119 lines
4.6 KiB
C++
119 lines
4.6 KiB
C++
//===- ScalarEvolutionNormalization.cpp - See below -----------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements utilities for working with "normalized" expressions.
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// See the comments at the top of ScalarEvolutionNormalization.h for details.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/ScalarEvolutionNormalization.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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using namespace llvm;
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/// TransformKind - Different types of transformations that
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/// TransformForPostIncUse can do.
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enum TransformKind {
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/// Normalize - Normalize according to the given loops.
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Normalize,
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/// Denormalize - Perform the inverse transform on the expression with the
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/// given loop set.
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Denormalize
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};
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namespace {
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struct NormalizeDenormalizeRewriter
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: public SCEVRewriteVisitor<NormalizeDenormalizeRewriter> {
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const TransformKind Kind;
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// NB! Pred is a function_ref. Storing it here is okay only because
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// we're careful about the lifetime of NormalizeDenormalizeRewriter.
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const NormalizePredTy Pred;
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NormalizeDenormalizeRewriter(TransformKind Kind, NormalizePredTy Pred,
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ScalarEvolution &SE)
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: SCEVRewriteVisitor<NormalizeDenormalizeRewriter>(SE), Kind(Kind),
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Pred(Pred) {}
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const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr);
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};
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} // namespace
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const SCEV *
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NormalizeDenormalizeRewriter::visitAddRecExpr(const SCEVAddRecExpr *AR) {
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SmallVector<const SCEV *, 8> Operands;
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transform(AR->operands(), std::back_inserter(Operands),
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[&](const SCEV *Op) { return visit(Op); });
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if (!Pred(AR))
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return SE.getAddRecExpr(Operands, AR->getLoop(), SCEV::FlagAnyWrap);
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// Normalization and denormalization are fancy names for decrementing and
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// incrementing a SCEV expression with respect to a set of loops. Since
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// Pred(AR) has returned true, we know we need to normalize or denormalize AR
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// with respect to its loop.
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if (Kind == Denormalize) {
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// Denormalization / "partial increment" is essentially the same as \c
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// SCEVAddRecExpr::getPostIncExpr. Here we use an explicit loop to make the
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// symmetry with Normalization clear.
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for (int i = 0, e = Operands.size() - 1; i < e; i++)
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Operands[i] = SE.getAddExpr(Operands[i], Operands[i + 1]);
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} else {
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assert(Kind == Normalize && "Only two possibilities!");
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// Normalization / "partial decrement" is a bit more subtle. Since
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// incrementing a SCEV expression (in general) changes the step of the SCEV
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// expression as well, we cannot use the step of the current expression.
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// Instead, we have to use the step of the very expression we're trying to
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// compute!
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//
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// We solve the issue by recursively building up the result, starting from
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// the "least significant" operand in the add recurrence:
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//
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// Base case:
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// Single operand add recurrence. It's its own normalization.
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//
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// N-operand case:
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// {S_{N-1},+,S_{N-2},+,...,+,S_0} = S
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//
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// Since the step recurrence of S is {S_{N-2},+,...,+,S_0}, we know its
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// normalization by induction. We subtract the normalized step
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// recurrence from S_{N-1} to get the normalization of S.
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for (int i = Operands.size() - 2; i >= 0; i--)
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Operands[i] = SE.getMinusSCEV(Operands[i], Operands[i + 1]);
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}
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return SE.getAddRecExpr(Operands, AR->getLoop(), SCEV::FlagAnyWrap);
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}
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const SCEV *llvm::normalizeForPostIncUse(const SCEV *S,
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const PostIncLoopSet &Loops,
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ScalarEvolution &SE) {
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auto Pred = [&](const SCEVAddRecExpr *AR) {
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return Loops.count(AR->getLoop());
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};
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return NormalizeDenormalizeRewriter(Normalize, Pred, SE).visit(S);
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}
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const SCEV *llvm::normalizeForPostIncUseIf(const SCEV *S, NormalizePredTy Pred,
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ScalarEvolution &SE) {
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return NormalizeDenormalizeRewriter(Normalize, Pred, SE).visit(S);
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}
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const SCEV *llvm::denormalizeForPostIncUse(const SCEV *S,
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const PostIncLoopSet &Loops,
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ScalarEvolution &SE) {
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auto Pred = [&](const SCEVAddRecExpr *AR) {
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return Loops.count(AR->getLoop());
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};
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return NormalizeDenormalizeRewriter(Denormalize, Pred, SE).visit(S);
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}
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