[clang] [clang][SPIR-V] Add x86 calling conventions and sse/sse2 for MSVC hosts (PR #227665)

[Tom Honermann via cfe-commits]

================
@@ -110,6 +110,22 @@ void SPIRV64TargetInfo::getTargetDefines(const LangOptions &Opts,
   DefineStd(Builder, "SPIRV64", Opts);
 }
 
+bool BaseSPIRTargetInfo::initFeatureMap(
+    llvm::StringMap<bool> &Features, DiagnosticsEngine &Diags, StringRef CPU,
+    const std::vector<std::string> &FeaturesVec) const {
+  // When the host predefines _M_X64, MSVC STL headers use always_inline _mm_*
+  // intrinsics, which require sse/sse2 in the device feature set.
+  if (const TargetInfo *Host = getHostTarget()) {
+    const llvm::Triple &HT = Host->getTriple();
+    if (HT.isWindowsMSVCEnvironment() &&
+        (HT.getArch() == llvm::Triple::x86_64 || HT.isWindowsArm64EC())) {
+      Features["sse"] = true;
+      Features["sse2"] = true;
+    }
+  }
+  return TargetInfo::initFeatureMap(Features, Diags, CPU, FeaturesVec);
----------------
tahonermann wrote:

Ah, interesting. I wonder if we should be using `setAuxTarget()` to receive the auxiliary host (and `copyAuxTarget()` to steal from it) rather than creating it ourselves (with arguably the wrong target options). I see that is what `SPIRV64AMDGCNTargetInfo` and `AMDGPUTargetInfo` are doing. Regardless, such a change seems out of scope for this PR. Thank you for looking into it; maybe we'll come back to this sometime later.

https://github.com/llvm/llvm-project/pull/227665