
+++ b/src/link/C.zig
@@ -322,29 +322,19 @@ pub fn flushModule(self: *C, _: *Compilation, prog_node: *std.Progress.Node) !vo
     self.lazy_code_buf.clearRetainingCapacity();
     try self.flushErrDecls(&f.lazy_ctypes);
 
+    // Unlike other backends, the .c code we are emitting has order-dependent decls.
     // `CType`s, forward decls, and non-functions first.
-    // Unlike other backends, the .c code we are emitting is order-dependent. Therefore
-    // we must traverse the set of Decls that we are emitting according to their dependencies.
-    // Our strategy is to populate a set of remaining decls, pop Decls one by one,
-    // recursively chasing their dependencies.
-    try f.remaining_decls.ensureUnusedCapacity(gpa, self.decl_table.count());
-
-    const decl_keys = self.decl_table.keys();
-    const decl_values = self.decl_table.values();
-    for (decl_keys) |decl_index| {
-        assert(module.declPtr(decl_index).has_tv);
-        f.remaining_decls.putAssumeCapacityNoClobber(decl_index, {});
-    }
 
     {
         var export_names: std.AutoHashMapUnmanaged(InternPool.NullTerminatedString, void) = .{};
         defer export_names.deinit(gpa);
-        try export_names.ensureTotalCapacity(gpa, @as(u32, @intCast(module.decl_exports.entries.len)));
+        try export_names.ensureTotalCapacity(gpa, @intCast(module.decl_exports.entries.len));
         for (module.decl_exports.values()) |exports| for (exports.items) |@"export"|
             try export_names.put(gpa, @"export".opts.name, {});
 
-        while (f.remaining_decls.popOrNull()) |kv| {
-            const decl_index = kv.key;
+        const decl_keys = self.decl_table.keys();
+        for (decl_keys) |decl_index| {
+            assert(module.declPtr(decl_index).has_tv);
             try self.flushDecl(&f, decl_index, export_names);
         }
     }
@@ -374,6 +364,7 @@ pub fn flushModule(self: *C, _: *Compilation, prog_node: *std.Progress.Node) !vo
     f.file_size += lazy_fwd_decl_len;
 
     // Now the code.
+    const decl_values = self.decl_table.values();
     try f.all_buffers.ensureUnusedCapacity(gpa, 1 + decl_values.len);
     f.appendBufAssumeCapacity(self.lazy_code_buf.items);
     for (decl_values) |decl| f.appendBufAssumeCapacity(self.getString(decl.code));
@@ -384,8 +375,6 @@ pub fn flushModule(self: *C, _: *Compilation, prog_node: *std.Progress.Node) !vo
 }
 
 const Flush = struct {
-    remaining_decls: std.AutoArrayHashMapUnmanaged(Module.Decl.Index, void) = .{},
-
     ctypes: codegen.CType.Store = .{},
     ctypes_map: std.ArrayListUnmanaged(codegen.CType.Index) = .{},
     ctypes_buf: std.ArrayListUnmanaged(u8) = .{},
@@ -416,7 +405,6 @@ const Flush = struct {
         f.ctypes_buf.deinit(gpa);
         f.ctypes_map.deinit(gpa);
         f.ctypes.deinit(gpa);
-        f.remaining_decls.deinit(gpa);
     }
 };
 
@@ -591,7 +579,6 @@ fn flushLazyFns(self: *C, f: *Flush, lazy_fns: codegen.LazyFnMap) FlushDeclError
     }
 }
 
-/// Assumes `decl` was in the `remaining_decls` set, and has already been removed.
 fn flushDecl(
     self: *C,
     f: *Flush,
@@ -601,14 +588,6 @@ fn flushDecl(
     const gpa = self.base.allocator;
     const mod = self.base.options.module.?;
     const decl = mod.declPtr(decl_index);
-    // Before flushing any particular Decl we must ensure its
-    // dependencies are already flushed, so that the order in the .c
-    // file comes out correctly.
-    for (decl.dependencies.keys()) |dep| {
-        if (f.remaining_decls.swapRemove(dep)) {
-            try flushDecl(self, f, dep, export_names);
-        }
-    }
 
     const decl_block = self.decl_table.getPtr(decl_index).?;