implement typeof undefined minification optimization (#22278)

## Summary

Implements the `typeof undefined === 'u'` minification optimization from
esbuild in Bun's minifier, and fixes dead code elimination (DCE) for
typeof comparisons with string literals.

### Part 1: Minification Optimization
This optimization transforms:
- `typeof x === "undefined"` → `typeof x > "u"`
- `typeof x !== "undefined"` → `typeof x < "u"`
- `typeof x == "undefined"` → `typeof x > "u"`
- `typeof x != "undefined"` → `typeof x < "u"`

Also handles flipped operands (`"undefined" === typeof x`).

### Part 2: DCE Fix for Typeof Comparisons
Fixed dead code elimination to properly handle typeof comparisons with
strings (e.g., `typeof x <= 'u'`). These patterns can now be correctly
eliminated when they reference unbound identifiers that would throw
ReferenceErrors.

## Before/After

### Minification
Before:
```javascript
console.log(typeof x === "undefined");
```

After:
```javascript
console.log(typeof x > "u");
```

### Dead Code Elimination
Before (incorrectly kept):
```javascript
var REMOVE_1 = typeof x <= 'u' ? x : null;
```

After (correctly eliminated):
```javascript
// removed
```

## Implementation

### Minification
- Added `tryOptimizeTypeofUndefined` function in
`src/ast/visitBinaryExpression.zig`
- Handles all 4 equality operators and both operand orders
- Only optimizes when both sides match the expected pattern (typeof
expression + "undefined" string)
- Replaces "undefined" with "u" and changes operators to `>` (for
equality) or `<` (for inequality)

### DCE Improvements
- Extended `isSideEffectFreeUnboundIdentifierRef` in `src/ast/P.zig` to
handle comparison operators (`<`, `>`, `<=`, `>=`)
- Added comparison operators to `simplifyUnusedExpr` in
`src/ast/SideEffects.zig`
- Now correctly identifies when typeof comparisons guard against
undefined references

## Test Plan

✅ Added comprehensive test in `test/bundler/bundler_minify.test.ts` that
verifies:
- All 8 variations work correctly (4 operators × 2 operand orders)
- Cases that shouldn't be optimized are left unchanged
- Matches esbuild's behavior exactly using inline snapshots

✅ DCE test `dce/DCETypeOfCompareStringGuardCondition` now passes:
- Correctly eliminates dead code with typeof comparison patterns
- Maintains compatibility with esbuild's DCE behavior

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

---------

Co-authored-by: Claude Bot <[email protected]>
Co-authored-by: Claude <[email protected]>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Jarred Sumner <[email protected]>
Co-authored-by: Dylan Conway <[email protected]>

Author: 6 people

src/ast/E.zig

@@ -98,6 +98,43 @@ pub const Array = struct {
 pub const Unary = struct {
     op: Op.Code,
     value: ExprNodeIndex,
+    flags: Unary.Flags = .{},
+
+    pub const Flags = packed struct(u8) {
+        /// The expression "typeof (0, x)" must not become "typeof x" if "x"
+        /// is unbound because that could suppress a ReferenceError from "x".
+        ///
+        /// Also if we know a typeof operator was originally an identifier, then
+        /// we know that this typeof operator always has no side effects (even if
+        /// we consider the identifier by itself to have a side effect).
+        ///
+        /// Note that there *is* actually a case where "typeof x" can throw an error:
+        /// when "x" is being referenced inside of its TDZ (temporal dead zone). TDZ
+        /// checks are not yet handled correctly by Bun, so this possibility is
+        /// currently ignored.
+        was_originally_typeof_identifier: bool = false,
+
+        /// Similarly the expression "delete (0, x)" must not become "delete x"
+        /// because that syntax is invalid in strict mode. We also need to make sure
+        /// we don't accidentally change the return value:
+        ///
+        ///   Returns false:
+        ///     "var a; delete (a)"
+        ///     "var a = Object.freeze({b: 1}); delete (a.b)"
+        ///     "var a = Object.freeze({b: 1}); delete (a?.b)"
+        ///     "var a = Object.freeze({b: 1}); delete (a['b'])"
+        ///     "var a = Object.freeze({b: 1}); delete (a?.['b'])"
+        ///
+        ///   Returns true:
+        ///     "var a; delete (0, a)"
+        ///     "var a = Object.freeze({b: 1}); delete (true && a.b)"
+        ///     "var a = Object.freeze({b: 1}); delete (false || a?.b)"
+        ///     "var a = Object.freeze({b: 1}); delete (null ?? a?.['b'])"
+        ///
+        ///     "var a = Object.freeze({b: 1}); delete (true ? a['b'] : a['b'])"
+        was_originally_delete_of_identifier_or_property_access: bool = false,
+        _: u6 = 0,
+    };
 };
 
 pub const Binary = struct {
@@ -940,6 +977,30 @@ pub const String = struct {
         return bun.handleOom(this.string(allocator));
     }
 
+    fn stringCompareForJavaScript(comptime T: type, a: []const T, b: []const T) std.math.Order {
+        const a_slice = a[0..@min(a.len, b.len)];
+        const b_slice = b[0..@min(a.len, b.len)];
+        for (a_slice, b_slice) |a_char, b_char| {
+            const delta: i32 = @as(i32, a_char) - @as(i32, b_char);
+            if (delta != 0) {
+                return if (delta < 0) .lt else .gt;
+            }
+        }
+        return std.math.order(a.len, b.len);
+    }
+
+    /// Compares two strings lexicographically for JavaScript semantics.
+    /// Both strings must share the same encoding (UTF-8 vs UTF-16).
+    pub inline fn order(this: *const String, other: *const String) std.math.Order {
+        bun.debugAssert(this.isUTF8() == other.isUTF8());
+
+        if (this.isUTF8()) {
+            return stringCompareForJavaScript(u8, this.data, other.data);
+        } else {
+            return stringCompareForJavaScript(u16, this.slice16(), other.slice16());
+        }
+    }
+
     pub var empty = String{};
     pub var @"true" = String{ .data = "true" };
     pub var @"false" = String{ .data = "false" };

src/ast/Expr.zig

@@ -647,13 +647,50 @@ pub fn jsonStringify(self: *const @This(), writer: anytype) !void {
     return try writer.write(Serializable{ .type = std.meta.activeTag(self.data), .object = "expr", .value = self.data, .loc = self.loc });
 }
 
+pub fn extractNumericValuesInSafeRange(left: Expr.Data, right: Expr.Data) ?[2]f64 {
+    const l_value = left.extractNumericValue() orelse return null;
+    const r_value = right.extractNumericValue() orelse return null;
+
+    // Check for NaN and return null if either value is NaN
+    if (std.math.isNan(l_value) or std.math.isNan(r_value)) {
+        return null;
+    }
+
+    if (std.math.isInf(l_value) or std.math.isInf(r_value)) {
+        return .{ l_value, r_value };
+    }
+
+    if (l_value > bun.jsc.MAX_SAFE_INTEGER or r_value > bun.jsc.MAX_SAFE_INTEGER) {
+        return null;
+    }
+    if (l_value < bun.jsc.MIN_SAFE_INTEGER or r_value < bun.jsc.MIN_SAFE_INTEGER) {
+        return null;
+    }
+
+    return .{ l_value, r_value };
+}
+
 pub fn extractNumericValues(left: Expr.Data, right: Expr.Data) ?[2]f64 {
     return .{
         left.extractNumericValue() orelse return null,
         right.extractNumericValue() orelse return null,
     };
 }
 
+pub fn extractStringValues(left: Expr.Data, right: Expr.Data, allocator: std.mem.Allocator) ?[2]*E.String {
+    const l_string = left.extractStringValue() orelse return null;
+    const r_string = right.extractStringValue() orelse return null;
+    l_string.resolveRopeIfNeeded(allocator);
+    r_string.resolveRopeIfNeeded(allocator);
+
+    if (l_string.isUTF8() != r_string.isUTF8()) return null;
+
+    return .{
+        l_string,
+        r_string,
+    };
+}
+
 pub var icount: usize = 0;
 
 // We don't need to dynamically allocate booleans
@@ -1407,11 +1444,17 @@ pub fn init(comptime Type: type, st: Type, loc: logger.Loc) Expr {
     }
 }
 
-pub fn isPrimitiveLiteral(this: Expr) bool {
+/// If this returns true, then calling this expression captures the target of
+/// the property access as "this" when calling the function in the property.
+pub inline fn isPropertyAccess(this: *const Expr) bool {
+    return this.hasValueForThisInCall();
+}
+
+pub inline fn isPrimitiveLiteral(this: *const Expr) bool {
     return @as(Tag, this.data).isPrimitiveLiteral();
 }
 
-pub fn isRef(this: Expr, ref: Ref) bool {
+pub inline fn isRef(this: *const Expr, ref: Ref) bool {
     return switch (this.data) {
         .e_import_identifier => |import_identifier| import_identifier.ref.eql(ref),
         .e_identifier => |ident| ident.ref.eql(ref),
@@ -1873,36 +1916,19 @@ pub const Tag = enum {
     }
 };
 
-pub fn isBoolean(a: Expr) bool {
-    switch (a.data) {
-        .e_boolean => {
-            return true;
-        },
-
-        .e_if => |ex| {
-            return isBoolean(ex.yes) and isBoolean(ex.no);
-        },
-        .e_unary => |ex| {
-            return ex.op == .un_not or ex.op == .un_delete;
-        },
-        .e_binary => |ex| {
-            switch (ex.op) {
-                .bin_strict_eq, .bin_strict_ne, .bin_loose_eq, .bin_loose_ne, .bin_lt, .bin_gt, .bin_le, .bin_ge, .bin_instanceof, .bin_in => {
-                    return true;
-                },
-                .bin_logical_or => {
-                    return isBoolean(ex.left) and isBoolean(ex.right);
-                },
-                .bin_logical_and => {
-                    return isBoolean(ex.left) and isBoolean(ex.right);
-                },
-                else => {},
-            }
+pub fn isBoolean(a: *const Expr) bool {
+    return switch (a.data) {
+        .e_boolean => true,
+        .e_if => |ex| ex.yes.isBoolean() and ex.no.isBoolean(),
+        .e_unary => |ex| ex.op == .un_not or ex.op == .un_delete,
+        .e_binary => |ex| switch (ex.op) {
+            .bin_strict_eq, .bin_strict_ne, .bin_loose_eq, .bin_loose_ne, .bin_lt, .bin_gt, .bin_le, .bin_ge, .bin_instanceof, .bin_in => true,
+            .bin_logical_or => ex.left.isBoolean() and ex.right.isBoolean(),
+            .bin_logical_and => ex.left.isBoolean() and ex.right.isBoolean(),
+            else => false,
         },
-        else => {},
-    }
-
-    return false;
+        else => false,
+    };
 }
 
 pub fn assign(a: Expr, b: Expr) Expr {
@@ -1912,29 +1938,27 @@ pub fn assign(a: Expr, b: Expr) Expr {
         .right = b,
     }, a.loc);
 }
-pub inline fn at(expr: Expr, comptime Type: type, t: Type, _: std.mem.Allocator) Expr {
+pub inline fn at(expr: *const Expr, comptime Type: type, t: Type, _: std.mem.Allocator) Expr {
     return init(Type, t, expr.loc);
 }
 
 // Wraps the provided expression in the "!" prefix operator. The expression
 // will potentially be simplified to avoid generating unnecessary extra "!"
 // operators. For example, calling this with "!!x" will return "!x" instead
 // of returning "!!!x".
-pub fn not(expr: Expr, allocator: std.mem.Allocator) Expr {
-    return maybeSimplifyNot(
-        expr,
-        allocator,
-    ) orelse Expr.init(
-        E.Unary,
-        E.Unary{
-            .op = .un_not,
-            .value = expr,
-        },
-        expr.loc,
-    );
+pub fn not(expr: *const Expr, allocator: std.mem.Allocator) Expr {
+    return expr.maybeSimplifyNot(allocator) orelse
+        Expr.init(
+            E.Unary,
+            E.Unary{
+                .op = .un_not,
+                .value = expr.*,
+            },
+            expr.loc,
+        );
 }
 
-pub fn hasValueForThisInCall(expr: Expr) bool {
+pub inline fn hasValueForThisInCall(expr: *const Expr) bool {
     return switch (expr.data) {
         .e_dot, .e_index => true,
         else => false,
@@ -1946,7 +1970,7 @@ pub fn hasValueForThisInCall(expr: Expr) bool {
 /// whole operator (i.e. the "!x") if it can be simplified, or false if not.
 /// It's separate from "Not()" above to avoid allocation on failure in case
 /// that is undesired.
-pub fn maybeSimplifyNot(expr: Expr, allocator: std.mem.Allocator) ?Expr {
+pub fn maybeSimplifyNot(expr: *const Expr, allocator: std.mem.Allocator) ?Expr {
     switch (expr.data) {
         .e_null, .e_undefined => {
             return expr.at(E.Boolean, E.Boolean{ .value = true }, allocator);
@@ -1968,7 +1992,7 @@ pub fn maybeSimplifyNot(expr: Expr, allocator: std.mem.Allocator) ?Expr {
         },
         // "!!!a" => "!a"
         .e_unary => |un| {
-            if (un.op == Op.Code.un_not and knownPrimitive(un.value) == .boolean) {
+            if (un.op == Op.Code.un_not and un.value.knownPrimitive() == .boolean) {
                 return un.value;
             }
         },
@@ -1981,33 +2005,33 @@ pub fn maybeSimplifyNot(expr: Expr, allocator: std.mem.Allocator) ?Expr {
                 Op.Code.bin_loose_eq => {
                     // "!(a == b)" => "a != b"
                     ex.op = .bin_loose_ne;
-                    return expr;
+                    return expr.*;
                 },
                 Op.Code.bin_loose_ne => {
                     // "!(a != b)" => "a == b"
                     ex.op = .bin_loose_eq;
-                    return expr;
+                    return expr.*;
                 },
                 Op.Code.bin_strict_eq => {
                     // "!(a === b)" => "a !== b"
                     ex.op = .bin_strict_ne;
-                    return expr;
+                    return expr.*;
                 },
                 Op.Code.bin_strict_ne => {
                     // "!(a !== b)" => "a === b"
                     ex.op = .bin_strict_eq;
-                    return expr;
+                    return expr.*;
                 },
                 Op.Code.bin_comma => {
                     // "!(a, b)" => "a, !b"
                     ex.right = ex.right.not(allocator);
-                    return expr;
+                    return expr.*;
                 },
                 else => {},
             }
         },
         .e_inlined_enum => |inlined| {
-            return maybeSimplifyNot(inlined.value, allocator);
+            return inlined.value.maybeSimplifyNot(allocator);
         },
 
         else => {},
@@ -2016,11 +2040,11 @@ pub fn maybeSimplifyNot(expr: Expr, allocator: std.mem.Allocator) ?Expr {
     return null;
 }
 
-pub fn toStringExprWithoutSideEffects(expr: Expr, allocator: std.mem.Allocator) ?Expr {
+pub fn toStringExprWithoutSideEffects(expr: *const Expr, allocator: std.mem.Allocator) ?Expr {
     const unwrapped = expr.unwrapInlined();
     const slice = switch (unwrapped.data) {
         .e_null => "null",
-        .e_string => return expr,
+        .e_string => return expr.*,
         .e_undefined => "undefined",
         .e_boolean => |data| if (data.value) "true" else "false",
         .e_big_int => |bigint| bigint.value,
@@ -2054,7 +2078,7 @@ pub fn isOptionalChain(self: *const @This()) bool {
     };
 }
 
-pub inline fn knownPrimitive(self: @This()) PrimitiveType {
+pub inline fn knownPrimitive(self: *const @This()) PrimitiveType {
     return self.data.knownPrimitive();
 }
 
@@ -2294,6 +2318,7 @@ pub const Data = union(Tag) {
                 const item = bun.create(allocator, E.Unary, .{
                     .op = el.op,
                     .value = try el.value.deepClone(allocator),
+                    .flags = el.flags,
                 });
                 return .{ .e_unary = item };
             },
@@ -2506,6 +2531,7 @@ pub const Data = union(Tag) {
                 }
             },
             .e_unary => |e| {
+                writeAnyToHasher(hasher, @as(u8, @bitCast(e.flags)));
                 writeAnyToHasher(hasher, .{e.op});
                 e.value.data.writeToHasher(hasher, symbol_table);
             },
@@ -2537,7 +2563,7 @@ pub const Data = union(Tag) {
             inline .e_spread, .e_await => |e| {
                 e.value.data.writeToHasher(hasher, symbol_table);
             },
-            inline .e_yield => |e| {
+            .e_yield => |e| {
                 writeAnyToHasher(hasher, .{ e.is_star, e.value });
                 if (e.value) |value|
                     value.data.writeToHasher(hasher, symbol_table);
@@ -2860,6 +2886,17 @@ pub const Data = union(Tag) {
         };
     }
 
+    pub fn extractStringValue(data: Expr.Data) ?*E.String {
+        return switch (data) {
+            .e_string => data.e_string,
+            .e_inlined_enum => |inlined| switch (inlined.value.data) {
+                .e_string => |str| str,
+                else => null,
+            },
+            else => null,
+        };
+    }
+
     pub const Equality = struct {
         equal: bool = false,
         ok: bool = false,