[llvm] [WIP][ADT] Avoid slow size queries on append (PR #136365)

[Jakub Kuderski via llvm-commits]

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@@ -887,8 +921,8 @@ class SmallVectorImpl : public SmallVectorTemplateBase<T> {
     this->assertSafeToAddRange(From, To);
 
     size_t NumToInsert = std::distance(From, To);
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kuhar wrote:

I think this is what the `if` statement above already handles -- it's not just the empty case, unlike what the comment claims.

https://github.com/llvm/llvm-project/pull/136365