Add compile time checks for memory layout of t_override, remove the hardcoded size of t_override

Author: xuqinziyue

vpr/src/place/place_delay_model.h

@@ -116,11 +116,28 @@ class OverrideDelayModel : public PlaceDelayModel {
         friend ALWAYS_INLINE bool operator<(const t_override& lhs, const t_override& rhs) {
             const short* left = reinterpret_cast<const short*>(&lhs);
             const short* right = reinterpret_cast<const short*>(&rhs);
-            return std::lexicographical_compare(left, left + 6, right, right + 6);
+            constexpr size_t NUM_T_OVERRIDE_MEMBERS = sizeof(t_override) / sizeof(short);
+            return std::lexicographical_compare(left, left + NUM_T_OVERRIDE_MEMBERS, right, right + NUM_T_OVERRIDE_MEMBERS);
         }
     };
 
     vtr::flat_map2<t_override, float> delay_overrides_;
+
+    //operator< treats memory layout of t_override as an array of short
+    //this requires all members of t_override are shorts and there is no padding between members of t_override
+    static_assert(sizeof(t_override) == sizeof(t_override::from_type)
+                                     + sizeof(t_override::to_type)
+                                     + sizeof(t_override::from_class)
+                                     + sizeof(t_override::to_class)
+                                     + sizeof(t_override::delta_x)
+                                     + sizeof(t_override::delta_y),
+                  "Expect t_override to have a memory layout equivalent to an array of short (no padding)");
+    static_assert(sizeof(t_override::from_type) == sizeof(short), "Expect all t_override data members to be shorts");
+    static_assert(sizeof(t_override::to_type) == sizeof(short), "Expect all t_override data members to be shorts");
+    static_assert(sizeof(t_override::from_class) == sizeof(short), "Expect all t_override data members to be shorts");
+    static_assert(sizeof(t_override::to_class) == sizeof(short), "Expect all t_override data members to be shorts");
+    static_assert(sizeof(t_override::delta_x) == sizeof(short), "Expect all t_override data members to be shorts");
+    static_assert(sizeof(t_override::delta_y) == sizeof(short), "Expect all t_override data members to be shorts");
 };
 
 #endif