[clang] Enable SSE4.1 intrinsics for Windows MSVC targets - Issue #172104

Author: dev-priyanshu15

clang/lib/Basic/Targets/X86.cpp

@@ -157,6 +157,14 @@ bool X86TargetInfo::initFeatureMap(
   if (getTriple().getArch() == llvm::Triple::x86_64)
     setFeatureEnabled(Features, "sse2", true);
 
+  // Enable SSE4.1 for Windows MSVC targets to support SIMD intrinsics like
+  // _mm_mullo_epi32 without requiring explicit /arch: flags.
+  if ((getTriple().getArch() == llvm::Triple::x86_64 ||
+       getTriple().getArch() == llvm::Triple::x86) &&
+      getTriple().isWindowsMSVCEnvironment()) {
+    setFeatureEnabled(Features, "sse4.1", true);
+  }
+
   using namespace llvm::X86;
 
   SmallVector<StringRef, 16> CPUFeatures;

clang/test/Sema/simd-intrinsic-sse41-default.c

@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -x c -triple i386-pc-windows-msvc -fsyntax-only %s
+// RUN: %clang_cc1 -x c -triple x86_64-pc-windows-msvc -fsyntax-only %s
+// RUN: %clang_cc1 -x c -triple i386-unknown-linux-gnu -fsyntax-only %s
+// RUN: %clang_cc1 -x c -triple x86_64-unknown-linux-gnu -fsyntax-only %s
+
+// This test verifies that SSE4.1 intrinsics are available by default
+// without requiring explicit /arch: or -msse4.1 flags.
+
+#include <immintrin.h>
+
+void test_sse41_intrinsics(void) {
+  __m128i a = _mm_set1_epi32(1);
+  __m128i b = _mm_set1_epi32(2);
+  __m128i result = _mm_mullo_epi32(a, b);
+  (void)result;
+}