[libc] Add add_with_carry to builtin wrapper.

[lntue]

Summary

Add add_with_carry to builtin wrapper to be used by UInt class.

[orex]

Another question to you is how the functions will work with implicit conversion. What I would do is to force input be the same with is_same of enable_if, if they are available.

libc/src/__support/builtin_wrappers.h

71

Don't you think it will be good to add here static assert, that T is integer and unsigned for this implementation?

74

Nit: From my point of view boolean OR will be more clear, than binary OR.

[lntue]

Address comments.

[lntue]

libc/src/__support/builtin_wrappers.h

71

Use enable_if to restrict to unsigned integers.

[orex]

libc/src/__support/builtin_wrappers.h

72

Thank you. Font you think, that you should put ::value everywhere here? I'm not so familiar with internal classes...

[lntue]

libc/src/__support/builtin_wrappers.h

72

Since C++17, _t and _v helpers were added to C++, and some of our internal cpp:: templates did follow.
https://en.cppreference.com/w/cpp/types/is_integral

libc/src/__support/CMakeLists.txt

 add_subdirectory(CPP)
 
 add_header_library(
   blockstore
   HDRS
     blockstore.h
 )
 
 add_header_library(
   builtin_wrappers
   HDRS
     builtin_wrappers.h
+  DEPENDS
+    libc.src.__support.CPP.type_traits
 )
 
 add_header_library(
   common
   HDRS
     architectures.h
     common.h
     endian.h

libc/src/__support/builtin_wrappers.h

 //===--Convenient template for builtins -------------------------*- C++ -*-===//
 //             (Count Lead Zeroes) and (Count Trailing Zeros)
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIBC_SRC_SUPPORT_BUILTIN_WRAPPERS_H
 #define LLVM_LIBC_SRC_SUPPORT_BUILTIN_WRAPPERS_H
 
+#include "src/__support/CPP/type_traits.h"
+
 namespace __llvm_libc {
 
 // The following overloads are matched based on what is accepted by
 // __builtin_clz/ctz* rather than using the exactly-sized aliases from stdint.h.
 // This way, we can avoid making any assumptions about integer sizes and let the
 // compiler match for us.
 namespace __internal {
 

 template <typename T> static inline int safe_clz(T val) {
   return __internal::correct_zero(val, __internal::clz(val));
 }
 
 template <typename T> static inline int unsafe_clz(T val) {
   return __internal::clz(val);
 }
 
+// Add with carry
+template <typename T>
+inline constexpr cpp::enable_if_t<
+    cpp::is_integral_v<T> && cpp::is_unsigned_v<T>, T>
+add_with_carry(T a, T b, T carry_in, T &carry_out) {
+  T tmp = a + carry_in;
+  T sum = b + tmp;
+  carry_out = (sum < b) || (tmp < a);
+  return sum;
+}
+
+#if __has_builtin(__builtin_addc)
+// https://clang.llvm.org/docs/LanguageExtensions.html#multiprecision-arithmetic-builtins
+
+template <>
+inline unsigned char add_with_carry<unsigned char>(unsigned char a,
+                                                   unsigned char b,
+                                                   unsigned char carry_in,
+                                                   unsigned char &carry_out) {
+  return __builtin_addcb(a, b, carry_in, &carry_out);
+}
+
+template <>
+inline unsigned short
+add_with_carry<unsigned short>(unsigned short a, unsigned short b,
+                               unsigned short carry_in,
+                               unsigned short &carry_out) {
+  return __builtin_addcs(a, b, carry_in, &carry_out);
+}
+
+template <>
+inline unsigned int add_with_carry<unsigned int>(unsigned int a, unsigned int b,
+                                                 unsigned int carry_in,
+                                                 unsigned int &carry_out) {
+  return __builtin_addc(a, b, carry_in, &carry_out);
+}
+
+template <>
+inline unsigned long add_with_carry<unsigned long>(unsigned long a,
+                                                   unsigned long b,
+                                                   unsigned long carry_in,
+                                                   unsigned long &carry_out) {
+  return __builtin_addcl(a, b, carry_in, &carry_out);
+}
+
+template <>
+inline unsigned long long
+add_with_carry<unsigned long long>(unsigned long long a, unsigned long long b,
+                                   unsigned long long carry_in,
+                                   unsigned long long &carry_out) {
+  return __builtin_addcll(a, b, carry_in, &carry_out);
+}
+#endif // __has_builtin(__builtin_addc)
+
 } // namespace __llvm_libc
 
 #endif // LLVM_LIBC_SRC_SUPPORT_BUILTIN_WRAPPERS_H

utils/bazel/llvm-project-overlay/libc/BUILD.bazel

deps = [
         ":libc_root",
     ],
 )
 
 cc_library(
     name = "__support_builtin_wrappers",
     hdrs = ["src/__support/builtin_wrappers.h"],
     deps = [
+        ":__support_cpp_type_traits",
         ":libc_root",
     ],
 )
 
 cc_library(
     name = "__support_fputil_division_and_remainder_operations",
     hdrs = ["src/__support/FPUtil/DivisionAndRemainderOperations.h"],
     deps = [