[libc-commits] [libc] [libc] Some MSVC compatibility fixes in src/__support. (PR #159428)
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Wed Sep 17 12:11:23 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libc
Author: None (lntue)
<details>
<summary>Changes</summary>
---
Full diff: https://github.com/llvm/llvm-project/pull/159428.diff
6 Files Affected:
- (modified) libc/src/__support/CMakeLists.txt (+1)
- (modified) libc/src/__support/CPP/CMakeLists.txt (+2)
- (modified) libc/src/__support/CPP/bit.h (+2-1)
- (modified) libc/src/__support/CPP/new.h (+5)
- (modified) libc/src/__support/big_int.h (+13-13)
- (modified) libc/src/__support/math_extras.h (+11)
``````````diff
diff --git a/libc/src/__support/CMakeLists.txt b/libc/src/__support/CMakeLists.txt
index 0ef09a9b8c9d0..73d0ad15584fc 100644
--- a/libc/src/__support/CMakeLists.txt
+++ b/libc/src/__support/CMakeLists.txt
@@ -123,6 +123,7 @@ add_header_library(
libc.src.__support.CPP.type_traits
libc.src.__support.macros.attributes
libc.src.__support.macros.config
+ libc.src.__support.macros.properties.compiler
)
add_header_library(
diff --git a/libc/src/__support/CPP/CMakeLists.txt b/libc/src/__support/CPP/CMakeLists.txt
index a9cb67df0b427..bdfbc6151c773 100644
--- a/libc/src/__support/CPP/CMakeLists.txt
+++ b/libc/src/__support/CPP/CMakeLists.txt
@@ -20,6 +20,7 @@ add_header_library(
libc.hdr.stdint_proxy
libc.src.__support.macros.attributes
libc.src.__support.macros.sanitizer
+ libc.src.__support.macros.properties.compiler
)
add_header_library(
@@ -209,6 +210,7 @@ add_object_library(
libc.hdr.func.malloc
libc.hdr.func.aligned_alloc
libc.src.__support.common
+ libc.src.__support.macros.properties.compiler
libc.src.__support.macros.properties.os
)
diff --git a/libc/src/__support/CPP/bit.h b/libc/src/__support/CPP/bit.h
index 8dbb30047faec..f602a7447ec10 100644
--- a/libc/src/__support/CPP/bit.h
+++ b/libc/src/__support/CPP/bit.h
@@ -16,6 +16,7 @@
#include "src/__support/CPP/type_traits.h"
#include "src/__support/macros/attributes.h"
#include "src/__support/macros/config.h"
+#include "src/__support/macros/properties/compiler.h"
#include "src/__support/macros/sanitizer.h"
namespace LIBC_NAMESPACE_DECL {
@@ -36,7 +37,7 @@ LIBC_INLINE constexpr cpp::enable_if_t<
To>
bit_cast(const From &from) {
MSAN_UNPOISON(&from, sizeof(From));
-#if __has_builtin(__builtin_bit_cast)
+#if __has_builtin(__builtin_bit_cast) || defined(LIBC_COMPILER_IS_MSVC)
return __builtin_bit_cast(To, from);
#else
To to{};
diff --git a/libc/src/__support/CPP/new.h b/libc/src/__support/CPP/new.h
index fe36de29468a8..67344b09e3833 100644
--- a/libc/src/__support/CPP/new.h
+++ b/libc/src/__support/CPP/new.h
@@ -14,6 +14,7 @@
#include "hdr/func/malloc.h"
#include "src/__support/common.h"
#include "src/__support/macros/config.h"
+#include "src/__support/macros/properties/compiler.h"
#include "src/__support/macros/properties/os.h"
#include <stddef.h> // For size_t
@@ -109,8 +110,12 @@ LIBC_INLINE void *operator new[](size_t, void *p) { return p; }
// header file in all libc source files where operator delete is called ensures
// that only libc call sites use these replacement operator delete functions.
+#ifndef LIBC_COMPILER_IS_MSVC
#define DELETE_NAME(name) \
__asm__(LIBC_MACRO_TO_STRING(LIBC_NAMESPACE) "_" LIBC_MACRO_TO_STRING(name))
+#else
+#define DELETE_NAME(name)
+#endif // LIBC_COMPILER_IS_MSVC
void operator delete(void *) noexcept DELETE_NAME(delete);
void operator delete(void *, std::align_val_t) noexcept
diff --git a/libc/src/__support/big_int.h b/libc/src/__support/big_int.h
index 10e35ef4fd24a..bb9cefd67b552 100644
--- a/libc/src/__support/big_int.h
+++ b/libc/src/__support/big_int.h
@@ -95,10 +95,10 @@ LIBC_INLINE constexpr DoubleWide<word> mul2(word a, word b) {
#endif
else {
using half_word = half_width_t<word>;
- const auto shiftl = [](word value) -> word {
+ constexpr auto shiftl = [](word value) -> word {
return value << cpp::numeric_limits<half_word>::digits;
};
- const auto shiftr = [](word value) -> word {
+ constexpr auto shiftr = [](word value) -> word {
return value >> cpp::numeric_limits<half_word>::digits;
};
// Here we do a one digit multiplication where 'a' and 'b' are of type
@@ -111,19 +111,19 @@ LIBC_INLINE constexpr DoubleWide<word> mul2(word a, word b) {
// c result
// We convert 'lo' and 'hi' from 'half_word' to 'word' so multiplication
// doesn't overflow.
- const word a_lo = lo(a);
- const word b_lo = lo(b);
- const word a_hi = hi(a);
- const word b_hi = hi(b);
- const word step1 = b_lo * a_lo; // no overflow;
- const word step2 = b_lo * a_hi; // no overflow;
- const word step3 = b_hi * a_lo; // no overflow;
- const word step4 = b_hi * a_hi; // no overflow;
+ word a_lo = lo(a);
+ word b_lo = lo(b);
+ word a_hi = hi(a);
+ word b_hi = hi(b);
+ word step1 = b_lo * a_lo; // no overflow;
+ word step2 = b_lo * a_hi; // no overflow;
+ word step3 = b_hi * a_lo; // no overflow;
+ word step4 = b_hi * a_hi; // no overflow;
word lo_digit = step1;
word hi_digit = step4;
- const word no_carry = 0;
- word carry;
- word _; // unused carry variable.
+ word no_carry = 0;
+ word carry = 0;
+ [[maybe_unused]] word _ = 0; // unused carry variable.
lo_digit = add_with_carry<word>(lo_digit, shiftl(step2), no_carry, carry);
hi_digit = add_with_carry<word>(hi_digit, shiftr(step2), carry, _);
lo_digit = add_with_carry<word>(lo_digit, shiftl(step3), no_carry, carry);
diff --git a/libc/src/__support/math_extras.h b/libc/src/__support/math_extras.h
index d4dc6dcb4acf6..093a3371de3cd 100644
--- a/libc/src/__support/math_extras.h
+++ b/libc/src/__support/math_extras.h
@@ -15,6 +15,7 @@
#include "src/__support/CPP/type_traits.h" // is_unsigned_v, is_constant_evaluated
#include "src/__support/macros/attributes.h" // LIBC_INLINE
#include "src/__support/macros/config.h"
+#include "src/__support/macros/properties/compiler.h"
namespace LIBC_NAMESPACE_DECL {
@@ -25,7 +26,17 @@ LIBC_INLINE constexpr cpp::enable_if_t<cpp::is_unsigned_v<T>, T>
mask_trailing_ones() {
constexpr unsigned T_BITS = CHAR_BIT * sizeof(T);
static_assert(count <= T_BITS && "Invalid bit index");
+#ifndef LIBC_COMPILER_IS_MSVC
return count == 0 ? 0 : (T(-1) >> (T_BITS - count));
+#else
+ // MSVC complains about out of range shifts.
+ if constexpr (count == 0)
+ return 0;
+ else if constexpr (count >= T_BITS)
+ return T(-1);
+ else
+ return T(-1) >> (T_BITS - count);
+#endif // !LIBC_COMPILER_IS_MSVC
}
// Create a bitmask with the count left-most bits set to 1, and all other bits
``````````
</details>
https://github.com/llvm/llvm-project/pull/159428
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