[clang] Enable SSE4.1 intrinsics for 32-bit x86 by default - Issue #172104

Author: dev-priyanshu15

clang/lib/Basic/Targets/X86.cpp

@@ -153,9 +153,13 @@ bool X86TargetInfo::initFeatureMap(
     llvm::StringMap<bool> &Features, DiagnosticsEngine &Diags, StringRef CPU,
     const std::vector<std::string> &FeaturesVec) const {
   // FIXME: This *really* should not be here.
-  // X86_64 always has SSE2.
-  if (getTriple().getArch() == llvm::Triple::x86_64)
+  // X86_64 always has SSE2 and SSE4.1 to support common SIMD intrinsics.
+  // Also enable these for 32-bit x86 to ensure MSVC-compatible SIMD support.
+  if (getTriple().getArch() == llvm::Triple::x86_64 ||
+      getTriple().getArch() == llvm::Triple::x86) {
     setFeatureEnabled(Features, "sse2", true);
+    setFeatureEnabled(Features, "sse4.1", true);
+  }
 
   using namespace llvm::X86;
 

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;
+}