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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
//
// Function calls and intrinsics that do not have side effects (readnone)
// or memory intrinsics (memset, memcpy, memmove) are allowed.
//
// 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/CodeGen/CodeGeneration.h"
#include "polly/LinkAllPasses.h"
#include "polly/Options.h"
#include "polly/ScopDetectionDiagnostic.h"
#include "polly/Support/SCEVValidator.h"
#include "polly/Support/ScopLocation.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/PostDominators.h"
#include "llvm/Analysis/RegionIterator.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/DiagnosticInfo.h"
#include "llvm/IR/DiagnosticPrinter.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/Support/Debug.h"
#include <set>
#include <stack>
using namespace llvm;
using namespace polly;
#define DEBUG_TYPE "polly-detect"
// This option is set to a very high value, as analyzing such loops increases
// compile time on several cases. For experiments that enable this option,
// a value of around 40 has been working to avoid run-time regressions with
// Polly while still exposing interesting optimization opportunities.
static cl::opt<int> ProfitabilityMinPerLoopInstructions(
"polly-detect-profitability-min-per-loop-insts",
cl::desc("The minimal number of per-loop instructions before a single loop "
"region is considered profitable"),
cl::Hidden, cl::ValueRequired, cl::init(100000000), cl::cat(PollyCategory));
bool polly::PollyProcessUnprofitable;
static cl::opt<bool, true> XPollyProcessUnprofitable(
"polly-process-unprofitable",
cl::desc(
"Process scops that are unlikely to benefit from Polly optimizations."),
cl::location(PollyProcessUnprofitable), cl::init(false), cl::ZeroOrMore,
cl::cat(PollyCategory));
static cl::opt<std::string> OnlyFunction(
"polly-only-func",
cl::desc("Only run on functions that contain a certain string"),
cl::value_desc("string"), cl::ValueRequired, cl::init(""),
cl::cat(PollyCategory));
static cl::opt<std::string> OnlyRegion(
"polly-only-region",
cl::desc("Only run on certain regions (The provided identifier must "
"appear in the name of the region's entry block"),
cl::value_desc("identifier"), cl::ValueRequired, cl::init(""),
cl::cat(PollyCategory));
static cl::opt<bool>
IgnoreAliasing("polly-ignore-aliasing",
cl::desc("Ignore possible aliasing of the array bases"),
cl::Hidden, cl::init(false), cl::ZeroOrMore,
cl::cat(PollyCategory));
bool polly::PollyAllowUnsignedOperations;
static cl::opt<bool, true> XPollyAllowUnsignedOperations(
"polly-allow-unsigned-operations",
cl::desc("Allow unsigned operations such as comparisons or zero-extends."),
cl::location(PollyAllowUnsignedOperations), cl::Hidden, cl::ZeroOrMore,
cl::init(true), cl::cat(PollyCategory));
bool polly::PollyUseRuntimeAliasChecks;
static cl::opt<bool, true> XPollyUseRuntimeAliasChecks(
"polly-use-runtime-alias-checks",
cl::desc("Use runtime alias checks to resolve possible aliasing."),
cl::location(PollyUseRuntimeAliasChecks), cl::Hidden, cl::ZeroOrMore,
cl::init(true), cl::cat(PollyCategory));
static cl::opt<bool>
ReportLevel("polly-report",
cl::desc("Print information about the activities of Polly"),
cl::init(false), cl::ZeroOrMore, cl::cat(PollyCategory));
static cl::opt<bool> AllowDifferentTypes(
"polly-allow-differing-element-types",
cl::desc("Allow different element types for array accesses"), cl::Hidden,
cl::init(true), cl::ZeroOrMore, cl::cat(PollyCategory));
static cl::opt<bool>
AllowNonAffine("polly-allow-nonaffine",
cl::desc("Allow non affine access functions in arrays"),
cl::Hidden, cl::init(false), cl::ZeroOrMore,
cl::cat(PollyCategory));
static cl::opt<bool>
AllowModrefCall("polly-allow-modref-calls",
cl::desc("Allow functions with known modref behavior"),
cl::Hidden, cl::init(false), cl::ZeroOrMore,
cl::cat(PollyCategory));
static cl::opt<bool> AllowNonAffineSubRegions(
"polly-allow-nonaffine-branches",
cl::desc("Allow non affine conditions for branches"), cl::Hidden,
cl::init(true), cl::ZeroOrMore, cl::cat(PollyCategory));
static cl::opt<bool>
AllowNonAffineSubLoops("polly-allow-nonaffine-loops",
cl::desc("Allow non affine conditions for loops"),
cl::Hidden, cl::init(false), cl::ZeroOrMore,
cl::cat(PollyCategory));
static cl::opt<bool, true>
TrackFailures("polly-detect-track-failures",
cl::desc("Track failure strings in detecting scop regions"),
cl::location(PollyTrackFailures), cl::Hidden, cl::ZeroOrMore,
cl::init(true), cl::cat(PollyCategory));
static cl::opt<bool> KeepGoing("polly-detect-keep-going",
cl::desc("Do not fail on the first error."),
cl::Hidden, cl::ZeroOrMore, cl::init(false),
cl::cat(PollyCategory));
static cl::opt<bool, true>
PollyDelinearizeX("polly-delinearize",
cl::desc("Delinearize array access functions"),
cl::location(PollyDelinearize), cl::Hidden,
cl::ZeroOrMore, cl::init(true), cl::cat(PollyCategory));
static cl::opt<bool>
VerifyScops("polly-detect-verify",
cl::desc("Verify the detected SCoPs after each transformation"),
cl::Hidden, cl::init(false), cl::ZeroOrMore,
cl::cat(PollyCategory));
bool polly::PollyInvariantLoadHoisting;
static cl::opt<bool, true> XPollyInvariantLoadHoisting(
"polly-invariant-load-hoisting", cl::desc("Hoist invariant loads."),
cl::location(PollyInvariantLoadHoisting), cl::Hidden, cl::ZeroOrMore,
cl::init(false), cl::cat(PollyCategory));
/// The minimal trip count under which loops are considered unprofitable.
static const unsigned MIN_LOOP_TRIP_COUNT = 8;
bool polly::PollyTrackFailures = false;
bool polly::PollyDelinearize = false;
StringRef polly::PollySkipFnAttr = "polly.skip.fn";
//===----------------------------------------------------------------------===//
// Statistics.
STATISTIC(NumScopRegions, "Number of scops");
STATISTIC(NumLoopsInScop, "Number of loops in scops");
STATISTIC(NumScopsDepthOne, "Number of scops with maximal loop depth 1");
STATISTIC(NumScopsDepthTwo, "Number of scops with maximal loop depth 2");
STATISTIC(NumScopsDepthThree, "Number of scops with maximal loop depth 3");
STATISTIC(NumScopsDepthFour, "Number of scops with maximal loop depth 4");
STATISTIC(NumScopsDepthFive, "Number of scops with maximal loop depth 5");
STATISTIC(NumScopsDepthLarger,
"Number of scops with maximal loop depth 6 and larger");
STATISTIC(NumProfScopRegions, "Number of scops (profitable scops only)");
STATISTIC(NumLoopsInProfScop,
"Number of loops in scops (profitable scops only)");
STATISTIC(NumLoopsOverall, "Number of total loops");
STATISTIC(NumProfScopsDepthOne,
"Number of scops with maximal loop depth 1 (profitable scops only)");
STATISTIC(NumProfScopsDepthTwo,
"Number of scops with maximal loop depth 2 (profitable scops only)");
STATISTIC(NumProfScopsDepthThree,
"Number of scops with maximal loop depth 3 (profitable scops only)");
STATISTIC(NumProfScopsDepthFour,
"Number of scops with maximal loop depth 4 (profitable scops only)");
STATISTIC(NumProfScopsDepthFive,
"Number of scops with maximal loop depth 5 (profitable scops only)");
STATISTIC(NumProfScopsDepthLarger, "Number of scops with maximal loop depth 6 "
"and larger (profitable scops only)");
class DiagnosticScopFound : public DiagnosticInfo {
private:
static int PluginDiagnosticKind;
Function &F;
std::string FileName;
unsigned EntryLine, ExitLine;
public:
DiagnosticScopFound(Function &F, std::string FileName, unsigned EntryLine,
unsigned ExitLine)
: DiagnosticInfo(PluginDiagnosticKind, DS_Note), F(F), FileName(FileName),
EntryLine(EntryLine), ExitLine(ExitLine) {}
virtual void print(DiagnosticPrinter &DP) const;
static bool classof(const DiagnosticInfo *DI) {
return DI->getKind() == PluginDiagnosticKind;
}
};
int DiagnosticScopFound::PluginDiagnosticKind =
getNextAvailablePluginDiagnosticKind();
void DiagnosticScopFound::print(DiagnosticPrinter &DP) const {
DP << "Polly detected an optimizable loop region (scop) in function '" << F
<< "'\n";
if (FileName.empty()) {
DP << "Scop location is unknown. Compile with debug info "
"(-g) to get more precise information. ";
return;
}
DP << FileName << ":" << EntryLine << ": Start of scop\n";
DP << FileName << ":" << ExitLine << ": End of scop";
}
//===----------------------------------------------------------------------===//
// ScopDetection.
ScopDetection::ScopDetection() : FunctionPass(ID) {
// Disable runtime alias checks if we ignore aliasing all together.
if (IgnoreAliasing)
PollyUseRuntimeAliasChecks = false;
}
template <class RR, typename... Args>
inline bool ScopDetection::invalid(DetectionContext &Context, bool Assert,
Args &&... Arguments) const {
if (!Context.Verifying) {
RejectLog &Log = Context.Log;
std::shared_ptr<RR> RejectReason = std::make_shared<RR>(Arguments...);
if (PollyTrackFailures)
Log.report(RejectReason);
DEBUG(dbgs() << RejectReason->getMessage());
DEBUG(dbgs() << "\n");
} else {
assert(!Assert && "Verification of detected scop failed");
}
return false;
}
bool ScopDetection::isMaxRegionInScop(const Region &R, bool Verify) const {
if (!ValidRegions.count(&R))
return false;
if (Verify) {
DetectionContextMap.erase(getBBPairForRegion(&R));
const auto &It = DetectionContextMap.insert(std::make_pair(
getBBPairForRegion(&R),
DetectionContext(const_cast<Region &>(R), *AA, false /*verifying*/)));
DetectionContext &Context = It.first->second;
return isValidRegion(Context);
}
return true;
}
std::string ScopDetection::regionIsInvalidBecause(const Region *R) const {
// Get the first error we found. Even in keep-going mode, this is the first
// reason that caused the candidate to be rejected.
auto *Log = lookupRejectionLog(R);
// This can happen when we marked a region invalid, but didn't track
// an error for it.
if (!Log || !Log->hasErrors())
return "";
RejectReasonPtr RR = *Log->begin();
return RR->getMessage();
}
bool ScopDetection::addOverApproximatedRegion(Region *AR,
DetectionContext &Context) const {
// If we already know about Ar we can exit.
if (!Context.NonAffineSubRegionSet.insert(AR))
return true;
// All loops in the region have to be overapproximated too if there
// are accesses that depend on the iteration count.
for (BasicBlock *BB : AR->blocks()) {
Loop *L = LI->getLoopFor(BB);
if (AR->contains(L))
Context.BoxedLoopsSet.insert(L);
}
return (AllowNonAffineSubLoops || Context.BoxedLoopsSet.empty());
}
bool ScopDetection::onlyValidRequiredInvariantLoads(
InvariantLoadsSetTy &RequiredILS, DetectionContext &Context) const {
Region &CurRegion = Context.CurRegion;
if (!PollyInvariantLoadHoisting && !RequiredILS.empty())
return false;
for (LoadInst *Load : RequiredILS)
if (!isHoistableLoad(Load, CurRegion, *LI, *SE, *DT))
return false;
Context.RequiredILS.insert(RequiredILS.begin(), RequiredILS.end());
return true;
}
bool ScopDetection::involvesMultiplePtrs(const SCEV *S0, const SCEV *S1,
Loop *Scope) const {
SetVector<Value *> Values;
findValues(S0, *SE, Values);
if (S1)
findValues(S1, *SE, Values);
SmallPtrSet<Value *, 8> PtrVals;
for (auto *V : Values) {
if (auto *P2I = dyn_cast<PtrToIntInst>(V))
V = P2I->getOperand(0);
if (!V->getType()->isPointerTy())
continue;
auto *PtrSCEV = SE->getSCEVAtScope(V, Scope);
if (isa<SCEVConstant>(PtrSCEV))
continue;
auto *BasePtr = dyn_cast<SCEVUnknown>(SE->getPointerBase(PtrSCEV));
if (!BasePtr)
return true;
auto *BasePtrVal = BasePtr->getValue();
if (PtrVals.insert(BasePtrVal).second) {
for (auto *PtrVal : PtrVals)
if (PtrVal != BasePtrVal && !AA->isNoAlias(PtrVal, BasePtrVal))
return true;
}
}
return false;
}
bool ScopDetection::isAffine(const SCEV *S, Loop *Scope,
DetectionContext &Context) const {
InvariantLoadsSetTy AccessILS;
if (!isAffineExpr(&Context.CurRegion, Scope, S, *SE, &AccessILS))
return false;
if (!onlyValidRequiredInvariantLoads(AccessILS, Context))
return false;
return true;
}
bool ScopDetection::isValidSwitch(BasicBlock &BB, SwitchInst *SI,
Value *Condition, bool IsLoopBranch,
DetectionContext &Context) const {
Loop *L = LI->getLoopFor(&BB);
const SCEV *ConditionSCEV = SE->getSCEVAtScope(Condition, L);
if (IsLoopBranch && L->isLoopLatch(&BB))
return false;
// Check for invalid usage of different pointers in one expression.
if (involvesMultiplePtrs(ConditionSCEV, nullptr, L))
return false;
if (isAffine(ConditionSCEV, L, Context))
return true;
if (AllowNonAffineSubRegions &&
addOverApproximatedRegion(RI->getRegionFor(&BB), Context))
return true;
return invalid<ReportNonAffBranch>(Context, /*Assert=*/true, &BB,
ConditionSCEV, ConditionSCEV, SI);
}
bool ScopDetection::isValidBranch(BasicBlock &BB, BranchInst *BI,
Value *Condition, bool IsLoopBranch,
DetectionContext &Context) const {
// Constant integer conditions are always affine.
if (isa<ConstantInt>(Condition))
return true;
if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(Condition)) {
auto Opcode = BinOp->getOpcode();
if (Opcode == Instruction::And || Opcode == Instruction::Or) {
Value *Op0 = BinOp->getOperand(0);
Value *Op1 = BinOp->getOperand(1);
return isValidBranch(BB, BI, Op0, IsLoopBranch, Context) &&
isValidBranch(BB, BI, Op1, IsLoopBranch, Context);
}
}
// Non constant conditions of branches need to be ICmpInst.
if (!isa<ICmpInst>(Condition)) {
if (!IsLoopBranch && AllowNonAffineSubRegions &&
addOverApproximatedRegion(RI->getRegionFor(&BB), Context))
return true;
return invalid<ReportInvalidCond>(Context, /*Assert=*/true, BI, &BB);
}
ICmpInst *ICmp = cast<ICmpInst>(Condition);
// Are both operands of the ICmp affine?
if (isa<UndefValue>(ICmp->getOperand(0)) ||
isa<UndefValue>(ICmp->getOperand(1)))
return invalid<ReportUndefOperand>(Context, /*Assert=*/true, &BB, ICmp);
Loop *L = LI->getLoopFor(&BB);
const SCEV *LHS = SE->getSCEVAtScope(ICmp->getOperand(0), L);
const SCEV *RHS = SE->getSCEVAtScope(ICmp->getOperand(1), L);
// If unsigned operations are not allowed try to approximate the region.
if (ICmp->isUnsigned() && !PollyAllowUnsignedOperations)
return !IsLoopBranch && AllowNonAffineSubRegions &&
addOverApproximatedRegion(RI->getRegionFor(&BB), Context);
// Check for invalid usage of different pointers in one expression.
if (ICmp->isEquality() && involvesMultiplePtrs(LHS, nullptr, L) &&
involvesMultiplePtrs(RHS, nullptr, L))
return false;
// Check for invalid usage of different pointers in a relational comparison.
if (ICmp->isRelational() && involvesMultiplePtrs(LHS, RHS, L))
return false;
if (isAffine(LHS, L, Context) && isAffine(RHS, L, Context))
return true;
if (!IsLoopBranch && AllowNonAffineSubRegions &&
addOverApproximatedRegion(RI->getRegionFor(&BB), Context))
return true;
if (IsLoopBranch)
return false;
return invalid<ReportNonAffBranch>(Context, /*Assert=*/true, &BB, LHS, RHS,
ICmp);
}
bool ScopDetection::isValidCFG(BasicBlock &BB, bool IsLoopBranch,
bool AllowUnreachable,
DetectionContext &Context) const {
Region &CurRegion = Context.CurRegion;
TerminatorInst *TI = BB.getTerminator();
if (AllowUnreachable && isa<UnreachableInst>(TI))
return true;
// Return instructions are only valid if the region is the top level region.
if (isa<ReturnInst>(TI) && !CurRegion.getExit() && TI->getNumOperands() == 0)
return true;
Value *Condition = getConditionFromTerminator(TI);
if (!Condition)
return invalid<ReportInvalidTerminator>(Context, /*Assert=*/true, &BB);
// UndefValue is not allowed as condition.
if (isa<UndefValue>(Condition))
return invalid<ReportUndefCond>(Context, /*Assert=*/true, TI, &BB);
if (BranchInst *BI = dyn_cast<BranchInst>(TI))
return isValidBranch(BB, BI, Condition, IsLoopBranch, Context);
SwitchInst *SI = dyn_cast<SwitchInst>(TI);
assert(SI && "Terminator was neither branch nor switch");
return isValidSwitch(BB, SI, Condition, IsLoopBranch, Context);
}
bool ScopDetection::isValidCallInst(CallInst &CI,
DetectionContext &Context) const {
if (CI.doesNotReturn())
return false;
if (CI.doesNotAccessMemory())
return true;
if (auto *II = dyn_cast<IntrinsicInst>(&CI))
if (isValidIntrinsicInst(*II, Context))
return true;
Function *CalledFunction = CI.getCalledFunction();
// Indirect calls are not supported.
if (CalledFunction == nullptr)
return false;
if (AllowModrefCall) {
switch (AA->getModRefBehavior(CalledFunction)) {
case FMRB_UnknownModRefBehavior:
return false;
case FMRB_DoesNotAccessMemory:
case FMRB_OnlyReadsMemory:
// Implicitly disable delinearization since we have an unknown
// accesses with an unknown access function.
Context.HasUnknownAccess = true;
Context.AST.add(&CI);
return true;
case FMRB_OnlyReadsArgumentPointees:
case FMRB_OnlyAccessesArgumentPointees:
for (const auto &Arg : CI.arg_operands()) {
if (!Arg->getType()->isPointerTy())
continue;
// Bail if a pointer argument has a base address not known to
// ScalarEvolution. Note that a zero pointer is acceptable.
auto *ArgSCEV = SE->getSCEVAtScope(Arg, LI->getLoopFor(CI.getParent()));
if (ArgSCEV->isZero())
continue;
auto *BP = dyn_cast<SCEVUnknown>(SE->getPointerBase(ArgSCEV));
if (!BP)
return false;
// Implicitly disable delinearization since we have an unknown
// accesses with an unknown access function.
Context.HasUnknownAccess = true;
}
Context.AST.add(&CI);
return true;
case FMRB_DoesNotReadMemory:
case FMRB_OnlyAccessesInaccessibleMem:
case FMRB_OnlyAccessesInaccessibleOrArgMem:
return false;
}
}
return false;
}
bool ScopDetection::isValidIntrinsicInst(IntrinsicInst &II,
DetectionContext &Context) const {
if (isIgnoredIntrinsic(&II))
return true;
// The closest loop surrounding the call instruction.
Loop *L = LI->getLoopFor(II.getParent());
// The access function and base pointer for memory intrinsics.
const SCEV *AF;
const SCEVUnknown *BP;
switch (II.getIntrinsicID()) {
// Memory intrinsics that can be represented are supported.
case llvm::Intrinsic::memmove:
case llvm::Intrinsic::memcpy:
AF = SE->getSCEVAtScope(cast<MemTransferInst>(II).getSource(), L);
if (!AF->isZero()) {
BP = dyn_cast<SCEVUnknown>(SE->getPointerBase(AF));
// Bail if the source pointer is not valid.
if (!isValidAccess(&II, AF, BP, Context))
return false;
}
// Fall through
case llvm::Intrinsic::memset:
AF = SE->getSCEVAtScope(cast<MemIntrinsic>(II).getDest(), L);
if (!AF->isZero()) {
BP = dyn_cast<SCEVUnknown>(SE->getPointerBase(AF));
// Bail if the destination pointer is not valid.
if (!isValidAccess(&II, AF, BP, Context))
return false;
}
// Bail if the length is not affine.
if (!isAffine(SE->getSCEVAtScope(cast<MemIntrinsic>(II).getLength(), L), L,
Context))
return false;
return true;
default:
break;
}
return false;
}
bool ScopDetection::isInvariant(const Value &Val, const Region &Reg) const {
// A reference to function argument or constant value is invariant.
if (isa<Argument>(Val) || isa<Constant>(Val))
return true;
const Instruction *I = dyn_cast<Instruction>(&Val);
if (!I)
return false;
if (!Reg.contains(I))
return true;
if (I->mayHaveSideEffects())
return false;
if (isa<SelectInst>(I))
return false;
// When Val is a Phi node, it is likely not invariant. We do not check whether
// Phi nodes are actually invariant, we assume that Phi nodes are usually not
// invariant.
if (isa<PHINode>(*I))
return false;
for (const Use &Operand : I->operands())
if (!isInvariant(*Operand, Reg))
return false;
return true;
}
/// Remove smax of smax(0, size) expressions from a SCEV expression and
/// register the '...' components.
///
/// Array access expressions as they are generated by gfortran contain smax(0,
/// size) expressions that confuse the 'normal' delinearization algorithm.
/// However, if we extract such expressions before the normal delinearization
/// takes place they can actually help to identify array size expressions in
/// fortran accesses. For the subsequently following delinearization the smax(0,
/// size) component can be replaced by just 'size'. This is correct as we will
/// always add and verify the assumption that for all subscript expressions
/// 'exp' the inequality 0 <= exp < size holds. Hence, we will also verify
/// that 0 <= size, which means smax(0, size) == size.
class SCEVRemoveMax : public SCEVRewriteVisitor<SCEVRemoveMax> {
public:
static const SCEV *rewrite(const SCEV *Scev, ScalarEvolution &SE,
std::vector<const SCEV *> *Terms = nullptr) {
SCEVRemoveMax Rewriter(SE, Terms);
return Rewriter.visit(Scev);
}
SCEVRemoveMax(ScalarEvolution &SE, std::vector<const SCEV *> *Terms)
: SCEVRewriteVisitor(SE), Terms(Terms) {}
const SCEV *visitSMaxExpr(const SCEVSMaxExpr *Expr) {
if ((Expr->getNumOperands() == 2) && Expr->getOperand(0)->isZero()) {
auto Res = visit(Expr->getOperand(1));
if (Terms)
(*Terms).push_back(Res);
return Res;
}
return Expr;
}
private:
std::vector<const SCEV *> *Terms;
};
SmallVector<const SCEV *, 4>
ScopDetection::getDelinearizationTerms(DetectionContext &Context,
const SCEVUnknown *BasePointer) const {
SmallVector<const SCEV *, 4> Terms;
for (const auto &Pair : Context.Accesses[BasePointer]) {
std::vector<const SCEV *> MaxTerms;
SCEVRemoveMax::rewrite(Pair.second, *SE, &MaxTerms);
if (MaxTerms.size() > 0) {
Terms.insert(Terms.begin(), MaxTerms.begin(), MaxTerms.end());
continue;
}
// In case the outermost expression is a plain add, we check if any of its
// terms has the form 4 * %inst * %param * %param ..., aka a term that
// contains a product between a parameter and an instruction that is
// inside the scop. Such instructions, if allowed at all, are instructions
// SCEV can not represent, but Polly is still looking through. As a
// result, these instructions can depend on induction variables and are
// most likely no array sizes. However, terms that are multiplied with
// them are likely candidates for array sizes.
if (auto *AF = dyn_cast<SCEVAddExpr>(Pair.second)) {
for (auto Op : AF->operands()) {
if (auto *AF2 = dyn_cast<SCEVAddRecExpr>(Op))
SE->collectParametricTerms(AF2, Terms);
if (auto *AF2 = dyn_cast<SCEVMulExpr>(Op)) {
SmallVector<const SCEV *, 0> Operands;
for (auto *MulOp : AF2->operands()) {
if (auto *Const = dyn_cast<SCEVConstant>(MulOp))
Operands.push_back(Const);
if (auto *Unknown = dyn_cast<SCEVUnknown>(MulOp)) {
if (auto *Inst = dyn_cast<Instruction>(Unknown->getValue())) {
if (!Context.CurRegion.contains(Inst))
Operands.push_back(MulOp);
} else {
Operands.push_back(MulOp);
}
}
}
if (Operands.size())
Terms.push_back(SE->getMulExpr(Operands));
}
}
}
if (Terms.empty())
SE->collectParametricTerms(Pair.second, Terms);
}
return Terms;
}
bool ScopDetection::hasValidArraySizes(DetectionContext &Context,
SmallVectorImpl<const SCEV *> &Sizes,
const SCEVUnknown *BasePointer,
Loop *Scope) const {
Value *BaseValue = BasePointer->getValue();
Region &CurRegion = Context.CurRegion;
for (const SCEV *DelinearizedSize : Sizes) {
if (!isAffine(DelinearizedSize, Scope, Context)) {
Sizes.clear();
break;
}
if (auto *Unknown = dyn_cast<SCEVUnknown>(DelinearizedSize)) {
auto *V = dyn_cast<Value>(Unknown->getValue());
if (auto *Load = dyn_cast<LoadInst>(V)) {
if (Context.CurRegion.contains(Load) &&
isHoistableLoad(Load, CurRegion, *LI, *SE, *DT))
Context.RequiredILS.insert(Load);
continue;
}
}
if (hasScalarDepsInsideRegion(DelinearizedSize, &CurRegion, Scope, false))
return invalid<ReportNonAffineAccess>(
Context, /*Assert=*/true, DelinearizedSize,
Context.Accesses[BasePointer].front().first, BaseValue);
}
// No array shape derived.
if (Sizes.empty()) {
if (AllowNonAffine)
return true;
for (const auto &Pair : Context.Accesses[BasePointer]) {
const Instruction *Insn = Pair.first;
const SCEV *AF = Pair.second;
if (!isAffine(AF, Scope, Context)) {
invalid<ReportNonAffineAccess>(Context, /*Assert=*/true, AF, Insn,
BaseValue);
if (!KeepGoing)
return false;
}
}
return false;
}
return true;
}
// We first store the resulting memory accesses in TempMemoryAccesses. Only
// if the access functions for all memory accesses have been successfully
// delinearized we continue. Otherwise, we either report a failure or, if
// non-affine accesses are allowed, we drop the information. In case the
// information is dropped the memory accesses need to be overapproximated
// when translated to a polyhedral representation.
bool ScopDetection::computeAccessFunctions(
DetectionContext &Context, const SCEVUnknown *BasePointer,
std::shared_ptr<ArrayShape> Shape) const {
Value *BaseValue = BasePointer->getValue();
bool BasePtrHasNonAffine = false;
MapInsnToMemAcc TempMemoryAccesses;
for (const auto &Pair : Context.Accesses[BasePointer]) {
const Instruction *Insn = Pair.first;
auto *AF = Pair.second;
AF = SCEVRemoveMax::rewrite(AF, *SE);
bool IsNonAffine = false;
TempMemoryAccesses.insert(std::make_pair(Insn, MemAcc(Insn, Shape)));
MemAcc *Acc = &TempMemoryAccesses.find(Insn)->second;
auto *Scope = LI->getLoopFor(Insn->getParent());
if (!AF) {
if (isAffine(Pair.second, Scope, Context))
Acc->DelinearizedSubscripts.push_back(Pair.second);
else
IsNonAffine = true;
} else {
SE->computeAccessFunctions(AF, Acc->DelinearizedSubscripts,
Shape->DelinearizedSizes);
if (Acc->DelinearizedSubscripts.size() == 0)
IsNonAffine = true;
for (const SCEV *S : Acc->DelinearizedSubscripts)
if (!isAffine(S, Scope, Context))
IsNonAffine = true;
}
// (Possibly) report non affine access
if (IsNonAffine) {
BasePtrHasNonAffine = true;
if (!AllowNonAffine)
invalid<ReportNonAffineAccess>(Context, /*Assert=*/true, Pair.second,
Insn, BaseValue);
if (!KeepGoing && !AllowNonAffine)
return false;
}
}
if (!BasePtrHasNonAffine)
Context.InsnToMemAcc.insert(TempMemoryAccesses.begin(),
TempMemoryAccesses.end());
return true;
}
bool ScopDetection::hasBaseAffineAccesses(DetectionContext &Context,
const SCEVUnknown *BasePointer,
Loop *Scope) const {
auto Shape = std::shared_ptr<ArrayShape>(new ArrayShape(BasePointer));
auto Terms = getDelinearizationTerms(Context, BasePointer);
SE->findArrayDimensions(Terms, Shape->DelinearizedSizes,
Context.ElementSize[BasePointer]);
if (!hasValidArraySizes(Context, Shape->DelinearizedSizes, BasePointer,
Scope))
return false;
return computeAccessFunctions(Context, BasePointer, Shape);
}
bool ScopDetection::hasAffineMemoryAccesses(DetectionContext &Context) const {
// TODO: If we have an unknown access and other non-affine accesses we do
// not try to delinearize them for now.
if (Context.HasUnknownAccess && !Context.NonAffineAccesses.empty())
return AllowNonAffine;
for (auto &Pair : Context.NonAffineAccesses) {
auto *BasePointer = Pair.first;
auto *Scope = Pair.second;
if (!hasBaseAffineAccesses(Context, BasePointer, Scope)) {
if (KeepGoing)
continue;
else
return false;
}
}
return true;
}
bool ScopDetection::isValidAccess(Instruction *Inst, const SCEV *AF,
const SCEVUnknown *BP,
DetectionContext &Context) const {
if (!BP)
return invalid<ReportNoBasePtr>(Context, /*Assert=*/true, Inst);
auto *BV = BP->getValue();
if (isa<UndefValue>(BV))
return invalid<ReportUndefBasePtr>(Context, /*Assert=*/true, Inst);
// FIXME: Think about allowing IntToPtrInst
if (IntToPtrInst *Inst = dyn_cast<IntToPtrInst>(BV))
return invalid<ReportIntToPtr>(Context, /*Assert=*/true, Inst);
// Check that the base address of the access is invariant in the current
// region.
if (!isInvariant(*BV, Context.CurRegion))
return invalid<ReportVariantBasePtr>(Context, /*Assert=*/true, BV, Inst);
AF = SE->getMinusSCEV(AF, BP);
const SCEV *Size;
if (!isa<MemIntrinsic>(Inst)) {
Size = SE->getElementSize(Inst);
} else {
auto *SizeTy =
SE->getEffectiveSCEVType(PointerType::getInt8PtrTy(SE->getContext()));
Size = SE->getConstant(SizeTy, 8);
}
if (Context.ElementSize[BP]) {
if (!AllowDifferentTypes && Context.ElementSize[BP] != Size)
return invalid<ReportDifferentArrayElementSize>(Context, /*Assert=*/true,
Inst, BV);
Context.ElementSize[BP] = SE->getSMinExpr(Size, Context.ElementSize[BP]);
} else {
Context.ElementSize[BP] = Size;
}
bool IsVariantInNonAffineLoop = false;
SetVector<const Loop *> Loops;
findLoops(AF, Loops);
for (const Loop *L : Loops)
if (Context.BoxedLoopsSet.count(L))
IsVariantInNonAffineLoop = true;
auto *Scope = LI->getLoopFor(Inst->getParent());
bool IsAffine = !IsVariantInNonAffineLoop && isAffine(AF, Scope, Context);
// Do not try to delinearize memory intrinsics and force them to be affine.
if (isa<MemIntrinsic>(Inst) && !IsAffine) {
return invalid<ReportNonAffineAccess>(Context, /*Assert=*/true, AF, Inst,
BV);
} else if (PollyDelinearize && !IsVariantInNonAffineLoop) {
Context.Accesses[BP].push_back({Inst, AF});
if (!IsAffine)
Context.NonAffineAccesses.insert(
std::make_pair(BP, LI->getLoopFor(Inst->getParent())));
} else if (!AllowNonAffine && !IsAffine) {
return invalid<ReportNonAffineAccess>(Context, /*Assert=*/true, AF, Inst,
BV);
}
if (IgnoreAliasing)
return true;
// Check if the base pointer of the memory access does alias with
// any other pointer. This cannot be handled at the moment.
AAMDNodes AATags;
Inst->getAAMetadata(AATags);
AliasSet &AS = Context.AST.getAliasSetForPointer(
BP->getValue(), MemoryLocation::UnknownSize, AATags);
if (!AS.isMustAlias()) {
if (PollyUseRuntimeAliasChecks) {
bool CanBuildRunTimeCheck = true;
// The run-time alias check places code that involves the base pointer at
// the beginning of the SCoP. This breaks if the base pointer is defined
// inside the scop. Hence, we can only create a run-time check if we are
// sure the base pointer is not an instruction defined inside the scop.
// However, we can ignore loads that will be hoisted.
for (const auto &Ptr : AS) {
Instruction *Inst = dyn_cast<Instruction>(Ptr.getValue());
if (Inst && Context.CurRegion.contains(Inst)) {
auto *Load = dyn_cast<LoadInst>(Inst);
if (Load && isHoistableLoad(Load, Context.CurRegion, *LI, *SE, *DT)) {
Context.RequiredILS.insert(Load);
continue;
}
CanBuildRunTimeCheck = false;
break;
}
}
if (CanBuildRunTimeCheck)
return true;
}
return invalid<ReportAlias>(Context, /*Assert=*/true, Inst, AS);
}
return true;
}
bool ScopDetection::isValidMemoryAccess(MemAccInst Inst,
DetectionContext &Context) const {
Value *Ptr = Inst.getPointerOperand();
Loop *L = LI->getLoopFor(Inst->getParent());
const SCEV *AccessFunction = SE->getSCEVAtScope(Ptr, L);
const SCEVUnknown *BasePointer;
BasePointer = dyn_cast<SCEVUnknown>(SE->getPointerBase(AccessFunction));
return isValidAccess(Inst, AccessFunction, BasePointer, Context);
}
bool ScopDetection::isValidInstruction(Instruction &Inst,
DetectionContext &Context) const {
for (auto &Op : Inst.operands()) {
auto *OpInst = dyn_cast<Instruction>(&Op);
if (!OpInst)
continue;
if (isErrorBlock(*OpInst->getParent(), Context.CurRegion, *LI, *DT))
return false;
}
if (isa<LandingPadInst>(&Inst) || isa<ResumeInst>(&Inst))
return false;
// We only check the call instruction but not invoke instruction.
if (CallInst *CI = dyn_cast<CallInst>(&Inst)) {
if (isValidCallInst(*CI, Context))
return true;
return invalid<ReportFuncCall>(Context, /*Assert=*/true, &Inst);
}
if (!Inst.mayReadOrWriteMemory()) {
if (!isa<AllocaInst>(Inst))
return true;
return invalid<ReportAlloca>(Context, /*Assert=*/true, &Inst);
}
// Check the access function.
if (auto MemInst = MemAccInst::dyn_cast(Inst)) {
Context.hasStores |= isa<StoreInst>(MemInst);
Context.hasLoads |= isa<LoadInst>(MemInst);
if (!MemInst.isSimple())
return invalid<ReportNonSimpleMemoryAccess>(Context, /*Assert=*/true,
&Inst);
return isValidMemoryAccess(MemInst, Context);
}
// We do not know this instruction, therefore we assume it is invalid.
return invalid<ReportUnknownInst>(Context, /*Assert=*/true, &Inst);
}
/// Check whether @p L has exiting blocks.
///
/// @param L The loop of interest
///
/// @return True if the loop has exiting blocks, false otherwise.
static bool hasExitingBlocks(Loop *L) {
SmallVector<BasicBlock *, 4> ExitingBlocks;
L->getExitingBlocks(ExitingBlocks);
return !ExitingBlocks.empty();
}
bool ScopDetection::canUseISLTripCount(Loop *L,
DetectionContext &Context) const {
// Ensure the loop has valid exiting blocks as well as latches, otherwise we
// need to overapproximate it as a boxed loop.
SmallVector<BasicBlock *, 4> LoopControlBlocks;
L->getExitingBlocks(LoopControlBlocks);
L->getLoopLatches(LoopControlBlocks);
for (BasicBlock *ControlBB : LoopControlBlocks) {
if (!isValidCFG(*ControlBB, true, false, Context))
return false;
}
// We can use ISL to compute the trip count of L.
return true;
}
bool ScopDetection::isValidLoop(Loop *L, DetectionContext &Context) const {
// Loops that contain part but not all of the blocks of a region cannot be
// handled by the schedule generation. Such loop constructs can happen
// because a region can contain BBs that have no path to the exit block
// (Infinite loops, UnreachableInst), but such blocks are never part of a
// loop.
//
// _______________
// | Loop Header | <-----------.
// --------------- |
// | |
// _______________ ______________
// | RegionEntry |-----> | RegionExit |----->
// --------------- --------------
// |
// _______________
// | EndlessLoop | <--.
// --------------- |
// | |
// \------------/
//
// In the example above, the loop (LoopHeader,RegionEntry,RegionExit) is
// neither entirely contained in the region RegionEntry->RegionExit
// (containing RegionEntry,EndlessLoop) nor is the region entirely contained
// in the loop.
// The block EndlessLoop is contained in the region because Region::contains
// tests whether it is not dominated by RegionExit. This is probably to not
// having to query the PostdominatorTree. Instead of an endless loop, a dead
// end can also be formed by an UnreachableInst. This case is already caught
// by isErrorBlock(). We hence only have to reject endless loops here.
if (!hasExitingBlocks(L))
return invalid<ReportLoopHasNoExit>(Context, /*Assert=*/true, L);
if (canUseISLTripCount(L, Context))
return true;
if (AllowNonAffineSubLoops && AllowNonAffineSubRegions) {
Region *R = RI->getRegionFor(L->getHeader());
while (R != &Context.CurRegion && !R->contains(L))
R = R->getParent();
if (addOverApproximatedRegion(R, Context))
return true;
}
const SCEV *LoopCount = SE->getBackedgeTakenCount(L);
return invalid<ReportLoopBound>(Context, /*Assert=*/true, L, LoopCount);
}
/// Return the number of loops in @p L (incl. @p L) that have a trip
/// count that is not known to be less than @MinProfitableTrips.
ScopDetection::LoopStats
ScopDetection::countBeneficialSubLoops(Loop *L, ScalarEvolution &SE,
unsigned MinProfitableTrips) const {
auto *TripCount = SE.getBackedgeTakenCount(L);
int NumLoops = 1;
int MaxLoopDepth = 1;
if (auto *TripCountC = dyn_cast<SCEVConstant>(TripCount))
if (TripCountC->getType()->getScalarSizeInBits() <= 64)
if (TripCountC->getValue()->getZExtValue() <= MinProfitableTrips)
NumLoops -= 1;
for (auto &SubLoop : *L) {
LoopStats Stats = countBeneficialSubLoops(SubLoop, SE, MinProfitableTrips);
NumLoops += Stats.NumLoops;
MaxLoopDepth += std::max(MaxLoopDepth, Stats.MaxDepth + 1);
}
return {NumLoops, MaxLoopDepth};
}
ScopDetection::LoopStats
ScopDetection::countBeneficialLoops(Region *R,
unsigned MinProfitableTrips) const {
int LoopNum = 0;
int MaxLoopDepth = 0;
auto L = LI->getLoopFor(R->getEntry());
L = L ? R->outermostLoopInRegion(L) : nullptr;
L = L ? L->getParentLoop() : nullptr;
auto SubLoops =
L ? L->getSubLoopsVector() : std::vector<Loop *>(LI->begin(), LI->end());
for (auto &SubLoop : SubLoops)
if (R->contains(SubLoop)) {
LoopStats Stats =
countBeneficialSubLoops(SubLoop, *SE, MinProfitableTrips);
LoopNum += Stats.NumLoops;
MaxLoopDepth = std::max(MaxLoopDepth, Stats.MaxDepth);
}
return {LoopNum, MaxLoopDepth};
}
Region *ScopDetection::expandRegion(Region &R) {
// Initial no valid region was found (greater than R)
std::unique_ptr<Region> LastValidRegion;
auto ExpandedRegion = std::unique_ptr<Region>(R.getExpandedRegion());
DEBUG(dbgs() << "\tExpanding " << R.getNameStr() << "\n");
while (ExpandedRegion) {
const auto &It = DetectionContextMap.insert(std::make_pair(
getBBPairForRegion(ExpandedRegion.get()),
DetectionContext(*ExpandedRegion, *AA, false /*verifying*/)));
DetectionContext &Context = It.first->second;
DEBUG(dbgs() << "\t\tTrying " << ExpandedRegion->getNameStr() << "\n");
// Only expand when we did not collect errors.
if (!Context.Log.hasErrors()) {
// 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) || Context.Log.hasErrors()) {
removeCachedResults(*ExpandedRegion);
DetectionContextMap.erase(It.first);
break;
}
// Store this region, because it is the greatest valid (encountered so
// far).
if (LastValidRegion) {
removeCachedResults(*LastValidRegion);
DetectionContextMap.erase(getBBPairForRegion(LastValidRegion.get()));
}
LastValidRegion = std::move(ExpandedRegion);
// Create and test the next greater region (if any)
ExpandedRegion =
std::unique_ptr<Region>(LastValidRegion->getExpandedRegion());
} else {
// Create and test the next greater region (if any)
removeCachedResults(*ExpandedRegion);
DetectionContextMap.erase(It.first);
ExpandedRegion =
std::unique_ptr<Region>(ExpandedRegion->getExpandedRegion());
}
}
DEBUG({
if (LastValidRegion)
dbgs() << "\tto " << LastValidRegion->getNameStr() << "\n";
else
dbgs() << "\tExpanding " << R.getNameStr() << " failed\n";
});
return LastValidRegion.release();
}
static bool regionWithoutLoops(Region &R, LoopInfo *LI) {
for (const BasicBlock *BB : R.blocks())
if (R.contains(LI->getLoopFor(BB)))
return false;
return true;
}
void ScopDetection::removeCachedResultsRecursively(const Region &R) {
for (auto &SubRegion : R) {
if (ValidRegions.count(SubRegion.get())) {
removeCachedResults(*SubRegion.get());
} else
removeCachedResultsRecursively(*SubRegion);
}
}
void ScopDetection::removeCachedResults(const Region &R) {
ValidRegions.remove(&R);
}
void ScopDetection::findScops(Region &R) {
const auto &It = DetectionContextMap.insert(std::make_pair(
getBBPairForRegion(&R), DetectionContext(R, *AA, false /*verifying*/)));
DetectionContext &Context = It.first->second;
bool RegionIsValid = false;
if (!PollyProcessUnprofitable && regionWithoutLoops(R, LI))
invalid<ReportUnprofitable>(Context, /*Assert=*/true, &R);
else
RegionIsValid = isValidRegion(Context);
bool HasErrors = !RegionIsValid || Context.Log.size() > 0;
if (HasErrors) {
removeCachedResults(R);
} else {
ValidRegions.insert(&R);
return;
}
for (auto &SubRegion : R)
findScops(*SubRegion);
// 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 (auto &SubRegion : R)
ToExpand.push_back(SubRegion.get());
for (Region *CurrentRegion : ToExpand) {
// Skip invalid regions. Regions may become invalid, if they are element of
// an already expanded region.
if (!ValidRegions.count(CurrentRegion))
continue;
// Skip regions that had errors.
bool HadErrors = lookupRejectionLog(CurrentRegion)->hasErrors();
if (HadErrors)
continue;
Region *ExpandedR = expandRegion(*CurrentRegion);
if (!ExpandedR)
continue;
R.addSubRegion(ExpandedR, true);
ValidRegions.insert(ExpandedR);
removeCachedResults(*CurrentRegion);
removeCachedResultsRecursively(*ExpandedR);
}
}
bool ScopDetection::allBlocksValid(DetectionContext &Context) const {
Region &CurRegion = Context.CurRegion;
for (const BasicBlock *BB : CurRegion.blocks()) {
Loop *L = LI->getLoopFor(BB);
if (L && L->getHeader() == BB && CurRegion.contains(L) &&
(!isValidLoop(L, Context) && !KeepGoing))
return false;
}
for (BasicBlock *BB : CurRegion.blocks()) {
bool IsErrorBlock = isErrorBlock(*BB, CurRegion, *LI, *DT);
// Also check exception blocks (and possibly register them as non-affine
// regions). Even though exception blocks are not modeled, we use them
// to forward-propagate domain constraints during ScopInfo construction.
if (!isValidCFG(*BB, false, IsErrorBlock, Context) && !KeepGoing)
return false;
if (IsErrorBlock)
continue;
for (BasicBlock::iterator I = BB->begin(), E = --BB->end(); I != E; ++I)
if (!isValidInstruction(*I, Context) && !KeepGoing)
return false;
}
if (!hasAffineMemoryAccesses(Context))
return false;
return true;
}
bool ScopDetection::hasSufficientCompute(DetectionContext &Context,
int NumLoops) const {
int InstCount = 0;
if (NumLoops == 0)
return false;
for (auto *BB : Context.CurRegion.blocks())
if (Context.CurRegion.contains(LI->getLoopFor(BB)))
InstCount += BB->size();
InstCount = InstCount / NumLoops;
return InstCount >= ProfitabilityMinPerLoopInstructions;
}
bool ScopDetection::hasPossiblyDistributableLoop(
DetectionContext &Context) const {
for (auto *BB : Context.CurRegion.blocks()) {
auto *L = LI->getLoopFor(BB);
if (!Context.CurRegion.contains(L))
continue;
if (Context.BoxedLoopsSet.count(L))
continue;
unsigned StmtsWithStoresInLoops = 0;
for (auto *LBB : L->blocks()) {
bool MemStore = false;
for (auto &I : *LBB)
MemStore |= isa<StoreInst>(&I);
StmtsWithStoresInLoops += MemStore;
}
return (StmtsWithStoresInLoops > 1);
}
return false;
}
bool ScopDetection::isProfitableRegion(DetectionContext &Context) const {
Region &CurRegion = Context.CurRegion;
if (PollyProcessUnprofitable)
return true;
// We can probably not do a lot on scops that only write or only read
// data.
if (!Context.hasStores || !Context.hasLoads)
return invalid<ReportUnprofitable>(Context, /*Assert=*/true, &CurRegion);
int NumLoops = countBeneficialLoops(&CurRegion, MIN_LOOP_TRIP_COUNT).NumLoops;
int NumAffineLoops = NumLoops - Context.BoxedLoopsSet.size();
// Scops with at least two loops may allow either loop fusion or tiling and
// are consequently interesting to look at.
if (NumAffineLoops >= 2)
return true;
// A loop with multiple non-trivial blocks migt be amendable to distribution.
if (NumAffineLoops == 1 && hasPossiblyDistributableLoop(Context))
return true;
// Scops that contain a loop with a non-trivial amount of computation per
// loop-iteration are interesting as we may be able to parallelize such
// loops. Individual loops that have only a small amount of computation
// per-iteration are performance-wise very fragile as any change to the
// loop induction variables may affect performance. To not cause spurious
// performance regressions, we do not consider such loops.
if (NumAffineLoops == 1 && hasSufficientCompute(Context, NumLoops))
return true;
return invalid<ReportUnprofitable>(Context, /*Assert=*/true, &CurRegion);
}
bool ScopDetection::isValidRegion(DetectionContext &Context) const {
Region &CurRegion = Context.CurRegion;
DEBUG(dbgs() << "Checking region: " << CurRegion.getNameStr() << "\n\t");
if (CurRegion.isTopLevelRegion()) {
DEBUG(dbgs() << "Top level region is invalid\n");
return false;
}
if (!CurRegion.getEntry()->getName().count(OnlyRegion)) {
DEBUG({
dbgs() << "Region entry does not match -polly-region-only";
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 (CurRegion.getEntry() ==
&(CurRegion.getEntry()->getParent()->getEntryBlock()))
return invalid<ReportEntry>(Context, /*Assert=*/true, CurRegion.getEntry());
if (!allBlocksValid(Context))
return false;
DebugLoc DbgLoc;
if (!isReducibleRegion(CurRegion, DbgLoc))
return invalid<ReportIrreducibleRegion>(Context, /*Assert=*/true,
&CurRegion, DbgLoc);
DEBUG(dbgs() << "OK\n");
return true;
}
void ScopDetection::markFunctionAsInvalid(Function *F) {
F->addFnAttr(PollySkipFnAttr);
}
bool ScopDetection::isValidFunction(llvm::Function &F) {
return !F.hasFnAttribute(PollySkipFnAttr);
}
void ScopDetection::printLocations(llvm::Function &F) {
for (const Region *R : *this) {
unsigned LineEntry, LineExit;
std::string FileName;
getDebugLocation(R, LineEntry, LineExit, FileName);
DiagnosticScopFound Diagnostic(F, FileName, LineEntry, LineExit);
F.getContext().diagnose(Diagnostic);
}
}
void ScopDetection::emitMissedRemarks(const Function &F) {
for (auto &DIt : DetectionContextMap) {
auto &DC = DIt.getSecond();
if (DC.Log.hasErrors())
emitRejectionRemarks(DIt.getFirst(), DC.Log);
}
}
bool ScopDetection::isReducibleRegion(Region &R, DebugLoc &DbgLoc) const {
/// Enum for coloring BBs in Region.
///
/// WHITE - Unvisited BB in DFS walk.
/// GREY - BBs which are currently on the DFS stack for processing.
/// BLACK - Visited and completely processed BB.
enum Color { WHITE, GREY, BLACK };
BasicBlock *REntry = R.getEntry();
BasicBlock *RExit = R.getExit();
// Map to match the color of a BasicBlock during the DFS walk.
DenseMap<const BasicBlock *, Color> BBColorMap;
// Stack keeping track of current BB and index of next child to be processed.
std::stack<std::pair<BasicBlock *, unsigned>> DFSStack;
unsigned AdjacentBlockIndex = 0;
BasicBlock *CurrBB, *SuccBB;
CurrBB = REntry;
// Initialize the map for all BB with WHITE color.
for (auto *BB : R.blocks())
BBColorMap[BB] = WHITE;
// Process the entry block of the Region.
BBColorMap[CurrBB] = GREY;
DFSStack.push(std::make_pair(CurrBB, 0));
while (!DFSStack.empty()) {
// Get next BB on stack to be processed.
CurrBB = DFSStack.top().first;
AdjacentBlockIndex = DFSStack.top().second;
DFSStack.pop();
// Loop to iterate over the successors of current BB.
const TerminatorInst *TInst = CurrBB->getTerminator();
unsigned NSucc = TInst->getNumSuccessors();
for (unsigned I = AdjacentBlockIndex; I < NSucc;
++I, ++AdjacentBlockIndex) {
SuccBB = TInst->getSuccessor(I);
// Checks for region exit block and self-loops in BB.
if (SuccBB == RExit || SuccBB == CurrBB)
continue;
// WHITE indicates an unvisited BB in DFS walk.
if (BBColorMap[SuccBB] == WHITE) {
// Push the current BB and the index of the next child to be visited.
DFSStack.push(std::make_pair(CurrBB, I + 1));
// Push the next BB to be processed.
DFSStack.push(std::make_pair(SuccBB, 0));
// First time the BB is being processed.
BBColorMap[SuccBB] = GREY;
break;
} else if (BBColorMap[SuccBB] == GREY) {
// GREY indicates a loop in the control flow.
// If the destination dominates the source, it is a natural loop
// else, an irreducible control flow in the region is detected.
if (!DT->dominates(SuccBB, CurrBB)) {
// Get debug info of instruction which causes irregular control flow.
DbgLoc = TInst->getDebugLoc();
return false;
}
}
}
// If all children of current BB have been processed,
// then mark that BB as fully processed.
if (AdjacentBlockIndex == NSucc)
BBColorMap[CurrBB] = BLACK;
}
return true;
}
void updateLoopCountStatistic(ScopDetection::LoopStats Stats,
bool OnlyProfitable) {
if (!OnlyProfitable) {
NumLoopsInScop += Stats.NumLoops;
if (Stats.MaxDepth == 1)
NumScopsDepthOne++;
else if (Stats.MaxDepth == 2)
NumScopsDepthTwo++;
else if (Stats.MaxDepth == 3)
NumScopsDepthThree++;
else if (Stats.MaxDepth == 4)
NumScopsDepthFour++;
else if (Stats.MaxDepth == 5)
NumScopsDepthFive++;
else
NumScopsDepthLarger++;
} else {
NumLoopsInProfScop += Stats.NumLoops;
if (Stats.MaxDepth == 1)
NumProfScopsDepthOne++;
else if (Stats.MaxDepth == 2)
NumProfScopsDepthTwo++;
else if (Stats.MaxDepth == 3)
NumProfScopsDepthThree++;
else if (Stats.MaxDepth == 4)
NumProfScopsDepthFour++;
else if (Stats.MaxDepth == 5)
NumProfScopsDepthFive++;
else
NumProfScopsDepthLarger++;
}
}
bool ScopDetection::runOnFunction(llvm::Function &F) {
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
RI = &getAnalysis<RegionInfoPass>().getRegionInfo();
if (!PollyProcessUnprofitable && LI->empty())
return false;
AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
Region *TopRegion = RI->getTopLevelRegion();
releaseMemory();
if (OnlyFunction != "" && !F.getName().count(OnlyFunction))
return false;
if (!isValidFunction(F))
return false;
findScops(*TopRegion);
NumScopRegions += ValidRegions.size();
// Prune non-profitable regions.
for (auto &DIt : DetectionContextMap) {
auto &DC = DIt.getSecond();
if (DC.Log.hasErrors())
continue;
if (!ValidRegions.count(&DC.CurRegion))
continue;
LoopStats Stats = countBeneficialLoops(&DC.CurRegion, 0);
updateLoopCountStatistic(Stats, false /* OnlyProfitable */);
if (isProfitableRegion(DC)) {
updateLoopCountStatistic(Stats, true /* OnlyProfitable */);
continue;
}
ValidRegions.remove(&DC.CurRegion);
}
NumProfScopRegions += ValidRegions.size();
NumLoopsOverall += countBeneficialLoops(TopRegion, 0).NumLoops;
// Only makes sense when we tracked errors.
if (PollyTrackFailures)
emitMissedRemarks(F);
if (ReportLevel)
printLocations(F);
assert(ValidRegions.size() <= DetectionContextMap.size() &&
"Cached more results than valid regions");
return false;
}
ScopDetection::DetectionContext *
ScopDetection::getDetectionContext(const Region *R) const {
auto DCMIt = DetectionContextMap.find(getBBPairForRegion(R));
if (DCMIt == DetectionContextMap.end())
return nullptr;
return &DCMIt->second;
}
const RejectLog *ScopDetection::lookupRejectionLog(const Region *R) const {
const DetectionContext *DC = getDetectionContext(R);
return DC ? &DC->Log : nullptr;
}
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 {
if (!VerifyScops)
return;
for (const Region *R : ValidRegions)
verifyRegion(*R);
}
void ScopDetection::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<LoopInfoWrapperPass>();
AU.addRequiredTransitive<ScalarEvolutionWrapperPass>();
AU.addRequired<DominatorTreeWrapperPass>();
// We also need AA and RegionInfo when we are verifying analysis.
AU.addRequiredTransitive<AAResultsWrapperPass>();
AU.addRequiredTransitive<RegionInfoPass>();
AU.setPreservesAll();
}
void ScopDetection::print(raw_ostream &OS, const Module *) const {
for (const Region *R : ValidRegions)
OS << "Valid Region for Scop: " << R->getNameStr() << '\n';
OS << "\n";
}
void ScopDetection::releaseMemory() {
ValidRegions.clear();
DetectionContextMap.clear();
// Do not clear the invalid function set.
}
char ScopDetection::ID = 0;
Pass *polly::createScopDetectionPass() { return new ScopDetection(); }
INITIALIZE_PASS_BEGIN(ScopDetection, "polly-detect",
"Polly - Detect static control parts (SCoPs)", false,
false);
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass);
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass);
INITIALIZE_PASS_DEPENDENCY(RegionInfoPass);
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass);
INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass);
INITIALIZE_PASS_END(ScopDetection, "polly-detect",
"Polly - Detect static control parts (SCoPs)", false, false)
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