1 files changed, 24 insertions, 1 deletions
diff --git a/src/codegen/spirv.zig b/src/codegen/spirv.zig
index 2fe759dc03..5a262de836 100644
--- a/src/codegen/spirv.zig
+++ b/src/codegen/spirv.zig
@@ -1,4 +1,6 @@
 const std = @import("std");
+const Allocator = std.mem.Allocator;
+
 const spec = @import("spirv/spec.zig");
 const Module = @import("../Module.zig");
 const Decl = Module.Decl;
@@ -10,14 +12,35 @@ pub fn writeInstruction(code: *std.ArrayList(u32), instr: spec.Opcode, args: []c
 }
 
 pub const SPIRVModule = struct {
-    // TODO: Also use a free list.
     next_id: u32 = 0,
+    free_id_list: std.ArrayList(u32),
+
+    pub fn init(allocator: *Allocator) SPIRVModule {
+        return .{
+            .free_id_list = std.ArrayList(u32).init(allocator),
+        };
+    }
+
+    pub fn deinit(self: *SPIRVModule) void {
+        self.free_id_list.deinit();
+    }
 
     pub fn allocId(self: *SPIRVModule) u32 {
+        if (self.free_id_list.popOrNull()) |id| return id;
+
         defer self.next_id += 1;
         return self.next_id;
     }
 
+    pub fn freeId(self: *SPIRVModule, id: u32) void {
+        if (id + 1 == self.next_id) {
+            self.next_id -= 1;
+        } else {
+            // If no more memory to append the id to the free list, just ignore it.
+            self.free_id_list.append(id) catch {};
+        }
+    }
+
     pub fn idBound(self: *SPIRVModule) u32 {
         return self.next_id;
     }