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llvm-project/polly/lib/Support/ScopHelper.cpp

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//===- ScopHelper.cpp - Some Helper Functions for Scop. ------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Small functions that help with Scop and LLVM-IR.
//
//===----------------------------------------------------------------------===//
#include "polly/Support/ScopHelper.h"
#include "polly/Options.h"
#include "polly/ScopInfo.h"
#include "polly/Support/SCEVValidator.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/RegionInfo.h"
#include "llvm/Analysis/RegionInfoImpl.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/ScalarEvolutionExpressions.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Support/Debug.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
using namespace polly;
#define DEBUG_TYPE "polly-scop-helper"
static cl::opt<bool> PollyAllowErrorBlocks(
"polly-allow-error-blocks",
cl::desc("Allow to speculate on the execution of 'error blocks'."),
cl::Hidden, cl::init(true), cl::ZeroOrMore, cl::cat(PollyCategory));
static cl::list<std::string> DebugFunctions(
"polly-debug-func",
cl::desc("Allow calls to the specified functions in SCoPs even if their "
"side-effects are unknown. This can be used to do debug output in "
"Polly-transformed code."),
cl::Hidden, cl::ZeroOrMore, cl::CommaSeparated, cl::cat(PollyCategory));
// Ensures that there is just one predecessor to the entry node from outside the
// region.
// The identity of the region entry node is preserved.
static void simplifyRegionEntry(Region *R, DominatorTree *DT, LoopInfo *LI,
RegionInfo *RI) {
BasicBlock *EnteringBB = R->getEnteringBlock();
BasicBlock *Entry = R->getEntry();
// Before (one of):
//
// \ / //
// EnteringBB //
// | \------> //
// \ / | //
// Entry <--\ Entry <--\ //
// / \ / / \ / //
// .... .... //
// Create single entry edge if the region has multiple entry edges.
if (!EnteringBB) {
SmallVector<BasicBlock *, 4> Preds;
for (BasicBlock *P : predecessors(Entry))
if (!R->contains(P))
Preds.push_back(P);
BasicBlock *NewEntering =
SplitBlockPredecessors(Entry, Preds, ".region_entering", DT, LI);
if (RI) {
// The exit block of predecessing regions must be changed to NewEntering
for (BasicBlock *ExitPred : predecessors(NewEntering)) {
Region *RegionOfPred = RI->getRegionFor(ExitPred);
if (RegionOfPred->getExit() != Entry)
continue;
while (!RegionOfPred->isTopLevelRegion() &&
RegionOfPred->getExit() == Entry) {
RegionOfPred->replaceExit(NewEntering);
RegionOfPred = RegionOfPred->getParent();
}
}
// Make all ancestors use EnteringBB as entry; there might be edges to it
Region *AncestorR = R->getParent();
RI->setRegionFor(NewEntering, AncestorR);
while (!AncestorR->isTopLevelRegion() && AncestorR->getEntry() == Entry) {
AncestorR->replaceEntry(NewEntering);
AncestorR = AncestorR->getParent();
}
}
EnteringBB = NewEntering;
}
assert(R->getEnteringBlock() == EnteringBB);
// After:
//
// \ / //
// EnteringBB //
// | //
// | //
// Entry <--\ //
// / \ / //
// .... //
}
// Ensure that the region has a single block that branches to the exit node.
static void simplifyRegionExit(Region *R, DominatorTree *DT, LoopInfo *LI,
RegionInfo *RI) {
BasicBlock *ExitBB = R->getExit();
BasicBlock *ExitingBB = R->getExitingBlock();
// Before:
//
// (Region) ______/ //
// \ | / //
// ExitBB //
// / \ //
if (!ExitingBB) {
SmallVector<BasicBlock *, 4> Preds;
for (BasicBlock *P : predecessors(ExitBB))
if (R->contains(P))
Preds.push_back(P);
// Preds[0] Preds[1] otherBB //
// \ | ________/ //
// \ | / //
// BB //
ExitingBB =
SplitBlockPredecessors(ExitBB, Preds, ".region_exiting", DT, LI);
// Preds[0] Preds[1] otherBB //
// \ / / //
// BB.region_exiting / //
// \ / //
// BB //
if (RI)
RI->setRegionFor(ExitingBB, R);
// Change the exit of nested regions, but not the region itself,
R->replaceExitRecursive(ExitingBB);
R->replaceExit(ExitBB);
}
assert(ExitingBB == R->getExitingBlock());
// After:
//
// \ / //
// ExitingBB _____/ //
// \ / //
// ExitBB //
// / \ //
}
void polly::simplifyRegion(Region *R, DominatorTree *DT, LoopInfo *LI,
RegionInfo *RI) {
assert(R && !R->isTopLevelRegion());
assert(!RI || RI == R->getRegionInfo());
assert((!RI || DT) &&
"RegionInfo requires DominatorTree to be updated as well");
simplifyRegionEntry(R, DT, LI, RI);
simplifyRegionExit(R, DT, LI, RI);
assert(R->isSimple());
}
// Split the block into two successive blocks.
//
// Like llvm::SplitBlock, but also preserves RegionInfo
static BasicBlock *splitBlock(BasicBlock *Old, Instruction *SplitPt,
DominatorTree *DT, llvm::LoopInfo *LI,
RegionInfo *RI) {
assert(Old && SplitPt);
// Before:
//
// \ / //
// Old //
// / \ //
BasicBlock *NewBlock = llvm::SplitBlock(Old, SplitPt, DT, LI);
if (RI) {
Region *R = RI->getRegionFor(Old);
RI->setRegionFor(NewBlock, R);
}
// After:
//
// \ / //
// Old //
// | //
// NewBlock //
// / \ //
return NewBlock;
}
void polly::splitEntryBlockForAlloca(BasicBlock *EntryBlock, DominatorTree *DT,
LoopInfo *LI, RegionInfo *RI) {
// Find first non-alloca instruction. Every basic block has a non-alloca
// instruction, as every well formed basic block has a terminator.
BasicBlock::iterator I = EntryBlock->begin();
while (isa<AllocaInst>(I))
++I;
// splitBlock updates DT, LI and RI.
splitBlock(EntryBlock, &*I, DT, LI, RI);
}
void polly::splitEntryBlockForAlloca(BasicBlock *EntryBlock, Pass *P) {
auto *DTWP = P->getAnalysisIfAvailable<DominatorTreeWrapperPass>();
auto *DT = DTWP ? &DTWP->getDomTree() : nullptr;
auto *LIWP = P->getAnalysisIfAvailable<LoopInfoWrapperPass>();
auto *LI = LIWP ? &LIWP->getLoopInfo() : nullptr;
RegionInfoPass *RIP = P->getAnalysisIfAvailable<RegionInfoPass>();
RegionInfo *RI = RIP ? &RIP->getRegionInfo() : nullptr;
// splitBlock updates DT, LI and RI.
polly::splitEntryBlockForAlloca(EntryBlock, DT, LI, RI);
}
/// The SCEVExpander will __not__ generate any code for an existing SDiv/SRem
/// instruction but just use it, if it is referenced as a SCEVUnknown. We want
/// however to generate new code if the instruction is in the analyzed region
/// and we generate code outside/in front of that region. Hence, we generate the
/// code for the SDiv/SRem operands in front of the analyzed region and then
/// create a new SDiv/SRem operation there too.
struct ScopExpander : SCEVVisitor<ScopExpander, const SCEV *> {
friend struct SCEVVisitor<ScopExpander, const SCEV *>;
explicit ScopExpander(const Region &R, ScalarEvolution &SE,
const DataLayout &DL, const char *Name, ValueMapT *VMap,
BasicBlock *RTCBB)
: Expander(SCEVExpander(SE, DL, Name)), SE(SE), Name(Name), R(R),
VMap(VMap), RTCBB(RTCBB) {}
Value *expandCodeFor(const SCEV *E, Type *Ty, Instruction *I) {
// If we generate code in the region we will immediately fall back to the
// SCEVExpander, otherwise we will stop at all unknowns in the SCEV and if
// needed replace them by copies computed in the entering block.
if (!R.contains(I))
E = visit(E);
return Expander.expandCodeFor(E, Ty, I);
}
const SCEV *visit(const SCEV *E) {
// Cache the expansion results for intermediate SCEV expressions. A SCEV
// expression can refer to an operand multiple times (e.g. "x*x), so
// a naive visitor takes exponential time.
if (SCEVCache.count(E))
return SCEVCache[E];
const SCEV *Result = SCEVVisitor::visit(E);
SCEVCache[E] = Result;
return Result;
}
private:
SCEVExpander Expander;
ScalarEvolution &SE;
const char *Name;
const Region &R;
ValueMapT *VMap;
BasicBlock *RTCBB;
DenseMap<const SCEV *, const SCEV *> SCEVCache;
const SCEV *visitGenericInst(const SCEVUnknown *E, Instruction *Inst,
Instruction *IP) {
if (!Inst || !R.contains(Inst))
return E;
assert(!Inst->mayThrow() && !Inst->mayReadOrWriteMemory() &&
!isa<PHINode>(Inst));
auto *InstClone = Inst->clone();
for (auto &Op : Inst->operands()) {
assert(SE.isSCEVable(Op->getType()));
auto *OpSCEV = SE.getSCEV(Op);
auto *OpClone = expandCodeFor(OpSCEV, Op->getType(), IP);
InstClone->replaceUsesOfWith(Op, OpClone);
}
InstClone->setName(Name + Inst->getName());
InstClone->insertBefore(IP);
return SE.getSCEV(InstClone);
}
const SCEV *visitUnknown(const SCEVUnknown *E) {
// If a value mapping was given try if the underlying value is remapped.
Value *NewVal = VMap ? VMap->lookup(E->getValue()) : nullptr;
if (NewVal) {
auto *NewE = SE.getSCEV(NewVal);
// While the mapped value might be different the SCEV representation might
// not be. To this end we will check before we go into recursion here.
if (E != NewE)
return visit(NewE);
}
Instruction *Inst = dyn_cast<Instruction>(E->getValue());
Instruction *IP;
if (Inst && !R.contains(Inst))
IP = Inst;
else if (Inst && RTCBB->getParent() == Inst->getFunction())
IP = RTCBB->getTerminator();
else
IP = RTCBB->getParent()->getEntryBlock().getTerminator();
if (!Inst || (Inst->getOpcode() != Instruction::SRem &&
Inst->getOpcode() != Instruction::SDiv))
return visitGenericInst(E, Inst, IP);
const SCEV *LHSScev = SE.getSCEV(Inst->getOperand(0));
const SCEV *RHSScev = SE.getSCEV(Inst->getOperand(1));
if (!SE.isKnownNonZero(RHSScev))
RHSScev = SE.getUMaxExpr(RHSScev, SE.getConstant(E->getType(), 1));
Value *LHS = expandCodeFor(LHSScev, E->getType(), IP);
Value *RHS = expandCodeFor(RHSScev, E->getType(), IP);
Inst = BinaryOperator::Create((Instruction::BinaryOps)Inst->getOpcode(),
LHS, RHS, Inst->getName() + Name, IP);
return SE.getSCEV(Inst);
}
/// The following functions will just traverse the SCEV and rebuild it with
/// the new operands returned by the traversal.
///
///{
const SCEV *visitConstant(const SCEVConstant *E) { return E; }
const SCEV *visitTruncateExpr(const SCEVTruncateExpr *E) {
return SE.getTruncateExpr(visit(E->getOperand()), E->getType());
}
const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *E) {
return SE.getZeroExtendExpr(visit(E->getOperand()), E->getType());
}
const SCEV *visitSignExtendExpr(const SCEVSignExtendExpr *E) {
return SE.getSignExtendExpr(visit(E->getOperand()), E->getType());
}
const SCEV *visitUDivExpr(const SCEVUDivExpr *E) {
auto *RHSScev = visit(E->getRHS());
if (!SE.isKnownNonZero(RHSScev))
RHSScev = SE.getUMaxExpr(RHSScev, SE.getConstant(E->getType(), 1));
return SE.getUDivExpr(visit(E->getLHS()), RHSScev);
}
const SCEV *visitAddExpr(const SCEVAddExpr *E) {
SmallVector<const SCEV *, 4> NewOps;
for (const SCEV *Op : E->operands())
NewOps.push_back(visit(Op));
return SE.getAddExpr(NewOps);
}
const SCEV *visitMulExpr(const SCEVMulExpr *E) {
SmallVector<const SCEV *, 4> NewOps;
for (const SCEV *Op : E->operands())
NewOps.push_back(visit(Op));
return SE.getMulExpr(NewOps);
}
const SCEV *visitUMaxExpr(const SCEVUMaxExpr *E) {
SmallVector<const SCEV *, 4> NewOps;
for (const SCEV *Op : E->operands())
NewOps.push_back(visit(Op));
return SE.getUMaxExpr(NewOps);
}
const SCEV *visitSMaxExpr(const SCEVSMaxExpr *E) {
SmallVector<const SCEV *, 4> NewOps;
for (const SCEV *Op : E->operands())
NewOps.push_back(visit(Op));
return SE.getSMaxExpr(NewOps);
}
const SCEV *visitAddRecExpr(const SCEVAddRecExpr *E) {
SmallVector<const SCEV *, 4> NewOps;
for (const SCEV *Op : E->operands())
NewOps.push_back(visit(Op));
return SE.getAddRecExpr(NewOps, E->getLoop(), E->getNoWrapFlags());
}
///}
};
Value *polly::expandCodeFor(Scop &S, ScalarEvolution &SE, const DataLayout &DL,
const char *Name, const SCEV *E, Type *Ty,
Instruction *IP, ValueMapT *VMap,
BasicBlock *RTCBB) {
ScopExpander Expander(S.getRegion(), SE, DL, Name, VMap, RTCBB);
return Expander.expandCodeFor(E, Ty, IP);
}
bool polly::isErrorBlock(BasicBlock &BB, const Region &R, LoopInfo &LI,
const DominatorTree &DT) {
if (!PollyAllowErrorBlocks)
return false;
if (isa<UnreachableInst>(BB.getTerminator()))
return true;
if (LI.isLoopHeader(&BB))
return false;
// Basic blocks that are always executed are not considered error blocks,
// as their execution can not be a rare event.
bool DominatesAllPredecessors = true;
if (R.isTopLevelRegion()) {
for (BasicBlock &I : *R.getEntry()->getParent())
if (isa<ReturnInst>(I.getTerminator()) && !DT.dominates(&BB, &I))
DominatesAllPredecessors = false;
} else {
for (auto Pred : predecessors(R.getExit()))
if (R.contains(Pred) && !DT.dominates(&BB, Pred))
DominatesAllPredecessors = false;
}
if (DominatesAllPredecessors)
return false;
for (Instruction &Inst : BB)
if (CallInst *CI = dyn_cast<CallInst>(&Inst)) {
if (isDebugCall(CI))
continue;
if (isIgnoredIntrinsic(CI))
continue;
// memset, memcpy and memmove are modeled intrinsics.
if (isa<MemSetInst>(CI) || isa<MemTransferInst>(CI))
continue;
if (!CI->doesNotAccessMemory())
return true;
if (CI->doesNotReturn())
return true;
}
return false;
}
Value *polly::getConditionFromTerminator(Instruction *TI) {
if (BranchInst *BR = dyn_cast<BranchInst>(TI)) {
if (BR->isUnconditional())
return ConstantInt::getTrue(Type::getInt1Ty(TI->getContext()));
return BR->getCondition();
}
if (SwitchInst *SI = dyn_cast<SwitchInst>(TI))
return SI->getCondition();
return nullptr;
}
static bool hasVariantIndex(GetElementPtrInst *Gep, Loop *L, Region &R,
ScalarEvolution &SE) {
for (const Use &Val : llvm::drop_begin(Gep->operands(), 1)) {
const SCEV *PtrSCEV = SE.getSCEVAtScope(Val, L);
Loop *OuterLoop = R.outermostLoopInRegion(L);
if (!SE.isLoopInvariant(PtrSCEV, OuterLoop))
return true;
}
return false;
}
bool polly::isHoistableLoad(LoadInst *LInst, Region &R, LoopInfo &LI,
ScalarEvolution &SE, const DominatorTree &DT,
const InvariantLoadsSetTy &KnownInvariantLoads) {
Loop *L = LI.getLoopFor(LInst->getParent());
auto *Ptr = LInst->getPointerOperand();
// A LoadInst is hoistable if the address it is loading from is also
// invariant; in this case: another invariant load (whether that address
// is also not written to has to be checked separately)
// TODO: This only checks for a LoadInst->GetElementPtrInst->LoadInst
// pattern generated by the Chapel frontend, but generally this applies
// for any chain of instruction that does not also depend on any
// induction variable
if (auto *GepInst = dyn_cast<GetElementPtrInst>(Ptr)) {
if (!hasVariantIndex(GepInst, L, R, SE)) {
if (auto *DecidingLoad =
dyn_cast<LoadInst>(GepInst->getPointerOperand())) {
if (KnownInvariantLoads.count(DecidingLoad))
return true;
}
}
}
const SCEV *PtrSCEV = SE.getSCEVAtScope(Ptr, L);
while (L && R.contains(L)) {
if (!SE.isLoopInvariant(PtrSCEV, L))
return false;
L = L->getParentLoop();
}
for (auto *User : Ptr->users()) {
auto *UserI = dyn_cast<Instruction>(User);
if (!UserI || !R.contains(UserI))
continue;
if (!UserI->mayWriteToMemory())
continue;
auto &BB = *UserI->getParent();
if (DT.dominates(&BB, LInst->getParent()))
return false;
bool DominatesAllPredecessors = true;
if (R.isTopLevelRegion()) {
for (BasicBlock &I : *R.getEntry()->getParent())
if (isa<ReturnInst>(I.getTerminator()) && !DT.dominates(&BB, &I))
DominatesAllPredecessors = false;
} else {
for (auto Pred : predecessors(R.getExit()))
if (R.contains(Pred) && !DT.dominates(&BB, Pred))
DominatesAllPredecessors = false;
}
if (!DominatesAllPredecessors)
continue;
return false;
}
return true;
}
bool polly::isIgnoredIntrinsic(const Value *V) {
if (auto *IT = dyn_cast<IntrinsicInst>(V)) {
switch (IT->getIntrinsicID()) {
// Lifetime markers are supported/ignored.
case llvm::Intrinsic::lifetime_start:
case llvm::Intrinsic::lifetime_end:
// Invariant markers are supported/ignored.
case llvm::Intrinsic::invariant_start:
case llvm::Intrinsic::invariant_end:
// Some misc annotations are supported/ignored.
case llvm::Intrinsic::var_annotation:
case llvm::Intrinsic::ptr_annotation:
case llvm::Intrinsic::annotation:
case llvm::Intrinsic::donothing:
case llvm::Intrinsic::assume:
// Some debug info intrinsics are supported/ignored.
case llvm::Intrinsic::dbg_value:
case llvm::Intrinsic::dbg_declare:
return true;
default:
break;
}
}
return false;
}
bool polly::canSynthesize(const Value *V, const Scop &S, ScalarEvolution *SE,
Loop *Scope) {
if (!V || !SE->isSCEVable(V->getType()))
return false;
const InvariantLoadsSetTy &ILS = S.getRequiredInvariantLoads();
if (const SCEV *Scev = SE->getSCEVAtScope(const_cast<Value *>(V), Scope))
if (!isa<SCEVCouldNotCompute>(Scev))
if (!hasScalarDepsInsideRegion(Scev, &S.getRegion(), Scope, false, ILS))
return true;
return false;
}
llvm::BasicBlock *polly::getUseBlock(const llvm::Use &U) {
Instruction *UI = dyn_cast<Instruction>(U.getUser());
if (!UI)
return nullptr;
if (PHINode *PHI = dyn_cast<PHINode>(UI))
return PHI->getIncomingBlock(U);
return UI->getParent();
}
std::tuple<std::vector<const SCEV *>, std::vector<int>>
polly::getIndexExpressionsFromGEP(GetElementPtrInst *GEP, ScalarEvolution &SE) {
std::vector<const SCEV *> Subscripts;
std::vector<int> Sizes;
Type *Ty = GEP->getPointerOperandType();
bool DroppedFirstDim = false;
for (unsigned i = 1; i < GEP->getNumOperands(); i++) {
const SCEV *Expr = SE.getSCEV(GEP->getOperand(i));
if (i == 1) {
if (auto *PtrTy = dyn_cast<PointerType>(Ty)) {
Ty = PtrTy->getElementType();
} else if (auto *ArrayTy = dyn_cast<ArrayType>(Ty)) {
Ty = ArrayTy->getElementType();
} else {
Subscripts.clear();
Sizes.clear();
break;
}
if (auto *Const = dyn_cast<SCEVConstant>(Expr))
if (Const->getValue()->isZero()) {
DroppedFirstDim = true;
continue;
}
Subscripts.push_back(Expr);
continue;
}
auto *ArrayTy = dyn_cast<ArrayType>(Ty);
if (!ArrayTy) {
Subscripts.clear();
Sizes.clear();
break;
}
Subscripts.push_back(Expr);
if (!(DroppedFirstDim && i == 2))
Sizes.push_back(ArrayTy->getNumElements());
Ty = ArrayTy->getElementType();
}
return std::make_tuple(Subscripts, Sizes);
}
llvm::Loop *polly::getFirstNonBoxedLoopFor(llvm::Loop *L, llvm::LoopInfo &LI,
const BoxedLoopsSetTy &BoxedLoops) {
while (BoxedLoops.count(L))
L = L->getParentLoop();
return L;
}
llvm::Loop *polly::getFirstNonBoxedLoopFor(llvm::BasicBlock *BB,
llvm::LoopInfo &LI,
const BoxedLoopsSetTy &BoxedLoops) {
Loop *L = LI.getLoopFor(BB);
return getFirstNonBoxedLoopFor(L, LI, BoxedLoops);
}
bool polly::isDebugCall(Instruction *Inst) {
auto *CI = dyn_cast<CallInst>(Inst);
if (!CI)
return false;
Function *CF = CI->getCalledFunction();
if (!CF)
return false;
return std::find(DebugFunctions.begin(), DebugFunctions.end(),
CF->getName()) != DebugFunctions.end();
}
static bool hasDebugCall(BasicBlock *BB) {
for (Instruction &Inst : *BB) {
if (isDebugCall(&Inst))
return true;
}
return false;
}
bool polly::hasDebugCall(ScopStmt *Stmt) {
// Quick skip if no debug functions have been defined.
if (DebugFunctions.empty())
return false;
if (!Stmt)
return false;
for (Instruction *Inst : Stmt->getInstructions())
if (isDebugCall(Inst))
return true;
if (Stmt->isRegionStmt()) {
for (BasicBlock *RBB : Stmt->getRegion()->blocks())
if (RBB != Stmt->getEntryBlock() && ::hasDebugCall(RBB))
return true;
}
return false;
}
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