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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
//
// 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/CodeGen/BlockGenerators.h"
#include "polly/CodeGen/CodeGeneration.h"
#include "polly/LinkAllPasses.h"
#include "polly/Options.h"
#include "polly/ScopDetection.h"
#include "polly/ScopDetectionDiagnostic.h"
#include "polly/Support/SCEVValidator.h"
#include "polly/Support/ScopHelper.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>
using namespace llvm;
using namespace polly;
#define DEBUG_TYPE "polly-detect"
static cl::opt<bool>
DetectScopsWithoutLoops("polly-detect-scops-in-functions-without-loops",
cl::desc("Detect scops in functions without loops"),
cl::Hidden, cl::init(false), cl::ZeroOrMore,
cl::cat(PollyCategory));
static cl::opt<bool>
DetectRegionsWithoutLoops("polly-detect-scops-in-regions-without-loops",
cl::desc("Detect scops in regions without loops"),
cl::Hidden, cl::init(false), cl::ZeroOrMore,
cl::cat(PollyCategory));
static cl::opt<bool> DetectUnprofitable("polly-detect-unprofitable",
cl::desc("Detect unprofitable scops"),
cl::Hidden, 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::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>
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> 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> AllowUnsigned("polly-allow-unsigned",
cl::desc("Allow unsigned expressions"),
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));
static cl::opt<bool> AllowNonSCEVBackedgeTakenCount(
"polly-allow-non-scev-backedge-taken-count",
cl::desc("Allow loops even if SCEV cannot provide a trip count"),
cl::Hidden, cl::init(true), cl::ZeroOrMore, cl::cat(PollyCategory));
bool polly::PollyTrackFailures = false;
bool polly::PollyDelinearize = false;
StringRef polly::PollySkipFnAttr = "polly.skip.fn";
//===----------------------------------------------------------------------===//
// Statistics.
STATISTIC(ValidRegion, "Number of regions that a valid part of Scop");
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 = 10;
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) {
if (!PollyUseRuntimeAliasChecks)
return;
// Disable runtime alias checks if we ignore aliasing all together.
if (IgnoreAliasing) {
PollyUseRuntimeAliasChecks = false;
return;
}
if (AllowNonAffine) {
DEBUG(errs() << "WARNING: We disable runtime alias checks as non affine "
"accesses are enabled.\n");
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) {
BoxedLoopsSetTy DummyBoxedLoopsSet;
NonAffineSubRegionSetTy DummyNonAffineSubRegionSet;
DetectionContext Context(const_cast<Region &>(R), *AA,
DummyNonAffineSubRegionSet, DummyBoxedLoopsSet,
false /*verifying*/);
return isValidRegion(Context);
}
return true;
}
std::string ScopDetection::regionIsInvalidBecause(const Region *R) const {
if (!RejectLogs.count(R))
return "";
// Get the first error we found. Even in keep-going mode, this is the first
// reason that caused the candidate to be rejected.
RejectLog Errors = RejectLogs.at(R);
// This can happen when we marked a region invalid, but didn't track
// an error for it.
if (Errors.size() == 0)
return "";
RejectReasonPtr RR = *Errors.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::isValidCFG(BasicBlock &BB,
DetectionContext &Context) const {
Region &CurRegion = Context.CurRegion;
TerminatorInst *TI = BB.getTerminator();
// Return instructions are only valid if the region is the top level region.
if (isa<ReturnInst>(TI) && !CurRegion.getExit() && TI->getNumOperands() == 0)
return true;
BranchInst *Br = dyn_cast<BranchInst>(TI);
if (!Br)
return invalid<ReportNonBranchTerminator>(Context, /*Assert=*/true, &BB);
if (Br->isUnconditional())
return true;
Value *Condition = Br->getCondition();
// UndefValue is not allowed as condition.
if (isa<UndefValue>(Condition))
return invalid<ReportUndefCond>(Context, /*Assert=*/true, Br, &BB);
// Only Constant and ICmpInst are allowed as condition.
if (!(isa<Constant>(Condition) || isa<ICmpInst>(Condition))) {
if (!AllowNonAffineSubRegions ||
!addOverApproximatedRegion(RI->getRegionFor(&BB), Context))
return invalid<ReportInvalidCond>(Context, /*Assert=*/true, Br, &BB);
}
// 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() && !AllowUnsigned)
return invalid<ReportUnsignedCond>(Context, /*Assert=*/true, Br, &BB);
// 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(ICmp->getParent());
const SCEV *LHS = SE->getSCEVAtScope(ICmp->getOperand(0), L);
const SCEV *RHS = SE->getSCEVAtScope(ICmp->getOperand(1), L);
if (!isAffineExpr(&CurRegion, LHS, *SE) ||
!isAffineExpr(&CurRegion, RHS, *SE)) {
if (!AllowNonAffineSubRegions ||
!addOverApproximatedRegion(RI->getRegionFor(&BB), Context))
return invalid<ReportNonAffBranch>(Context, /*Assert=*/true, &BB, LHS,
RHS, ICmp);
}
}
// 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)
return invalid<ReportCondition>(Context, /*Assert=*/true, &BB);
return true;
}
bool ScopDetection::isValidCallInst(CallInst &CI) {
if (CI.doesNotReturn())
return false;
if (CI.doesNotAccessMemory())
return true;
Function *CalledFunction = CI.getCalledFunction();
// Indirect calls are not supported.
if (CalledFunction == 0)
return false;
if (isIgnoredIntrinsic(&CI))
return true;
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;
// 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. Recursively checking the operators of Phi nodes would lead to
// infinite recursion.
if (isa<PHINode>(*I))
return false;
for (const Use &Operand : I->operands())
if (!isInvariant(*Operand, Reg))
return false;
// When the instruction is a load instruction, check that no write to memory
// in the region aliases with the load.
if (const LoadInst *LI = dyn_cast<LoadInst>(I)) {
auto Loc = MemoryLocation::get(LI);
// Check if any basic block in the region can modify the location pointed to
// by 'Loc'. If so, 'Val' is (likely) not invariant in the region.
for (const BasicBlock *BB : Reg.blocks())
if (AA->canBasicBlockModify(*BB, Loc))
return false;
}
return true;
}
MapInsnToMemAcc InsnToMemAcc;
bool ScopDetection::hasAffineMemoryAccesses(DetectionContext &Context) const {
Region &CurRegion = Context.CurRegion;
for (const SCEVUnknown *BasePointer : Context.NonAffineAccesses) {
Value *BaseValue = BasePointer->getValue();
auto Shape = std::shared_ptr<ArrayShape>(new ArrayShape(BasePointer));
bool BasePtrHasNonAffine = false;
// First step: collect parametric terms in all array references.
SmallVector<const SCEV *, 4> Terms;
for (const auto &Pair : Context.Accesses[BasePointer]) {
if (auto *AF = dyn_cast<SCEVAddRecExpr>(Pair.second))
SE->collectParametricTerms(AF, Terms);
// 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);
}
}
}
Terms.push_back(SE->getMulExpr(Operands));
}
}
}
}
// Second step: find array shape.
SE->findArrayDimensions(Terms, Shape->DelinearizedSizes,
Context.ElementSize[BasePointer]);
if (!AllowNonAffine)
for (const SCEV *DelinearizedSize : Shape->DelinearizedSizes) {
if (auto *Unknown = dyn_cast<SCEVUnknown>(DelinearizedSize)) {
auto *value = dyn_cast<Value>(Unknown->getValue());
if (isa<UndefValue>(value)) {
invalid<ReportDifferentArrayElementSize>(
Context, /*Assert=*/true,
Context.Accesses[BasePointer].front().first, BaseValue);
return false;
}
}
if (hasScalarDepsInsideRegion(DelinearizedSize, &CurRegion))
invalid<ReportNonAffineAccess>(
Context, /*Assert=*/true, DelinearizedSize,
Context.Accesses[BasePointer].front().first, BaseValue);
}
// No array shape derived.
if (Shape->DelinearizedSizes.empty()) {
if (AllowNonAffine)
continue;
for (const auto &Pair : Context.Accesses[BasePointer]) {
const Instruction *Insn = Pair.first;
const SCEV *AF = Pair.second;
if (!isAffineExpr(&CurRegion, AF, *SE, BaseValue)) {
invalid<ReportNonAffineAccess>(Context, /*Assert=*/true, AF, Insn,
BaseValue);
if (!KeepGoing)
return false;
}
}
continue;
}
// Third step: compute the access functions for each subscript.
//
// 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.
MapInsnToMemAcc TempMemoryAccesses;
for (const auto &Pair : Context.Accesses[BasePointer]) {
const Instruction *Insn = Pair.first;
auto *AF = Pair.second;
bool IsNonAffine = false;
TempMemoryAccesses.insert(std::make_pair(Insn, MemAcc(Insn, Shape)));
MemAcc *Acc = &TempMemoryAccesses.find(Insn)->second;
if (!AF) {
if (isAffineExpr(&CurRegion, Pair.second, *SE, BaseValue))
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 (!isAffineExpr(&CurRegion, S, *SE, BaseValue))
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)
InsnToMemAcc.insert(TempMemoryAccesses.begin(), TempMemoryAccesses.end());
}
return true;
}
bool ScopDetection::isValidMemoryAccess(Instruction &Inst,
DetectionContext &Context) const {
Region &CurRegion = Context.CurRegion;
Value *Ptr = getPointerOperand(Inst);
Loop *L = LI->getLoopFor(Inst.getParent());
const SCEV *AccessFunction = SE->getSCEVAtScope(Ptr, L);
const SCEVUnknown *BasePointer;
Value *BaseValue;
BasePointer = dyn_cast<SCEVUnknown>(SE->getPointerBase(AccessFunction));
if (!BasePointer)
return invalid<ReportNoBasePtr>(Context, /*Assert=*/true, &Inst);
BaseValue = BasePointer->getValue();
if (isa<UndefValue>(BaseValue))
return invalid<ReportUndefBasePtr>(Context, /*Assert=*/true, &Inst);
// Check that the base address of the access is invariant in the current
// region.
if (!isInvariant(*BaseValue, CurRegion))
// Verification of this property is difficult as the independent blocks
// pass may introduce aliasing that we did not have when running the
// scop detection.
return invalid<ReportVariantBasePtr>(Context, /*Assert=*/false, BaseValue,
&Inst);
AccessFunction = SE->getMinusSCEV(AccessFunction, BasePointer);
const SCEV *Size = SE->getElementSize(&Inst);
if (Context.ElementSize.count(BasePointer)) {
if (Context.ElementSize[BasePointer] != Size)
return invalid<ReportDifferentArrayElementSize>(Context, /*Assert=*/true,
&Inst, BaseValue);
} else {
Context.ElementSize[BasePointer] = Size;
}
bool isVariantInNonAffineLoop = false;
SetVector<const Loop *> Loops;
findLoops(AccessFunction, Loops);
for (const Loop *L : Loops)
if (Context.BoxedLoopsSet.count(L))
isVariantInNonAffineLoop = true;
if (PollyDelinearize && !isVariantInNonAffineLoop) {
Context.Accesses[BasePointer].push_back({&Inst, AccessFunction});
if (!isAffineExpr(&CurRegion, AccessFunction, *SE, BaseValue))
Context.NonAffineAccesses.insert(BasePointer);
} else if (!AllowNonAffine) {
if (isVariantInNonAffineLoop ||
!isAffineExpr(&CurRegion, AccessFunction, *SE, BaseValue))
return invalid<ReportNonAffineAccess>(Context, /*Assert=*/true,
AccessFunction, &Inst, BaseValue);
}
// FIXME: Alias Analysis thinks IntToPtrInst aliases with alloca instructions
// created by IndependentBlocks Pass.
if (IntToPtrInst *Inst = dyn_cast<IntToPtrInst>(BaseValue))
return invalid<ReportIntToPtr>(Context, /*Assert=*/true, Inst);
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(
BaseValue, MemoryLocation::UnknownSize, AATags);
// 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()) {
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.
for (const auto &Ptr : AS) {
Instruction *Inst = dyn_cast<Instruction>(Ptr.getValue());
if (Inst && CurRegion.contains(Inst)) {
CanBuildRunTimeCheck = false;
break;
}
}
if (CanBuildRunTimeCheck)
return true;
}
return invalid<ReportAlias>(Context, /*Assert=*/false, &Inst, AS);
}
return true;
}
bool ScopDetection::isValidInstruction(Instruction &Inst,
DetectionContext &Context) const {
// We only check the call instruction but not invoke instruction.
if (CallInst *CI = dyn_cast<CallInst>(&Inst)) {
if (isValidCallInst(*CI))
return true;
return invalid<ReportFuncCall>(Context, /*Assert=*/true, &Inst);
}
if (!Inst.mayWriteToMemory() && !Inst.mayReadFromMemory()) {
if (!isa<AllocaInst>(Inst))
return true;
return invalid<ReportAlloca>(Context, /*Assert=*/true, &Inst);
}
// Check the access function.
if (isa<LoadInst>(Inst) || isa<StoreInst>(Inst)) {
Context.hasStores |= isa<StoreInst>(Inst);
Context.hasLoads |= isa<LoadInst>(Inst);
return isValidMemoryAccess(Inst, Context);
}
// We do not know this instruction, therefore we assume it is invalid.
return invalid<ReportUnknownInst>(Context, /*Assert=*/true, &Inst);
}
bool ScopDetection::canUseISLTripCount(Loop *L,
DetectionContext &Context) const {
Region &CurRegion = Context.CurRegion;
// Ensure the loop has a single back edge.
if (L->getNumBackEdges() != 1)
return false;
// Ensure the loop has a single exiting block.
BasicBlock *ExitingBB = L->getExitingBlock();
if (!ExitingBB)
return false;
// Ensure the exiting block is terminated by a conditional branch.
BranchInst *Term = dyn_cast<BranchInst>(ExitingBB->getTerminator());
if (!Term || !Term->isConditional())
return false;
Value *Cond = Term->getCondition();
// If the terminating condition is an integer comparison, ensure that it is a
// comparison between a recurrence and an invariant value.
if (ICmpInst *I = dyn_cast<ICmpInst>(Cond)) {
const Value *Op0 = I->getOperand(0);
const Value *Op1 = I->getOperand(1);
const SCEV *LHS = SE->getSCEVAtScope(const_cast<Value *>(Op0), L);
const SCEV *RHS = SE->getSCEVAtScope(const_cast<Value *>(Op1), L);
if ((isa<SCEVAddRecExpr>(LHS) && !isInvariant(*Op1, CurRegion)) ||
(isa<SCEVAddRecExpr>(RHS) && !isInvariant(*Op0, CurRegion)))
return false;
}
// If the terminating condition is not an integer comparison, ensure that it
// is a constant.
else if (!isa<ConstantInt>(Cond))
return false;
// We can use ISL to compute the trip count of L.
return true;
}
bool ScopDetection::isValidLoop(Loop *L, DetectionContext &Context) const {
// Is the loop count affine?
bool IsLoopCountAffine = false;
const SCEV *LoopCount = SE->getBackedgeTakenCount(L);
if (!isa<SCEVCouldNotCompute>(LoopCount))
IsLoopCountAffine = isAffineExpr(&Context.CurRegion, LoopCount, *SE);
else
IsLoopCountAffine = canUseISLTripCount(L, Context);
if (IsLoopCountAffine) {
Context.hasAffineLoops = true;
return true;
}
if (AllowNonAffineSubRegions) {
Region *R = RI->getRegionFor(L->getHeader());
if (R->contains(L))
if (addOverApproximatedRegion(R, Context))
return true;
}
return invalid<ReportLoopBound>(Context, /*Assert=*/true, L, LoopCount);
}
bool ScopDetection::hasMoreThanOneLoop(Region *R) const {
auto LoopNum = 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)) {
LoopNum++;
if (SubLoop->getSubLoopsVector().size() > 0)
LoopNum++;
if (LoopNum >= 2)
return true;
}
return false;
}
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) {
DetectionContext Context(
*ExpandedRegion, *AA, NonAffineSubRegionMap[ExpandedRegion.get()],
BoxedLoopsMap[ExpandedRegion.get()], false /* verifying */);
DEBUG(dbgs() << "\t\tTrying " << ExpandedRegion->getNameStr() << "\n");
// Only expand when we did not collect errors.
// Check the exit first (cheap)
if (isValidExit(Context) && !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())
break;
// Store this region, because it is the greatest valid (encountered so
// far).
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)
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;
}
// Remove all direct and indirect children of region R from the region set Regs,
// but do not recurse further if the first child has been found.
//
// Return the number of regions erased from Regs.
static unsigned eraseAllChildren(ScopDetection::RegionSet &Regs,
const Region &R) {
unsigned Count = 0;
for (auto &SubRegion : R) {
if (Regs.count(SubRegion.get())) {
++Count;
Regs.remove(SubRegion.get());
} else {
Count += eraseAllChildren(Regs, *SubRegion);
}
}
return Count;
}
void ScopDetection::findScops(Region &R) {
DetectionContext Context(R, *AA, NonAffineSubRegionMap[&R], BoxedLoopsMap[&R],
false /*verifying*/);
bool RegionIsValid = false;
if (!DetectRegionsWithoutLoops && regionWithoutLoops(R, LI))
invalid<ReportUnprofitable>(Context, /*Assert=*/true, &R);
else
RegionIsValid = isValidRegion(Context);
bool HasErrors = !RegionIsValid || Context.Log.size() > 0;
if (PollyTrackFailures && HasErrors)
RejectLogs.insert(std::make_pair(&R, Context.Log));
if (!HasErrors) {
++ValidRegion;
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 regions that had errors.
bool HadErrors = RejectLogs.hasErrors(CurrentRegion);
if (HadErrors)
continue;
// Skip invalid regions. Regions may become invalid, if they are element of
// an already expanded region.
if (!ValidRegions.count(CurrentRegion))
continue;
Region *ExpandedR = expandRegion(*CurrentRegion);
if (!ExpandedR)
continue;
R.addSubRegion(ExpandedR, true);
ValidRegions.insert(ExpandedR);
ValidRegions.remove(CurrentRegion);
// Erase all (direct and indirect) children of ExpandedR from the valid
// regions and update the number of valid regions.
ValidRegion -= eraseAllChildren(ValidRegions, *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 && (!isValidLoop(L, Context) && !KeepGoing))
return false;
}
for (BasicBlock *BB : CurRegion.blocks())
if (!isValidCFG(*BB, Context) && !KeepGoing)
return false;
for (BasicBlock *BB : CurRegion.blocks())
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::isValidExit(DetectionContext &Context) const {
// PHI nodes are not allowed in the exit basic block.
if (BasicBlock *Exit = Context.CurRegion.getExit()) {
BasicBlock::iterator I = Exit->begin();
if (I != Exit->end() && isa<PHINode>(*I))
return invalid<ReportPHIinExit>(Context, /*Assert=*/true, I);
}
return true;
}
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;
}
if (!CurRegion.getEnteringBlock()) {
BasicBlock *entry = CurRegion.getEntry();
Loop *L = LI->getLoopFor(entry);
if (L) {
if (!L->isLoopSimplifyForm())
return invalid<ReportSimpleLoop>(Context, /*Assert=*/true);
for (pred_iterator PI = pred_begin(entry), PE = pred_end(entry); PI != PE;
++PI) {
// Region entering edges come from the same loop but outside the region
// are not allowed.
if (L->contains(*PI) && !CurRegion.contains(*PI))
return invalid<ReportIndEdge>(Context, /*Assert=*/true, *PI);
}
}
}
// 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 (!DetectUnprofitable && !hasMoreThanOneLoop(&CurRegion))
invalid<ReportUnprofitable>(Context, /*Assert=*/true, &CurRegion);
if (!isValidExit(Context))
return false;
if (!allBlocksValid(Context))
return false;
// We can probably not do a lot on scops that only write or only read
// data.
if (!DetectUnprofitable && (!Context.hasStores || !Context.hasLoads))
invalid<ReportUnprofitable>(Context, /*Assert=*/true, &CurRegion);
// Check if there was at least one non-overapproximated loop in the region or
// we allow regions without loops.
if (!DetectRegionsWithoutLoops && !Context.hasAffineLoops)
invalid<ReportUnprofitable>(Context, /*Assert=*/true, &CurRegion);
DEBUG(dbgs() << "OK\n");
return true;
}
void ScopDetection::markFunctionAsInvalid(Function *F) const {
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::emitMissedRemarksForValidRegions(
const Function &F, const RegionSet &ValidRegions) {
for (const Region *R : ValidRegions) {
const Region *Parent = R->getParent();
if (Parent && !Parent->isTopLevelRegion() && RejectLogs.count(Parent))
emitRejectionRemarks(F, RejectLogs.at(Parent));
}
}
void ScopDetection::emitMissedRemarksForLeaves(const Function &F,
const Region *R) {
for (const std::unique_ptr<Region> &Child : *R) {
bool IsValid = ValidRegions.count(Child.get());
if (IsValid)
continue;
bool IsLeaf = Child->begin() == Child->end();
if (!IsLeaf)
emitMissedRemarksForLeaves(F, Child.get());
else {
if (RejectLogs.count(Child.get())) {
emitRejectionRemarks(F, RejectLogs.at(Child.get()));
}
}
}
}
bool ScopDetection::runOnFunction(llvm::Function &F) {
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
RI = &getAnalysis<RegionInfoPass>().getRegionInfo();
if (!DetectScopsWithoutLoops && LI->empty())
return false;
AA = &getAnalysis<AliasAnalysis>();
SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
Region *TopRegion = RI->getTopLevelRegion();
releaseMemory();
if (OnlyFunction != "" && !F.getName().count(OnlyFunction))
return false;
if (!isValidFunction(F))
return false;
findScops(*TopRegion);
// Only makes sense when we tracked errors.
if (PollyTrackFailures) {
emitMissedRemarksForValidRegions(F, ValidRegions);
emitMissedRemarksForLeaves(F, TopRegion);
}
for (const Region *R : ValidRegions)
emitValidRemarks(F, R);
if (ReportLevel)
printLocations(F);
return false;
}
bool ScopDetection::isNonAffineSubRegion(const Region *SubR,
const Region *ScopR) const {
return NonAffineSubRegionMap.lookup(ScopR).count(SubR);
}
const ScopDetection::BoxedLoopsSetTy *
ScopDetection::getBoxedLoops(const Region *R) const {
auto BLMIt = BoxedLoopsMap.find(R);
if (BLMIt == BoxedLoopsMap.end())
return nullptr;
return &BLMIt->second;
}
void polly::ScopDetection::verifyRegion(const Region &R) const {
assert(isMaxRegionInScop(R) && "Expect R is a valid region.");
BoxedLoopsSetTy DummyBoxedLoopsSet;
NonAffineSubRegionSetTy DummyNonAffineSubRegionSet;
DetectionContext Context(const_cast<Region &>(R), *AA,
DummyNonAffineSubRegionSet, DummyBoxedLoopsSet,
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.addRequired<ScalarEvolutionWrapperPass>();
// We also need AA and RegionInfo when we are verifying analysis.
AU.addRequiredTransitive<AliasAnalysis>();
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();
RejectLogs.clear();
NonAffineSubRegionMap.clear();
InsnToMemAcc.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_AG_DEPENDENCY(AliasAnalysis);
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass);
INITIALIZE_PASS_DEPENDENCY(RegionInfoPass);
INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass);
INITIALIZE_PASS_END(ScopDetection, "polly-detect",
"Polly - Detect static control parts (SCoPs)", false, false)
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