Don't struct-promote opaque vectors

src/jit/compiler.h

@@ -7640,6 +7640,17 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
         return NO_CLASS_HANDLE;
     }
 
+    // Returns true if this is a SIMD type that should be considered an opaque
+    // vector type (i.e. do not analyze or promote its fields).
+    // Note that all but the fixed vector types are opaque, even though they may
+    // actually be declared as having fields.
+    bool isOpaqueSIMDType(CORINFO_CLASS_HANDLE structHandle)
+    {
+        return ((m_simdHandleCache != nullptr) && (structHandle != m_simdHandleCache->SIMDVector2Handle) &&
+                (structHandle != m_simdHandleCache->SIMDVector3Handle) &&
+                (structHandle != m_simdHandleCache->SIMDVector4Handle));
+    }
+
     // Returns true if the tree corresponds to a TYP_SIMD lcl var.
     // Note that both SIMD vector args and locals are mared as lvSIMDType = true, but
     // type of an arg node is TYP_BYREF and a local node is TYP_SIMD or TYP_STRUCT.
@@ -7648,6 +7659,16 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
         return tree->OperIsLocal() && lvaTable[tree->AsLclVarCommon()->gtLclNum].lvSIMDType;
     }
 
+    // Returns true if the lclVar is an opaque SIMD type.
+    bool isOpaqueSIMDLclVar(LclVarDsc* varDsc)
+    {
+        if (!varDsc->lvSIMDType)
+        {
+            return false;
+        }
+        return isOpaqueSIMDType(varDsc->lvVerTypeInfo.GetClassHandle());
+    }
+
     // Returns true if the type of the tree is a byref of TYP_SIMD
     bool isAddrOfSIMDType(GenTree* tree)
     {
@@ -7987,6 +8008,11 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
         return lvaSIMDInitTempVarNum;
     }
 
+#else  // !FEATURE_SIMD
+    bool isOpaqueSIMDLclVar(LclVarDsc* varDsc)
+    {
+        return false;
+    }
 #endif // FEATURE_SIMD
 
 public:

src/jit/morph.cpp

@@ -16973,7 +16973,7 @@ void Compiler::fgPromoteStructs()
 
         // If we have marked this as lvUsedInSIMDIntrinsic, then we do not want to promote
         // its fields.  Instead, we will attempt to enregister the entire struct.
-        if (varDsc->lvIsSIMDType() && varDsc->lvIsUsedInSIMDIntrinsic())
+        if (varDsc->lvIsSIMDType() && (varDsc->lvIsUsedInSIMDIntrinsic() || isOpaqueSIMDLclVar(varDsc)))
         {
             varDsc->lvRegStruct = true;
         }