Fixing the handling of Vector512.CreateScalar

Author: tannergooding

src/coreclr/jit/lowerxarch.cpp

@@ -3551,24 +3551,34 @@ GenTree* Lowering::LowerHWIntrinsicCreate(GenTreeHWIntrinsic* node)
                 }
             }
 
-            if (simdSize == 32)
+            if (simdSize > 16)
             {
-                // We're creating a Vector256 scalar so we need to treat the original op as Vector128,
-                // we need to unsafely extend up to Vector256 (which is actually safe since the 128-bit
-                // op will zero extend up to 256-bits), and then we need to replace the original use
-                // with the new TYP_SIMD32 node.
+                assert((simdSize == 32) || (simdSize == 64));
+
+                // We're creating a Vector256/512 scalar so we need to treat the original op as Vector128,
+                // we need to unsafely extend up to Vector256/512 (which is actually safe since the 128-bit
+                // op will zero extend up to 256/512-bits), and then we need to replace the original use
+                // with the new TYP_SIMD32/64 node.
 
                 node->ChangeType(TYP_SIMD16);
                 node->SetSimdSize(16);
                 LowerNode(node);
 
-                tmp2 = comp->gtNewSimdHWIntrinsicNode(TYP_SIMD32, node, NI_Vector128_ToVector256Unsafe, simdBaseJitType,
-                                                      16);
-
                 LIR::Use use;
                 bool     foundUse = BlockRange().TryGetUse(node, &use);
+
+                tmp2 = comp->gtNewSimdHWIntrinsicNode(TYP_SIMD32, node, NI_Vector128_ToVector256Unsafe, simdBaseJitType,
+                                                      16);
                 BlockRange().InsertAfter(node, tmp2);
 
+                if (simdSize == 64)
+                {
+                    tmp3 = comp->gtNewSimdHWIntrinsicNode(TYP_SIMD64, tmp2, NI_Vector256_ToVector512Unsafe,
+                                                          simdBaseJitType, 32);
+                    BlockRange().InsertAfter(tmp2, tmp3);
+                    tmp2 = tmp3;
+                }
+
                 if (foundUse)
                 {
                     use.ReplaceWith(tmp2);