diff --git a/src/codegen/c.zig b/src/codegen/c.zig
index f2594209a5..c63cb27529 100644
--- a/src/codegen/c.zig
+++ b/src/codegen/c.zig
@@ -842,7 +842,8 @@ pub const DeclGen = struct {
         var index: usize = 0;
         var params_written: usize = 0;
         while (index < param_len) : (index += 1) {
-            if (dg.decl.ty.fnParamType(index).zigTypeTag() == .Void) continue;
+            const param_type = dg.decl.ty.fnParamType(index);
+            if (!param_type.hasRuntimeBitsIgnoreComptime()) continue;
             if (params_written > 0) {
                 try w.writeAll(", ");
             }
@@ -882,7 +883,7 @@ pub const DeclGen = struct {
         var params_written: usize = 0;
         var index: usize = 0;
         while (index < param_len) : (index += 1) {
-            if (fn_info.param_types[index].zigTypeTag() == .Void) continue;
+            if (!fn_info.param_types[index].hasRuntimeBitsIgnoreComptime()) continue;
             if (params_written > 0) {
                 try bw.writeAll(", ");
             }
@@ -1708,8 +1709,8 @@ fn genBody(f: *Function, body: []const Air.Inst.Index) error{ AnalysisFail, OutO
             .memcpy           => try airMemcpy(f, inst),
             .set_union_tag    => try airSetUnionTag(f, inst),
             .get_union_tag    => try airGetUnionTag(f, inst),
-            .clz              => try airCountZeroes(f, inst, "clz"),
-            .ctz              => try airCountZeroes(f, inst, "ctz"),
+            .clz              => try airBuiltinCall(f, inst, "clz"),
+            .ctz              => try airBuiltinCall(f, inst, "ctz"),
             .popcount         => try airBuiltinCall(f, inst, "popcount"),
             .byte_swap        => try airBuiltinCall(f, inst, "byte_swap"),
             .bit_reverse      => try airBuiltinCall(f, inst, "bit_reverse"),
@@ -2625,8 +2626,11 @@ fn airCall(
     }
 
     try writer.writeAll("(");
-    for (args) |arg, i| {
-        if (i != 0) {
+    var args_written: usize = 0;
+    for (args) |arg| {
+        const ty = f.air.typeOf(arg);
+        if (!ty.hasRuntimeBitsIgnoreComptime()) continue;
+        if (args_written != 0) {
             try writer.writeAll(", ");
         }
         if (f.air.value(arg)) |val| {
@@ -2635,6 +2639,7 @@ fn airCall(
             const val = try f.resolveInst(arg);
             try f.writeCValue(writer, val);
         }
+        args_written += 1;
     }
     try writer.writeAll(");\n");
     return result_local;
@@ -3349,23 +3354,6 @@ fn airPtrToInt(f: *Function, inst: Air.Inst.Index) !CValue {
 fn airBuiltinCall(f: *Function, inst: Air.Inst.Index, fn_name: [*:0]const u8) !CValue {
     if (f.liveness.isUnused(inst)) return CValue.none;
 
-    const inst_ty = f.air.typeOfIndex(inst);
-    const local = try f.allocLocal(inst_ty, .Const);
-    const ty_op = f.air.instructions.items(.data)[inst].ty_op;
-    const writer = f.object.writer();
-    const operand = try f.resolveInst(ty_op.operand);
-
-    // TODO implement the function in zig.h and call it here
-
-    try writer.print(" = {s}(", .{fn_name});
-    try f.writeCValue(writer, operand);
-    try writer.writeAll(");\n");
-    return local;
-}
-
-fn airCountZeroes(f: *Function, inst: Air.Inst.Index, fn_name: [*:0]const u8) !CValue {
-    if (f.liveness.isUnused(inst)) return CValue.none;
-
     const inst_ty = f.air.typeOfIndex(inst);
     const local = try f.allocLocal(inst_ty, .Const);
     const operand = f.air.instructions.items(.data)[inst].ty_op.operand;
@@ -3373,13 +3361,18 @@ fn airCountZeroes(f: *Function, inst: Air.Inst.Index, fn_name: [*:0]const u8) !C
     const target = f.object.dg.module.getTarget();
     const writer = f.object.writer();
 
-    const zig_bits = operand_ty.intInfo(target).bits;
-    _ = toCIntBits(zig_bits) orelse
+    const int_info = operand_ty.intInfo(target);
+    const c_bits = toCIntBits(int_info.bits) orelse
         return f.fail("TODO: C backend: implement integer types larger than 128 bits", .{});
 
-    try writer.print(" = zig_{s}(", .{fn_name});
+    try writer.print(" = zig_{s}_", .{fn_name});
+    const prefix_byte: u8 = switch (int_info.signedness) {
+        .signed => 'i',
+        .unsigned => 'u',
+    };
+    try writer.print("{c}{d}(", .{ prefix_byte, c_bits });
     try f.writeCValue(writer, try f.resolveInst(operand));
-    try writer.print(", {d});\n", .{zig_bits});
+    try writer.print(", {d});\n", .{int_info.bits});
     return local;
 }
 
diff --git a/src/link/C/zig.h b/src/link/C/zig.h
index a5534f86aa..ce22b5221f 100644
--- a/src/link/C/zig.h
+++ b/src/link/C/zig.h
@@ -502,19 +502,249 @@ zig_shl_sat_s(int,        int, ((sizeof(int     )) * CHAR_BIT - 1))
 zig_shl_sat_s(long,      long, ((sizeof(long    )) * CHAR_BIT - 1))
 
 #define zig_bitsizeof(T) (CHAR_BIT * sizeof(T))
+#define zig_bit_mask(T, bit_width) \
+    ((bit_width) == zig_bitsizeof(T) \
+     ? ((T)-1) \
+     : (((T)1 << (T)(bit_width)) - 1))
 
-static inline int zig_clz(uint64_t value, uint8_t zig_type_bit_width) {
+static inline int zig_clz(unsigned int value, uint8_t zig_type_bit_width) {
     if (value == 0) return zig_type_bit_width;
-    if (zig_type_bit_width <= zig_bitsizeof(unsigned int))
-        return (__builtin_clz(value) - zig_bitsizeof(unsigned int) + zig_type_bit_width);
-    if (zig_type_bit_width <= zig_bitsizeof(unsigned long))
-        return (__builtin_clzl(value) - zig_bitsizeof(unsigned long) + zig_type_bit_width);
-    return (__builtin_clzll(value) - zig_bitsizeof(unsigned long long) + zig_type_bit_width);
+    return __builtin_clz(value) - zig_bitsizeof(unsigned int) + zig_type_bit_width;
 }
 
-static inline int zig_ctz(uint64_t value, uint8_t zig_type_bit_width) {
+static inline int zig_clzl(unsigned long value, uint8_t zig_type_bit_width) {
     if (value == 0) return zig_type_bit_width;
-    if (zig_type_bit_width <= zig_bitsizeof(unsigned int)) return __builtin_ctz(value);
-    if (zig_type_bit_width <= zig_bitsizeof(unsigned long)) return __builtin_ctzl(value);
-    return __builtin_ctzll(value);
+    return __builtin_clzl(value) - zig_bitsizeof(unsigned long) + zig_type_bit_width;
 }
+
+static inline int zig_clzll(unsigned long long value, uint8_t zig_type_bit_width) {
+    if (value == 0) return zig_type_bit_width;
+    return __builtin_clzll(value) - zig_bitsizeof(unsigned long long) + zig_type_bit_width;
+}
+
+#define zig_clz_u8  zig_clz
+#define zig_clz_i8  zig_clz
+#define zig_clz_u16 zig_clz
+#define zig_clz_i16 zig_clz
+#define zig_clz_u32 zig_clzl
+#define zig_clz_i32 zig_clzl
+#define zig_clz_u64 zig_clzll
+#define zig_clz_i64 zig_clzll
+
+static inline int zig_clz_u128(uint128_t value, uint8_t zig_type_bit_width) {
+    if (value == 0) return zig_type_bit_width;
+    const uint128_t mask = zig_bit_mask(uint128_t, zig_type_bit_width);
+    const uint64_t hi = (value & mask) >> 64;
+    const uint64_t lo = (value & mask);
+    const int leading_zeroes = (
+        hi != 0 ? __builtin_clzll(hi) : 64 + (lo != 0 ? __builtin_clzll(lo) : 64));
+    return leading_zeroes - zig_bitsizeof(uint128_t) + zig_type_bit_width;
+}
+
+#define zig_clz_i128 zig_clz_u128
+
+static inline int zig_ctz(unsigned int value, uint8_t zig_type_bit_width) {
+    if (value == 0) return zig_type_bit_width;
+    return __builtin_ctz(value & zig_bit_mask(unsigned int, zig_type_bit_width));
+}
+
+static inline int zig_ctzl(unsigned long value, uint8_t zig_type_bit_width) {
+    if (value == 0) return zig_type_bit_width;
+    return __builtin_ctzl(value & zig_bit_mask(unsigned long, zig_type_bit_width));
+}
+
+static inline int zig_ctzll(unsigned long value, uint8_t zig_type_bit_width) {
+    if (value == 0) return zig_type_bit_width;
+    return __builtin_ctzll(value & zig_bit_mask(unsigned long, zig_type_bit_width));
+}
+
+#define zig_ctz_u8  zig_ctz
+#define zig_ctz_i8  zig_ctz
+#define zig_ctz_u16 zig_ctz
+#define zig_ctz_i16 zig_ctz
+#define zig_ctz_u32 zig_ctzl
+#define zig_ctz_i32 zig_ctzl
+#define zig_ctz_u64 zig_ctzll
+#define zig_ctz_i64 zig_ctzll
+
+static inline int zig_ctz_u128(uint128_t value, uint8_t zig_type_bit_width) {
+    const uint128_t mask = zig_bit_mask(uint128_t, zig_type_bit_width);
+    const uint64_t hi = (value & mask) >> 64;
+    const uint64_t lo = (value & mask);
+    return (lo != 0 ? __builtin_ctzll(lo) : 64 + (hi != 0 ? __builtin_ctzll(hi) : 64));
+}
+
+#define zig_ctz_i128 zig_ctz_u128
+
+static inline int zig_popcount(unsigned int value, uint8_t zig_type_bit_width) {
+    return __builtin_popcount(value & zig_bit_mask(unsigned int, zig_type_bit_width));
+}
+
+static inline int zig_popcountl(unsigned long value, uint8_t zig_type_bit_width) {
+    return __builtin_popcountl(value & zig_bit_mask(unsigned long, zig_type_bit_width));
+}
+
+static inline int zig_popcountll(unsigned long value, uint8_t zig_type_bit_width) {
+    return __builtin_popcountll(value & zig_bit_mask(unsigned long, zig_type_bit_width));
+}
+
+#define zig_popcount_u8  zig_popcount
+#define zig_popcount_i8  zig_popcount
+#define zig_popcount_u16 zig_popcount
+#define zig_popcount_i16 zig_popcount
+#define zig_popcount_u32 zig_popcountl
+#define zig_popcount_i32 zig_popcountl
+#define zig_popcount_u64 zig_popcountll
+#define zig_popcount_i64 zig_popcountll
+
+static inline int zig_popcount_u128(uint128_t value, uint8_t zig_type_bit_width) {
+    const uint128_t mask = zig_bit_mask(uint128_t, zig_type_bit_width);
+    const uint64_t hi = (value & mask) >> 64;
+    const uint64_t lo = (value & mask);
+    return __builtin_popcountll(hi) + __builtin_popcountll(lo);
+}
+
+#define zig_popcount_i128 zig_popcount_u128
+
+#define zig_sign_extend(T) \
+    static inline T zig_sign_extend_##T(T value, uint8_t zig_type_bit_width) { \
+        const T m = (T)1 << (T)(zig_type_bit_width - 1); \
+        return (value ^ m) - m; \
+    }
+
+zig_sign_extend(uint8_t)
+zig_sign_extend(uint16_t)
+zig_sign_extend(uint32_t)
+zig_sign_extend(uint64_t)
+zig_sign_extend(uint128_t)
+
+#define zig_byte_swap_u(ZigTypeBits, CTypeBits) \
+    static inline uint##CTypeBits##_t zig_byte_swap_u##ZigTypeBits(uint##CTypeBits##_t value, uint8_t zig_type_bit_width) { \
+        return __builtin_bswap##CTypeBits(value) >> (CTypeBits - zig_type_bit_width); \
+    }
+
+#define zig_byte_swap_s(ZigTypeBits, CTypeBits) \
+    static inline int##CTypeBits##_t zig_byte_swap_i##ZigTypeBits(int##CTypeBits##_t value, uint8_t zig_type_bit_width) { \
+        const uint##CTypeBits##_t swapped = zig_byte_swap_u##ZigTypeBits(value, zig_type_bit_width); \
+        return zig_sign_extend_uint##CTypeBits##_t(swapped, zig_type_bit_width); \
+    }
+
+#define zig_byte_swap(ZigTypeBits, CTypeBits) \
+    zig_byte_swap_u(ZigTypeBits, CTypeBits) \
+    zig_byte_swap_s(ZigTypeBits, CTypeBits)
+
+zig_byte_swap( 8, 16)
+zig_byte_swap(16, 16)
+zig_byte_swap(32, 32)
+zig_byte_swap(64, 64)
+
+static inline uint128_t zig_byte_swap_u128(uint128_t value, uint8_t zig_type_bit_width) {
+    const uint128_t mask = zig_bit_mask(uint128_t, zig_type_bit_width);
+    const uint128_t hi = __builtin_bswap64((uint64_t)(value >> 64));
+    const uint128_t lo = __builtin_bswap64((uint64_t)value);
+    return (((lo << 64 | hi) >> (128 - zig_type_bit_width))) & mask;
+}
+
+zig_byte_swap_s(128, 128)
+
+static const uint8_t zig_bit_reverse_lut[256] = {
+    0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0, 0x10, 0x90, 0x50, 0xd0,
+    0x30, 0xb0, 0x70, 0xf0, 0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8,
+    0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8, 0x04, 0x84, 0x44, 0xc4,
+    0x24, 0xa4, 0x64, 0xe4, 0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4,
+    0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec, 0x1c, 0x9c, 0x5c, 0xdc,
+    0x3c, 0xbc, 0x7c, 0xfc, 0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2,
+    0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2, 0x0a, 0x8a, 0x4a, 0xca,
+    0x2a, 0xaa, 0x6a, 0xea, 0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa,
+    0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6, 0x16, 0x96, 0x56, 0xd6,
+    0x36, 0xb6, 0x76, 0xf6, 0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee,
+    0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe, 0x01, 0x81, 0x41, 0xc1,
+    0x21, 0xa1, 0x61, 0xe1, 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1,
+    0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9, 0x19, 0x99, 0x59, 0xd9,
+    0x39, 0xb9, 0x79, 0xf9, 0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5,
+    0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5, 0x0d, 0x8d, 0x4d, 0xcd,
+    0x2d, 0xad, 0x6d, 0xed, 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd,
+    0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3, 0x13, 0x93, 0x53, 0xd3,
+    0x33, 0xb3, 0x73, 0xf3, 0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb,
+    0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb, 0x07, 0x87, 0x47, 0xc7,
+    0x27, 0xa7, 0x67, 0xe7, 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7,
+    0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef, 0x1f, 0x9f, 0x5f, 0xdf,
+    0x3f, 0xbf, 0x7f, 0xff
+};
+
+static inline uint8_t zig_bit_reverse_u8(uint8_t value, uint8_t zig_type_bit_width) {
+    const uint8_t reversed = zig_bit_reverse_lut[value] >> (8 - zig_type_bit_width);
+    return zig_sign_extend_uint8_t(reversed, zig_type_bit_width);
+}
+
+#define zig_bit_reverse_i8 zig_bit_reverse_u8
+
+static inline uint16_t zig_bit_reverse_u16(uint16_t value, uint8_t zig_type_bit_width) {
+    const uint16_t swapped = zig_byte_swap_u16(value, zig_type_bit_width);
+    const uint16_t reversed = (
+        ((uint16_t)zig_bit_reverse_lut[(swapped >> 0x08) & 0xff] << 0x08) |
+        ((uint16_t)zig_bit_reverse_lut[(swapped >> 0x00) & 0xff] << 0x00));
+    return zig_sign_extend_uint16_t(
+        reversed & zig_bit_mask(uint16_t, zig_type_bit_width),
+        zig_type_bit_width);
+}
+
+#define zig_bit_reverse_i16 zig_bit_reverse_u16
+
+static inline uint32_t zig_bit_reverse_u32(uint32_t value, uint8_t zig_type_bit_width) {
+    const uint32_t swapped = zig_byte_swap_u32(value, zig_type_bit_width);
+    const uint32_t reversed = (
+         ((uint32_t)zig_bit_reverse_lut[(swapped >> 0x18) & 0xff] << 0x18) |
+         ((uint32_t)zig_bit_reverse_lut[(swapped >> 0x10) & 0xff] << 0x10) |
+         ((uint32_t)zig_bit_reverse_lut[(swapped >> 0x08) & 0xff] << 0x08) |
+         ((uint32_t)zig_bit_reverse_lut[(swapped >> 0x00) & 0xff] << 0x00));
+    return zig_sign_extend_uint32_t(
+        reversed & zig_bit_mask(uint32_t, zig_type_bit_width),
+        zig_type_bit_width);
+}
+
+#define zig_bit_reverse_i32 zig_bit_reverse_u32
+
+static inline uint64_t zig_bit_reverse_u64(uint64_t value, uint8_t zig_type_bit_width) {
+    const uint64_t swapped = zig_byte_swap_u64(value, zig_type_bit_width);
+    const uint64_t reversed = (
+        ((uint64_t)zig_bit_reverse_lut[(swapped >> 0x38) & 0xff] << 0x38) |
+        ((uint64_t)zig_bit_reverse_lut[(swapped >> 0x30) & 0xff] << 0x30) |
+        ((uint64_t)zig_bit_reverse_lut[(swapped >> 0x28) & 0xff] << 0x28) |
+        ((uint64_t)zig_bit_reverse_lut[(swapped >> 0x20) & 0xff] << 0x20) |
+        ((uint64_t)zig_bit_reverse_lut[(swapped >> 0x18) & 0xff] << 0x18) |
+        ((uint64_t)zig_bit_reverse_lut[(swapped >> 0x10) & 0xff] << 0x10) |
+        ((uint64_t)zig_bit_reverse_lut[(swapped >> 0x08) & 0xff] << 0x08) |
+        ((uint64_t)zig_bit_reverse_lut[(swapped >> 0x00) & 0xff] << 0x00));
+    return zig_sign_extend_uint64_t(
+        reversed & zig_bit_mask(uint64_t, zig_type_bit_width),
+        zig_type_bit_width);
+}
+
+#define zig_bit_reverse_i64 zig_bit_reverse_u64
+
+static inline uint128_t zig_bit_reverse_u128(uint128_t value, uint8_t zig_type_bit_width) {
+    const uint128_t swapped = zig_byte_swap_u128(value, zig_type_bit_width);
+    const uint128_t reversed = (
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x78) & 0xff] << 0x78) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x70) & 0xff] << 0x70) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x68) & 0xff] << 0x68) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x60) & 0xff] << 0x60) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x58) & 0xff] << 0x58) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x50) & 0xff] << 0x50) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x48) & 0xff] << 0x48) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x40) & 0xff] << 0x40) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x38) & 0xff] << 0x38) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x30) & 0xff] << 0x30) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x28) & 0xff] << 0x28) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x20) & 0xff] << 0x20) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x18) & 0xff] << 0x18) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x10) & 0xff] << 0x10) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x08) & 0xff] << 0x08) |
+        ((uint128_t)zig_bit_reverse_lut[(swapped >> 0x00) & 0xff] << 0x00));
+    return zig_sign_extend_uint128_t(
+        reversed & zig_bit_mask(uint128_t, zig_type_bit_width),
+        zig_type_bit_width);
+}
+
+#define zig_bit_reverse_i128 zig_bit_reverse_u128
diff --git a/test/behavior.zig b/test/behavior.zig
index 7efe687c75..b353ee78c9 100644
--- a/test/behavior.zig
+++ b/test/behavior.zig
@@ -139,6 +139,7 @@ test {
         _ = @import("behavior/eval.zig");
         _ = @import("behavior/export_self_referential_type_info.zig");
         _ = @import("behavior/int128.zig");
+        _ = @import("behavior/popcount.zig");
         _ = @import("behavior/translate_c_macros.zig");
         _ = @import("behavior/union_with_members.zig");
 
@@ -147,7 +148,6 @@ test {
             _ = @import("behavior/atomics.zig");
             _ = @import("behavior/export.zig");
             _ = @import("behavior/maximum_minimum.zig");
-            _ = @import("behavior/popcount.zig");
             _ = @import("behavior/saturating_arithmetic.zig");
             _ = @import("behavior/widening.zig");
             _ = @import("behavior/bugs/2114.zig");
diff --git a/test/behavior/bitreverse.zig b/test/behavior/bitreverse.zig
index a355572f84..183e9aac55 100644
--- a/test/behavior/bitreverse.zig
+++ b/test/behavior/bitreverse.zig
@@ -5,7 +5,6 @@ const minInt = std.math.minInt;
 
 test "@bitReverse large exotic integer" {
     if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest;
-    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest;
     // Currently failing on stage1 for big-endian targets
     if (builtin.zig_backend == .stage1) return error.SkipZigTest;
 
@@ -14,7 +13,6 @@ test "@bitReverse large exotic integer" {
 
 test "@bitReverse" {
     if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest;
-    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest;
diff --git a/test/behavior/byteswap.zig b/test/behavior/byteswap.zig
index 265bc40f99..15046cc0e1 100644
--- a/test/behavior/byteswap.zig
+++ b/test/behavior/byteswap.zig
@@ -4,7 +4,6 @@ const expect = std.testing.expect;
 
 test "@byteSwap integers" {
     if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest;
-    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest;
diff --git a/test/behavior/math.zig b/test/behavior/math.zig
index 31dd6d09f3..05decb348e 100644
--- a/test/behavior/math.zig
+++ b/test/behavior/math.zig
@@ -81,7 +81,6 @@ test "@clz big ints" {
     if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
-    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
 
     try testClzBigInts();
     comptime try testClzBigInts();
diff --git a/test/behavior/popcount.zig b/test/behavior/popcount.zig
index d906c1bcc0..bad067a6f3 100644
--- a/test/behavior/popcount.zig
+++ b/test/behavior/popcount.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("std");
 const expect = std.testing.expect;
 const expectEqual = std.testing.expectEqual;
@@ -36,6 +37,10 @@ fn testPopCountIntegers() !void {
         var x: i8 = -120;
         try expect(@popCount(i8, x) == 2);
     }
+    {
+        var x: u128 = 0b11111111000110001100010000100001000011000011100101010001;
+        try expect(@popCount(u128, x) == 24);
+    }
     comptime {
         try expect(@popCount(u8, @bitCast(u8, @as(i8, -120))) == 2);
     }
@@ -45,6 +50,8 @@ fn testPopCountIntegers() !void {
 }
 
 test "@popCount vectors" {
+    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
+
     comptime try testPopCountVectors();
     try testPopCountVectors();
 }