From 2a37ff523f9ce32fce8f6c673b019642f6d10e03 Mon Sep 17 00:00:00 2001
From: Sutou Kouhei <kou@clear-code.com>
Date: Fri, 16 Oct 2026 16:56:40 +0900
Subject: [PATCH] Allow setting XSIMD_WITH_SSE3, SSSE3, SSE4_1 and SSE4_2
 manually with MSVC

MSVC doesn't define __SSE3__, __SSSE3__, __SSE4_1__ or __SSE4_2__ even
with /arch:SSE4.2. So users need to define these reserved identifiers
to enable these instruction sets with MSVC since #881. But defining
them may break other libraries. For example, simdjson >= 5 uses GCC
builtins such as __builtin_ctz when __SSE2__ is defined:
https://github.com/apache/arrow/issues/51690

This allows users to set XSIMD_WITH_SSE3, XSIMD_WITH_SSSE3,
XSIMD_WITH_SSE4_1 and XSIMD_WITH_SSE4_2 manually only with MSVC. For
example, users can enable SSE4.2 with MSVC by -DXSIMD_WITH_SSE4_2=1.
Lower instruction sets are enabled automatically by the existing MSVC
workaround. This also allows selecting SSE3 or SSSE3 with MSVC
requested in #878.

Other compilers including clang-cl define these macros based on
compiler flags and require the corresponding compiler flags to use
intrinsics. So setting them manually with other compilers is reported
as an error.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 include/xsimd/config/xsimd_config.hpp | 36 ++++++++++++++++++++++++---
 1 file changed, 32 insertions(+), 4 deletions(-)

diff --git a/include/xsimd/config/xsimd_config.hpp b/include/xsimd/config/xsimd_config.hpp
index 7c570b3cd..86dde7d12 100644
--- a/include/xsimd/config/xsimd_config.hpp
+++ b/include/xsimd/config/xsimd_config.hpp
@@ -111,8 +111,15 @@
  * @ingroup xsimd_config_macro
  *
  * Set to 1 if SSE3 is available at compile-time, to 0 otherwise.
+ *
+ * It can be set manually only with MSVC because MSVC doesn't define
+ * __SSE3__ even when SSE3 is enabled.
  */
-#ifdef __SSE3__
+#ifdef XSIMD_WITH_SSE3
+#if !defined(_MSC_VER) || defined(__clang__)
+#error "XSIMD_WITH_SSE3 can be set manually only with MSVC"
+#endif
+#elif defined(__SSE3__)
 #define XSIMD_WITH_SSE3 1
 #else
 #define XSIMD_WITH_SSE3 0
@@ -122,8 +129,15 @@
  * @ingroup xsimd_config_macro
  *
  * Set to 1 if SSSE3 is available at compile-time, to 0 otherwise.
+ *
+ * It can be set manually only with MSVC because MSVC doesn't define
+ * __SSSE3__ even when SSSE3 is enabled.
  */
-#ifdef __SSSE3__
+#ifdef XSIMD_WITH_SSSE3
+#if !defined(_MSC_VER) || defined(__clang__)
+#error "XSIMD_WITH_SSSE3 can be set manually only with MSVC"
+#endif
+#elif defined(__SSSE3__)
 #define XSIMD_WITH_SSSE3 1
 #else
 #define XSIMD_WITH_SSSE3 0
@@ -133,8 +147,15 @@
  * @ingroup xsimd_config_macro
  *
  * Set to 1 if SSE4.1 is available at compile-time, to 0 otherwise.
+ *
+ * It can be set manually only with MSVC because MSVC doesn't define
+ * __SSE4_1__ even when SSE4.1 is enabled.
  */
-#ifdef __SSE4_1__
+#ifdef XSIMD_WITH_SSE4_1
+#if !defined(_MSC_VER) || defined(__clang__)
+#error "XSIMD_WITH_SSE4_1 can be set manually only with MSVC"
+#endif
+#elif defined(__SSE4_1__)
 #define XSIMD_WITH_SSE4_1 1
 #else
 #define XSIMD_WITH_SSE4_1 0
@@ -144,8 +165,15 @@
  * @ingroup xsimd_config_macro
  *
  * Set to 1 if SSE4.2 is available at compile-time, to 0 otherwise.
+ *
+ * It can be set manually only with MSVC because MSVC doesn't define
+ * __SSE4_2__ even when SSE4.2 is enabled.
  */
-#ifdef __SSE4_2__
+#ifdef XSIMD_WITH_SSE4_2
+#if !defined(_MSC_VER) || defined(__clang__)
+#error "XSIMD_WITH_SSE4_2 can be set manually only with MSVC"
+#endif
+#elif defined(__SSE4_2__)
 #define XSIMD_WITH_SSE4_2 1
 #else
 #define XSIMD_WITH_SSE4_2 0