Revert "[libc] Make BigInt bit_cast-able to compatible types" (#74887)

This reverts the following commits:
 - a539a090009378ecfcfbfaaa280eeac8f5b9d695
 - 31316b3f8511d659cc14ebc72fb2b226f78478a9

Rationale for revert:
https://github.com/llvm/llvm-project/issues/74258#issuecomment-1847836861

5 files changed, 22 insertions, 81 deletions

diff --git a/libc/src/__support/UInt.h b/libc/src/__support/UInt.h
index bdc713e..f72b995 100644
--- a/libc/src/__support/UInt.h
+++ b/libc/src/__support/UInt.h
@@ -25,13 +25,12 @@
 
 namespace LIBC_NAMESPACE::cpp {
 
-// BigInt has the same semantics as the 'standard integer types' and can be
-// safely 'bit_cast'ed to compatible types.
 template <size_t Bits, bool Signed> struct BigInt {
+
   static_assert(Bits > 0 && Bits % 64 == 0,
                 "Number of bits in BigInt should be a multiple of 64.");
   LIBC_INLINE_VAR static constexpr size_t WORDCOUNT = Bits / 64;
-  uint64_t val[WORDCOUNT];
+  uint64_t val[WORDCOUNT]{};
 
   LIBC_INLINE_VAR static constexpr uint64_t MASK32 = 0xFFFFFFFFu;
 
@@ -159,7 +158,7 @@ template <size_t Bits, bool Signed> struct BigInt {
 
   LIBC_INLINE constexpr BigInt<Bits, Signed>
   operator+(const BigInt<Bits, Signed> &other) const {
-    BigInt<Bits, Signed> result(0);
+    BigInt<Bits, Signed> result;
     SumCarry<uint64_t> s{0, 0};
     for (size_t i = 0; i < WORDCOUNT; ++i) {
       s = add_with_carry(val[i], other.val[i], s.carry);
@@ -172,7 +171,7 @@ template <size_t Bits, bool Signed> struct BigInt {
   // it will always use the constexpr version of add_with_carry.
   LIBC_INLINE constexpr BigInt<Bits, Signed>
   operator+(BigInt<Bits, Signed> &&other) const {
-    BigInt<Bits, Signed> result(0);
+    BigInt<Bits, Signed> result;
     SumCarry<uint64_t> s{0, 0};
     for (size_t i = 0; i < WORDCOUNT; ++i) {
       s = add_with_carry_const(val[i], other.val[i], s.carry);
@@ -200,7 +199,7 @@ template <size_t Bits, bool Signed> struct BigInt {
 
   LIBC_INLINE BigInt<Bits, Signed>
   operator-(const BigInt<Bits, Signed> &other) const {
-    BigInt<Bits, Signed> result(0);
+    BigInt<Bits, Signed> result;
     DiffBorrow<uint64_t> d{0, 0};
     for (size_t i = 0; i < WORDCOUNT; ++i) {
       d = sub_with_borrow(val[i], other.val[i], d.borrow);
@@ -211,7 +210,7 @@ template <size_t Bits, bool Signed> struct BigInt {
 
   LIBC_INLINE constexpr BigInt<Bits, Signed>
   operator-(BigInt<Bits, Signed> &&other) const {
-    BigInt<Bits, Signed> result(0);
+    BigInt<Bits, Signed> result;
     DiffBorrow<uint64_t> d{0, 0};
     for (size_t i = 0; i < WORDCOUNT; ++i) {
       d = sub_with_borrow_const(val[i], other.val[i], d.borrow);
@@ -691,7 +690,7 @@ template <size_t Bits, bool Signed> struct BigInt {
 
   LIBC_INLINE constexpr BigInt<Bits, Signed>
   operator&(const BigInt<Bits, Signed> &other) const {
-    BigInt<Bits, Signed> result(0);
+    BigInt<Bits, Signed> result;
     for (size_t i = 0; i < WORDCOUNT; ++i)
       result.val[i] = val[i] & other.val[i];
     return result;
@@ -706,7 +705,7 @@ template <size_t Bits, bool Signed> struct BigInt {
 
   LIBC_INLINE constexpr BigInt<Bits, Signed>
   operator|(const BigInt<Bits, Signed> &other) const {
-    BigInt<Bits, Signed> result(0);
+    BigInt<Bits, Signed> result;
     for (size_t i = 0; i < WORDCOUNT; ++i)
       result.val[i] = val[i] | other.val[i];
     return result;
@@ -721,7 +720,7 @@ template <size_t Bits, bool Signed> struct BigInt {
 
   LIBC_INLINE constexpr BigInt<Bits, Signed>
   operator^(const BigInt<Bits, Signed> &other) const {
-    BigInt<Bits, Signed> result(0);
+    BigInt<Bits, Signed> result;
     for (size_t i = 0; i < WORDCOUNT; ++i)
       result.val[i] = val[i] ^ other.val[i];
     return result;
@@ -735,7 +734,7 @@ template <size_t Bits, bool Signed> struct BigInt {
   }
 
   LIBC_INLINE constexpr BigInt<Bits, Signed> operator~() const {
-    BigInt<Bits, Signed> result(0);
+    BigInt<Bits, Signed> result;
     for (size_t i = 0; i < WORDCOUNT; ++i)
       result.val[i] = ~val[i];
     return result;
diff --git a/libc/src/__support/float_to_string.h b/libc/src/__support/float_to_string.h
index 92dd2e8..34c0c0c 100644
--- a/libc/src/__support/float_to_string.h
+++ b/libc/src/__support/float_to_string.h
@@ -653,7 +653,7 @@ FloatToString<long double>::get_positive_block(int block_index) {
 
     // shift_amount = -(c0 - exponent) = c_0 + 16 * ceil(exponent/16) - exponent
 
-    cpp::UInt<MID_INT_SIZE> val(0);
+    cpp::UInt<MID_INT_SIZE> val;
 #ifdef LIBC_COPT_FLOAT_TO_STR_USE_MEGA_LONG_DOUBLE_TABLE
     // ------------------------------ TABLE MODE -------------------------------
     const int32_t SHIFT_CONST = TABLE_SHIFT_CONST;
@@ -704,7 +704,7 @@ FloatToString<long double>::get_negative_block(int block_index) {
   if (exponent < 0) {
     const int32_t idx = -exponent / IDX_SIZE;
 
-    cpp::UInt<MID_INT_SIZE> val(0);
+    cpp::UInt<MID_INT_SIZE> val;
 #ifdef LIBC_COPT_FLOAT_TO_STR_USE_MEGA_LONG_DOUBLE_TABLE
     // ------------------------------ TABLE MODE -------------------------------
     const int32_t SHIFT_CONST = TABLE_SHIFT_CONST;
diff --git a/libc/test/src/__support/CMakeLists.txt b/libc/test/src/__support/CMakeLists.txt
index 187b707..740209b 100644
--- a/libc/test/src/__support/CMakeLists.txt
+++ b/libc/test/src/__support/CMakeLists.txt
@@ -89,11 +89,8 @@ add_libc_test(
   SRCS
     uint_test.cpp
   DEPENDS
-    libc.src.__support.CPP.bit
-    libc.src.__support.CPP.optional
-    libc.src.__support.CPP.type_traits
-    libc.src.__support.macros.properties.float
     libc.src.__support.uint
+    libc.src.__support.CPP.optional
 )
 
 add_libc_test(
diff --git a/libc/test/src/__support/uint_test.cpp b/libc/test/src/__support/uint_test.cpp
index e4d24b0..971bac5 100644
--- a/libc/test/src/__support/uint_test.cpp
+++ b/libc/test/src/__support/uint_test.cpp
@@ -6,73 +6,23 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "src/__support/CPP/bit.h" // bit_cast
 #include "src/__support/CPP/optional.h"
-#include "src/__support/CPP/type_traits.h" // is_trivially_constructible
 #include "src/__support/UInt.h"
-#include "src/__support/macros/properties/float.h" // LIBC_COMPILER_HAS_FLOAT128
 
 #include "test/UnitTest/Test.h"
 
-#include <math.h> // HUGE_VALF, HUGE_VALF
-
-namespace LIBC_NAMESPACE {
-
-using LL_UInt64 = cpp::UInt<64>;
-// We want to test cpp::UInt<128> explicitly. So, for
+// We want to test LIBC_NAMESPACE::cpp::UInt<128> explicitly. So, for
 // convenience, we use a sugar which does not conflict with the UInt128 type
 // which can resolve to __uint128_t if the platform has it.
-using LL_UInt128 = cpp::UInt<128>;
-using LL_UInt192 = cpp::UInt<192>;
-using LL_UInt256 = cpp::UInt<256>;
-using LL_UInt320 = cpp::UInt<320>;
-using LL_UInt512 = cpp::UInt<512>;
-using LL_UInt1024 = cpp::UInt<1024>;
-
-using LL_Int128 = cpp::Int<128>;
-using LL_Int192 = cpp::Int<192>;
-
-TEST(LlvmLibcUIntClassTest, BitCastToFromDouble) {
-  static_assert(cpp::is_trivially_constructible<LL_UInt64>::value);
-  static_assert(cpp::is_trivially_copyable<LL_UInt64>::value);
-  static_assert(sizeof(LL_UInt64) == sizeof(double));
-  const double inf = HUGE_VAL;
-  const double max = DBL_MAX;
-  const double array[] = {0.0, 0.1, 1.0, max, inf};
-  for (double value : array) {
-    LL_UInt64 back = cpp::bit_cast<LL_UInt64>(value);
-    double forth = cpp::bit_cast<double>(back);
-    EXPECT_TRUE(value == forth);
-  }
-}
+using LL_UInt128 = LIBC_NAMESPACE::cpp::UInt<128>;
+using LL_UInt192 = LIBC_NAMESPACE::cpp::UInt<192>;
+using LL_UInt256 = LIBC_NAMESPACE::cpp::UInt<256>;
+using LL_UInt320 = LIBC_NAMESPACE::cpp::UInt<320>;
+using LL_UInt512 = LIBC_NAMESPACE::cpp::UInt<512>;
+using LL_UInt1024 = LIBC_NAMESPACE::cpp::UInt<1024>;
 
-#ifdef __SIZEOF_INT128__
-TEST(LlvmLibcUIntClassTest, BitCastToFromNativeUint128) {
-  static_assert(cpp::is_trivially_constructible<LL_UInt128>::value);
-  static_assert(cpp::is_trivially_copyable<LL_UInt128>::value);
-  static_assert(sizeof(LL_UInt128) == sizeof(__uint128_t));
-  const __uint128_t array[] = {0, 1, ~__uint128_t(0)};
-  for (__uint128_t value : array) {
-    LL_UInt128 back = cpp::bit_cast<LL_UInt128>(value);
-    __uint128_t forth = cpp::bit_cast<__uint128_t>(back);
-    EXPECT_TRUE(value == forth);
-  }
-}
-#endif
-
-#ifdef LIBC_COMPILER_HAS_FLOAT128
-TEST(LlvmLibcUIntClassTest, BitCastToFromNativeFloat128) {
-  static_assert(cpp::is_trivially_constructible<LL_UInt128>::value);
-  static_assert(cpp::is_trivially_copyable<LL_UInt128>::value);
-  static_assert(sizeof(LL_UInt128) == sizeof(float128));
-  const float128 array[] = {0, 0.1, 1};
-  for (float128 value : array) {
-    LL_UInt128 back = cpp::bit_cast<LL_UInt128>(value);
-    float128 forth = cpp::bit_cast<float128>(back);
-    EXPECT_TRUE(value == forth);
-  }
-}
-#endif
+using LL_Int128 = LIBC_NAMESPACE::cpp::Int<128>;
+using LL_Int192 = LIBC_NAMESPACE::cpp::Int<192>;
 
 TEST(LlvmLibcUIntClassTest, BasicInit) {
   LL_UInt128 half_val(12345);
@@ -684,5 +634,3 @@ TEST(LlvmLibcUIntClassTest, ConstructorFromUInt128Tests) {
 }
 
 #endif // __SIZEOF_INT128__
-
-} // namespace LIBC_NAMESPACE
diff --git a/utils/bazel/llvm-project-overlay/libc/test/src/__support/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/test/src/__support/BUILD.bazel
index f775183..a973e65 100644
--- a/utils/bazel/llvm-project-overlay/libc/test/src/__support/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/test/src/__support/BUILD.bazel
@@ -74,10 +74,7 @@ libc_test(
     name = "uint_test",
     srcs = ["uint_test.cpp"],
     deps = [
-        "//libc:__support_cpp_bit",
         "//libc:__support_cpp_optional",
-        "//libc:__support_cpp_type_traits",
-        "//libc:__support_macros_properties_float",
         "//libc:__support_uint",
     ],
 )