JIT: Optimize *x = dblCns to *x = intCns

src/coreclr/jit/lowerxarch.cpp

@@ -130,6 +130,38 @@ void Lowering::LowerStoreIndir(GenTreeIndir* node)
  return;
  }
  }
+ else if (node->AsStoreInd()->Data()->OperIs(GT_CNS_DBL))
+ {
+ // Optimize *x = DCON to *x = ICON which is slightly faster on xarch
+ GenTree* data = node->AsStoreInd()->Data();
+ double dblCns = data->AsDblCon()->gtDconVal;
+ ssize_t intCns = 0;
+ var_types type = TYP_UNKNOWN;
+
+ if (node->TypeIs(TYP_FLOAT))
+ {
+ float fltCns = static_cast<float>(dblCns); // should be a safe round-trip
+ intCns = static_cast<ssize_t>(*reinterpret_cast<UINT32*>(&fltCns));
+ type = TYP_UINT;
+ }
+#ifdef TARGET_AMD64
+ else
+ {
+ assert(node->TypeIs(TYP_DOUBLE));
+ intCns = static_cast<ssize_t>(*reinterpret_cast<UINT64*>(&dblCns));
+ type = TYP_ULONG;
+ }
+#endif
+
+ if (type != TYP_UNKNOWN)
+ {
+ data->SetContained();
+ data->ChangeOperConst(GT_CNS_INT);
+ data->AsIntCon()->SetIconValue(intCns);
+ data->ChangeType(type);
+ node->ChangeType(type);
+ }
+ }
  ContainCheckStoreIndir(node);
 }