llvm-6502/lib/Analysis/LoopVR.cpp
2009-08-13 21:58:54 +00:00

299 lines
11 KiB
C++

//===- LoopVR.cpp - Value Range analysis driven by loop information -------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// FIXME: What does this do?
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "loopvr"
#include "llvm/Analysis/LoopVR.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/LLVMContext.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
char LoopVR::ID = 0;
static RegisterPass<LoopVR> X("loopvr", "Loop Value Ranges", false, true);
/// getRange - determine the range for a particular SCEV within a given Loop
ConstantRange LoopVR::getRange(const SCEV *S, Loop *L, ScalarEvolution &SE) {
const SCEV *T = SE.getBackedgeTakenCount(L);
if (isa<SCEVCouldNotCompute>(T))
return ConstantRange(cast<IntegerType>(S->getType())->getBitWidth(), true);
T = SE.getTruncateOrZeroExtend(T, S->getType());
return getRange(S, T, SE);
}
/// getRange - determine the range for a particular SCEV with a given trip count
ConstantRange LoopVR::getRange(const SCEV *S, const SCEV *T, ScalarEvolution &SE){
if (const SCEVConstant *C = dyn_cast<SCEVConstant>(S))
return ConstantRange(C->getValue()->getValue());
ConstantRange FullSet(cast<IntegerType>(S->getType())->getBitWidth(), true);
// {x,+,y,+,...z}. We detect overflow by checking the size of the set after
// summing the upper and lower.
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S)) {
ConstantRange X = getRange(Add->getOperand(0), T, SE);
if (X.isFullSet()) return FullSet;
for (unsigned i = 1, e = Add->getNumOperands(); i != e; ++i) {
ConstantRange Y = getRange(Add->getOperand(i), T, SE);
if (Y.isFullSet()) return FullSet;
APInt Spread_X = X.getSetSize(), Spread_Y = Y.getSetSize();
APInt NewLower = X.getLower() + Y.getLower();
APInt NewUpper = X.getUpper() + Y.getUpper() - 1;
if (NewLower == NewUpper)
return FullSet;
X = ConstantRange(NewLower, NewUpper);
if (X.getSetSize().ult(Spread_X) || X.getSetSize().ult(Spread_Y))
return FullSet; // we've wrapped, therefore, full set.
}
return X;
}
// {x,*,y,*,...,z}. In order to detect overflow, we use k*bitwidth where
// k is the number of terms being multiplied.
if (const SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S)) {
ConstantRange X = getRange(Mul->getOperand(0), T, SE);
if (X.isFullSet()) return FullSet;
const IntegerType *Ty = IntegerType::get(SE.getContext(), X.getBitWidth());
const IntegerType *ExTy = IntegerType::get(SE.getContext(),
X.getBitWidth() * Mul->getNumOperands());
ConstantRange XExt = X.zeroExtend(ExTy->getBitWidth());
for (unsigned i = 1, e = Mul->getNumOperands(); i != e; ++i) {
ConstantRange Y = getRange(Mul->getOperand(i), T, SE);
if (Y.isFullSet()) return FullSet;
ConstantRange YExt = Y.zeroExtend(ExTy->getBitWidth());
XExt = ConstantRange(XExt.getLower() * YExt.getLower(),
((XExt.getUpper()-1) * (YExt.getUpper()-1)) + 1);
}
return XExt.truncate(Ty->getBitWidth());
}
// X smax Y smax ... Z is: range(smax(X_smin, Y_smin, ..., Z_smin),
// smax(X_smax, Y_smax, ..., Z_smax))
// It doesn't matter if one of the SCEVs has FullSet because we're taking
// a maximum of the minimums across all of them.
if (const SCEVSMaxExpr *SMax = dyn_cast<SCEVSMaxExpr>(S)) {
ConstantRange X = getRange(SMax->getOperand(0), T, SE);
if (X.isFullSet()) return FullSet;
APInt smin = X.getSignedMin(), smax = X.getSignedMax();
for (unsigned i = 1, e = SMax->getNumOperands(); i != e; ++i) {
ConstantRange Y = getRange(SMax->getOperand(i), T, SE);
smin = APIntOps::smax(smin, Y.getSignedMin());
smax = APIntOps::smax(smax, Y.getSignedMax());
}
if (smax + 1 == smin) return FullSet;
return ConstantRange(smin, smax + 1);
}
// X umax Y umax ... Z is: range(umax(X_umin, Y_umin, ..., Z_umin),
// umax(X_umax, Y_umax, ..., Z_umax))
// It doesn't matter if one of the SCEVs has FullSet because we're taking
// a maximum of the minimums across all of them.
if (const SCEVUMaxExpr *UMax = dyn_cast<SCEVUMaxExpr>(S)) {
ConstantRange X = getRange(UMax->getOperand(0), T, SE);
if (X.isFullSet()) return FullSet;
APInt umin = X.getUnsignedMin(), umax = X.getUnsignedMax();
for (unsigned i = 1, e = UMax->getNumOperands(); i != e; ++i) {
ConstantRange Y = getRange(UMax->getOperand(i), T, SE);
umin = APIntOps::umax(umin, Y.getUnsignedMin());
umax = APIntOps::umax(umax, Y.getUnsignedMax());
}
if (umax + 1 == umin) return FullSet;
return ConstantRange(umin, umax + 1);
}
// L udiv R. Luckily, there's only ever 2 sides to a udiv.
if (const SCEVUDivExpr *UDiv = dyn_cast<SCEVUDivExpr>(S)) {
ConstantRange L = getRange(UDiv->getLHS(), T, SE);
ConstantRange R = getRange(UDiv->getRHS(), T, SE);
if (L.isFullSet() && R.isFullSet()) return FullSet;
if (R.getUnsignedMax() == 0) {
// RHS must be single-element zero. Return an empty set.
return ConstantRange(R.getBitWidth(), false);
}
APInt Lower = L.getUnsignedMin().udiv(R.getUnsignedMax());
APInt Upper;
if (R.getUnsignedMin() == 0) {
// Just because it contains zero, doesn't mean it will also contain one.
ConstantRange NotZero(APInt(L.getBitWidth(), 1),
APInt::getNullValue(L.getBitWidth()));
R = R.intersectWith(NotZero);
}
// But, the intersection might still include zero. If it does, then we know
// it also included one.
if (R.contains(APInt::getNullValue(L.getBitWidth())))
Upper = L.getUnsignedMax();
else
Upper = L.getUnsignedMax().udiv(R.getUnsignedMin());
return ConstantRange(Lower, Upper);
}
// ConstantRange already implements the cast operators.
if (const SCEVZeroExtendExpr *ZExt = dyn_cast<SCEVZeroExtendExpr>(S)) {
T = SE.getTruncateOrZeroExtend(T, ZExt->getOperand()->getType());
ConstantRange X = getRange(ZExt->getOperand(), T, SE);
return X.zeroExtend(cast<IntegerType>(ZExt->getType())->getBitWidth());
}
if (const SCEVSignExtendExpr *SExt = dyn_cast<SCEVSignExtendExpr>(S)) {
T = SE.getTruncateOrZeroExtend(T, SExt->getOperand()->getType());
ConstantRange X = getRange(SExt->getOperand(), T, SE);
return X.signExtend(cast<IntegerType>(SExt->getType())->getBitWidth());
}
if (const SCEVTruncateExpr *Trunc = dyn_cast<SCEVTruncateExpr>(S)) {
T = SE.getTruncateOrZeroExtend(T, Trunc->getOperand()->getType());
ConstantRange X = getRange(Trunc->getOperand(), T, SE);
if (X.isFullSet()) return FullSet;
return X.truncate(cast<IntegerType>(Trunc->getType())->getBitWidth());
}
if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(S)) {
const SCEVConstant *Trip = dyn_cast<SCEVConstant>(T);
if (!Trip) return FullSet;
if (AddRec->isAffine()) {
const SCEV *StartHandle = AddRec->getStart();
const SCEV *StepHandle = AddRec->getOperand(1);
const SCEVConstant *Step = dyn_cast<SCEVConstant>(StepHandle);
if (!Step) return FullSet;
uint32_t ExWidth = 2 * Trip->getValue()->getBitWidth();
APInt TripExt = Trip->getValue()->getValue(); TripExt.zext(ExWidth);
APInt StepExt = Step->getValue()->getValue(); StepExt.zext(ExWidth);
if ((TripExt * StepExt).ugt(APInt::getLowBitsSet(ExWidth, ExWidth >> 1)))
return FullSet;
const SCEV *EndHandle = SE.getAddExpr(StartHandle,
SE.getMulExpr(T, StepHandle));
const SCEVConstant *Start = dyn_cast<SCEVConstant>(StartHandle);
const SCEVConstant *End = dyn_cast<SCEVConstant>(EndHandle);
if (!Start || !End) return FullSet;
const APInt &StartInt = Start->getValue()->getValue();
const APInt &EndInt = End->getValue()->getValue();
const APInt &StepInt = Step->getValue()->getValue();
if (StepInt.isNegative()) {
if (EndInt == StartInt + 1) return FullSet;
return ConstantRange(EndInt, StartInt + 1);
} else {
if (StartInt == EndInt + 1) return FullSet;
return ConstantRange(StartInt, EndInt + 1);
}
}
}
// TODO: non-affine addrec, udiv, SCEVUnknown (narrowed from elsewhere)?
return FullSet;
}
void LoopVR::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredTransitive<LoopInfo>();
AU.addRequiredTransitive<ScalarEvolution>();
AU.setPreservesAll();
}
bool LoopVR::runOnFunction(Function &F) { Map.clear(); return false; }
void LoopVR::print(std::ostream &os, const Module *) const {
raw_os_ostream OS(os);
for (std::map<Value *, ConstantRange *>::const_iterator I = Map.begin(),
E = Map.end(); I != E; ++I) {
OS << *I->first << ": " << *I->second << '\n';
}
}
void LoopVR::releaseMemory() {
for (std::map<Value *, ConstantRange *>::iterator I = Map.begin(),
E = Map.end(); I != E; ++I) {
delete I->second;
}
Map.clear();
}
ConstantRange LoopVR::compute(Value *V) {
if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
return ConstantRange(CI->getValue());
Instruction *I = dyn_cast<Instruction>(V);
if (!I)
return ConstantRange(cast<IntegerType>(V->getType())->getBitWidth(), false);
LoopInfo &LI = getAnalysis<LoopInfo>();
Loop *L = LI.getLoopFor(I->getParent());
if (!L || L->isLoopInvariant(I))
return ConstantRange(cast<IntegerType>(V->getType())->getBitWidth(), false);
ScalarEvolution &SE = getAnalysis<ScalarEvolution>();
const SCEV *S = SE.getSCEV(I);
if (isa<SCEVUnknown>(S) || isa<SCEVCouldNotCompute>(S))
return ConstantRange(cast<IntegerType>(V->getType())->getBitWidth(), false);
return ConstantRange(getRange(S, L, SE));
}
ConstantRange LoopVR::get(Value *V) {
std::map<Value *, ConstantRange *>::iterator I = Map.find(V);
if (I == Map.end()) {
ConstantRange *CR = new ConstantRange(compute(V));
Map[V] = CR;
return *CR;
}
return *I->second;
}
void LoopVR::remove(Value *V) {
std::map<Value *, ConstantRange *>::iterator I = Map.find(V);
if (I != Map.end()) {
delete I->second;
Map.erase(I);
}
}
void LoopVR::narrow(Value *V, const ConstantRange &CR) {
if (CR.isFullSet()) return;
std::map<Value *, ConstantRange *>::iterator I = Map.find(V);
if (I == Map.end())
Map[V] = new ConstantRange(CR);
else
Map[V] = new ConstantRange(Map[V]->intersectWith(CR));
}