vendor/llvm/llvm-trunk-r375505vendor/llvm

1 files changed, 281 insertions, 0 deletions

diff --git a/include/llvm/Analysis/LoopCacheAnalysis.h b/include/llvm/Analysis/LoopCacheAnalysis.h
new file mode 100644
index 000000000000..ffec78b6db2c
--- /dev/null
+++ b/include/llvm/Analysis/LoopCacheAnalysis.h
@@ -0,0 +1,281 @@
+//===- llvm/Analysis/LoopCacheAnalysis.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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file defines the interface for the loop cache analysis.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_LOOPCACHEANALYSIS_H
+#define LLVM_ANALYSIS_LOOPCACHEANALYSIS_H
+
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/DependenceAnalysis.h"
+#include "llvm/Analysis/LoopAnalysisManager.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace llvm {
+
+class LPMUpdater;
+using CacheCostTy = int64_t;
+using LoopVectorTy = SmallVector<Loop *, 8>;
+
+/// Represents a memory reference as a base pointer and a set of indexing
+/// operations. For example given the array reference A[i][2j+1][3k+2] in a
+/// 3-dim loop nest:
+///   for(i=0;i<n;++i)
+///     for(j=0;j<m;++j)
+///       for(k=0;k<o;++k)
+///         ... A[i][2j+1][3k+2] ...
+/// We expect:
+///   BasePointer -> A
+///   Subscripts -> [{0,+,1}<%for.i>][{1,+,2}<%for.j>][{2,+,3}<%for.k>]
+///   Sizes -> [m][o][4]
+class IndexedReference {
+  friend raw_ostream &operator<<(raw_ostream &OS, const IndexedReference &R);
+
+public:
+  /// Construct an indexed reference given a \p StoreOrLoadInst instruction.
+  IndexedReference(Instruction &StoreOrLoadInst, const LoopInfo &LI,
+                   ScalarEvolution &SE);
+
+  bool isValid() const { return IsValid; }
+  const SCEV *getBasePointer() const { return BasePointer; }
+  size_t getNumSubscripts() const { return Subscripts.size(); }
+  const SCEV *getSubscript(unsigned SubNum) const {
+    assert(SubNum < getNumSubscripts() && "Invalid subscript number");
+    return Subscripts[SubNum];
+  }
+  const SCEV *getFirstSubscript() const {
+    assert(!Subscripts.empty() && "Expecting non-empty container");
+    return Subscripts.front();
+  }
+  const SCEV *getLastSubscript() const {
+    assert(!Subscripts.empty() && "Expecting non-empty container");
+    return Subscripts.back();
+  }
+
+  /// Return true/false if the current object and the indexed reference \p Other
+  /// are/aren't in the same cache line of size \p CLS. Two references are in
+  /// the same chace line iff the distance between them in the innermost
+  /// dimension is less than the cache line size. Return None if unsure.
+  Optional<bool> hasSpacialReuse(const IndexedReference &Other, unsigned CLS,
+                                 AliasAnalysis &AA) const;
+
+  /// Return true if the current object and the indexed reference \p Other
+  /// have distance smaller than \p MaxDistance in the dimension associated with
+  /// the given loop \p L. Return false if the distance is not smaller than \p
+  /// MaxDistance and None if unsure.
+  Optional<bool> hasTemporalReuse(const IndexedReference &Other,
+                                  unsigned MaxDistance, const Loop &L,
+                                  DependenceInfo &DI, AliasAnalysis &AA) const;
+
+  /// Compute the cost of the reference w.r.t. the given loop \p L when it is
+  /// considered in the innermost position in the loop nest.
+  /// The cost is defined as:
+  ///   - equal to one if the reference is loop invariant, or
+  ///   - equal to '(TripCount * stride) / cache_line_size' if:
+  ///     + the reference stride is less than the cache line size, and
+  ///     + the coefficient of this loop's index variable used in all other
+  ///       subscripts is zero
+  ///   - or otherwise equal to 'TripCount'.
+  CacheCostTy computeRefCost(const Loop &L, unsigned CLS) const;
+
+private:
+  /// Attempt to delinearize the indexed reference.
+  bool delinearize(const LoopInfo &LI);
+
+  /// Return true if the index reference is invariant with respect to loop \p L.
+  bool isLoopInvariant(const Loop &L) const;
+
+  /// Return true if the indexed reference is 'consecutive' in loop \p L.
+  /// An indexed reference is 'consecutive' if the only coefficient that uses
+  /// the loop induction variable is the rightmost one, and the access stride is
+  /// smaller than the cache line size \p CLS.
+  bool isConsecutive(const Loop &L, unsigned CLS) const;
+
+  /// Return the coefficient used in the rightmost dimension.
+  const SCEV *getLastCoefficient() const;
+
+  /// Return true if the coefficient corresponding to induction variable of
+  /// loop \p L in the given \p Subscript is zero or is loop invariant in \p L.
+  bool isCoeffForLoopZeroOrInvariant(const SCEV &Subscript,
+                                     const Loop &L) const;
+
+  /// Verify that the given \p Subscript is 'well formed' (must be a simple add
+  /// recurrence).
+  bool isSimpleAddRecurrence(const SCEV &Subscript, const Loop &L) const;
+
+  /// Return true if the given reference \p Other is definetely aliased with
+  /// the indexed reference represented by this class.
+  bool isAliased(const IndexedReference &Other, AliasAnalysis &AA) const;
+
+private:
+  /// True if the reference can be delinearized, false otherwise.
+  bool IsValid = false;
+
+  /// Represent the memory reference instruction.
+  Instruction &StoreOrLoadInst;
+
+  /// The base pointer of the memory reference.
+  const SCEV *BasePointer = nullptr;
+
+  /// The subscript (indexes) of the memory reference.
+  SmallVector<const SCEV *, 3> Subscripts;
+
+  /// The dimensions of the memory reference.
+  SmallVector<const SCEV *, 3> Sizes;
+
+  ScalarEvolution &SE;
+};
+
+/// A reference group represents a set of memory references that exhibit
+/// temporal or spacial reuse. Two references belong to the same
+/// reference group with respect to a inner loop L iff:
+/// 1. they have a loop independent dependency, or
+/// 2. they have a loop carried dependence with a small dependence distance
+///    (e.g. less than 2) carried by the inner loop, or
+/// 3. they refer to the same array, and the subscript in their innermost
+///    dimension is less than or equal to 'd' (where 'd' is less than the cache
+///    line size)
+///
+/// Intuitively a reference group represents memory references that access
+/// the same cache line. Conditions 1,2 above account for temporal reuse, while
+/// contition 3 accounts for spacial reuse.
+using ReferenceGroupTy = SmallVector<std::unique_ptr<IndexedReference>, 8>;
+using ReferenceGroupsTy = SmallVector<ReferenceGroupTy, 8>;
+
+/// \c CacheCost represents the estimated cost of a inner loop as the number of
+/// cache lines used by the memory references it contains.
+/// The 'cache cost' of a loop 'L' in a loop nest 'LN' is computed as the sum of
+/// the cache costs of all of its reference groups when the loop is considered
+/// to be in the innermost position in the nest.
+/// A reference group represents memory references that fall into the same cache
+/// line. Each reference group is analysed with respect to the innermost loop in
+/// a loop nest. The cost of a reference is defined as follow:
+///  - one if it is loop invariant w.r.t the innermost loop,
+///  - equal to the loop trip count divided by the cache line times the
+///    reference stride if the reference stride is less than the cache line
+///    size (CLS), and the coefficient of this loop's index variable used in all
+///    other subscripts is zero (e.g. RefCost = TripCount/(CLS/RefStride))
+///  - equal to the innermost loop trip count if the reference stride is greater
+///    or equal to the cache line size CLS.
+class CacheCost {
+  friend raw_ostream &operator<<(raw_ostream &OS, const CacheCost &CC);
+  using LoopTripCountTy = std::pair<const Loop *, unsigned>;
+  using LoopCacheCostTy = std::pair<const Loop *, CacheCostTy>;
+
+public:
+  static CacheCostTy constexpr InvalidCost = -1;
+
+  /// Construct a CacheCost object for the loop nest described by \p Loops.
+  /// The optional parameter \p TRT can be used to specify the max. distance
+  /// between array elements accessed in a loop so that the elements are
+  /// classified to have temporal reuse.
+  CacheCost(const LoopVectorTy &Loops, const LoopInfo &LI, ScalarEvolution &SE,
+            TargetTransformInfo &TTI, AliasAnalysis &AA, DependenceInfo &DI,
+            Optional<unsigned> TRT = None);
+
+  /// Create a CacheCost for the loop nest rooted by \p Root.
+  /// The optional parameter \p TRT can be used to specify the max. distance
+  /// between array elements accessed in a loop so that the elements are
+  /// classified to have temporal reuse.
+  static std::unique_ptr<CacheCost>
+  getCacheCost(Loop &Root, LoopStandardAnalysisResults &AR, DependenceInfo &DI,
+               Optional<unsigned> TRT = None);
+
+  /// Return the estimated cost of loop \p L if the given loop is part of the
+  /// loop nest associated with this object. Return -1 otherwise.
+  CacheCostTy getLoopCost(const Loop &L) const {
+    auto IT = std::find_if(
+        LoopCosts.begin(), LoopCosts.end(),
+        [&L](const LoopCacheCostTy &LCC) { return LCC.first == &L; });
+    return (IT != LoopCosts.end()) ? (*IT).second : -1;
+  }
+
+  /// Return the estimated ordered loop costs.
+  const ArrayRef<LoopCacheCostTy> getLoopCosts() const { return LoopCosts; }
+
+private:
+  /// Calculate the cache footprint of each loop in the nest (when it is
+  /// considered to be in the innermost position).
+  void calculateCacheFootprint();
+
+  /// Partition store/load instructions in the loop nest into reference groups.
+  /// Two or more memory accesses belong in the same reference group if they
+  /// share the same cache line.
+  bool populateReferenceGroups(ReferenceGroupsTy &RefGroups) const;
+
+  /// Calculate the cost of the given loop \p L assuming it is the innermost
+  /// loop in nest.
+  CacheCostTy computeLoopCacheCost(const Loop &L,
+                                   const ReferenceGroupsTy &RefGroups) const;
+
+  /// Compute the cost of a representative reference in reference group \p RG
+  /// when the given loop \p L is considered as the innermost loop in the nest.
+  /// The computed cost is an estimate for the number of cache lines used by the
+  /// reference group. The representative reference cost is defined as:
+  ///   - equal to one if the reference is loop invariant, or
+  ///   - equal to '(TripCount * stride) / cache_line_size' if (a) loop \p L's
+  ///     induction variable is used only in the reference subscript associated
+  ///     with loop \p L, and (b) the reference stride is less than the cache
+  ///     line size, or
+  ///   - TripCount otherwise
+  CacheCostTy computeRefGroupCacheCost(const ReferenceGroupTy &RG,
+                                       const Loop &L) const;
+
+  /// Sort the LoopCosts vector by decreasing cache cost.
+  void sortLoopCosts() {
+    sort(LoopCosts, [](const LoopCacheCostTy &A, const LoopCacheCostTy &B) {
+      return A.second > B.second;
+    });
+  }
+
+private:
+  /// Loops in the loop nest associated with this object.
+  LoopVectorTy Loops;
+
+  /// Trip counts for the loops in the loop nest associated with this object.
+  SmallVector<LoopTripCountTy, 3> TripCounts;
+
+  /// Cache costs for the loops in the loop nest associated with this object.
+  SmallVector<LoopCacheCostTy, 3> LoopCosts;
+
+  /// The max. distance between array elements accessed in a loop so that the
+  /// elements are classified to have temporal reuse.
+  Optional<unsigned> TRT;
+
+  const LoopInfo &LI;
+  ScalarEvolution &SE;
+  TargetTransformInfo &TTI;
+  AliasAnalysis &AA;
+  DependenceInfo &DI;
+};
+
+raw_ostream &operator<<(raw_ostream &OS, const IndexedReference &R);
+raw_ostream &operator<<(raw_ostream &OS, const CacheCost &CC);
+
+/// Printer pass for the \c CacheCost results.
+class LoopCachePrinterPass : public PassInfoMixin<LoopCachePrinterPass> {
+  raw_ostream &OS;
+
+public:
+  explicit LoopCachePrinterPass(raw_ostream &OS) : OS(OS) {}
+
+  PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM,
+                        LoopStandardAnalysisResults &AR, LPMUpdater &U);
+};
+
+} // namespace llvm
+
+#endif // LLVM_ANALYSIS_LOOPCACHEANALYSIS_H