[SandboxVec][BottomUpVec] Use SeedCollector and slice seeds

With this patch we switch from the temporary dummy seeds to actual seeds
provided by the seed collector.
The seeds get sliced and each slice is used as the starting point for
vectorization.

Author: Vasileios Porpodas

llvm/include/llvm/SandboxIR/Pass.h

@@ -16,6 +16,7 @@ namespace llvm {
 
 class AAResults;
 class ScalarEvolution;
+class TargetTransformInfo;
 
 namespace sandboxir {
 
@@ -25,15 +26,18 @@ class Region;
 class Analyses {
   AAResults *AA = nullptr;
   ScalarEvolution *SE = nullptr;
+  TargetTransformInfo *TTI = nullptr;
 
   Analyses() = default;
 
 public:
-  Analyses(AAResults &AA, ScalarEvolution &SE) : AA(&AA), SE(&SE) {}
+  Analyses(AAResults &AA, ScalarEvolution &SE, TargetTransformInfo &TTI)
+      : AA(&AA), SE(&SE), TTI(&TTI) {}
 
 public:
   AAResults &getAA() const { return *AA; }
   ScalarEvolution &getScalarEvolution() const { return *SE; }
+  TargetTransformInfo &getTTI() const { return *TTI; }
   /// For use by unit tests.
   static Analyses emptyForTesting() { return Analyses(); }
 };

llvm/include/llvm/SandboxIR/Utils.h

@@ -60,11 +60,16 @@ class Utils {
         getUnderlyingObject(LSI->getPointerOperand()->Val));
   }
 
+  /// \Returns the number of bits of \p Ty.
+  static unsigned getNumBits(Type *Ty, const DataLayout &DL) {
+    return DL.getTypeSizeInBits(Ty->LLVMTy);
+  }
+
   /// \Returns the number of bits required to represent the operands or return
   /// value of \p V in \p DL.
   static unsigned getNumBits(Value *V, const DataLayout &DL) {
     Type *Ty = getExpectedType(V);
-    return DL.getTypeSizeInBits(Ty->LLVMTy);
+    return getNumBits(Ty, DL);
   }
 
   /// \Returns the number of bits required to represent the operands or

llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/Legality.h

@@ -177,6 +177,7 @@ class LegalityAnalysis {
   // TODO: Try to remove the SkipScheduling argument by refactoring the tests.
   const LegalityResult &canVectorize(ArrayRef<Value *> Bndl,
                                      bool SkipScheduling = false);
+  void clear() { Sched.clear(); }
 };
 
 } // namespace llvm::sandboxir

llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/Scheduler.h

@@ -143,6 +143,13 @@ class Scheduler {
   ~Scheduler() {}
 
   bool trySchedule(ArrayRef<Instruction *> Instrs);
+  /// Clear the scheduler's state, including the DAG.
+  void clear() {
+    Bndls.clear();
+    // TODO: clear view once it lands.
+    DAG.clear();
+    ScheduleTopItOpt = std::nullopt;
+  }
 
 #ifndef NDEBUG
   void dump(raw_ostream &OS) const;

llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/SeedCollector.h

@@ -95,8 +95,8 @@ class SeedBundle {
   /// with a total size <= \p MaxVecRegBits, or an empty slice if the
   /// requirements cannot be met . If \p ForcePowOf2 is true, then the returned
   /// slice will have a total number of bits that is a power of 2.
-  MutableArrayRef<Instruction *>
-  getSlice(unsigned StartIdx, unsigned MaxVecRegBits, bool ForcePowOf2);
+  ArrayRef<Instruction *> getSlice(unsigned StartIdx, unsigned MaxVecRegBits,
+                                   bool ForcePowOf2);
 
   /// \Returns the number of seed elements in the bundle.
   std::size_t size() const { return Seeds.size(); }

llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/VecUtils.h

@@ -133,6 +133,16 @@ class VecUtils {
     assert(tryGetCommonScalarType(Bndl) && "Expected common scalar type!");
     return ScalarTy;
   }
+  /// \Returns the first integer power of 2 that is <= Num.
+  static unsigned getFloorPowerOf2(unsigned Num) {
+    if (Num == 0)
+      return Num;
+    unsigned Mask = Num;
+    Mask >>= 1;
+    for (int ShiftBy = 1; ShiftBy < 32; ShiftBy <<= 1)
+      Mask |= Mask >> ShiftBy;
+    return Num & ~Mask;
+  }
 };
 
 } // namespace llvm::sandboxir

llvm/lib/Transforms/Vectorize/SandboxVectorizer/Passes/BottomUpVec.cpp

@@ -8,29 +8,31 @@
 
 #include "llvm/Transforms/Vectorize/SandboxVectorizer/Passes/BottomUpVec.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/SandboxIR/Function.h"
 #include "llvm/SandboxIR/Instruction.h"
 #include "llvm/SandboxIR/Module.h"
 #include "llvm/SandboxIR/Utils.h"
 #include "llvm/Transforms/Vectorize/SandboxVectorizer/SandboxVectorizerPassBuilder.h"
+#include "llvm/Transforms/Vectorize/SandboxVectorizer/SeedCollector.h"
 #include "llvm/Transforms/Vectorize/SandboxVectorizer/VecUtils.h"
 
-namespace llvm::sandboxir {
+namespace llvm {
+
+static cl::opt<unsigned>
+    OverrideVecRegBits("sbvec-vec-reg-bits", cl::init(0), cl::Hidden,
+                       cl::desc("Override the vector register size in bits, "
+                                "which is otherwise found by querying TTI."));
+static cl::opt<bool>
+    AllowNonPow2("sbvec-allow-non-pow2", cl::init(false), cl::Hidden,
+                 cl::desc("Allow non-power-of-2 vectorization."));
+
+namespace sandboxir {
 
 BottomUpVec::BottomUpVec(StringRef Pipeline)
     : FunctionPass("bottom-up-vec"),
       RPM("rpm", Pipeline, SandboxVectorizerPassBuilder::createRegionPass) {}
 
-// TODO: This is a temporary function that returns some seeds.
-//       Replace this with SeedCollector's function when it lands.
-static llvm::SmallVector<Value *, 4> collectSeeds(BasicBlock &BB) {
-  llvm::SmallVector<Value *, 4> Seeds;
-  for (auto &I : BB)
-    if (auto *SI = llvm::dyn_cast<StoreInst>(&I))
-      Seeds.push_back(SI);
-  return Seeds;
-}
-
 static SmallVector<Value *, 4> getOperand(ArrayRef<Value *> Bndl,
                                           unsigned OpIdx) {
   SmallVector<Value *, 4> Operands;
@@ -265,6 +267,7 @@ Value *BottomUpVec::vectorizeRec(ArrayRef<Value *> Bndl, unsigned Depth) {
 
 bool BottomUpVec::tryVectorize(ArrayRef<Value *> Bndl) {
   DeadInstrCandidates.clear();
+  Legality->clear();
   vectorizeRec(Bndl, /*Depth=*/0);
   tryEraseDeadInstrs();
   return Change;
@@ -275,17 +278,67 @@ bool BottomUpVec::runOnFunction(Function &F, const Analyses &A) {
       A.getAA(), A.getScalarEvolution(), F.getParent()->getDataLayout(),
       F.getContext());
   Change = false;
+  const auto &DL = F.getParent()->getDataLayout();
+  unsigned VecRegBits =
+      OverrideVecRegBits != 0
+          ? OverrideVecRegBits
+          : A.getTTI()
+                .getRegisterBitWidth(TargetTransformInfo::RGK_FixedWidthVector)
+                .getFixedValue();
+
   // TODO: Start from innermost BBs first
   for (auto &BB : F) {
-    // TODO: Replace with proper SeedCollector function.
-    auto Seeds = collectSeeds(BB);
-    // TODO: Slice Seeds into smaller chunks.
-    // TODO: If vectorization succeeds, run the RegionPassManager on the
-    // resulting region.
-    if (Seeds.size() >= 2)
-      Change |= tryVectorize(Seeds);
+    SeedCollector SC(&BB, A.getScalarEvolution());
+    for (SeedBundle &Seeds : SC.getStoreSeeds()) {
+      unsigned ElmBits =
+          Utils::getNumBits(VecUtils::getElementType(Utils::getExpectedType(
+                                Seeds[Seeds.getFirstUnusedElementIdx()])),
+                            DL);
+
+      auto DivideBy2 = [](unsigned Num) {
+        auto Floor = VecUtils::getFloorPowerOf2(Num);
+        if (Floor == Num)
+          return Floor / 2;
+        return Floor;
+      };
+      // Try to create the largest vector supported by the target. If it fails
+      // reduce the vector size by half.
+      for (unsigned SliceElms = std::min(VecRegBits / ElmBits,
+                                         Seeds.getNumUnusedBits() / ElmBits);
+           SliceElms >= 2u; SliceElms = DivideBy2(SliceElms)) {
+        if (Seeds.allUsed())
+          break;
+        // Keep trying offsets after FirstUnusedElementIdx, until we vectorize
+        // the slice. This could be quite expensive, so we enforce a limit.
+        for (unsigned Offset = Seeds.getFirstUnusedElementIdx(),
+                      OE = Seeds.size();
+             Offset + 1 < OE; Offset += 1) {
+          // Seeds are getting used as we vectorize, so skip them.
+          if (Seeds.isUsed(Offset))
+            continue;
+          if (Seeds.allUsed())
+            break;
+
+          auto SeedSlice =
+              Seeds.getSlice(Offset, SliceElms * ElmBits, !AllowNonPow2);
+          if (SeedSlice.empty())
+            continue;
+
+          assert(SeedSlice.size() >= 2 && "Should have been rejected!");
+
+          // TODO: If vectorization succeeds, run the RegionPassManager on the
+          // resulting region.
+
+          // TODO: Refactor to remove the unnecessary copy to SeedSliceVals.
+          SmallVector<Value *> SeedSliceVals(SeedSlice.begin(),
+                                             SeedSlice.end());
+          Change |= tryVectorize(SeedSliceVals);
+        }
+      }
+    }
   }
   return Change;
 }
 
-} // namespace llvm::sandboxir
+} // namespace sandboxir
+} // namespace llvm

llvm/lib/Transforms/Vectorize/SandboxVectorizer/SandboxVectorizer.cpp

@@ -86,6 +86,6 @@ bool SandboxVectorizerPass::runImpl(Function &LLVMF) {
 
   // Create SandboxIR for LLVMF and run BottomUpVec on it.
   sandboxir::Function &F = *Ctx->createFunction(&LLVMF);
-  sandboxir::Analyses A(*AA, *SE);
+  sandboxir::Analyses A(*AA, *SE, *TTI);
   return FPM.runOnFunction(F, A);
 }

llvm/lib/Transforms/Vectorize/SandboxVectorizer/SeedCollector.cpp

@@ -31,9 +31,9 @@ cl::opt<unsigned> SeedGroupsLimit(
     cl::desc("Limit the number of collected seeds groups in a BB to "
              "cap compilation time."));
 
-MutableArrayRef<Instruction *> SeedBundle::getSlice(unsigned StartIdx,
-                                                    unsigned MaxVecRegBits,
-                                                    bool ForcePowerOf2) {
+ArrayRef<Instruction *> SeedBundle::getSlice(unsigned StartIdx,
+                                             unsigned MaxVecRegBits,
+                                             bool ForcePowerOf2) {
   // Use uint32_t here for compatibility with IsPowerOf2_32
 
   // BitCount tracks the size of the working slice. From that we can tell
@@ -47,10 +47,13 @@ MutableArrayRef<Instruction *> SeedBundle::getSlice(unsigned StartIdx,
   // Can't start a slice with a used instruction.
   assert(!isUsed(StartIdx) && "Expected unused at StartIdx");
   for (auto S : make_range(Seeds.begin() + StartIdx, Seeds.end())) {
+    // Stop if this instruction is used. This needs to be done before
+    // getNumBits() because a "used" instruction may have been erased.
+    if (isUsed(StartIdx + NumElements))
+      break;
     uint32_t InstBits = Utils::getNumBits(S);
-    // Stop if this instruction is used, or if adding it puts the slice over
-    // the limit.
-    if (isUsed(StartIdx + NumElements) || BitCount + InstBits > MaxVecRegBits)
+    // Stop if adding it puts the slice over the limit.
+    if (BitCount + InstBits > MaxVecRegBits)
       break;
     NumElements++;
     BitCount += InstBits;
@@ -68,7 +71,7 @@ MutableArrayRef<Instruction *> SeedBundle::getSlice(unsigned StartIdx,
          "Must be a power of two");
   // Return any non-empty slice
   if (NumElements > 1)
-    return MutableArrayRef<Instruction *>(&Seeds[StartIdx], NumElements);
+    return ArrayRef<Instruction *>(&Seeds[StartIdx], NumElements);
   else
     return {};
 }

llvm/test/Transforms/SandboxVectorizer/bottomup_basic.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
-; RUN: opt -passes=sandbox-vectorizer -sbvec-passes="bottom-up-vec<>" %s -S | FileCheck %s
+; RUN: opt -passes=sandbox-vectorizer -sbvec-vec-reg-bits=1024 -sbvec-allow-non-pow2 -sbvec-passes="bottom-up-vec<>" %s -S | FileCheck %s
 
 define void @store_load(ptr %ptr) {
 ; CHECK-LABEL: define void @store_load(