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Add a value range analysis that lazily computes ranges using ScalarEvolutions.

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llvm-svn: 52885
This commit is contained in:
Nick Lewycky 2008-06-30 00:04:21 +00:00
parent 6f260767ec
commit d63159dcd4
3 changed files with 381 additions and 0 deletions
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90
include/llvm/Analysis/LoopVR.h Normal file
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@ -0,0 +1,90 @@
//===- 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.
//
//===----------------------------------------------------------------------===//
//
// This file defines the interface for the loop-driven value range pass.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ANALYSIS_LOOPVR_H
#define LLVM_ANALYSIS_LOOPVR_H
#include "llvm/Pass.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Support/ConstantRange.h"
#include <iosfwd>
#include <map>
namespace llvm {
/// LoopVR - This class maintains a mapping of Values to ConstantRanges.
/// There are interfaces to look up and update ranges by value, and for
/// accessing all values with range information.
///
class LoopVR : public FunctionPass {
public:
static char ID; // Class identification, replacement for typeinfo
LoopVR() : FunctionPass(intptr_t(&ID)) {}
bool runOnFunction(Function &F);
virtual void print(std::ostream &os, const Module *) const;
void releaseMemory();
void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LoopInfo>();
AU.addRequired<ScalarEvolution>();
AU.setPreservesAll();
}
//===---------------------------------------------------------------------
// Methods that are used to look up and update particular values.
/// get - return the ConstantRange for a given Value of IntegerType.
ConstantRange get(Value *V);
/// remove - remove a value from this analysis.
void remove(Value *V);
/// narrow - improve our unterstanding of a Value by pointing out that it
/// must fall within ConstantRange. To replace a range, remove it first.
void narrow(Value *V, const ConstantRange &CR);
//===---------------------------------------------------------------------
// Methods that are used to iterate across all values with information.
/// size - returns the number of Values with information
unsigned size() const { return Map.size(); }
typedef std::map<Value *, ConstantRange *>::iterator iterator;
/// begin - return an iterator to the first Value, ConstantRange pair
iterator begin() { return Map.begin(); }
/// end - return an iterator one past the last Value, ConstantRange pair
iterator end() { return Map.end(); }
/// getValue - return the Value referenced by an iterator
Value *getValue(iterator I) { return I->first; }
/// getConstantRange - return the ConstantRange referenced by an iterator
ConstantRange getConstantRange(iterator I) { return *I->second; }
private:
ConstantRange compute(Value *V);
ConstantRange getRange(SCEVHandle S, Loop *L, ScalarEvolution &SE);
ConstantRange getRange(SCEVHandle S, SCEVHandle T, ScalarEvolution &SE);
std::map<Value *, ConstantRange *> Map;
};
} // end llvm namespace
#endif

2
include/llvm/LinkAllPasses.h
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@ -19,6 +19,7 @@
#include "llvm/Analysis/FindUsedTypes.h"
#include "llvm/Analysis/IntervalPartition.h"
#include "llvm/Analysis/LoadValueNumbering.h"
#include "llvm/Analysis/LoopVR.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Analysis/PostDominators.h"
#include "llvm/Analysis/ScalarEvolution.h"
@ -122,6 +123,7 @@ namespace {
(void)new llvm::IntervalPartition();
(void)new llvm::FindUsedTypes();
(void)new llvm::ScalarEvolution();
(void)new llvm::LoopVR();
((llvm::Function*)0)->viewCFGOnly();
llvm::AliasSetTracker X(*(llvm::AliasAnalysis*)0);
X.add((llvm::Value*)0, 0); // for -print-alias-sets

289
lib/Analysis/LoopVR.cpp Normal file
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//===- 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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "loopvr"
#include "llvm/Analysis/LoopVR.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Streams.h"
using namespace llvm;
char LoopVR::ID = 0;
namespace {
static RegisterPass<LoopVR> X("loopvr", "Loop Value Ranges", true, true);
}
/// getRange - determine the range for a particular SCEV within a given Loop
ConstantRange LoopVR::getRange(SCEVHandle S, Loop *L, ScalarEvolution &SE) {
SCEVHandle T = SE.getIterationCount(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(SCEVHandle S, SCEVHandle T, ScalarEvolution &SE){
if (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 (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 (SCEVMulExpr *Mul = dyn_cast<SCEVMulExpr>(S)) {
ConstantRange X = getRange(Mul->getOperand(0), T, SE);
if (X.isFullSet()) return FullSet;
const IntegerType *Ty = IntegerType::get(X.getBitWidth());
const IntegerType *ExTy = IntegerType::get(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 (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 (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 (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.
// Use maximalIntersectWith to get the right behaviour.
ConstantRange NotZero(APInt(L.getBitWidth(), 1),
APInt::getNullValue(L.getBitWidth()));
R = R.maximalIntersectWith(NotZero);
}
// But, the maximal 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 (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 (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 (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 (SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(S)) {
SCEVConstant *Trip = dyn_cast<SCEVConstant>(T);
if (!Trip) return FullSet;
if (AddRec->isAffine()) {
SCEVHandle StartHandle = AddRec->getStart();
SCEVHandle StepHandle = AddRec->getOperand(1);
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;
SCEVHandle EndHandle = SE.getAddExpr(StartHandle,
SE.getMulExpr(T, StepHandle));
SCEVConstant *Start = dyn_cast<SCEVConstant>(StartHandle);
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;
}
bool LoopVR::runOnFunction(Function &F) { Map.clear(); return false; }
void LoopVR::print(std::ostream &os, const Module *) const {
for (std::map<Value *, ConstantRange *>::const_iterator I = Map.begin(),
E = Map.end(); I != E; ++I) {
os << *I->first << ": ";
I->second->print(os);
os << "\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>();
ScalarEvolution &SE = getAnalysis<ScalarEvolution>();
Loop *L = LI.getLoopFor(I->getParent());
if (L->isLoopInvariant(I))
return ConstantRange(cast<IntegerType>(V->getType())->getBitWidth(), false);
SCEVHandle 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]->maximalIntersectWith(CR));
}