[llvm] [SLP] Use costing to decide between Strided Loads and Compressed Loads (PR #226540)

[Alexey Bataev via llvm-commits]

================
@@ -14917,6 +14819,62 @@ void BoUpSLP::transformNodes() {
     }
   }
 
+  // Perform transformations that modify nodes in-place last.
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alexey-bataev wrote:

Outline this to a function, like `void BoUpSLP::convertCompressedLoadToStrided(TreeEntry &E)` and use
```
  llvm::scope_exit PreferStridedLoads([&] {
    for (std::unique_ptr<TreeEntry> &E : VectorizableTree)
      if (E->State == TreeEntry::CompressVectorize)
        convertCompressedLoadToStrided(*E);
  });
```
 to process such nodes

https://github.com/llvm/llvm-project/pull/226540