LLVM  6.0.0svn
ScalarEvolutionNormalization.cpp
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1 //===- ScalarEvolutionNormalization.cpp - See below -----------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements utilities for working with "normalized" expressions.
11 // See the comments at the top of ScalarEvolutionNormalization.h for details.
12 //
13 //===----------------------------------------------------------------------===//
14 
16 #include "llvm/Analysis/LoopInfo.h"
18 using namespace llvm;
19 
20 /// TransformKind - Different types of transformations that
21 /// TransformForPostIncUse can do.
23  /// Normalize - Normalize according to the given loops.
25  /// Denormalize - Perform the inverse transform on the expression with the
26  /// given loop set.
28 };
29 
30 namespace {
31 struct NormalizeDenormalizeRewriter
32  : public SCEVRewriteVisitor<NormalizeDenormalizeRewriter> {
33  const TransformKind Kind;
34 
35  // NB! Pred is a function_ref. Storing it here is okay only because
36  // we're careful about the lifetime of NormalizeDenormalizeRewriter.
37  const NormalizePredTy Pred;
38 
39  NormalizeDenormalizeRewriter(TransformKind Kind, NormalizePredTy Pred,
40  ScalarEvolution &SE)
42  Pred(Pred) {}
43  const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr);
44 };
45 } // namespace
46 
47 const SCEV *
48 NormalizeDenormalizeRewriter::visitAddRecExpr(const SCEVAddRecExpr *AR) {
50 
51  transform(AR->operands(), std::back_inserter(Operands),
52  [&](const SCEV *Op) { return visit(Op); });
53 
54  if (!Pred(AR))
55  return SE.getAddRecExpr(Operands, AR->getLoop(), SCEV::FlagAnyWrap);
56 
57  // Normalization and denormalization are fancy names for decrementing and
58  // incrementing a SCEV expression with respect to a set of loops. Since
59  // Pred(AR) has returned true, we know we need to normalize or denormalize AR
60  // with respect to its loop.
61 
62  if (Kind == Denormalize) {
63  // Denormalization / "partial increment" is essentially the same as \c
64  // SCEVAddRecExpr::getPostIncExpr. Here we use an explicit loop to make the
65  // symmetry with Normalization clear.
66  for (int i = 0, e = Operands.size() - 1; i < e; i++)
67  Operands[i] = SE.getAddExpr(Operands[i], Operands[i + 1]);
68  } else {
69  assert(Kind == Normalize && "Only two possibilities!");
70 
71  // Normalization / "partial decrement" is a bit more subtle. Since
72  // incrementing a SCEV expression (in general) changes the step of the SCEV
73  // expression as well, we cannot use the step of the current expression.
74  // Instead, we have to use the step of the very expression we're trying to
75  // compute!
76  //
77  // We solve the issue by recursively building up the result, starting from
78  // the "least significant" operand in the add recurrence:
79  //
80  // Base case:
81  // Single operand add recurrence. It's its own normalization.
82  //
83  // N-operand case:
84  // {S_{N-1},+,S_{N-2},+,...,+,S_0} = S
85  //
86  // Since the step recurrence of S is {S_{N-2},+,...,+,S_0}, we know its
87  // normalization by induction. We subtract the normalized step
88  // recurrence from S_{N-1} to get the normalization of S.
89 
90  for (int i = Operands.size() - 2; i >= 0; i--)
91  Operands[i] = SE.getMinusSCEV(Operands[i], Operands[i + 1]);
92  }
93 
94  return SE.getAddRecExpr(Operands, AR->getLoop(), SCEV::FlagAnyWrap);
95 }
96 
98  const PostIncLoopSet &Loops,
99  ScalarEvolution &SE) {
100  auto Pred = [&](const SCEVAddRecExpr *AR) {
101  return Loops.count(AR->getLoop());
102  };
103  return NormalizeDenormalizeRewriter(Normalize, Pred, SE).visit(S);
104 }
105 
107  ScalarEvolution &SE) {
108  return NormalizeDenormalizeRewriter(Normalize, Pred, SE).visit(S);
109 }
110 
112  const PostIncLoopSet &Loops,
113  ScalarEvolution &SE) {
114  auto Pred = [&](const SCEVAddRecExpr *AR) {
115  return Loops.count(AR->getLoop());
116  };
117  return NormalizeDenormalizeRewriter(Denormalize, Pred, SE).visit(S);
118 }
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
LLVM_ATTRIBUTE_ALWAYS_INLINE size_type size() const
Definition: SmallVector.h:136
const SCEV * normalizeForPostIncUse(const SCEV *S, const PostIncLoopSet &Loops, ScalarEvolution &SE)
Normalize S to be post-increment for all loops present in Loops.
The main scalar evolution driver.
An efficient, type-erasing, non-owning reference to a callable.
Definition: STLExtras.h:89
Normalize - Normalize according to the given loops.
Hexagon Hardware Loops
Denormalize - Perform the inverse transform on the expression with the given loop set...
This node represents a polynomial recurrence on the trip count of the specified loop.
const SCEV * normalizeForPostIncUseIf(const SCEV *S, NormalizePredTy Pred, ScalarEvolution &SE)
Normalize S for all add recurrence sub-expressions for which Pred returns true.
size_type count(ConstPtrType Ptr) const
count - Return 1 if the specified pointer is in the set, 0 otherwise.
Definition: SmallPtrSet.h:382
This is a &#39;vector&#39; (really, a variable-sized array), optimized for the case when the array is small...
Definition: SmallVector.h:864
This class represents an analyzed expression in the program.
OutputIt transform(R &&Range, OutputIt d_first, UnaryPredicate P)
Wrapper function around std::transform to apply a function to a range and store the result elsewhere...
Definition: STLExtras.h:890
const unsigned Kind
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
const SCEV * denormalizeForPostIncUse(const SCEV *S, const PostIncLoopSet &Loops, ScalarEvolution &SE)
Denormalize S to be post-increment for all loops present in Loops.
TransformKind
TransformKind - Different types of transformations that TransformForPostIncUse can do...
This visitor recursively visits a SCEV expression and re-writes it.