diff --git a/src/util/rangemap.zig b/src/util/rangemap.zig
index 4a5e957..b661db8 100644
--- a/src/util/rangemap.zig
+++ b/src/util/rangemap.zig
@@ -7,11 +7,22 @@ const Allocator = std.mem.Allocator;
 const BTree = btree.BTree;
 pub const Order = btree.Order;
 
-pub fn RangeMap(comptime K: type, comptime V: type, comptime deinit_fn: ?fn (*V) void) type {
+pub fn RangeMap(
+    comptime K: type,
+    comptime V: type,
+    comptime ops: struct {
+        deinit_fn: ?fn(*V) void = null,
+        merge_fn: ?fn (*const V, *const V) bool = null,
+    },
+) type {
     return struct {
         pub const Node = struct {
             key: Range(K),
             value: V,
+
+            pub fn len(self: *const @This()) K {
+                return self.key.len;
+            }
         };
 
         pub const WalkFn = fn (*const Node) void;
@@ -28,10 +39,11 @@ pub fn RangeMap(comptime K: type, comptime V: type, comptime deinit_fn: ?fn (*V)
             }
         };
 
-        const Tree = BTree(Node, compare_fn, deinit_node_fn);
+        pub const Tree = BTree(Node, compare_fn, deinit_node_fn);
 
-        const Error = error{
+        pub const Error = error{
             scalar_out_of_range,
+            range_out_of_bounds,
         } || Tree.Error;
 
         fn compare_fn(a: *const Node, b: *const Node) Order {
@@ -39,7 +51,7 @@ pub fn RangeMap(comptime K: type, comptime V: type, comptime deinit_fn: ?fn (*V)
         }
 
         fn deinit_node_fn(n: *Node) void {
-            if (comptime deinit_fn) |f| {
+            if (comptime ops.deinit_fn) |f| {
                 f(&n.value);
             }
         }
@@ -122,6 +134,42 @@ pub fn RangeMap(comptime K: type, comptime V: type, comptime deinit_fn: ?fn (*V)
         /// Maps some range to a value. Returns an error if the requested range crosses another
         /// mapped range.
         pub fn insert(self: *@This(), start: K, len: K, value: V) Error!*Tree.Node {
+            try validate_range(start, len);
+
+            if (comptime ops.merge_fn) |merge_fn| {
+                const left: ?*Tree.Node = if (start > 0) self.get_scalar_node(start - 1) else null;
+                const right = self.get_scalar_node(start + len);
+
+                if (left) |l| {
+                    const l_start = l.key.key.start;
+
+                    if (merge_fn(&l.key.value, &value)) {
+                        if (right) |r| {
+                            if (merge_fn(&r.key.value, &value)) {
+                                l.key.key.len += len + r.key.key.len;
+                                try self.btree.remove_node(r, true);
+                                return self.get_scalar_node(l_start).?;
+                            }
+                        }
+
+                        l.key.key.len += len;
+                        return l;
+                    }
+                }
+
+                if (right) |r| {
+                    // Only right node to potentially merge with
+                    if (merge_fn(&r.key.value, &value)) {
+                        const r_len = r.key.key.len;
+                        try self.btree.remove_node(r, true);
+                        return self.btree.insert(.{
+                            .key = .{ .start = start, .len = len + r_len },
+                            .value = value,
+                        });
+                    }
+                }
+            }
+
             return self.btree.insert(.{
                 .key = .{ .start = start, .len = len },
                 .value = value,
@@ -143,11 +191,18 @@ pub fn RangeMap(comptime K: type, comptime V: type, comptime deinit_fn: ?fn (*V)
                 }
             }.call);
         }
+
+        fn validate_range(start: K, end: K) Error!void {
+            // Check for addition overflowing the K's bit size
+            if (std.math.add(K, start, end) == error.Overflow) {
+                return error.range_out_of_bounds;
+            }
+        }
     };
 }
 
 test "Range map insertion" {
-    const Map = RangeMap(u32, []const u8, null);
+    const Map = RangeMap(u32, []const u8, .{});
     var map = Map.init(std.testing.allocator);
     defer map.deinit();
 
@@ -160,8 +215,155 @@ test "Range map insertion" {
     _ = try map.insert(1000, 10, "Range 4");
 }
 
+test "Range map merging insertion" {
+    const Map = RangeMap(u32, bool, .{
+        .merge_fn = struct {
+            fn call(lhs: *const bool, rhs: *const bool) bool {
+                return !lhs.* and !rhs.*;
+            }
+        }.call,
+    });
+    var map = Map.init(std.testing.allocator);
+    defer map.deinit();
+
+    // Should not merge
+    _ = try map.insert(10, 10, false);
+    _ = try map.insert(0, 10, true);
+
+    {
+        var it = map.iterator();
+        try std.testing.expectEqual(true, it.next().?.value);
+        try std.testing.expectEqual(false, it.next().?.value);
+        try std.testing.expectEqual(null, it.next());
+    }
+
+    // Merge left + inserted + right
+    _ = try map.insert(30, 10, false);
+    _ = try map.insert(20, 10, false);
+
+    {
+        var it = map.iterator();
+        const n0 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 0, .len = 10 }, n0.key);
+        try std.testing.expectEqual(true, n0.value);
+
+        const n1 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 10, .len = 30 }, n1.key);
+        try std.testing.expectEqual(false, n1.value);
+
+        try std.testing.expectEqual(null, it.next());
+    }
+
+    // Should not merge again
+    _ = try map.insert(40, 10, true);
+    _ = try map.insert(50, 10, false);
+
+    {
+        var it = map.iterator();
+        const n0 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 0, .len = 10 }, n0.key);
+        try std.testing.expectEqual(true, n0.value);
+
+        const n1 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 10, .len = 30 }, n1.key);
+        try std.testing.expectEqual(false, n1.value);
+
+        const n2 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 40, .len = 10 }, n2.key);
+        try std.testing.expectEqual(true, n2.value);
+
+        const n3 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 50, .len = 10 }, n3.key);
+        try std.testing.expectEqual(false, n3.value);
+
+        try std.testing.expectEqual(null, it.next());
+    }
+
+    // Should merge left + shouldn't merge right non-contiguous
+    _ = try map.insert(71, 9, false);
+    _ = try map.insert(60, 10, false);
+
+    {
+        var it = map.iterator();
+        const n0 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 0, .len = 10 }, n0.key);
+        try std.testing.expectEqual(true, n0.value);
+
+        const n1 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 10, .len = 30 }, n1.key);
+        try std.testing.expectEqual(false, n1.value);
+
+        const n2 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 40, .len = 10 }, n2.key);
+        try std.testing.expectEqual(true, n2.value);
+
+        const n3 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 50, .len = 20 }, n3.key);
+        try std.testing.expectEqual(false, n3.value);
+
+        const n4 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 71, .len = 9 }, n4.key);
+        try std.testing.expectEqual(false, n4.value);
+
+        try std.testing.expectEqual(null, it.next());
+    }
+
+    // Should merge left and right
+    _ = try map.insert(70, 1, false);
+
+    {
+        var it = map.iterator();
+        const n0 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 0, .len = 10 }, n0.key);
+        try std.testing.expectEqual(true, n0.value);
+
+        const n1 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 10, .len = 30 }, n1.key);
+        try std.testing.expectEqual(false, n1.value);
+
+        const n2 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 40, .len = 10 }, n2.key);
+        try std.testing.expectEqual(true, n2.value);
+
+        const n3 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 50, .len = 30 }, n3.key);
+        try std.testing.expectEqual(false, n3.value);
+
+        try std.testing.expectEqual(null, it.next());
+    }
+
+    // Should merge right
+    _ = try map.insert(110, 10, false);
+    _ = try map.insert(100, 10, false);
+
+    {
+        var it = map.iterator();
+        const n0 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 0, .len = 10 }, n0.key);
+        try std.testing.expectEqual(true, n0.value);
+
+        const n1 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 10, .len = 30 }, n1.key);
+        try std.testing.expectEqual(false, n1.value);
+
+        const n2 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 40, .len = 10 }, n2.key);
+        try std.testing.expectEqual(true, n2.value);
+
+        const n3 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 50, .len = 30 }, n3.key);
+        try std.testing.expectEqual(false, n3.value);
+
+        const n4 = it.next().?;
+        try std.testing.expectEqual(Range(u32) { .start = 100, .len = 20 }, n4.key);
+        try std.testing.expectEqual(false, n4.value);
+
+        try std.testing.expectEqual(null, it.next());
+    }
+}
+
 test "Range map get scalar" {
-    const Map = RangeMap(u32, []const u8, null);
+    const Map = RangeMap(u32, []const u8, .{});
     var map = Map.init(std.testing.allocator);
     defer map.deinit();
 
@@ -195,7 +397,7 @@ test "Range map get scalar" {
 }
 
 test "Range map split" {
-    const Map = RangeMap(u32, []const u8, null);
+    const Map = RangeMap(u32, []const u8, .{});
     var map = Map.init(std.testing.allocator);
     defer map.deinit();
 
@@ -222,7 +424,7 @@ test "Range map split" {
 }
 
 test "Range map iterator" {
-    const Map = RangeMap(u32, []const u8, null);
+    const Map = RangeMap(u32, []const u8, .{});
     var map = Map.init(std.testing.allocator);
     defer map.deinit();
 
@@ -238,3 +440,11 @@ test "Range map iterator" {
     try std.testing.expectEqualStrings("Range [0x4000..0x5000)", it.next().?.value);
     try std.testing.expectEqual(null, it.next());
 }
+
+test "Range map should disallow overflowing ranges" {
+    const Map = RangeMap(u32, bool, .{});
+    var map = Map.init(std.testing.allocator);
+    defer map.deinit();
+
+    try std.testing.expectError(error.range_out_of_bounds, map.insert(0xF0000000, 0x20000000, false));
+}