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1136 lines
38 KiB
1136 lines
38 KiB
//===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the LoopInfo class that is used to identify natural loops
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// and determine the loop depth of various nodes of the CFG. Note that the
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// loops identified may actually be several natural loops that share the same
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// header node... not just a single natural loop.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/ScopeExit.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/Analysis/IVDescriptors.h"
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#include "llvm/Analysis/LoopInfoImpl.h"
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#include "llvm/Analysis/LoopIterator.h"
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#include "llvm/Analysis/MemorySSA.h"
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#include "llvm/Analysis/MemorySSAUpdater.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/Config/llvm-config.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DebugLoc.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/IRPrintingPasses.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Metadata.h"
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#include "llvm/IR/PassManager.h"
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#include "llvm/IR/PrintPasses.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include <algorithm>
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using namespace llvm;
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// Explicitly instantiate methods in LoopInfoImpl.h for IR-level Loops.
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template class llvm::LoopBase<BasicBlock, Loop>;
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template class llvm::LoopInfoBase<BasicBlock, Loop>;
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// Always verify loopinfo if expensive checking is enabled.
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#ifdef EXPENSIVE_CHECKS
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bool llvm::VerifyLoopInfo = true;
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#else
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bool llvm::VerifyLoopInfo = false;
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#endif
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static cl::opt<bool, true>
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VerifyLoopInfoX("verify-loop-info", cl::location(VerifyLoopInfo),
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cl::Hidden, cl::desc("Verify loop info (time consuming)"));
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//===----------------------------------------------------------------------===//
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// Loop implementation
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//
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bool Loop::isLoopInvariant(const Value *V) const {
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if (const Instruction *I = dyn_cast<Instruction>(V))
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return !contains(I);
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return true; // All non-instructions are loop invariant
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}
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bool Loop::hasLoopInvariantOperands(const Instruction *I) const {
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return all_of(I->operands(), [this](Value *V) { return isLoopInvariant(V); });
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}
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bool Loop::makeLoopInvariant(Value *V, bool &Changed, Instruction *InsertPt,
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MemorySSAUpdater *MSSAU) const {
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if (Instruction *I = dyn_cast<Instruction>(V))
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return makeLoopInvariant(I, Changed, InsertPt, MSSAU);
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return true; // All non-instructions are loop-invariant.
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}
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bool Loop::makeLoopInvariant(Instruction *I, bool &Changed,
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Instruction *InsertPt,
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MemorySSAUpdater *MSSAU) const {
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// Test if the value is already loop-invariant.
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if (isLoopInvariant(I))
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return true;
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if (!isSafeToSpeculativelyExecute(I))
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return false;
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if (I->mayReadFromMemory())
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return false;
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// EH block instructions are immobile.
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if (I->isEHPad())
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return false;
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// Determine the insertion point, unless one was given.
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if (!InsertPt) {
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BasicBlock *Preheader = getLoopPreheader();
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// Without a preheader, hoisting is not feasible.
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if (!Preheader)
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return false;
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InsertPt = Preheader->getTerminator();
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}
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// Don't hoist instructions with loop-variant operands.
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for (Value *Operand : I->operands())
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if (!makeLoopInvariant(Operand, Changed, InsertPt, MSSAU))
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return false;
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// Hoist.
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I->moveBefore(InsertPt);
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if (MSSAU)
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if (auto *MUD = MSSAU->getMemorySSA()->getMemoryAccess(I))
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MSSAU->moveToPlace(MUD, InsertPt->getParent(),
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MemorySSA::BeforeTerminator);
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// There is possibility of hoisting this instruction above some arbitrary
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// condition. Any metadata defined on it can be control dependent on this
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// condition. Conservatively strip it here so that we don't give any wrong
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// information to the optimizer.
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I->dropUnknownNonDebugMetadata();
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Changed = true;
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return true;
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}
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bool Loop::getIncomingAndBackEdge(BasicBlock *&Incoming,
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BasicBlock *&Backedge) const {
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BasicBlock *H = getHeader();
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Incoming = nullptr;
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Backedge = nullptr;
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pred_iterator PI = pred_begin(H);
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assert(PI != pred_end(H) && "Loop must have at least one backedge!");
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Backedge = *PI++;
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if (PI == pred_end(H))
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return false; // dead loop
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Incoming = *PI++;
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if (PI != pred_end(H))
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return false; // multiple backedges?
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if (contains(Incoming)) {
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if (contains(Backedge))
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return false;
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std::swap(Incoming, Backedge);
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} else if (!contains(Backedge))
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return false;
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assert(Incoming && Backedge && "expected non-null incoming and backedges");
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return true;
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}
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PHINode *Loop::getCanonicalInductionVariable() const {
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BasicBlock *H = getHeader();
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BasicBlock *Incoming = nullptr, *Backedge = nullptr;
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if (!getIncomingAndBackEdge(Incoming, Backedge))
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return nullptr;
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// Loop over all of the PHI nodes, looking for a canonical indvar.
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for (BasicBlock::iterator I = H->begin(); isa<PHINode>(I); ++I) {
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PHINode *PN = cast<PHINode>(I);
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if (ConstantInt *CI =
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dyn_cast<ConstantInt>(PN->getIncomingValueForBlock(Incoming)))
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if (CI->isZero())
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if (Instruction *Inc =
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dyn_cast<Instruction>(PN->getIncomingValueForBlock(Backedge)))
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if (Inc->getOpcode() == Instruction::Add && Inc->getOperand(0) == PN)
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if (ConstantInt *CI = dyn_cast<ConstantInt>(Inc->getOperand(1)))
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if (CI->isOne())
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return PN;
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}
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return nullptr;
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}
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/// Get the latch condition instruction.
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static ICmpInst *getLatchCmpInst(const Loop &L) {
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if (BasicBlock *Latch = L.getLoopLatch())
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if (BranchInst *BI = dyn_cast_or_null<BranchInst>(Latch->getTerminator()))
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if (BI->isConditional())
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return dyn_cast<ICmpInst>(BI->getCondition());
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return nullptr;
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}
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/// Return the final value of the loop induction variable if found.
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static Value *findFinalIVValue(const Loop &L, const PHINode &IndVar,
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const Instruction &StepInst) {
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ICmpInst *LatchCmpInst = getLatchCmpInst(L);
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if (!LatchCmpInst)
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return nullptr;
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Value *Op0 = LatchCmpInst->getOperand(0);
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Value *Op1 = LatchCmpInst->getOperand(1);
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if (Op0 == &IndVar || Op0 == &StepInst)
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return Op1;
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if (Op1 == &IndVar || Op1 == &StepInst)
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return Op0;
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return nullptr;
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}
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Optional<Loop::LoopBounds> Loop::LoopBounds::getBounds(const Loop &L,
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PHINode &IndVar,
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ScalarEvolution &SE) {
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InductionDescriptor IndDesc;
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if (!InductionDescriptor::isInductionPHI(&IndVar, &L, &SE, IndDesc))
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return None;
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Value *InitialIVValue = IndDesc.getStartValue();
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Instruction *StepInst = IndDesc.getInductionBinOp();
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if (!InitialIVValue || !StepInst)
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return None;
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const SCEV *Step = IndDesc.getStep();
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Value *StepInstOp1 = StepInst->getOperand(1);
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Value *StepInstOp0 = StepInst->getOperand(0);
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Value *StepValue = nullptr;
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if (SE.getSCEV(StepInstOp1) == Step)
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StepValue = StepInstOp1;
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else if (SE.getSCEV(StepInstOp0) == Step)
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StepValue = StepInstOp0;
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Value *FinalIVValue = findFinalIVValue(L, IndVar, *StepInst);
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if (!FinalIVValue)
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return None;
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return LoopBounds(L, *InitialIVValue, *StepInst, StepValue, *FinalIVValue,
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SE);
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}
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using Direction = Loop::LoopBounds::Direction;
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ICmpInst::Predicate Loop::LoopBounds::getCanonicalPredicate() const {
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BasicBlock *Latch = L.getLoopLatch();
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assert(Latch && "Expecting valid latch");
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BranchInst *BI = dyn_cast_or_null<BranchInst>(Latch->getTerminator());
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assert(BI && BI->isConditional() && "Expecting conditional latch branch");
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ICmpInst *LatchCmpInst = dyn_cast<ICmpInst>(BI->getCondition());
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assert(LatchCmpInst &&
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"Expecting the latch compare instruction to be a CmpInst");
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// Need to inverse the predicate when first successor is not the loop
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// header
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ICmpInst::Predicate Pred = (BI->getSuccessor(0) == L.getHeader())
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? LatchCmpInst->getPredicate()
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: LatchCmpInst->getInversePredicate();
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if (LatchCmpInst->getOperand(0) == &getFinalIVValue())
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Pred = ICmpInst::getSwappedPredicate(Pred);
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// Need to flip strictness of the predicate when the latch compare instruction
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// is not using StepInst
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if (LatchCmpInst->getOperand(0) == &getStepInst() ||
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LatchCmpInst->getOperand(1) == &getStepInst())
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return Pred;
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// Cannot flip strictness of NE and EQ
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if (Pred != ICmpInst::ICMP_NE && Pred != ICmpInst::ICMP_EQ)
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return ICmpInst::getFlippedStrictnessPredicate(Pred);
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Direction D = getDirection();
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if (D == Direction::Increasing)
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return ICmpInst::ICMP_SLT;
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if (D == Direction::Decreasing)
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return ICmpInst::ICMP_SGT;
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// If cannot determine the direction, then unable to find the canonical
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// predicate
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return ICmpInst::BAD_ICMP_PREDICATE;
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}
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Direction Loop::LoopBounds::getDirection() const {
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if (const SCEVAddRecExpr *StepAddRecExpr =
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dyn_cast<SCEVAddRecExpr>(SE.getSCEV(&getStepInst())))
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if (const SCEV *StepRecur = StepAddRecExpr->getStepRecurrence(SE)) {
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if (SE.isKnownPositive(StepRecur))
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return Direction::Increasing;
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if (SE.isKnownNegative(StepRecur))
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return Direction::Decreasing;
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}
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return Direction::Unknown;
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}
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Optional<Loop::LoopBounds> Loop::getBounds(ScalarEvolution &SE) const {
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if (PHINode *IndVar = getInductionVariable(SE))
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return LoopBounds::getBounds(*this, *IndVar, SE);
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return None;
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}
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PHINode *Loop::getInductionVariable(ScalarEvolution &SE) const {
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if (!isLoopSimplifyForm())
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return nullptr;
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BasicBlock *Header = getHeader();
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assert(Header && "Expected a valid loop header");
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ICmpInst *CmpInst = getLatchCmpInst(*this);
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if (!CmpInst)
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return nullptr;
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Instruction *LatchCmpOp0 = dyn_cast<Instruction>(CmpInst->getOperand(0));
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Instruction *LatchCmpOp1 = dyn_cast<Instruction>(CmpInst->getOperand(1));
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for (PHINode &IndVar : Header->phis()) {
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InductionDescriptor IndDesc;
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if (!InductionDescriptor::isInductionPHI(&IndVar, this, &SE, IndDesc))
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continue;
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Instruction *StepInst = IndDesc.getInductionBinOp();
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// case 1:
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// IndVar = phi[{InitialValue, preheader}, {StepInst, latch}]
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// StepInst = IndVar + step
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// cmp = StepInst < FinalValue
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if (StepInst == LatchCmpOp0 || StepInst == LatchCmpOp1)
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return &IndVar;
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// case 2:
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// IndVar = phi[{InitialValue, preheader}, {StepInst, latch}]
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// StepInst = IndVar + step
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// cmp = IndVar < FinalValue
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if (&IndVar == LatchCmpOp0 || &IndVar == LatchCmpOp1)
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return &IndVar;
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}
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return nullptr;
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}
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bool Loop::getInductionDescriptor(ScalarEvolution &SE,
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InductionDescriptor &IndDesc) const {
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if (PHINode *IndVar = getInductionVariable(SE))
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return InductionDescriptor::isInductionPHI(IndVar, this, &SE, IndDesc);
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return false;
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}
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bool Loop::isAuxiliaryInductionVariable(PHINode &AuxIndVar,
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ScalarEvolution &SE) const {
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// Located in the loop header
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BasicBlock *Header = getHeader();
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if (AuxIndVar.getParent() != Header)
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return false;
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// No uses outside of the loop
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for (User *U : AuxIndVar.users())
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if (const Instruction *I = dyn_cast<Instruction>(U))
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if (!contains(I))
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return false;
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InductionDescriptor IndDesc;
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if (!InductionDescriptor::isInductionPHI(&AuxIndVar, this, &SE, IndDesc))
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return false;
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// The step instruction opcode should be add or sub.
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if (IndDesc.getInductionOpcode() != Instruction::Add &&
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IndDesc.getInductionOpcode() != Instruction::Sub)
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return false;
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// Incremented by a loop invariant step for each loop iteration
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return SE.isLoopInvariant(IndDesc.getStep(), this);
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}
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BranchInst *Loop::getLoopGuardBranch() const {
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if (!isLoopSimplifyForm())
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return nullptr;
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BasicBlock *Preheader = getLoopPreheader();
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assert(Preheader && getLoopLatch() &&
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"Expecting a loop with valid preheader and latch");
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// Loop should be in rotate form.
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if (!isRotatedForm())
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return nullptr;
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// Disallow loops with more than one unique exit block, as we do not verify
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// that GuardOtherSucc post dominates all exit blocks.
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BasicBlock *ExitFromLatch = getUniqueExitBlock();
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if (!ExitFromLatch)
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return nullptr;
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BasicBlock *ExitFromLatchSucc = ExitFromLatch->getUniqueSuccessor();
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if (!ExitFromLatchSucc)
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return nullptr;
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BasicBlock *GuardBB = Preheader->getUniquePredecessor();
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if (!GuardBB)
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return nullptr;
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assert(GuardBB->getTerminator() && "Expecting valid guard terminator");
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BranchInst *GuardBI = dyn_cast<BranchInst>(GuardBB->getTerminator());
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if (!GuardBI || GuardBI->isUnconditional())
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return nullptr;
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BasicBlock *GuardOtherSucc = (GuardBI->getSuccessor(0) == Preheader)
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? GuardBI->getSuccessor(1)
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: GuardBI->getSuccessor(0);
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return (GuardOtherSucc == ExitFromLatchSucc) ? GuardBI : nullptr;
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}
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bool Loop::isCanonical(ScalarEvolution &SE) const {
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InductionDescriptor IndDesc;
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if (!getInductionDescriptor(SE, IndDesc))
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return false;
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ConstantInt *Init = dyn_cast_or_null<ConstantInt>(IndDesc.getStartValue());
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if (!Init || !Init->isZero())
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return false;
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if (IndDesc.getInductionOpcode() != Instruction::Add)
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return false;
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ConstantInt *Step = IndDesc.getConstIntStepValue();
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if (!Step || !Step->isOne())
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return false;
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return true;
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}
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// Check that 'BB' doesn't have any uses outside of the 'L'
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static bool isBlockInLCSSAForm(const Loop &L, const BasicBlock &BB,
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const DominatorTree &DT) {
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for (const Instruction &I : BB) {
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// Tokens can't be used in PHI nodes and live-out tokens prevent loop
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// optimizations, so for the purposes of considered LCSSA form, we
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// can ignore them.
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if (I.getType()->isTokenTy())
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continue;
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for (const Use &U : I.uses()) {
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const Instruction *UI = cast<Instruction>(U.getUser());
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const BasicBlock *UserBB = UI->getParent();
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// For practical purposes, we consider that the use in a PHI
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// occurs in the respective predecessor block. For more info,
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// see the `phi` doc in LangRef and the LCSSA doc.
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if (const PHINode *P = dyn_cast<PHINode>(UI))
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UserBB = P->getIncomingBlock(U);
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// Check the current block, as a fast-path, before checking whether
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// the use is anywhere in the loop. Most values are used in the same
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// block they are defined in. Also, blocks not reachable from the
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// entry are special; uses in them don't need to go through PHIs.
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if (UserBB != &BB && !L.contains(UserBB) &&
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DT.isReachableFromEntry(UserBB))
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return false;
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}
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}
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return true;
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}
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bool Loop::isLCSSAForm(const DominatorTree &DT) const {
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// For each block we check that it doesn't have any uses outside of this loop.
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return all_of(this->blocks(), [&](const BasicBlock *BB) {
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return isBlockInLCSSAForm(*this, *BB, DT);
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});
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}
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bool Loop::isRecursivelyLCSSAForm(const DominatorTree &DT,
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const LoopInfo &LI) const {
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// For each block we check that it doesn't have any uses outside of its
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// innermost loop. This process will transitively guarantee that the current
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// loop and all of the nested loops are in LCSSA form.
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return all_of(this->blocks(), [&](const BasicBlock *BB) {
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return isBlockInLCSSAForm(*LI.getLoopFor(BB), *BB, DT);
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});
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}
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bool Loop::isLoopSimplifyForm() const {
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// Normal-form loops have a preheader, a single backedge, and all of their
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// exits have all their predecessors inside the loop.
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return getLoopPreheader() && getLoopLatch() && hasDedicatedExits();
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}
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// Routines that reform the loop CFG and split edges often fail on indirectbr.
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bool Loop::isSafeToClone() const {
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// Return false if any loop blocks contain indirectbrs, or there are any calls
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// to noduplicate functions.
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// FIXME: it should be ok to clone CallBrInst's if we correctly update the
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// operand list to reflect the newly cloned labels.
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for (BasicBlock *BB : this->blocks()) {
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if (isa<IndirectBrInst>(BB->getTerminator()) ||
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isa<CallBrInst>(BB->getTerminator()))
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return false;
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|
|
for (Instruction &I : *BB)
|
|
if (auto *CB = dyn_cast<CallBase>(&I))
|
|
if (CB->cannotDuplicate())
|
|
return false;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
MDNode *Loop::getLoopID() const {
|
|
MDNode *LoopID = nullptr;
|
|
|
|
// Go through the latch blocks and check the terminator for the metadata.
|
|
SmallVector<BasicBlock *, 4> LatchesBlocks;
|
|
getLoopLatches(LatchesBlocks);
|
|
for (BasicBlock *BB : LatchesBlocks) {
|
|
Instruction *TI = BB->getTerminator();
|
|
MDNode *MD = TI->getMetadata(LLVMContext::MD_loop);
|
|
|
|
if (!MD)
|
|
return nullptr;
|
|
|
|
if (!LoopID)
|
|
LoopID = MD;
|
|
else if (MD != LoopID)
|
|
return nullptr;
|
|
}
|
|
if (!LoopID || LoopID->getNumOperands() == 0 ||
|
|
LoopID->getOperand(0) != LoopID)
|
|
return nullptr;
|
|
return LoopID;
|
|
}
|
|
|
|
void Loop::setLoopID(MDNode *LoopID) const {
|
|
assert((!LoopID || LoopID->getNumOperands() > 0) &&
|
|
"Loop ID needs at least one operand");
|
|
assert((!LoopID || LoopID->getOperand(0) == LoopID) &&
|
|
"Loop ID should refer to itself");
|
|
|
|
SmallVector<BasicBlock *, 4> LoopLatches;
|
|
getLoopLatches(LoopLatches);
|
|
for (BasicBlock *BB : LoopLatches)
|
|
BB->getTerminator()->setMetadata(LLVMContext::MD_loop, LoopID);
|
|
}
|
|
|
|
void Loop::setLoopAlreadyUnrolled() {
|
|
LLVMContext &Context = getHeader()->getContext();
|
|
|
|
MDNode *DisableUnrollMD =
|
|
MDNode::get(Context, MDString::get(Context, "llvm.loop.unroll.disable"));
|
|
MDNode *LoopID = getLoopID();
|
|
MDNode *NewLoopID = makePostTransformationMetadata(
|
|
Context, LoopID, {"llvm.loop.unroll."}, {DisableUnrollMD});
|
|
setLoopID(NewLoopID);
|
|
}
|
|
|
|
void Loop::setLoopMustProgress() {
|
|
LLVMContext &Context = getHeader()->getContext();
|
|
|
|
MDNode *MustProgress = findOptionMDForLoop(this, "llvm.loop.mustprogress");
|
|
|
|
if (MustProgress)
|
|
return;
|
|
|
|
MDNode *MustProgressMD =
|
|
MDNode::get(Context, MDString::get(Context, "llvm.loop.mustprogress"));
|
|
MDNode *LoopID = getLoopID();
|
|
MDNode *NewLoopID =
|
|
makePostTransformationMetadata(Context, LoopID, {}, {MustProgressMD});
|
|
setLoopID(NewLoopID);
|
|
}
|
|
|
|
bool Loop::isAnnotatedParallel() const {
|
|
MDNode *DesiredLoopIdMetadata = getLoopID();
|
|
|
|
if (!DesiredLoopIdMetadata)
|
|
return false;
|
|
|
|
MDNode *ParallelAccesses =
|
|
findOptionMDForLoop(this, "llvm.loop.parallel_accesses");
|
|
SmallPtrSet<MDNode *, 4>
|
|
ParallelAccessGroups; // For scalable 'contains' check.
|
|
if (ParallelAccesses) {
|
|
for (const MDOperand &MD : drop_begin(ParallelAccesses->operands(), 1)) {
|
|
MDNode *AccGroup = cast<MDNode>(MD.get());
|
|
assert(isValidAsAccessGroup(AccGroup) &&
|
|
"List item must be an access group");
|
|
ParallelAccessGroups.insert(AccGroup);
|
|
}
|
|
}
|
|
|
|
// The loop branch contains the parallel loop metadata. In order to ensure
|
|
// that any parallel-loop-unaware optimization pass hasn't added loop-carried
|
|
// dependencies (thus converted the loop back to a sequential loop), check
|
|
// that all the memory instructions in the loop belong to an access group that
|
|
// is parallel to this loop.
|
|
for (BasicBlock *BB : this->blocks()) {
|
|
for (Instruction &I : *BB) {
|
|
if (!I.mayReadOrWriteMemory())
|
|
continue;
|
|
|
|
if (MDNode *AccessGroup = I.getMetadata(LLVMContext::MD_access_group)) {
|
|
auto ContainsAccessGroup = [&ParallelAccessGroups](MDNode *AG) -> bool {
|
|
if (AG->getNumOperands() == 0) {
|
|
assert(isValidAsAccessGroup(AG) && "Item must be an access group");
|
|
return ParallelAccessGroups.count(AG);
|
|
}
|
|
|
|
for (const MDOperand &AccessListItem : AG->operands()) {
|
|
MDNode *AccGroup = cast<MDNode>(AccessListItem.get());
|
|
assert(isValidAsAccessGroup(AccGroup) &&
|
|
"List item must be an access group");
|
|
if (ParallelAccessGroups.count(AccGroup))
|
|
return true;
|
|
}
|
|
return false;
|
|
};
|
|
|
|
if (ContainsAccessGroup(AccessGroup))
|
|
continue;
|
|
}
|
|
|
|
// The memory instruction can refer to the loop identifier metadata
|
|
// directly or indirectly through another list metadata (in case of
|
|
// nested parallel loops). The loop identifier metadata refers to
|
|
// itself so we can check both cases with the same routine.
|
|
MDNode *LoopIdMD =
|
|
I.getMetadata(LLVMContext::MD_mem_parallel_loop_access);
|
|
|
|
if (!LoopIdMD)
|
|
return false;
|
|
|
|
bool LoopIdMDFound = false;
|
|
for (const MDOperand &MDOp : LoopIdMD->operands()) {
|
|
if (MDOp == DesiredLoopIdMetadata) {
|
|
LoopIdMDFound = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (!LoopIdMDFound)
|
|
return false;
|
|
}
|
|
}
|
|
return true;
|
|
}
|
|
|
|
DebugLoc Loop::getStartLoc() const { return getLocRange().getStart(); }
|
|
|
|
Loop::LocRange Loop::getLocRange() const {
|
|
// If we have a debug location in the loop ID, then use it.
|
|
if (MDNode *LoopID = getLoopID()) {
|
|
DebugLoc Start;
|
|
// We use the first DebugLoc in the header as the start location of the loop
|
|
// and if there is a second DebugLoc in the header we use it as end location
|
|
// of the loop.
|
|
for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
|
|
if (DILocation *L = dyn_cast<DILocation>(LoopID->getOperand(i))) {
|
|
if (!Start)
|
|
Start = DebugLoc(L);
|
|
else
|
|
return LocRange(Start, DebugLoc(L));
|
|
}
|
|
}
|
|
|
|
if (Start)
|
|
return LocRange(Start);
|
|
}
|
|
|
|
// Try the pre-header first.
|
|
if (BasicBlock *PHeadBB = getLoopPreheader())
|
|
if (DebugLoc DL = PHeadBB->getTerminator()->getDebugLoc())
|
|
return LocRange(DL);
|
|
|
|
// If we have no pre-header or there are no instructions with debug
|
|
// info in it, try the header.
|
|
if (BasicBlock *HeadBB = getHeader())
|
|
return LocRange(HeadBB->getTerminator()->getDebugLoc());
|
|
|
|
return LocRange();
|
|
}
|
|
|
|
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
|
|
LLVM_DUMP_METHOD void Loop::dump() const { print(dbgs()); }
|
|
|
|
LLVM_DUMP_METHOD void Loop::dumpVerbose() const {
|
|
print(dbgs(), /*Depth=*/0, /*Verbose=*/true);
|
|
}
|
|
#endif
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// UnloopUpdater implementation
|
|
//
|
|
|
|
namespace {
|
|
/// Find the new parent loop for all blocks within the "unloop" whose last
|
|
/// backedges has just been removed.
|
|
class UnloopUpdater {
|
|
Loop &Unloop;
|
|
LoopInfo *LI;
|
|
|
|
LoopBlocksDFS DFS;
|
|
|
|
// Map unloop's immediate subloops to their nearest reachable parents. Nested
|
|
// loops within these subloops will not change parents. However, an immediate
|
|
// subloop's new parent will be the nearest loop reachable from either its own
|
|
// exits *or* any of its nested loop's exits.
|
|
DenseMap<Loop *, Loop *> SubloopParents;
|
|
|
|
// Flag the presence of an irreducible backedge whose destination is a block
|
|
// directly contained by the original unloop.
|
|
bool FoundIB;
|
|
|
|
public:
|
|
UnloopUpdater(Loop *UL, LoopInfo *LInfo)
|
|
: Unloop(*UL), LI(LInfo), DFS(UL), FoundIB(false) {}
|
|
|
|
void updateBlockParents();
|
|
|
|
void removeBlocksFromAncestors();
|
|
|
|
void updateSubloopParents();
|
|
|
|
protected:
|
|
Loop *getNearestLoop(BasicBlock *BB, Loop *BBLoop);
|
|
};
|
|
} // end anonymous namespace
|
|
|
|
/// Update the parent loop for all blocks that are directly contained within the
|
|
/// original "unloop".
|
|
void UnloopUpdater::updateBlockParents() {
|
|
if (Unloop.getNumBlocks()) {
|
|
// Perform a post order CFG traversal of all blocks within this loop,
|
|
// propagating the nearest loop from successors to predecessors.
|
|
LoopBlocksTraversal Traversal(DFS, LI);
|
|
for (BasicBlock *POI : Traversal) {
|
|
|
|
Loop *L = LI->getLoopFor(POI);
|
|
Loop *NL = getNearestLoop(POI, L);
|
|
|
|
if (NL != L) {
|
|
// For reducible loops, NL is now an ancestor of Unloop.
|
|
assert((NL != &Unloop && (!NL || NL->contains(&Unloop))) &&
|
|
"uninitialized successor");
|
|
LI->changeLoopFor(POI, NL);
|
|
} else {
|
|
// Or the current block is part of a subloop, in which case its parent
|
|
// is unchanged.
|
|
assert((FoundIB || Unloop.contains(L)) && "uninitialized successor");
|
|
}
|
|
}
|
|
}
|
|
// Each irreducible loop within the unloop induces a round of iteration using
|
|
// the DFS result cached by Traversal.
|
|
bool Changed = FoundIB;
|
|
for (unsigned NIters = 0; Changed; ++NIters) {
|
|
assert(NIters < Unloop.getNumBlocks() && "runaway iterative algorithm");
|
|
|
|
// Iterate over the postorder list of blocks, propagating the nearest loop
|
|
// from successors to predecessors as before.
|
|
Changed = false;
|
|
for (LoopBlocksDFS::POIterator POI = DFS.beginPostorder(),
|
|
POE = DFS.endPostorder();
|
|
POI != POE; ++POI) {
|
|
|
|
Loop *L = LI->getLoopFor(*POI);
|
|
Loop *NL = getNearestLoop(*POI, L);
|
|
if (NL != L) {
|
|
assert(NL != &Unloop && (!NL || NL->contains(&Unloop)) &&
|
|
"uninitialized successor");
|
|
LI->changeLoopFor(*POI, NL);
|
|
Changed = true;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Remove unloop's blocks from all ancestors below their new parents.
|
|
void UnloopUpdater::removeBlocksFromAncestors() {
|
|
// Remove all unloop's blocks (including those in nested subloops) from
|
|
// ancestors below the new parent loop.
|
|
for (Loop::block_iterator BI = Unloop.block_begin(), BE = Unloop.block_end();
|
|
BI != BE; ++BI) {
|
|
Loop *OuterParent = LI->getLoopFor(*BI);
|
|
if (Unloop.contains(OuterParent)) {
|
|
while (OuterParent->getParentLoop() != &Unloop)
|
|
OuterParent = OuterParent->getParentLoop();
|
|
OuterParent = SubloopParents[OuterParent];
|
|
}
|
|
// Remove blocks from former Ancestors except Unloop itself which will be
|
|
// deleted.
|
|
for (Loop *OldParent = Unloop.getParentLoop(); OldParent != OuterParent;
|
|
OldParent = OldParent->getParentLoop()) {
|
|
assert(OldParent && "new loop is not an ancestor of the original");
|
|
OldParent->removeBlockFromLoop(*BI);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Update the parent loop for all subloops directly nested within unloop.
|
|
void UnloopUpdater::updateSubloopParents() {
|
|
while (!Unloop.isInnermost()) {
|
|
Loop *Subloop = *std::prev(Unloop.end());
|
|
Unloop.removeChildLoop(std::prev(Unloop.end()));
|
|
|
|
assert(SubloopParents.count(Subloop) && "DFS failed to visit subloop");
|
|
if (Loop *Parent = SubloopParents[Subloop])
|
|
Parent->addChildLoop(Subloop);
|
|
else
|
|
LI->addTopLevelLoop(Subloop);
|
|
}
|
|
}
|
|
|
|
/// Return the nearest parent loop among this block's successors. If a successor
|
|
/// is a subloop header, consider its parent to be the nearest parent of the
|
|
/// subloop's exits.
|
|
///
|
|
/// For subloop blocks, simply update SubloopParents and return NULL.
|
|
Loop *UnloopUpdater::getNearestLoop(BasicBlock *BB, Loop *BBLoop) {
|
|
|
|
// Initially for blocks directly contained by Unloop, NearLoop == Unloop and
|
|
// is considered uninitialized.
|
|
Loop *NearLoop = BBLoop;
|
|
|
|
Loop *Subloop = nullptr;
|
|
if (NearLoop != &Unloop && Unloop.contains(NearLoop)) {
|
|
Subloop = NearLoop;
|
|
// Find the subloop ancestor that is directly contained within Unloop.
|
|
while (Subloop->getParentLoop() != &Unloop) {
|
|
Subloop = Subloop->getParentLoop();
|
|
assert(Subloop && "subloop is not an ancestor of the original loop");
|
|
}
|
|
// Get the current nearest parent of the Subloop exits, initially Unloop.
|
|
NearLoop = SubloopParents.insert({Subloop, &Unloop}).first->second;
|
|
}
|
|
|
|
succ_iterator I = succ_begin(BB), E = succ_end(BB);
|
|
if (I == E) {
|
|
assert(!Subloop && "subloop blocks must have a successor");
|
|
NearLoop = nullptr; // unloop blocks may now exit the function.
|
|
}
|
|
for (; I != E; ++I) {
|
|
if (*I == BB)
|
|
continue; // self loops are uninteresting
|
|
|
|
Loop *L = LI->getLoopFor(*I);
|
|
if (L == &Unloop) {
|
|
// This successor has not been processed. This path must lead to an
|
|
// irreducible backedge.
|
|
assert((FoundIB || !DFS.hasPostorder(*I)) && "should have seen IB");
|
|
FoundIB = true;
|
|
}
|
|
if (L != &Unloop && Unloop.contains(L)) {
|
|
// Successor is in a subloop.
|
|
if (Subloop)
|
|
continue; // Branching within subloops. Ignore it.
|
|
|
|
// BB branches from the original into a subloop header.
|
|
assert(L->getParentLoop() == &Unloop && "cannot skip into nested loops");
|
|
|
|
// Get the current nearest parent of the Subloop's exits.
|
|
L = SubloopParents[L];
|
|
// L could be Unloop if the only exit was an irreducible backedge.
|
|
}
|
|
if (L == &Unloop) {
|
|
continue;
|
|
}
|
|
// Handle critical edges from Unloop into a sibling loop.
|
|
if (L && !L->contains(&Unloop)) {
|
|
L = L->getParentLoop();
|
|
}
|
|
// Remember the nearest parent loop among successors or subloop exits.
|
|
if (NearLoop == &Unloop || !NearLoop || NearLoop->contains(L))
|
|
NearLoop = L;
|
|
}
|
|
if (Subloop) {
|
|
SubloopParents[Subloop] = NearLoop;
|
|
return BBLoop;
|
|
}
|
|
return NearLoop;
|
|
}
|
|
|
|
LoopInfo::LoopInfo(const DomTreeBase<BasicBlock> &DomTree) { analyze(DomTree); }
|
|
|
|
bool LoopInfo::invalidate(Function &F, const PreservedAnalyses &PA,
|
|
FunctionAnalysisManager::Invalidator &) {
|
|
// Check whether the analysis, all analyses on functions, or the function's
|
|
// CFG have been preserved.
|
|
auto PAC = PA.getChecker<LoopAnalysis>();
|
|
return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>() ||
|
|
PAC.preservedSet<CFGAnalyses>());
|
|
}
|
|
|
|
void LoopInfo::erase(Loop *Unloop) {
|
|
assert(!Unloop->isInvalid() && "Loop has already been erased!");
|
|
|
|
auto InvalidateOnExit = make_scope_exit([&]() { destroy(Unloop); });
|
|
|
|
// First handle the special case of no parent loop to simplify the algorithm.
|
|
if (Unloop->isOutermost()) {
|
|
// Since BBLoop had no parent, Unloop blocks are no longer in a loop.
|
|
for (Loop::block_iterator I = Unloop->block_begin(),
|
|
E = Unloop->block_end();
|
|
I != E; ++I) {
|
|
|
|
// Don't reparent blocks in subloops.
|
|
if (getLoopFor(*I) != Unloop)
|
|
continue;
|
|
|
|
// Blocks no longer have a parent but are still referenced by Unloop until
|
|
// the Unloop object is deleted.
|
|
changeLoopFor(*I, nullptr);
|
|
}
|
|
|
|
// Remove the loop from the top-level LoopInfo object.
|
|
for (iterator I = begin();; ++I) {
|
|
assert(I != end() && "Couldn't find loop");
|
|
if (*I == Unloop) {
|
|
removeLoop(I);
|
|
break;
|
|
}
|
|
}
|
|
|
|
// Move all of the subloops to the top-level.
|
|
while (!Unloop->isInnermost())
|
|
addTopLevelLoop(Unloop->removeChildLoop(std::prev(Unloop->end())));
|
|
|
|
return;
|
|
}
|
|
|
|
// Update the parent loop for all blocks within the loop. Blocks within
|
|
// subloops will not change parents.
|
|
UnloopUpdater Updater(Unloop, this);
|
|
Updater.updateBlockParents();
|
|
|
|
// Remove blocks from former ancestor loops.
|
|
Updater.removeBlocksFromAncestors();
|
|
|
|
// Add direct subloops as children in their new parent loop.
|
|
Updater.updateSubloopParents();
|
|
|
|
// Remove unloop from its parent loop.
|
|
Loop *ParentLoop = Unloop->getParentLoop();
|
|
for (Loop::iterator I = ParentLoop->begin();; ++I) {
|
|
assert(I != ParentLoop->end() && "Couldn't find loop");
|
|
if (*I == Unloop) {
|
|
ParentLoop->removeChildLoop(I);
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
AnalysisKey LoopAnalysis::Key;
|
|
|
|
LoopInfo LoopAnalysis::run(Function &F, FunctionAnalysisManager &AM) {
|
|
// FIXME: Currently we create a LoopInfo from scratch for every function.
|
|
// This may prove to be too wasteful due to deallocating and re-allocating
|
|
// memory each time for the underlying map and vector datastructures. At some
|
|
// point it may prove worthwhile to use a freelist and recycle LoopInfo
|
|
// objects. I don't want to add that kind of complexity until the scope of
|
|
// the problem is better understood.
|
|
LoopInfo LI;
|
|
LI.analyze(AM.getResult<DominatorTreeAnalysis>(F));
|
|
return LI;
|
|
}
|
|
|
|
PreservedAnalyses LoopPrinterPass::run(Function &F,
|
|
FunctionAnalysisManager &AM) {
|
|
AM.getResult<LoopAnalysis>(F).print(OS);
|
|
return PreservedAnalyses::all();
|
|
}
|
|
|
|
void llvm::printLoop(Loop &L, raw_ostream &OS, const std::string &Banner) {
|
|
|
|
if (forcePrintModuleIR()) {
|
|
// handling -print-module-scope
|
|
OS << Banner << " (loop: ";
|
|
L.getHeader()->printAsOperand(OS, false);
|
|
OS << ")\n";
|
|
|
|
// printing whole module
|
|
OS << *L.getHeader()->getModule();
|
|
return;
|
|
}
|
|
|
|
OS << Banner;
|
|
|
|
auto *PreHeader = L.getLoopPreheader();
|
|
if (PreHeader) {
|
|
OS << "\n; Preheader:";
|
|
PreHeader->print(OS);
|
|
OS << "\n; Loop:";
|
|
}
|
|
|
|
for (auto *Block : L.blocks())
|
|
if (Block)
|
|
Block->print(OS);
|
|
else
|
|
OS << "Printing <null> block";
|
|
|
|
SmallVector<BasicBlock *, 8> ExitBlocks;
|
|
L.getExitBlocks(ExitBlocks);
|
|
if (!ExitBlocks.empty()) {
|
|
OS << "\n; Exit blocks";
|
|
for (auto *Block : ExitBlocks)
|
|
if (Block)
|
|
Block->print(OS);
|
|
else
|
|
OS << "Printing <null> block";
|
|
}
|
|
}
|
|
|
|
MDNode *llvm::findOptionMDForLoopID(MDNode *LoopID, StringRef Name) {
|
|
// No loop metadata node, no loop properties.
|
|
if (!LoopID)
|
|
return nullptr;
|
|
|
|
// First operand should refer to the metadata node itself, for legacy reasons.
|
|
assert(LoopID->getNumOperands() > 0 && "requires at least one operand");
|
|
assert(LoopID->getOperand(0) == LoopID && "invalid loop id");
|
|
|
|
// Iterate over the metdata node operands and look for MDString metadata.
|
|
for (unsigned i = 1, e = LoopID->getNumOperands(); i < e; ++i) {
|
|
MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
|
|
if (!MD || MD->getNumOperands() < 1)
|
|
continue;
|
|
MDString *S = dyn_cast<MDString>(MD->getOperand(0));
|
|
if (!S)
|
|
continue;
|
|
// Return the operand node if MDString holds expected metadata.
|
|
if (Name.equals(S->getString()))
|
|
return MD;
|
|
}
|
|
|
|
// Loop property not found.
|
|
return nullptr;
|
|
}
|
|
|
|
MDNode *llvm::findOptionMDForLoop(const Loop *TheLoop, StringRef Name) {
|
|
return findOptionMDForLoopID(TheLoop->getLoopID(), Name);
|
|
}
|
|
|
|
bool llvm::isValidAsAccessGroup(MDNode *Node) {
|
|
return Node->getNumOperands() == 0 && Node->isDistinct();
|
|
}
|
|
|
|
MDNode *llvm::makePostTransformationMetadata(LLVMContext &Context,
|
|
MDNode *OrigLoopID,
|
|
ArrayRef<StringRef> RemovePrefixes,
|
|
ArrayRef<MDNode *> AddAttrs) {
|
|
// First remove any existing loop metadata related to this transformation.
|
|
SmallVector<Metadata *, 4> MDs;
|
|
|
|
// Reserve first location for self reference to the LoopID metadata node.
|
|
MDs.push_back(nullptr);
|
|
|
|
// Remove metadata for the transformation that has been applied or that became
|
|
// outdated.
|
|
if (OrigLoopID) {
|
|
for (unsigned i = 1, ie = OrigLoopID->getNumOperands(); i < ie; ++i) {
|
|
bool IsVectorMetadata = false;
|
|
Metadata *Op = OrigLoopID->getOperand(i);
|
|
if (MDNode *MD = dyn_cast<MDNode>(Op)) {
|
|
const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
|
|
if (S)
|
|
IsVectorMetadata =
|
|
llvm::any_of(RemovePrefixes, [S](StringRef Prefix) -> bool {
|
|
return S->getString().startswith(Prefix);
|
|
});
|
|
}
|
|
if (!IsVectorMetadata)
|
|
MDs.push_back(Op);
|
|
}
|
|
}
|
|
|
|
// Add metadata to avoid reapplying a transformation, such as
|
|
// llvm.loop.unroll.disable and llvm.loop.isvectorized.
|
|
MDs.append(AddAttrs.begin(), AddAttrs.end());
|
|
|
|
MDNode *NewLoopID = MDNode::getDistinct(Context, MDs);
|
|
// Replace the temporary node with a self-reference.
|
|
NewLoopID->replaceOperandWith(0, NewLoopID);
|
|
return NewLoopID;
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// LoopInfo implementation
|
|
//
|
|
|
|
LoopInfoWrapperPass::LoopInfoWrapperPass() : FunctionPass(ID) {
|
|
initializeLoopInfoWrapperPassPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
char LoopInfoWrapperPass::ID = 0;
|
|
INITIALIZE_PASS_BEGIN(LoopInfoWrapperPass, "loops", "Natural Loop Information",
|
|
true, true)
|
|
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
|
|
INITIALIZE_PASS_END(LoopInfoWrapperPass, "loops", "Natural Loop Information",
|
|
true, true)
|
|
|
|
bool LoopInfoWrapperPass::runOnFunction(Function &) {
|
|
releaseMemory();
|
|
LI.analyze(getAnalysis<DominatorTreeWrapperPass>().getDomTree());
|
|
return false;
|
|
}
|
|
|
|
void LoopInfoWrapperPass::verifyAnalysis() const {
|
|
// LoopInfoWrapperPass is a FunctionPass, but verifying every loop in the
|
|
// function each time verifyAnalysis is called is very expensive. The
|
|
// -verify-loop-info option can enable this. In order to perform some
|
|
// checking by default, LoopPass has been taught to call verifyLoop manually
|
|
// during loop pass sequences.
|
|
if (VerifyLoopInfo) {
|
|
auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
|
|
LI.verify(DT);
|
|
}
|
|
}
|
|
|
|
void LoopInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
|
|
AU.setPreservesAll();
|
|
AU.addRequiredTransitive<DominatorTreeWrapperPass>();
|
|
}
|
|
|
|
void LoopInfoWrapperPass::print(raw_ostream &OS, const Module *) const {
|
|
LI.print(OS);
|
|
}
|
|
|
|
PreservedAnalyses LoopVerifierPass::run(Function &F,
|
|
FunctionAnalysisManager &AM) {
|
|
LoopInfo &LI = AM.getResult<LoopAnalysis>(F);
|
|
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
|
|
LI.verify(DT);
|
|
return PreservedAnalyses::all();
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
// LoopBlocksDFS implementation
|
|
//
|
|
|
|
/// Traverse the loop blocks and store the DFS result.
|
|
/// Useful for clients that just want the final DFS result and don't need to
|
|
/// visit blocks during the initial traversal.
|
|
void LoopBlocksDFS::perform(LoopInfo *LI) {
|
|
LoopBlocksTraversal Traversal(*this, LI);
|
|
for (LoopBlocksTraversal::POTIterator POI = Traversal.begin(),
|
|
POE = Traversal.end();
|
|
POI != POE; ++POI)
|
|
;
|
|
}
|