[llvm] [LLVM][ADT] Explicitly convert size_t values to SmallVector's size type (PR #77939)

[Andrew Browne via llvm-commits]

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@@ -99,8 +99,9 @@ template <class Size_T> class SmallVectorBase {
   ///
   /// This does not construct or destroy any elements in the vector.
   void set_size(size_t N) {
-    assert(N <= capacity());
-    Size = N;
+    auto n = static_cast<Size_T>(N);
+    assert(n <= capacity());
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browneee wrote:

Thinking a little more: `N <= capacity()` implies  `static_cast<size_t>(Size) == N` because `capacity()` is from a Size_T variable.

https://github.com/llvm/llvm-project/pull/77939