[PATCH] D80241: [SLP] PR45269 Fix getVectorElementSize() is slow

[Dinar Temirbulatov via Phabricator via llvm-commits]

dtemirbulatov created this revision.
dtemirbulatov added reviewers: ABataev, RKSimon, spatel, anton-afanasyev, nikic.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

The algorithm inside getVectorElementSize() is almost O(x^2) complexity and when, for example, we compile MultiSource/Applications/ClamAV/shared_sha256.c with 1k instructions inside sha256_transform() function that resulted in almost ~800k iterations. The following change improves the algorithm with a map to a liner complexity. Also, I added a check for the root instruction basic block belongings to avoid any instruction from a different basic block.


https://reviews.llvm.org/D80241

Files:
  llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp


Index: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -629,7 +629,7 @@
   /// the stored value. Otherwise, the size is the width of the largest loaded
   /// value reaching V. This method is used by the vectorizer to calculate
   /// vectorization factors.
-  unsigned getVectorElementSize(Value *V) const;
+  unsigned getVectorElementSize(Value *V);
 
   /// Compute the minimum type sizes required to represent the entries in a
   /// vectorizable tree.
@@ -1715,6 +1715,9 @@
   /// Maps a specific scalar to its tree entry.
   SmallDenseMap<Value*, TreeEntry *> ScalarToTreeEntry;
 
+  /// Maps an instruction to the proposed vectorizable size.
+  SmallDenseMap<Instruction *, unsigned> InstrElementSize;
+
   /// A list of scalars that we found that we need to keep as scalars.
   ValueSet MustGather;
 
@@ -4797,6 +4800,7 @@
   }
 
   Builder.ClearInsertionPoint();
+  InstrElementSize.clear();
 
   return VectorizableTree[0]->VectorizedValue;
 }
@@ -5333,7 +5337,7 @@
   BS->ScheduleStart = nullptr;
 }
 
-unsigned BoUpSLP::getVectorElementSize(Value *V) const {
+unsigned BoUpSLP::getVectorElementSize(Value *V) {
   // If V is a store, just return the width of the stored value without
   // traversing the expression tree. This is the common case.
   if (auto *Store = dyn_cast<StoreInst>(V))
@@ -5343,11 +5347,17 @@
   // that feed it. The type of the loaded value may indicate a more suitable
   // width than V's type. We want to base the vector element size on the width
   // of memory operations where possible.
+  auto *Inst = dyn_cast<Instruction>(V);
   SmallVector<Instruction *, 16> Worklist;
   SmallPtrSet<Instruction *, 16> Visited;
-  if (auto *I = dyn_cast<Instruction>(V)) {
-    Worklist.push_back(I);
-    Visited.insert(I);
+  BasicBlock *P = nullptr;
+  if (Inst) {
+    P = Inst->getParent();
+    auto E = InstrElementSize.find(Inst);
+    if (E != InstrElementSize.end())
+      return E->second;
+    Worklist.push_back(Inst);
+    Visited.insert(Inst);
   }
 
   // Traverse the expression tree in bottom-up order looking for loads. If we
@@ -5375,7 +5385,7 @@
              isa<CmpInst>(I) || isa<SelectInst>(I) || isa<BinaryOperator>(I)) {
       for (Use &U : I->operands())
         if (auto *J = dyn_cast<Instruction>(U.get()))
-          if (Visited.insert(J).second)
+          if (P == J->getParent() && Visited.insert(J).second)
             Worklist.push_back(J);
     }
 
@@ -5384,13 +5394,16 @@
       FoundUnknownInst = true;
   }
 
+  int Width = MaxWidth;
   // If we didn't encounter a memory access in the expression tree, or if we
   // gave up for some reason, just return the width of V.
   if (!MaxWidth || FoundUnknownInst)
-    return DL->getTypeSizeInBits(V->getType());
+    Width = DL->getTypeSizeInBits(V->getType());
+
+  for (Instruction *I : Visited)
+    InstrElementSize[I] = Width;
 
-  // Otherwise, return the maximum width we found.
-  return MaxWidth;
+  return Width;
 }
 
 // Determine if a value V in a vectorizable expression Expr can be demoted to a


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