From fa76357d336ed44e3f2c5250a85c81b965f60946 Mon Sep 17 00:00:00 2001
From: Arlie Davis <ardavis@microsoft.com>
Date: Tue, 4 Aug 2026 11:11:04 -0700
Subject: [PATCH] Fix __FINITE_MATH_ONLY__ guard to test the value, not
 definedness

XMVectorIsNaN, XMVector2IsNaN, XMVector3IsNaN and XMVector4IsNaN each guard a
scalar fallback with:

    #if defined(__clang__) && defined(__FINITE_MATH_ONLY__)

but clang defines __FINITE_MATH_ONLY__ unconditionally -- 0 by default, and 1
only under -ffast-math / -ffinite-math-only (clang-cl /fp:fast).  The guard is
therefore always true under clang, so the fallback is compiled into every clang
build instead of only finite-math ones.

Two consequences:

- The fallback calls unqualified isnan(), so any clang target whose C++ library
  does not declare isnan() fails to compile.  This is how the bug surfaced.
- Where it does compile, a single vector compare is replaced by a store, four
  scalar tests and a reassemble.

Test the macro's value instead.  Verified with clang-cl that the guard is now
false at the default /fp:precise and still true under /fp:fast.

Affects both the NEON and SSE paths of all four functions (8 sites).
---
 Inc/DirectXMathVector.inl | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/Inc/DirectXMathVector.inl b/Inc/DirectXMathVector.inl
index 20bbab1d..761cf677 100644
--- a/Inc/DirectXMathVector.inl
+++ b/Inc/DirectXMathVector.inl
@@ -2186,7 +2186,7 @@ inline XMVECTOR XM_CALLCONV XMVectorIsNaN(FXMVECTOR V) noexcept
     return Control.v;
 
 #elif defined(_XM_ARM_NEON_INTRINSICS_)
-#if defined(__clang__) && defined(__FINITE_MATH_ONLY__)
+#if defined(__clang__) && __FINITE_MATH_ONLY__
     XMVECTORU32 vResult = { { {
         isnan(vgetq_lane_f32(V, 0)) ? 0xFFFFFFFFU : 0,
         isnan(vgetq_lane_f32(V, 1)) ? 0xFFFFFFFFU : 0,
@@ -2200,7 +2200,7 @@ inline XMVECTOR XM_CALLCONV XMVectorIsNaN(FXMVECTOR V) noexcept
     return vreinterpretq_f32_u32(vmvnq_u32(vTempNan));
 #endif
 #elif defined(_XM_SSE_INTRINSICS_)
-#if defined(__clang__) && defined(__FINITE_MATH_ONLY__)
+#if defined(__clang__) && __FINITE_MATH_ONLY__
     XM_ALIGNED_DATA(16) float tmp[4];
     _mm_store_ps(tmp, V);
     XMVECTORU32 vResult = { { {
@@ -6653,7 +6653,7 @@ inline bool XM_CALLCONV XMVector2IsNaN(FXMVECTOR V) noexcept
     return (XMISNAN(V.vector4_f32[0]) ||
         XMISNAN(V.vector4_f32[1]));
 #elif defined(_XM_ARM_NEON_INTRINSICS_)
-#if defined(__clang__) && defined(__FINITE_MATH_ONLY__)
+#if defined(__clang__) && __FINITE_MATH_ONLY__
     return isnan(vgetq_lane_f32(V, 0)) || isnan(vgetq_lane_f32(V, 1));
 #else
     float32x2_t VL = vget_low_f32(V);
@@ -6663,7 +6663,7 @@ inline bool XM_CALLCONV XMVector2IsNaN(FXMVECTOR V) noexcept
     return (vget_lane_u64(vreinterpret_u64_u32(vTempNan), 0) != 0xFFFFFFFFFFFFFFFFU);
 #endif
 #elif defined(_XM_SSE_INTRINSICS_)
-#if defined(__clang__) && defined(__FINITE_MATH_ONLY__)
+#if defined(__clang__) && __FINITE_MATH_ONLY__
     XM_ALIGNED_DATA(16) float tmp[4];
     _mm_store_ps(tmp, V);
     return isnan(tmp[0]) || isnan(tmp[1]);
@@ -9418,7 +9418,7 @@ inline bool XM_CALLCONV XMVector3IsNaN(FXMVECTOR V) noexcept
         XMISNAN(V.vector4_f32[2]));
 
 #elif defined(_XM_ARM_NEON_INTRINSICS_)
-#if defined(__clang__) && defined(__FINITE_MATH_ONLY__)
+#if defined(__clang__) && __FINITE_MATH_ONLY__
     return isnan(vgetq_lane_f32(V, 0)) || isnan(vgetq_lane_f32(V, 1)) || isnan(vgetq_lane_f32(V, 2));
 #else
 // Test against itself. NaN is always not equal
@@ -9429,7 +9429,7 @@ inline bool XM_CALLCONV XMVector3IsNaN(FXMVECTOR V) noexcept
     return ((vget_lane_u32(vreinterpret_u32_u16(vTemp2.val[1]), 1) & 0xFFFFFFU) != 0xFFFFFFU);
 #endif
 #elif defined(_XM_SSE_INTRINSICS_)
-#if defined(__clang__) && defined(__FINITE_MATH_ONLY__)
+#if defined(__clang__) && __FINITE_MATH_ONLY__
     XM_ALIGNED_DATA(16) float tmp[4];
     _mm_store_ps(tmp, V);
     return isnan(tmp[0]) || isnan(tmp[1]) || isnan(tmp[2]);
@@ -13309,7 +13309,7 @@ inline bool XM_CALLCONV XMVector4IsNaN(FXMVECTOR V) noexcept
         XMISNAN(V.vector4_f32[2]) ||
         XMISNAN(V.vector4_f32[3]));
 #elif defined(_XM_ARM_NEON_INTRINSICS_)
-#if defined(__clang__) && defined(__FINITE_MATH_ONLY__)
+#if defined(__clang__) && __FINITE_MATH_ONLY__
     return isnan(vgetq_lane_f32(V, 0)) || isnan(vgetq_lane_f32(V, 1)) || isnan(vgetq_lane_f32(V, 2)) || isnan(vgetq_lane_f32(V, 3));
 #else
 // Test against itself. NaN is always not equal
@@ -13320,7 +13320,7 @@ inline bool XM_CALLCONV XMVector4IsNaN(FXMVECTOR V) noexcept
     return (vget_lane_u32(vreinterpret_u32_u16(vTemp2.val[1]), 1) != 0xFFFFFFFFU);
 #endif
 #elif defined(_XM_SSE_INTRINSICS_)
-#if defined(__clang__) && defined(__FINITE_MATH_ONLY__)
+#if defined(__clang__) && __FINITE_MATH_ONLY__
     XM_ALIGNED_DATA(16) float tmp[4];
     _mm_store_ps(tmp, V);
     return isnan(tmp[0]) || isnan(tmp[1]) || isnan(tmp[2]) || isnan(tmp[3]);