[SLP]Attempt to vectorize long stores, if short one failed.

We can try to vectorize long store sequences, if short ones were
unsuccessful because of the non-profitable vectorization. It should not
increase compile time significantly (stores are sorted already,
complexity is n x log n), but vectorize extra code.

Metric: size..text

Program                                                                         size..text
                                                                                results     results0    diff
         test-suite :: External/SPEC/CINT2006/400.perlbench/400.perlbench.test  1088012.00  1088236.00  0.0%
                  test-suite :: SingleSource/UnitTests/matrix-types-spec.test   480396.00   480476.00  0.0%
          test-suite :: External/SPEC/CINT2017rate/525.x264_r/525.x264_r.test   664613.00   664661.00  0.0%
         test-suite :: External/SPEC/CINT2017speed/625.x264_s/625.x264_s.test   664613.00   664661.00  0.0%
        test-suite :: External/SPEC/CFP2017rate/510.parest_r/510.parest_r.test  2041105.00  2040961.00 -0.0%
                 test-suite :: MultiSource/Applications/JM/lencod/lencod.test   836563.00   836387.00 -0.0%
                 test-suite :: MultiSource/Benchmarks/7zip/7zip-benchmark.test  1035100.00  1032140.00 -0.3%

In all benchmarks extra code gets vectorized

Reviewers: RKSimon

Reviewed By: RKSimon

Pull Request: #88563

llvm/include/llvm/Transforms/Vectorize/SLPVectorizer.h

@@ -153,10 +153,15 @@ struct SLPVectorizerPass : public PassInfoMixin<SLPVectorizerPass> {
   /// a vectorization chain.
   bool vectorizeChainsInBlock(BasicBlock *BB, slpvectorizer::BoUpSLP &R);
 
-  bool vectorizeStoreChain(ArrayRef<Value *> Chain, slpvectorizer::BoUpSLP &R,
-                           unsigned Idx, unsigned MinVF);
-
-  bool vectorizeStores(ArrayRef<StoreInst *> Stores, slpvectorizer::BoUpSLP &R);
+  std::optional<bool> vectorizeStoreChain(ArrayRef<Value *> Chain,
+                                          slpvectorizer::BoUpSLP &R,
+                                          unsigned Idx, unsigned MinVF,
+                                          unsigned &Size);
+
+  bool vectorizeStores(
+      ArrayRef<StoreInst *> Stores, slpvectorizer::BoUpSLP &R,
+      DenseSet<std::tuple<Value *, Value *, Value *, Value *, unsigned>>
+          &Visited);
 
   /// The store instructions in a basic block organized by base pointer.
   StoreListMap Stores;