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

[Ryan Buchner via llvm-commits]

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@@ -14519,6 +14565,58 @@ void BoUpSLP::transformNodes() {
       continue;
     switch (E.getOpcode()) {
     case Instruction::Load: {
+      if (E.State == TreeEntry::CompressVectorize) {
+        StridedPtrInfo SPtrInfo;
+        auto PreferStridedOverCompressed = [&]() -> bool {
+          // In cases where a shuffle is mandatory regarless of load type,
+          // prefer Compressed since the reorder/reuse shuffle can be merged
+          // with the compress shuffle.
+          if (!E.ReorderIndices.empty() || !E.ReuseShuffleIndices.empty())
+            return false;
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bababuck wrote:

Will do follow up MR to avoid making this one too large.

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