llvm-project/polly/lib/Analysis/ScopDetection.cpp

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//===----- ScopDetection.cpp - Detect Scops --------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Detect the maximal Scops of a function.
//
// A static control part (Scop) is a subgraph of the control flow graph (CFG)
// that only has statically known control flow and can therefore be described
// within the polyhedral model.
//
// Every Scop fullfills these restrictions:
//
// * It is a single entry single exit region
//
// * Only affine linear bounds in the loops
//
// Every natural loop in a Scop must have a number of loop iterations that can
// be described as an affine linear function in surrounding loop iterators or
// parameters. (A parameter is a scalar that does not change its value during
// execution of the Scop).
//
// * Only comparisons of affine linear expressions in conditions
//
// * All loops and conditions perfectly nested
//
// The control flow needs to be structured such that it could be written using
// just 'for' and 'if' statements, without the need for any 'goto', 'break' or
// 'continue'.
//
// * Side effect free functions call
//
// Only function calls and intrinsics that do not have side effects are allowed
// (readnone).
//
// The Scop detection finds the largest Scops by checking if the largest
// region is a Scop. If this is not the case, its canonical subregions are
// checked until a region is a Scop. It is now tried to extend this Scop by
// creating a larger non canonical region.
//
//===----------------------------------------------------------------------===//
#include "polly/ScopDetection.h"
#include "polly/LinkAllPasses.h"
#include "polly/Support/ScopHelper.h"
#include "polly/Support/SCEVValidator.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/RegionIterator.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/DebugInfo.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Assembly/Writer.h"
#define DEBUG_TYPE "polly-detect"
#include "llvm/Support/Debug.h"
#include <set>
using namespace llvm;
using namespace polly;
static cl::opt<std::string>
OnlyFunction("polly-detect-only",
cl::desc("Only detect scops in function"), cl::Hidden,
cl::value_desc("The function name to detect scops in"),
cl::ValueRequired, cl::init(""));
static cl::opt<bool>
IgnoreAliasing("polly-ignore-aliasing",
cl::desc("Ignore possible aliasing of the array bases"),
cl::Hidden, cl::init(false));
static cl::opt<bool>
ReportLevel("polly-report",
cl::desc("Print information about Polly"),
cl::Hidden, cl::init(false));
static cl::opt<bool>
AllowNonAffine("polly-allow-nonaffine",
cl::desc("Allow non affine access functions in arrays"),
cl::Hidden, cl::init(false));
//===----------------------------------------------------------------------===//
// Statistics.
STATISTIC(ValidRegion, "Number of regions that a valid part of Scop");
#define BADSCOP_STAT(NAME, DESC) STATISTIC(Bad##NAME##ForScop, \
"Number of bad regions for Scop: "\
DESC)
#define INVALID(NAME, MESSAGE) \
do { \
std::string Buf; \
raw_string_ostream fmt(Buf); \
fmt << MESSAGE; \
fmt.flush(); \
LastFailure = Buf; \
DEBUG(dbgs() << MESSAGE); \
DEBUG(dbgs() << "\n"); \
assert(!Context.Verifying && #NAME); \
if (!Context.Verifying) ++Bad##NAME##ForScop; \
return false; \
} while (0);
#define INVALID_NOVERIFY(NAME, MESSAGE) \
do { \
std::string Buf; \
raw_string_ostream fmt(Buf); \
fmt << MESSAGE; \
fmt.flush(); \
LastFailure = Buf; \
DEBUG(dbgs() << MESSAGE); \
DEBUG(dbgs() << "\n"); \
/* DISABLED: assert(!Context.Verifying && #NAME); */ \
if (!Context.Verifying) ++Bad##NAME##ForScop; \
return false; \
} while (0);
BADSCOP_STAT(CFG, "CFG too complex");
BADSCOP_STAT(IndVar, "Non canonical induction variable in loop");
BADSCOP_STAT(LoopBound, "Loop bounds can not be computed");
BADSCOP_STAT(FuncCall, "Function call with side effects appeared");
BADSCOP_STAT(AffFunc, "Expression not affine");
BADSCOP_STAT(Scalar, "Found scalar dependency");
BADSCOP_STAT(Alias, "Found base address alias");
BADSCOP_STAT(SimpleRegion, "Region not simple");
BADSCOP_STAT(Other, "Others");
//===----------------------------------------------------------------------===//
// ScopDetection.
bool ScopDetection::isMaxRegionInScop(const Region &R) const {
// The Region is valid only if it could be found in the set.
return ValidRegions.count(&R);
}
std::string ScopDetection::regionIsInvalidBecause(const Region *R) const {
if (!InvalidRegions.count(R))
return "";
return InvalidRegions.find(R)->second;
}
bool ScopDetection::isValidCFG(BasicBlock &BB,
DetectionContext &Context) const {
Region &RefRegion = Context.CurRegion;
TerminatorInst *TI = BB.getTerminator();
// Return instructions are only valid if the region is the top level region.
if (isa<ReturnInst>(TI) && !RefRegion.getExit() && TI->getNumOperands() == 0)
return true;
BranchInst *Br = dyn_cast<BranchInst>(TI);
if (!Br)
INVALID(CFG, "Non branch instruction terminates BB: " + BB.getName());
if (Br->isUnconditional()) return true;
Value *Condition = Br->getCondition();
// UndefValue is not allowed as condition.
if (isa<UndefValue>(Condition))
INVALID(AffFunc, "Condition based on 'undef' value in BB: " + BB.getName());
// Only Constant and ICmpInst are allowed as condition.
if (!(isa<Constant>(Condition) || isa<ICmpInst>(Condition)))
INVALID(AffFunc, "Condition in BB '" + BB.getName() + "' neither "
"constant nor an icmp instruction");
// Allow perfectly nested conditions.
assert(Br->getNumSuccessors() == 2 && "Unexpected number of successors");
if (ICmpInst *ICmp = dyn_cast<ICmpInst>(Condition)) {
// Unsigned comparisons are not allowed. They trigger overflow problems
// in the code generation.
//
// TODO: This is not sufficient and just hides bugs. However it does pretty
// well.
if (ICmp->isUnsigned())
return false;
// Are both operands of the ICmp affine?
if (isa<UndefValue>(ICmp->getOperand(0))
|| isa<UndefValue>(ICmp->getOperand(1)))
INVALID(AffFunc, "undef operand in branch at BB: " + BB.getName());
const SCEV *LHS = SE->getSCEV(ICmp->getOperand(0));
const SCEV *RHS = SE->getSCEV(ICmp->getOperand(1));
if (!isAffineExpr(&Context.CurRegion, LHS, *SE) ||
!isAffineExpr(&Context.CurRegion, RHS, *SE))
INVALID(AffFunc, "Non affine branch in BB '" << BB.getName()
<< "' with LHS: " << *LHS << " and RHS: " << *RHS);
}
// Allow loop exit conditions.
Loop *L = LI->getLoopFor(&BB);
if (L && L->getExitingBlock() == &BB)
return true;
// Allow perfectly nested conditions.
Region *R = RI->getRegionFor(&BB);
if (R->getEntry() != &BB)
INVALID(CFG, "Not well structured condition at BB: " + BB.getName());
return true;
}
bool ScopDetection::isValidCallInst(CallInst &CI) {
if (CI.mayHaveSideEffects() || CI.doesNotReturn())
return false;
if (CI.doesNotAccessMemory())
return true;
Function *CalledFunction = CI.getCalledFunction();
// Indirect calls are not supported.
if (CalledFunction == 0)
return false;
// TODO: Intrinsics.
return false;
}
bool ScopDetection::isValidMemoryAccess(Instruction &Inst,
DetectionContext &Context) const {
Value *Ptr = getPointerOperand(Inst);
const SCEV *AccessFunction = SE->getSCEV(Ptr);
const SCEVUnknown *BasePointer;
Value *BaseValue;
BasePointer = dyn_cast<SCEVUnknown>(SE->getPointerBase(AccessFunction));
if (!BasePointer)
INVALID(AffFunc, "No base pointer");
BaseValue = BasePointer->getValue();
if (isa<UndefValue>(BaseValue))
INVALID(AffFunc, "Undefined base pointer");
AccessFunction = SE->getMinusSCEV(AccessFunction, BasePointer);
if (!isAffineExpr(&Context.CurRegion, AccessFunction, *SE, BaseValue) &&
!AllowNonAffine)
INVALID(AffFunc, "Non affine access function: " << *AccessFunction);
// FIXME: Alias Analysis thinks IntToPtrInst aliases with alloca instructions
// created by IndependentBlocks Pass.
if (isa<IntToPtrInst>(BaseValue))
INVALID(Other, "Find bad intToptr prt: " << *BaseValue);
// Check if the base pointer of the memory access does alias with
// any other pointer. This cannot be handled at the moment.
AliasSet &AS =
Context.AST.getAliasSetForPointer(BaseValue, AliasAnalysis::UnknownSize,
Inst.getMetadata(LLVMContext::MD_tbaa));
// INVALID triggers an assertion in verifying mode, if it detects that a SCoP
// was detected by SCoP detection and that this SCoP was invalidated by a pass
// that stated it would preserve the SCoPs.
// We disable this check as the independent blocks pass may create memory
// references which seem to alias, if -basicaa is not available. They actually
// do not, but as we can not proof this without -basicaa we would fail. We
// disable this check to not cause irrelevant verification failures.
if (!AS.isMustAlias() && !IgnoreAliasing)
INVALID_NOVERIFY(Alias,
"Possible aliasing for value: " << BaseValue->getName()
<< "\n");
return true;
}
bool ScopDetection::hasScalarDependency(Instruction &Inst,
Region &RefRegion) const {
for (Instruction::use_iterator UI = Inst.use_begin(), UE = Inst.use_end();
UI != UE; ++UI)
if (Instruction *Use = dyn_cast<Instruction>(*UI))
if (!RefRegion.contains(Use->getParent())) {
// DirtyHack 1: PHINode user outside the Scop is not allow, if this
// PHINode is induction variable, the scalar to array transform may
// break it and introduce a non-indvar PHINode, which is not allow in
// Scop.
// This can be fix by:
// Introduce a IndependentBlockPrepare pass, which translate all
// PHINodes not in Scop to array.
// The IndependentBlockPrepare pass can also split the entry block of
// the function to hold the alloca instruction created by scalar to
// array. and split the exit block of the Scop so the new create load
// instruction for escape users will not break other Scops.
if (isa<PHINode>(Use))
return true;
}
return false;
}
bool ScopDetection::isValidInstruction(Instruction &Inst,
DetectionContext &Context) const {
// Only canonical IVs are allowed.
if (PHINode *PN = dyn_cast<PHINode>(&Inst))
if (!isIndVar(PN, LI))
INVALID(IndVar, "Non canonical PHI node: " << Inst);
// Scalar dependencies are not allowed.
if (hasScalarDependency(Inst, Context.CurRegion))
INVALID(Scalar, "Scalar dependency found: " << Inst);
// We only check the call instruction but not invoke instruction.
if (CallInst *CI = dyn_cast<CallInst>(&Inst)) {
if (isValidCallInst(*CI))
return true;
INVALID(FuncCall, "Call instruction: " << Inst);
}
if (!Inst.mayWriteToMemory() && !Inst.mayReadFromMemory()) {
if (isa<AllocaInst>(Inst))
INVALID(Other, "Alloca instruction: " << Inst);
return true;
}
// Check the access function.
if (isa<LoadInst>(Inst) || isa<StoreInst>(Inst))
return isValidMemoryAccess(Inst, Context);
// We do not know this instruction, therefore we assume it is invalid.
INVALID(Other, "Unknown instruction: " << Inst);
}
bool ScopDetection::isValidBasicBlock(BasicBlock &BB,
DetectionContext &Context) const {
if (!isValidCFG(BB, Context))
return false;
// Check all instructions, except the terminator instruction.
for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
if (!isValidInstruction(*I, Context))
return false;
Loop *L = LI->getLoopFor(&BB);
if (L && L->getHeader() == &BB && !isValidLoop(L, Context))
return false;
return true;
}
bool ScopDetection::isValidLoop(Loop *L, DetectionContext &Context) const {
PHINode *IndVar = L->getCanonicalInductionVariable();
// No canonical induction variable.
if (!IndVar)
INVALID(IndVar, "No canonical IV at loop header: "
<< L->getHeader()->getName());
// Is the loop count affine?
const SCEV *LoopCount = SE->getBackedgeTakenCount(L);
if (!isAffineExpr(&Context.CurRegion, LoopCount, *SE))
INVALID(LoopBound, "Non affine loop bound '" << *LoopCount << "' in loop: "
<< L->getHeader()->getName());
return true;
}
Region *ScopDetection::expandRegion(Region &R) {
// Initial no valid region was found (greater than R)
Region *LastValidRegion = NULL;
Region *ExpandedRegion = R.getExpandedRegion();
DEBUG(dbgs() << "\tExpanding " << R.getNameStr() << "\n");
while (ExpandedRegion) {
DetectionContext Context(*ExpandedRegion, *AA, false /* verifying */);
DEBUG(dbgs() << "\t\tTrying " << ExpandedRegion->getNameStr() << "\n");
// Check the exit first (cheap)
if (isValidExit(Context)) {
// If the exit is valid check all blocks
// - if true, a valid region was found => store it + keep expanding
// - if false, .tbd. => stop (should this really end the loop?)
if (!allBlocksValid(Context))
break;
// Delete unnecessary regions (allocated by getExpandedRegion)
if (LastValidRegion)
delete LastValidRegion;
// Store this region, because it is the greatest valid (encountered so far)
LastValidRegion = ExpandedRegion;
// Create and test the next greater region (if any)
ExpandedRegion = ExpandedRegion->getExpandedRegion();
} else {
// Create and test the next greater region (if any)
Region *TmpRegion = ExpandedRegion->getExpandedRegion();
// Delete unnecessary regions (allocated by getExpandedRegion)
delete ExpandedRegion;
ExpandedRegion = TmpRegion;
}
}
DEBUG(
if (LastValidRegion)
dbgs() << "\tto " << LastValidRegion->getNameStr() << "\n";
else
dbgs() << "\tExpanding " << R.getNameStr() << " failed\n";
);
return LastValidRegion;
}
void ScopDetection::findScops(Region &R) {
DetectionContext Context(R, *AA, false /*verifying*/);
LastFailure = "";
if (isValidRegion(Context)) {
++ValidRegion;
ValidRegions.insert(&R);
return;
}
InvalidRegions[&R] = LastFailure;
for (Region::iterator I = R.begin(), E = R.end(); I != E; ++I)
findScops(**I);
// Try to expand regions.
//
// As the region tree normally only contains canonical regions, non canonical
// regions that form a Scop are not found. Therefore, those non canonical
// regions are checked by expanding the canonical ones.
std::vector<Region*> ToExpand;
for (Region::iterator I = R.begin(), E = R.end(); I != E; ++I)
ToExpand.push_back(*I);
for (std::vector<Region*>::iterator RI = ToExpand.begin(),
RE = ToExpand.end(); RI != RE; ++RI) {
Region *CurrentRegion = *RI;
// Skip invalid regions. Regions may become invalid, if they are element of
// an already expanded region.
if (ValidRegions.find(CurrentRegion) == ValidRegions.end())
continue;
Region *ExpandedR = expandRegion(*CurrentRegion);
if (!ExpandedR)
continue;
R.addSubRegion(ExpandedR, true);
ValidRegions.insert(ExpandedR);
ValidRegions.erase(CurrentRegion);
for (Region::iterator I = ExpandedR->begin(), E = ExpandedR->end(); I != E;
++I)
ValidRegions.erase(*I);
}
}
bool ScopDetection::allBlocksValid(DetectionContext &Context) const {
Region &R = Context.CurRegion;
for (Region::block_iterator I = R.block_begin(), E = R.block_end(); I != E;
++I)
if (!isValidBasicBlock(**I, Context))
return false;
return true;
}
bool ScopDetection::isValidExit(DetectionContext &Context) const {
Region &R = Context.CurRegion;
// PHI nodes are not allowed in the exit basic block.
if (BasicBlock *Exit = R.getExit()) {
BasicBlock::iterator I = Exit->begin();
if (I != Exit->end() && isa<PHINode>(*I))
INVALID(Other, "PHI node in exit BB");
}
return true;
}
bool ScopDetection::isValidRegion(DetectionContext &Context) const {
Region &R = Context.CurRegion;
DEBUG(dbgs() << "Checking region: " << R.getNameStr() << "\n\t");
// The toplevel region is no valid region.
if (!R.getParent()) {
DEBUG(dbgs() << "Top level region is invalid";
dbgs() << "\n");
return false;
}
// SCoP cannot contain the entry block of the function, because we need
// to insert alloca instruction there when translate scalar to array.
if (R.getEntry() == &(R.getEntry()->getParent()->getEntryBlock()))
INVALID(Other, "Region containing entry block of function is invalid!");
// Only a simple region is allowed.
if (!R.isSimple())
INVALID(SimpleRegion, "Region not simple: " << R.getNameStr());
if (!isValidExit(Context))
return false;
if (!allBlocksValid(Context))
return false;
DEBUG(dbgs() << "OK\n");
return true;
}
bool ScopDetection::isValidFunction(llvm::Function &F) {
return !InvalidFunctions.count(&F);
}
void ScopDetection::getDebugLocation(const Region *R, unsigned &LineBegin,
unsigned &LineEnd, std::string &FileName) {
LineBegin = -1;
LineEnd = 0;
for (Region::const_block_iterator RI = R->block_begin(), RE = R->block_end();
RI != RE; ++RI)
for (BasicBlock::iterator BI = (*RI)->begin(), BE = (*RI)->end(); BI != BE;
++BI) {
DebugLoc DL = BI->getDebugLoc();
if (DL.isUnknown())
continue;
DIScope Scope(DL.getScope(BI->getContext()));
if (FileName.empty())
FileName = Scope.getFilename();
unsigned NewLine = DL.getLine();
LineBegin = std::min(LineBegin, NewLine);
LineEnd = std::max(LineEnd, NewLine);
break;
}
}
void ScopDetection::printLocations() {
for (iterator RI = begin(), RE = end(); RI != RE; ++RI) {
unsigned LineEntry, LineExit;
std::string FileName;
getDebugLocation(*RI, LineEntry, LineExit, FileName);
if (FileName.empty()) {
outs() << "Scop detected at unknown location. Compile with debug info "
"(-g) to get more precise information. \n";
return;
}
outs() << FileName << ":" << LineEntry << ": Scop start\n";
outs() << FileName << ":" << LineExit << ": Scop end\n";
}
}
bool ScopDetection::runOnFunction(llvm::Function &F) {
AA = &getAnalysis<AliasAnalysis>();
SE = &getAnalysis<ScalarEvolution>();
LI = &getAnalysis<LoopInfo>();
RI = &getAnalysis<RegionInfo>();
Region *TopRegion = RI->getTopLevelRegion();
releaseMemory();
if (OnlyFunction != "" && F.getName() != OnlyFunction)
return false;
if (!isValidFunction(F))
return false;
findScops(*TopRegion);
if (ReportLevel >= 1)
printLocations();
return false;
}
void polly::ScopDetection::verifyRegion(const Region &R) const {
assert(isMaxRegionInScop(R) && "Expect R is a valid region.");
DetectionContext Context(const_cast<Region&>(R), *AA, true /*verifying*/);
isValidRegion(Context);
}
void polly::ScopDetection::verifyAnalysis() const {
for (RegionSet::const_iterator I = ValidRegions.begin(),
E = ValidRegions.end(); I != E; ++I)
verifyRegion(**I);
}
void ScopDetection::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<DominatorTree>();
AU.addRequired<PostDominatorTree>();
AU.addRequired<LoopInfo>();
AU.addRequired<ScalarEvolution>();
// We also need AA and RegionInfo when we are verifying analysis.
AU.addRequiredTransitive<AliasAnalysis>();
AU.addRequiredTransitive<RegionInfo>();
AU.setPreservesAll();
}
void ScopDetection::print(raw_ostream &OS, const Module *) const {
for (RegionSet::const_iterator I = ValidRegions.begin(),
E = ValidRegions.end(); I != E; ++I)
OS << "Valid Region for Scop: " << (*I)->getNameStr() << '\n';
OS << "\n";
}
void ScopDetection::releaseMemory() {
ValidRegions.clear();
InvalidRegions.clear();
// Do not clear the invalid function set.
}
char ScopDetection::ID = 0;
INITIALIZE_PASS_BEGIN(ScopDetection, "polly-detect",
"Polly - Detect static control parts (SCoPs)", false,
false)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_DEPENDENCY(DominatorTree)
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
INITIALIZE_PASS_DEPENDENCY(PostDominatorTree)
INITIALIZE_PASS_DEPENDENCY(RegionInfo)
INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
INITIALIZE_PASS_END(ScopDetection, "polly-detect",
"Polly - Detect static control parts (SCoPs)", false, false)
Pass *polly::createScopDetectionPass() {
return new ScopDetection();
}