[PATCH] D26962: [LoadStoreVectorizer] Split the chain if the prefix is empty

[Volkan Keles via llvm-commits]

volkan created this revision.
volkan added reviewers: jlebar, asbirlea, arsenm.
volkan added a subscriber: llvm-commits.
Herald added subscribers: wdng, mzolotukhin.

Currently, the vectorizer discards all of the instructions in the chain if
the vectorizable prefix is empty. Instead, we can try to vectorize smaller
chunks in order to increase the number of vector instructions generated.


https://reviews.llvm.org/D26962

Files:
  lib/Transforms/Vectorize/LoadStoreVectorizer.cpp


Index: lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
===================================================================
--- lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
+++ lib/Transforms/Vectorize/LoadStoreVectorizer.cpp
@@ -737,9 +737,18 @@
 
   ArrayRef<Instruction *> NewChain = getVectorizablePrefix(Chain);
   if (NewChain.empty()) {
-    // No vectorization possible.
-    InstructionsProcessed->insert(Chain.begin(), Chain.end());
-    return false;
+    // No vectorization possible if the number of instructions
+    // is less than or equal to VF.
+    if (ChainSize <= VF) {
+      InstructionsProcessed->insert(Chain.begin(), Chain.end());
+      return false;
+    }
+    // Split the chain and try each slice seperately in order
+    // to increase the number of vector instructions generated.
+    ArrayRef<Instruction *> Left = Chain.slice(0, VF);
+    ArrayRef<Instruction *> Right = Chain.slice(VF);
+    return vectorizeStoreChain(Left, InstructionsProcessed) |
+           vectorizeStoreChain(Right, InstructionsProcessed);
   }
   if (NewChain.size() == 1) {
     // Failed after the first instruction. Discard it and try the smaller chain.
@@ -885,9 +894,18 @@
 
   ArrayRef<Instruction *> NewChain = getVectorizablePrefix(Chain);
   if (NewChain.empty()) {
-    // No vectorization possible.
-    InstructionsProcessed->insert(Chain.begin(), Chain.end());
-    return false;
+    // No vectorization possible if the number of instructions
+    // is less than or equal to VF.
+    if (ChainSize <= VF) {
+      InstructionsProcessed->insert(Chain.begin(), Chain.end());
+      return false;
+    }
+    // Split the chain and try each slice seperately in order
+    // to increase the number of vector instructions generated.
+    ArrayRef<Instruction *> Left = Chain.slice(0, VF);
+    ArrayRef<Instruction *> Right = Chain.slice(VF);
+    return vectorizeLoadChain(Left, InstructionsProcessed) |
+           vectorizeLoadChain(Right, InstructionsProcessed);
   }
   if (NewChain.size() == 1) {
     // Failed after the first instruction. Discard it and try the smaller chain.


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