[libc-commits] [libc] [libc] Fix add_with_carry constexpr (PR #154282)

[Guillaume Chatelet via libc-commits]

https://github.com/gchatelet updated https://github.com/llvm/llvm-project/pull/154282

>From 1e57b21482e670d56049bcd3158eb79e17ffff98 Mon Sep 17 00:00:00 2001
From: Guillaume Chatelet <gchatelet at google.com>
Date: Tue, 19 Aug 2025 08:06:26 +0000
Subject: [PATCH 1/2] [libc] Fix add_with_carry constexpr

The previous version of the code would prevent the use of the add with
carry compiler builtin.
---
 libc/src/__support/math_extras.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libc/src/__support/math_extras.h b/libc/src/__support/math_extras.h
index 47df2a43250c8..0a0a2a829e1bf 100644
--- a/libc/src/__support/math_extras.h
+++ b/libc/src/__support/math_extras.h
@@ -66,7 +66,7 @@ template <typename T>
 
 #define RETURN_IF(TYPE, BUILTIN)                                               \
   if constexpr (cpp::is_same_v<T, TYPE>)                                       \
-    return BUILTIN(a, b, carry_in, carry_out);
+    return BUILTIN(a, b, carry_in, &carry_out);
 
 // Returns the result of 'a + b' taking into account 'carry_in'.
 // The carry out is stored in 'carry_out' it not 'nullptr', dropped otherwise.
@@ -74,7 +74,7 @@ template <typename T>
 template <typename T>
 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
 add_with_carry(T a, T b, T carry_in, T &carry_out) {
-  if constexpr (!cpp::is_constant_evaluated()) {
+  if (!cpp::is_constant_evaluated()) {
 #if __has_builtin(__builtin_addcb)
     RETURN_IF(unsigned char, __builtin_addcb)
 #elif __has_builtin(__builtin_addcs)

>From b9ff9b11266d3e7cc9542de4a30d6e90c18abd64 Mon Sep 17 00:00:00 2001
From: Guillaume Chatelet <gchatelet at google.com>
Date: Tue, 19 Aug 2025 08:15:11 +0000
Subject: [PATCH 2/2] Also fix sub_with_borrow.

---
 libc/src/__support/math_extras.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libc/src/__support/math_extras.h b/libc/src/__support/math_extras.h
index 0a0a2a829e1bf..954bcb1b6ef89 100644
--- a/libc/src/__support/math_extras.h
+++ b/libc/src/__support/math_extras.h
@@ -100,7 +100,7 @@ add_with_carry(T a, T b, T carry_in, T &carry_out) {
 template <typename T>
 [[nodiscard]] LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
 sub_with_borrow(T a, T b, T carry_in, T &carry_out) {
-  if constexpr (!cpp::is_constant_evaluated()) {
+  if (!cpp::is_constant_evaluated()) {
 #if __has_builtin(__builtin_subcb)
     RETURN_IF(unsigned char, __builtin_subcb)
 #elif __has_builtin(__builtin_subcs)