[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/CodeGen/x86-sse41-windows-msvc.c

@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -triple x86_64-pc-windows-msvc -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -triple i386-pc-windows-msvc -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o - | FileCheck %s --check-prefix=LINUX
+// RUN: %clang_cc1 -triple i386-unknown-linux-gnu -emit-llvm %s -o - | FileCheck %s --check-prefix=LINUX
+
+// This test verifies that SSE4.1 is enabled by default for Windows MSVC targets
+// to support SIMD intrinsics like _mm_mullo_epi32
+
+#include <immintrin.h>
+
+__m128i test_sse41(void) {
+  __m128i a = _mm_set1_epi32(5);
+  __m128i b = _mm_set1_epi32(3);
+  return _mm_mullo_epi32(a, b);
+}
+
+// CHECK: "target-features"="+sse4.1"
+// LINUX-NOT: "target-features"="+sse4.1"