[SandboxVec] Move seed collection into its own separate pass (llvm#127132)

This patch moves the seed collection logic from the BottomUpVec pass
into a new Sandbox IR Function pass. The new "seed-collection" pass
collects the seeds, builds a region and runs the region pass pipeline.

Author: vporpo

llvm/include/llvm/SandboxIR/Region.h

@@ -120,6 +120,10 @@ class Region {
   /// Set \p I as the \p Idx'th element in the auxiliary vector.
   /// NOTE: This is for internal use, it does not set the metadata.
   void setAux(unsigned Idx, Instruction *I);
+  /// Helper for dropping Aux metadata for \p I.
+  void dropAuxMetadata(Instruction *I);
+  /// Remove instruction \p I from Aux and drop metadata.
+  void removeFromAux(Instruction *I);
 
 public:
   Region(Context &Ctx, TargetTransformInfo &TTI);

llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/Passes/BottomUpVec.h

@@ -16,14 +16,23 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/SandboxIR/Constant.h"
 #include "llvm/SandboxIR/Pass.h"
-#include "llvm/SandboxIR/PassManager.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Transforms/Vectorize/SandboxVectorizer/InstrMaps.h"
 #include "llvm/Transforms/Vectorize/SandboxVectorizer/Legality.h"
 
 namespace llvm::sandboxir {
 
-class BottomUpVec final : public FunctionPass {
+/// This is a simple bottom-up vectorizer Region pass.
+/// It expects a "seed slice" as an input in the Region's Aux vector.
+/// The "seed slice" is a vector of instructions that can be used as a starting
+/// point for vectorization, like stores to consecutive memory addresses.
+/// Starting from the seed instructions, it walks up the def-use chain looking
+/// for more instructions that can be vectorized. This pass will generate vector
+/// code if it can legally vectorize the code, regardless of whether it is
+/// profitable or not. For now profitability is checked at the end of the region
+/// pass pipeline by a dedicated pass that accepts or rejects the IR
+/// transaction, depending on the cost.
+class BottomUpVec final : public RegionPass {
   bool Change = false;
   std::unique_ptr<LegalityAnalysis> Legality;
   /// The original instructions that are potentially dead after vectorization.
@@ -55,16 +64,9 @@ class BottomUpVec final : public FunctionPass {
   /// Entry point for vectorization starting from \p Seeds.
   bool tryVectorize(ArrayRef<Value *> Seeds);
 
-  /// The PM containing the pipeline of region passes.
-  RegionPassManager RPM;
-
 public:
-  BottomUpVec(StringRef Pipeline);
-  bool runOnFunction(Function &F, const Analyses &A) final;
-  void printPipeline(raw_ostream &OS) const final {
-    OS << getName() << "\n";
-    RPM.printPipeline(OS);
-  }
+  BottomUpVec() : RegionPass("bottom-up-vec") {}
+  bool runOnRegion(Region &Rgn, const Analyses &A) final;
 };
 
 } // namespace llvm::sandboxir

llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/Passes/SeedCollection.h

@@ -0,0 +1,40 @@
+//===- SeedCollection.h -----------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// The seed-collection pass of the bottom-up vectorizer.
+//
+
+#ifndef LLVM_TRANSFORMS_VECTORIZE_SANDBOXVECTORIZER_PASSES_SEEDCOLLECTION_H
+#define LLVM_TRANSFORMS_VECTORIZE_SANDBOXVECTORIZER_PASSES_SEEDCOLLECTION_H
+
+#include "llvm/SandboxIR/Pass.h"
+#include "llvm/SandboxIR/PassManager.h"
+
+namespace llvm::sandboxir {
+
+/// This pass collects the instructions that can become vectorization "seeds",
+/// like stores to consecutive memory addresses. It then goes over the collected
+/// seeds, slicing them into appropriately sized chunks, creating a Region with
+/// the seed slice as the Auxiliary vector and runs the region pass pipeline.
+class SeedCollection final : public FunctionPass {
+
+  /// The PM containing the pipeline of region passes.
+  RegionPassManager RPM;
+
+public:
+  SeedCollection(StringRef Pipeline);
+  bool runOnFunction(Function &F, const Analyses &A) final;
+  void printPipeline(raw_ostream &OS) const final {
+    OS << getName() << "\n";
+    RPM.printPipeline(OS);
+  }
+};
+
+} // namespace llvm::sandboxir
+
+#endif // LLVM_TRANSFORMS_VECTORIZE_SANDBOXVECTORIZER_PASSES_SEEDCOLLECTION_H

llvm/lib/SandboxIR/Region.cpp

@@ -40,8 +40,10 @@ Region::Region(Context &Ctx, TargetTransformInfo &TTI)
 
   CreateInstCB = Ctx.registerCreateInstrCallback(
       [this](Instruction *NewInst) { add(NewInst); });
-  EraseInstCB = Ctx.registerEraseInstrCallback(
-      [this](Instruction *ErasedInst) { remove(ErasedInst); });
+  EraseInstCB = Ctx.registerEraseInstrCallback([this](Instruction *ErasedInst) {
+    remove(ErasedInst);
+    removeFromAux(ErasedInst);
+  });
 }
 
 Region::~Region() {
@@ -84,11 +86,22 @@ void Region::setAux(unsigned Idx, Instruction *I) {
   Aux[Idx] = I;
 }
 
+void Region::dropAuxMetadata(Instruction *I) {
+  auto *LLVMI = cast<llvm::Instruction>(I->Val);
+  LLVMI->setMetadata(AuxMDKind, nullptr);
+}
+
+void Region::removeFromAux(Instruction *I) {
+  auto It = find(Aux, I);
+  if (It == Aux.end())
+    return;
+  dropAuxMetadata(I);
+  Aux.erase(It);
+}
+
 void Region::clearAux() {
-  for (unsigned Idx : seq<unsigned>(0, Aux.size())) {
-    auto *LLVMI = cast<llvm::Instruction>(Aux[Idx]->Val);
-    LLVMI->setMetadata(AuxMDKind, nullptr);
-  }
+  for (unsigned Idx : seq<unsigned>(0, Aux.size()))
+    dropAuxMetadata(Aux[Idx]);
   Aux.clear();
 }
 

llvm/lib/Transforms/Vectorize/CMakeLists.txt

@@ -9,6 +9,7 @@ add_llvm_component_library(LLVMVectorize
   SandboxVectorizer/Legality.cpp
   SandboxVectorizer/Passes/BottomUpVec.cpp
   SandboxVectorizer/Passes/RegionsFromMetadata.cpp
+  SandboxVectorizer/Passes/SeedCollection.cpp
   SandboxVectorizer/Passes/TransactionAcceptOrRevert.cpp
   SandboxVectorizer/SandboxVectorizer.cpp
   SandboxVectorizer/SandboxVectorizerPassBuilder.cpp

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

@@ -14,20 +14,10 @@
 #include "llvm/SandboxIR/Module.h"
 #include "llvm/SandboxIR/Region.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 {
 
-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."));
-
 #ifndef NDEBUG
 static cl::opt<bool>
     AlwaysVerify("sbvec-always-verify", cl::init(false), cl::Hidden,
@@ -37,10 +27,6 @@ static cl::opt<bool>
 
 namespace sandboxir {
 
-BottomUpVec::BottomUpVec(StringRef Pipeline)
-    : FunctionPass("bottom-up-vec"),
-      RPM("rpm", Pipeline, SandboxVectorizerPassBuilder::createRegionPass) {}
-
 static SmallVector<Value *, 4> getOperand(ArrayRef<Value *> Bndl,
                                           unsigned OpIdx) {
   SmallVector<Value *, 4> Operands;
@@ -413,90 +399,29 @@ Value *BottomUpVec::vectorizeRec(ArrayRef<Value *> Bndl,
 }
 
 bool BottomUpVec::tryVectorize(ArrayRef<Value *> Bndl) {
+  Change = false;
   DeadInstrCandidates.clear();
   Legality->clear();
   vectorizeRec(Bndl, {}, /*Depth=*/0);
   tryEraseDeadInstrs();
   return Change;
 }
 
-bool BottomUpVec::runOnFunction(Function &F, const Analyses &A) {
+bool BottomUpVec::runOnRegion(Region &Rgn, const Analyses &A) {
+  const auto &SeedSlice = Rgn.getAux();
+  assert(SeedSlice.size() >= 2 && "Bad slice!");
+  Function &F = *SeedSlice[0]->getParent()->getParent();
   IMaps = std::make_unique<InstrMaps>(F.getContext());
   Legality = std::make_unique<LegalityAnalysis>(
       A.getAA(), A.getScalarEvolution(), F.getParent()->getDataLayout(),
       F.getContext(), *IMaps);
-  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) {
-    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: Refactor to remove the unnecessary copy to SeedSliceVals.
-          SmallVector<Value *> SeedSliceVals(SeedSlice.begin(),
-                                             SeedSlice.end());
-          // Create an empty region. Instructions get added to the region
-          // automatically by the callbacks.
-          auto &Ctx = F.getContext();
-          Region Rgn(Ctx, A.getTTI());
-          // Save the state of the IR before we make any changes. The
-          // transaction gets accepted/reverted by the tr-accept-or-revert pass.
-          Ctx.save();
-          // Try to vectorize starting from the seed slice. The returned value
-          // is true if we found vectorizable code and generated some vector
-          // code for it. It does not mean that the code is profitable.
-          bool VecSuccess = tryVectorize(SeedSliceVals);
-          if (VecSuccess)
-            // WARNING: All passes should return false, except those that
-            // accept/revert the state.
-            Change |= RPM.runOnRegion(Rgn, A);
-        }
-      }
-    }
-  }
-  return Change;
+  // TODO: Refactor to remove the unnecessary copy to SeedSliceVals.
+  SmallVector<Value *> SeedSliceVals(SeedSlice.begin(), SeedSlice.end());
+  // Try to vectorize starting from the seed slice. The returned value
+  // is true if we found vectorizable code and generated some vector
+  // code for it. It does not mean that the code is profitable.
+  return tryVectorize(SeedSliceVals);
 }
 
 } // namespace sandboxir

llvm/lib/Transforms/Vectorize/SandboxVectorizer/Passes/PassRegistry.def

@@ -21,14 +21,15 @@ REGION_PASS("null", ::llvm::sandboxir::NullPass)
 REGION_PASS("print-instruction-count", ::llvm::sandboxir::PrintInstructionCount)
 REGION_PASS("tr-accept", ::llvm::sandboxir::TransactionAlwaysAccept)
 REGION_PASS("tr-accept-or-revert", ::llvm::sandboxir::TransactionAcceptOrRevert)
+REGION_PASS("bottom-up-vec", ::llvm::sandboxir::BottomUpVec)
 
 #undef REGION_PASS
 
 #ifndef FUNCTION_PASS_WITH_PARAMS
 #define FUNCTION_PASS_WITH_PARAMS(NAME, CLASS_NAME)
 #endif
 
-FUNCTION_PASS_WITH_PARAMS("bottom-up-vec", ::llvm::sandboxir::BottomUpVec)
+FUNCTION_PASS_WITH_PARAMS("seed-collection", ::llvm::sandboxir::SeedCollection)
 FUNCTION_PASS_WITH_PARAMS("regions-from-metadata", ::llvm::sandboxir::RegionsFromMetadata)
 
 #undef FUNCTION_PASS_WITH_PARAMS

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

@@ -0,0 +1,98 @@
+//===- SeedCollection.cpp - Seed collection pass --------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Vectorize/SandboxVectorizer/Passes/SeedCollection.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/SandboxIR/Module.h"
+#include "llvm/SandboxIR/Region.h"
+#include "llvm/Transforms/Vectorize/SandboxVectorizer/SandboxVectorizerPassBuilder.h"
+#include "llvm/Transforms/Vectorize/SandboxVectorizer/SeedCollector.h"
+#include "llvm/Transforms/Vectorize/SandboxVectorizer/VecUtils.h"
+
+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 {
+SeedCollection::SeedCollection(StringRef Pipeline)
+    : FunctionPass("seed-collection"),
+      RPM("rpm", Pipeline, SandboxVectorizerPassBuilder::createRegionPass) {}
+
+bool SeedCollection::runOnFunction(Function &F, const Analyses &A) {
+  bool 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) {
+    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!");
+
+          // Create a region containing the seed slice.
+          auto &Ctx = F.getContext();
+          Region Rgn(Ctx, A.getTTI());
+          // TODO: Replace save() with a save pass in the pass pipeline.
+          Ctx.save();
+          Rgn.setAux(SeedSlice);
+          // Run the region pass pipeline.
+          Change |= RPM.runOnRegion(Rgn, A);
+          Rgn.clearAux();
+        }
+      }
+    }
+  }
+  return Change;
+}
+} // namespace sandboxir
+} // namespace llvm