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Merged
Stephan T. Lavavej (StephanTLavavej) merged 3 commits into from
Sep 3, 2026
+97 −28
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<cmath>: Support /Zc:cmath downlevel #6425

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21c1255
cmath: Use builtins for MSVC /Zc:cmath in all Standard modes, not jus…
StephanTLavavej Aug 31, 2026
99ceb88
P0533R9_constexpr_for_cmath_and_cstdlib/test.cpp: Update to work in a…
StephanTLavavej Aug 31, 2026
8a5a918
P0533R9_constexpr_for_cmath_and_cstdlib/env.lst: Expand test matrix d…
StephanTLavavej Aug 31, 2026
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6 changes: 3 additions & 3 deletions stl/inc/cmath
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Original file line number Diff line number Diff line change
Expand Up @@ -11,14 +11,14 @@
#include <cstdlib>
#include <type_traits>

// MSVC provides constexpr builtins in C++23 and later, except when /Zc:cmath- opts out of constexpr.
#if defined(__clang__) || defined(__cpp_lib_constexpr_cmath)
// Clang and MSVC /Zc:cmath provide builtins.
#if defined(__clang__) || defined(_MSVC_LIBC_MATH)
#define _HAS_CMATH_BUILTINS 1
#else // ^^^ builtins available / builtins unavailable vvv
#define _HAS_CMATH_BUILTINS 0
#endif // ^^^ builtins unavailable ^^^

// When constexpr builtins are unavailable, fall back to intrinsics for better codegen.
// When builtins are unavailable, fall back to intrinsics for better codegen.
#if !_HAS_CMATH_BUILTINS && !defined(_M_CEE) // TRANSITION, VSO-1663104
#define _HAS_CMATH_INTRINSICS 1
#else // ^^^ intrinsics available / intrinsics unavailable vvv
Expand Down
74 changes: 61 additions & 13 deletions tests/std/tests/P0533R9_constexpr_for_cmath_and_cstdlib/env.lst
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Original file line number Diff line number Diff line change
@@ -1,23 +1,71 @@
# Copyright (c) Microsoft Corporation.
# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

RUNALL_INCLUDE ..\usual_latest_matrix.lst
RUNALL_INCLUDE ..\usual_matrix.lst

# Explicitly enable libc-based math:
# TRANSITION, MSVC-PR-766982 renamed /experimental:mathlib to /Zc:cmath, pass both until this change ships
PM_CL="/MD /Zc:cmath /experimental:mathlib"
PM_CL="/MDd /Zc:cmath /experimental:mathlib"
PM_CL="/MT /Zc:cmath /experimental:mathlib"
PM_CL="/MTd /Zc:cmath /experimental:mathlib"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++14 /MD"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++14 /MDd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++14 /MT"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++14 /MTd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++17 /MD"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++17 /MDd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++17 /MT"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++17 /MTd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++20 /MD"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++20 /MDd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++20 /MT"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++20 /MTd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++23preview /MD"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++23preview /MDd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++23preview /MT"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++23preview /MTd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++latest /MD"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++latest /MDd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++latest /MT"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /std:c++latest /MTd"

# /O2 implies /Oi which affects <__msvc_math.hpp>:
PM_CL="/MD /Zc:cmath /experimental:mathlib /O2"
PM_CL="/MDd /Zc:cmath /experimental:mathlib /O2"
PM_CL="/MT /Zc:cmath /experimental:mathlib /O2"
PM_CL="/MTd /Zc:cmath /experimental:mathlib /O2"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++14 /MD"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++14 /MDd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++14 /MT"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++14 /MTd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++17 /MD"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++17 /MDd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++17 /MT"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++17 /MTd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++20 /MD"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++20 /MDd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++20 /MT"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++20 /MTd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++23preview /MD"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++23preview /MDd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++23preview /MT"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++23preview /MTd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++latest /MD"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++latest /MDd"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++latest /MT"
PM_CL="/EHsc /Zc:cmath /experimental:mathlib /O2 /std:c++latest /MTd"

# Explicitly disable libc-based math:
PM_CL="/MD /Zc:cmath-"
PM_CL="/MDd /Zc:cmath-"
PM_CL="/MT /Zc:cmath-"
PM_CL="/MTd /Zc:cmath-"
PM_CL="/EHsc /Zc:cmath- /std:c++14 /MD"
PM_CL="/EHsc /Zc:cmath- /std:c++14 /MDd"
PM_CL="/EHsc /Zc:cmath- /std:c++14 /MT"
PM_CL="/EHsc /Zc:cmath- /std:c++14 /MTd"
PM_CL="/EHsc /Zc:cmath- /std:c++17 /MD"
PM_CL="/EHsc /Zc:cmath- /std:c++17 /MDd"
PM_CL="/EHsc /Zc:cmath- /std:c++17 /MT"
PM_CL="/EHsc /Zc:cmath- /std:c++17 /MTd"
PM_CL="/EHsc /Zc:cmath- /std:c++20 /MD"
PM_CL="/EHsc /Zc:cmath- /std:c++20 /MDd"
PM_CL="/EHsc /Zc:cmath- /std:c++20 /MT"
PM_CL="/EHsc /Zc:cmath- /std:c++20 /MTd"
PM_CL="/EHsc /Zc:cmath- /std:c++23preview /MD"
PM_CL="/EHsc /Zc:cmath- /std:c++23preview /MDd"
PM_CL="/EHsc /Zc:cmath- /std:c++23preview /MT"
PM_CL="/EHsc /Zc:cmath- /std:c++23preview /MTd"
PM_CL="/EHsc /Zc:cmath- /std:c++latest /MD"
PM_CL="/EHsc /Zc:cmath- /std:c++latest /MDd"
PM_CL="/EHsc /Zc:cmath- /std:c++latest /MT"
PM_CL="/EHsc /Zc:cmath- /std:c++latest /MTd"
45 changes: 33 additions & 12 deletions tests/std/tests/P0533R9_constexpr_for_cmath_and_cstdlib/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8,13 +8,32 @@
#include <type_traits>
using namespace std;

#if !_HAS_CXX17
#pragma warning(disable : 4984) // 'if constexpr' is a C++17 language extension
#ifdef __clang__
#pragma clang diagnostic ignored "-Wc++17-extensions" // warning: constexpr if is a C++17 extension
#endif // ^^^ defined(__clang__) ^^^
#endif // ^^^ !_HAS_CXX17 ^^^

#ifdef __cpp_lib_constexpr_cmath
#define CONSTEXPR_CMATH23 constexpr
#else
#define CONSTEXPR_CMATH23 inline
#endif

#if _HAS_CXX26 && defined(_MSVC_LIBC_MATH) // TRANSITION, GH-3789, should be `__cpp_lib_constexpr_cmath >= 202306L`
#define CONSTEXPR_CMATH26 constexpr
#else
#define CONSTEXPR_CMATH26 inline
#endif

template <class T>
constexpr void test_classification_functions_cxx23();
CONSTEXPR_CMATH23 void test_classification_functions_cxx23();

template <class T>
constexpr void test_comparison_functions_cxx23();
CONSTEXPR_CMATH23 void test_comparison_functions_cxx23();

constexpr bool test_cmath_cxx23() {
CONSTEXPR_CMATH23 bool test_cmath_cxx23() {
#if defined(_MSVC_INTERNAL_TESTING) || !defined(_MSVC_LIBC_MATH) // TRANSITION, MSVC-PR-767184/772024 fixed LNK2005
{
int exponent = 0;
Expand Down Expand Up @@ -220,7 +239,7 @@ constexpr bool test_cmath_cxx23() {
test_classification_functions_cxx23<int>();

#ifndef _MSVC_INTERNAL_TESTING // TRANSITION, MSVC-PR-767404 fixed the comparison functions in constant evaluation
if !consteval
if (!_Is_constant_evaluated())
#endif // ^^^ workaround ^^^
{
test_comparison_functions_cxx23<float>();
Expand All @@ -233,7 +252,7 @@ constexpr bool test_cmath_cxx23() {
}

template <class T>
constexpr void test_classification_functions_cxx23() {
CONSTEXPR_CMATH23 void test_classification_functions_cxx23() {
{
constexpr T zro{};
constexpr T val = static_cast<T>(5);
Expand Down Expand Up @@ -292,7 +311,7 @@ constexpr void test_classification_functions_cxx23() {
}

template <class T>
constexpr void test_comparison_functions_cxx23() {
CONSTEXPR_CMATH23 void test_comparison_functions_cxx23() {
constexpr T lo = static_cast<T>(-3);
constexpr T hi = static_cast<T>(4);

Expand Down Expand Up @@ -352,7 +371,7 @@ constexpr void test_comparison_functions_cxx23() {
}
}

constexpr bool test_cstdlib_cxx23() {
CONSTEXPR_CMATH23 bool test_cstdlib_cxx23() {
assert(abs(-5) == 5);
assert(abs(-5L) == 5L);
assert(abs(-5LL) == 5LL);
Expand Down Expand Up @@ -380,7 +399,7 @@ constexpr bool test_cstdlib_cxx23() {
return true;
}

constexpr bool test_cmath_cxx26() {
CONSTEXPR_CMATH26 bool test_cmath_cxx26() {
// These tests use round() because they're checking for basic functionality, not precision.

assert(round(acos(0.6f) * 1000.0f) == 927.0f);
Expand Down Expand Up @@ -432,7 +451,7 @@ constexpr bool test_cmath_cxx26() {
assert(round(tanl(0.6l) * 1000.0l) == 684.0l);
assert(round(tan(1729) * 1000.0) == 2087.0);

if !consteval { // TRANSITION, GH-3789
if (!_Is_constant_evaluated()) { // TRANSITION, GH-3789
assert(round(acosh(3.3f) * 1000.0f) == 1863.0f);
assert(round(acosh(3.3) * 1000.0) == 1863.0);
assert(round(acosh(3.3l) * 1000.0l) == 1863.0l);
Expand Down Expand Up @@ -483,7 +502,7 @@ constexpr bool test_cmath_cxx26() {
assert(round(expl(0.6l) * 1000.0l) == 1822.0l);
assert(round(exp(2) * 1000.0) == 7389.0);

if !consteval { // TRANSITION, GH-3789
if (!_Is_constant_evaluated()) { // TRANSITION, GH-3789
assert(round(exp2(0.6f) * 1000.0f) == 1516.0f);
assert(round(exp2(0.6) * 1000.0) == 1516.0);
assert(round(exp2(0.6l) * 1000.0l) == 1516.0l);
Expand Down Expand Up @@ -541,13 +560,15 @@ constexpr bool test_cmath_cxx26() {
assert(round(hypotl(3.3l, 7.7l) * 1000.0l) == 8377.0l);
assert(round(hypot(3, 7) * 1000.0) == 7616.0);

if !consteval { // TRANSITION, GH-3789
#if _HAS_CXX17
if (!_Is_constant_evaluated()) { // TRANSITION, GH-3789
assert(round(hypot(2.2f, 3.3f, 4.4f) * 1000.0f) == 5924.0f);
assert(round(hypot(2.2, 3.3, 4.4) * 1000.0) == 5924.0);
assert(round(hypot(2.2l, 3.3l, 4.4l) * 1000.0l) == 5924.0l);
assert(round(hypot(2, 3, 4) * 1000.0) == 5385.0);
// No 3-arg overloads for hypotf() and hypotl()
}
#endif // ^^^ _HAS_CXX17 ^^^

assert(round(pow(3.3f, 0.6f) * 1000.0f) == 2047.0f);
assert(round(pow(3.3, 0.6) * 1000.0) == 2047.0);
Expand All @@ -563,7 +584,7 @@ constexpr bool test_cmath_cxx26() {
assert(round(sqrtl(0.6l) * 1000.0l) == 775.0l);
assert(round(sqrt(7) * 1000.0) == 2646.0);

if !consteval { // TRANSITION, GH-3789
if (!_Is_constant_evaluated()) { // TRANSITION, GH-3789
assert(round(erf(0.6f) * 1000.0f) == 604.0f);
assert(round(erf(0.6) * 1000.0) == 604.0);
assert(round(erf(0.6l) * 1000.0l) == 604.0l);
Expand Down