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//===- ScalarEvolutionNormalization.cpp - See below -----------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements utilities for working with "normalized" expressions.
// See the comments at the top of ScalarEvolutionNormalization.h for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Analysis/ScalarEvolutionNormalization.h"
using namespace llvm;
/// TransformKind - Different types of transformations that
/// TransformForPostIncUse can do.
enum TransformKind {
/// Normalize - Normalize according to the given loops.
Normalize,
/// Denormalize - Perform the inverse transform on the expression with the
/// given loop set.
Denormalize
};
typedef DenseMap<const SCEV *, const SCEV *> NormalizedCacheTy;
static const SCEV *transformSubExpr(const TransformKind Kind,
NormalizePredTy Pred, ScalarEvolution &SE,
NormalizedCacheTy &Cache, const SCEV *S);
/// Implement post-inc transformation for all valid expression types.
static const SCEV *transformImpl(const TransformKind Kind, NormalizePredTy Pred,
ScalarEvolution &SE, NormalizedCacheTy &Cache,
const SCEV *S) {
if (const SCEVCastExpr *X = dyn_cast<SCEVCastExpr>(S)) {
const SCEV *O = X->getOperand();
const SCEV *N = transformSubExpr(Kind, Pred, SE, Cache, O);
if (O != N)
switch (S->getSCEVType()) {
case scZeroExtend: return SE.getZeroExtendExpr(N, S->getType());
case scSignExtend: return SE.getSignExtendExpr(N, S->getType());
case scTruncate: return SE.getTruncateExpr(N, S->getType());
default: llvm_unreachable("Unexpected SCEVCastExpr kind!");
}
return S;
}
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
// An addrec. This is the interesting part.
SmallVector<const SCEV *, 8> Operands;
transform(AR->operands(), std::back_inserter(Operands),
[&](const SCEV *Op) {
return transformSubExpr(Kind, Pred, SE, Cache, Op);
});
// Conservatively use AnyWrap until/unless we need FlagNW.
const SCEV *Result =
SE.getAddRecExpr(Operands, AR->getLoop(), SCEV::FlagAnyWrap);
switch (Kind) {
case Normalize:
// We want to normalize step expression, because otherwise we might not be
// able to denormalize to the original expression.
//
// Here is an example what will happen if we don't normalize step:
// ORIGINAL ISE:
// {(100 /u {1,+,1}<%bb16>),+,(100 /u {1,+,1}<%bb16>)}<%bb25>
// NORMALIZED ISE:
// {((-1 * (100 /u {1,+,1}<%bb16>)) + (100 /u {0,+,1}<%bb16>)),+,
// (100 /u {0,+,1}<%bb16>)}<%bb25>
// DENORMALIZED BACK ISE:
// {((2 * (100 /u {1,+,1}<%bb16>)) + (-1 * (100 /u {2,+,1}<%bb16>))),+,
// (100 /u {1,+,1}<%bb16>)}<%bb25>
// Note that the initial value changes after normalization +
// denormalization, which isn't correct.
if (Pred(AR)) {
const SCEV *TransformedStep =
transformSubExpr(Kind, Pred, SE, Cache, AR->getStepRecurrence(SE));
Result = SE.getMinusSCEV(Result, TransformedStep);
}
break;
case Denormalize:
// Here we want to normalize step expressions for the same reasons, as
// stated above.
if (Pred(AR)) {
const SCEV *TransformedStep =
transformSubExpr(Kind, Pred, SE, Cache, AR->getStepRecurrence(SE));
Result = SE.getAddExpr(Result, TransformedStep);
}
break;
}
return Result;
}
if (const SCEVNAryExpr *X = dyn_cast<SCEVNAryExpr>(S)) {
SmallVector<const SCEV *, 8> Operands;
bool Changed = false;
// Transform each operand.
for (auto *O : X->operands()) {
const SCEV *N = transformSubExpr(Kind, Pred, SE, Cache, O);
Changed |= N != O;
Operands.push_back(N);
}
// If any operand actually changed, return a transformed result.
if (Changed)
switch (S->getSCEVType()) {
case scAddExpr: return SE.getAddExpr(Operands);
case scMulExpr: return SE.getMulExpr(Operands);
case scSMaxExpr: return SE.getSMaxExpr(Operands);
case scUMaxExpr: return SE.getUMaxExpr(Operands);
default: llvm_unreachable("Unexpected SCEVNAryExpr kind!");
}
return S;
}
if (const SCEVUDivExpr *X = dyn_cast<SCEVUDivExpr>(S)) {
const SCEV *LO = X->getLHS();
const SCEV *RO = X->getRHS();
const SCEV *LN = transformSubExpr(Kind, Pred, SE, Cache, LO);
const SCEV *RN = transformSubExpr(Kind, Pred, SE, Cache, RO);
if (LO != LN || RO != RN)
return SE.getUDivExpr(LN, RN);
return S;
}
llvm_unreachable("Unexpected SCEV kind!");
}
/// Manage recursive transformation across an expression DAG. Revisiting
/// expressions would lead to exponential recursion.
static const SCEV *transformSubExpr(const TransformKind Kind,
NormalizePredTy Pred, ScalarEvolution &SE,
NormalizedCacheTy &Cache, const SCEV *S) {
if (isa<SCEVConstant>(S) || isa<SCEVUnknown>(S))
return S;
const SCEV *Result = Cache.lookup(S);
if (Result)
return Result;
Result = transformImpl(Kind, Pred, SE, Cache, S);
Cache[S] = Result;
return Result;
}
const SCEV *llvm::normalizeForPostIncUse(const SCEV *S,
const PostIncLoopSet &Loops,
ScalarEvolution &SE) {
auto Pred = [&](const SCEVAddRecExpr *AR) {
return Loops.count(AR->getLoop());
};
NormalizedCacheTy Cache;
return transformSubExpr(Normalize, Pred, SE, Cache, S);
}
const SCEV *llvm::normalizeForPostIncUseIf(const SCEV *S, NormalizePredTy Pred,
ScalarEvolution &SE) {
NormalizedCacheTy Cache;
return transformSubExpr(Normalize, Pred, SE, Cache, S);
}
const SCEV *llvm::denormalizeForPostIncUse(const SCEV *S,
const PostIncLoopSet &Loops,
ScalarEvolution &SE) {
auto Pred = [&](const SCEVAddRecExpr *AR) {
return Loops.count(AR->getLoop());
};
NormalizedCacheTy Cache;
return transformSubExpr(Denormalize, Pred, SE, Cache, S);
}
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