[SLPVectorizer] Get rid of IndexQueue array from vectorizeStores. NFCI.

[yrouban]

Summary

Indices are checked as they are generated. No need to fill the whole array of indices.

[ABataev]

lib/Transforms/Vectorize/SLPVectorizer.cpp

4749

1. Use auto &&.
2. Do not use default capture, better to use explicit capture list.

4767

Offset < E is too much here, better to use max(Idx + 1, E - Idx) as the limit

[yrouban]

lib/Transforms/Vectorize/SLPVectorizer.cpp

4749

any reference on why auto &&' differs?

[yrouban]

addressed all comments

[ABataev]

LG

lib/Transforms/Vectorize/SLPVectorizer.cpp

4749

It is just to be sure that we don't do copy here, but a move.

lib/Transforms/Vectorize/SLPVectorizer.cpp

bool SLPVectorizerPass::vectorizeStores(ArrayRef<StoreInst *> Stores,
   SmallDenseSet<StoreInst *> Tails;
   SmallDenseMap<StoreInst *, StoreInst *> ConsecutiveChain;
 
   // We may run into multiple chains that merge into a single chain. We mark the
   // stores that we vectorized so that we don't visit the same store twice.
   BoUpSLP::ValueSet VectorizedStores;
   bool Changed = false;
 
-  // Do a quadratic search on all of the given stores in reverse order and find
-  // all of the pairs of stores that follow each other.
-  SmallVector<unsigned, 16> IndexQueue;
-  unsigned E = Stores.size();
-  IndexQueue.resize(E - 1);
-  for (unsigned I = E; I > 0; --I) {
-    unsigned Idx = I - 1;
-    // If a store has multiple consecutive store candidates, search Stores
-    // array according to the sequence: Idx-1, Idx+1, Idx-2, Idx+2, ...
-    // This is because usually pairing with immediate succeeding or preceding
-    // candidate create the best chance to find slp vectorization opportunity.
-    unsigned Offset = 1;
-    unsigned Cnt = 0;
-    for (unsigned J = 0; J < E - 1; ++J, ++Offset) {
-      if (Idx >= Offset) {
-        IndexQueue[Cnt] = Idx - Offset;
-        ++Cnt;
-      }
-      if (Idx + Offset < E) {
-        IndexQueue[Cnt] = Idx + Offset;
-        ++Cnt;
-      }
-    }
+  auto FindConsecutiveAccess = [&] (int K, int Idx) {
+    if (!isConsecutiveAccess(Stores[K], Stores[Idx], *DL, *SE))
+      return false;
 
-    for (auto K : IndexQueue) {
-      if (isConsecutiveAccess(Stores[K], Stores[Idx], *DL, *SE)) {
-        Tails.insert(Stores[Idx]);
-        Heads.insert(Stores[K]);
-        ConsecutiveChain[Stores[K]] = Stores[Idx];
+    return true;
+  };
+
+  // Do a quadratic search on all of the given stores in reverse order and find
+  // all of the pairs of stores that follow each other.
+  int E = Stores.size();
+  for (int Idx = E - 1; Idx >= 0; --Idx) {
+    // If a store has multiple consecutive store candidates, search according
+    // to the sequence: Idx-1, Idx+1, Idx-2, Idx+2, ...
+    // This is because usually pairing with immediate succeeding or preceding
+    // candidate create the best chance to find slp vectorization opportunity.
+    for (int Offset = 1; Offset < E; ++Offset)
+      if ((Idx >= Offset && FindConsecutiveAccess(Idx - Offset, Idx)) ||
+          (Idx + Offset < E && FindConsecutiveAccess(Idx + Offset, Idx)))
         break;
-      }
-    }
-  }
 
   // For stores that start but don't end a link in the chain:
   for (auto *SI : llvm::reverse(Heads)) {
     if (Tails.count(SI))
       continue;
 
     // We found a store instr that starts a chain. Now follow the chain and try
     // to vectorize it.