[llvm] DynamicAPInt: optimize size of structure (PR #97831)

[Arjun P via llvm-commits]

================
@@ -203,6 +211,14 @@ class DynamicAPInt {
 
   friend hash_code hash_value(const DynamicAPInt &x); // NOLINT
 
+  void static_assert_layout() { // NOLINT
+    constexpr size_t ValLargeOff =
+        offsetof(DynamicAPInt, ValLarge.Val.BitWidth);
+    constexpr size_t ValSmallOff = offsetof(DynamicAPInt, ValSmall);
+    constexpr size_t ValSmallSz = sizeof(ValSmall);
+    static_assert(ValLargeOff >= ValSmallOff + ValSmallSz);
+  }
+
----------------
Superty wrote:

Nice, glad to see this could be made a `static_assert`.

Keeping this in the class body clutters it and is unnecessary; moreover, there is no need to compile this every time the header is included. I suggest moving it to the `.cpp` file.

https://github.com/llvm/llvm-project/pull/97831