[llvm] r328766 - [LoopRotate] Restructuring LoopRotation.cpp to create Loop Rotation Pass with Loop Rotation Utility Interface
David Green via llvm-commits
llvm-commits at lists.llvm.org
Thu Mar 29 01:48:15 PDT 2018
Author: dmgreen
Date: Thu Mar 29 01:48:15 2018
New Revision: 328766
URL: http://llvm.org/viewvc/llvm-project?rev=328766&view=rev
Log:
[LoopRotate] Restructuring LoopRotation.cpp to create Loop Rotation Pass with Loop Rotation Utility Interface
The existing LoopRotation.cpp is implemented as one of loop passes instead of
being a utility. The user cannot easily perform the loop rotation selectively
(or on demand) under different optimization level. For example, the loop
rotation is needed as part of the logic to convert a loop into a loop with
bottom test for a transformation. If the loop rotation is simply added as a
loop pass before the transformation, the pass is skipped if it is compiled at
–O0 or if it is explicitly disabled by the user, causing the compiler to
generate incorrect code. Furthermore, as a loop pass it will rotate all loops
instead of just the relevant loops.
We provide a utility interface for the loop rotation so that the loop rotation
can be called on demand. The changeset is as follows:
- Create a new file lib/Transforms/Utils/LoopRotationUtils.cpp and move the main
implementation of class LoopRotate into this file.
- Create a new file llvm/include/Transform/Utils/LoopRotationUtils.h with the
interface LoopRotation(...).
- Original LoopRotation.cpp is changed to use the utility function LoopRotation
in LoopRotationUtils.cpp. This is done in the same way community did for
mem-to-reg implementation.
Patch by Jin Lin!
Differential Revision: https://reviews.llvm.org/D44595
Added:
llvm/trunk/include/llvm/Transforms/Utils/LoopRotationUtils.h
llvm/trunk/lib/Transforms/Utils/LoopRotationUtils.cpp
Modified:
llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp
llvm/trunk/lib/Transforms/Utils/CMakeLists.txt
Added: llvm/trunk/include/llvm/Transforms/Utils/LoopRotationUtils.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Utils/LoopRotationUtils.h?rev=328766&view=auto
==============================================================================
--- llvm/trunk/include/llvm/Transforms/Utils/LoopRotationUtils.h (added)
+++ llvm/trunk/include/llvm/Transforms/Utils/LoopRotationUtils.h Thu Mar 29 01:48:15 2018
@@ -0,0 +1,35 @@
+//===- LoopRotationUtils.h - Utilities to perform loop rotation -*- C++ -*-===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides utilities to convert a loop into a loop with bottom test.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_LOOPROTATIONUTILS_H
+#define LLVM_TRANSFORMS_UTILS_LOOPROTATIONUTILS_H
+
+namespace llvm {
+
+class AssumptionCache;
+class DominatorTree;
+class Loop;
+class LoopInfo;
+class ScalarEvolution;
+struct SimplifyQuery;
+class TargetTransformInfo;
+
+/// \brief Convert a loop into a loop with bottom test.
+bool LoopRotation(Loop *L, unsigned MaxHeaderSize, LoopInfo *LI,
+ const TargetTransformInfo *TTI, AssumptionCache *AC,
+ DominatorTree *DT, ScalarEvolution *SE,
+ const SimplifyQuery &SQ);
+
+} // namespace llvm
+
+#endif
Modified: llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp?rev=328766&r1=328765&r2=328766&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp Thu Mar 29 01:48:15 2018
@@ -13,33 +13,15 @@
#include "llvm/Transforms/Scalar/LoopRotation.h"
#include "llvm/ADT/Statistic.h"
-#include "llvm/Analysis/AliasAnalysis.h"
-#include "llvm/Analysis/AssumptionCache.h"
-#include "llvm/Analysis/BasicAliasAnalysis.h"
-#include "llvm/Analysis/CodeMetrics.h"
-#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolution.h"
-#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
#include "llvm/Analysis/TargetTransformInfo.h"
-#include "llvm/Analysis/Utils/Local.h"
-#include "llvm/Analysis/ValueTracking.h"
-#include "llvm/IR/CFG.h"
-#include "llvm/IR/DebugInfoMetadata.h"
-#include "llvm/IR/Dominators.h"
-#include "llvm/IR/Function.h"
-#include "llvm/IR/IntrinsicInst.h"
-#include "llvm/IR/Module.h"
-#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
-#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Scalar/LoopPassManager.h"
-#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/LoopRotationUtils.h"
#include "llvm/Transforms/Utils/LoopUtils.h"
-#include "llvm/Transforms/Utils/SSAUpdater.h"
-#include "llvm/Transforms/Utils/ValueMapper.h"
using namespace llvm;
#define DEBUG_TYPE "loop-rotate"
@@ -48,563 +30,6 @@ static cl::opt<unsigned> DefaultRotation
"rotation-max-header-size", cl::init(16), cl::Hidden,
cl::desc("The default maximum header size for automatic loop rotation"));
-STATISTIC(NumRotated, "Number of loops rotated");
-
-namespace {
-/// A simple loop rotation transformation.
-class LoopRotate {
- const unsigned MaxHeaderSize;
- LoopInfo *LI;
- const TargetTransformInfo *TTI;
- AssumptionCache *AC;
- DominatorTree *DT;
- ScalarEvolution *SE;
- const SimplifyQuery &SQ;
-
-public:
- LoopRotate(unsigned MaxHeaderSize, LoopInfo *LI,
- const TargetTransformInfo *TTI, AssumptionCache *AC,
- DominatorTree *DT, ScalarEvolution *SE, const SimplifyQuery &SQ)
- : MaxHeaderSize(MaxHeaderSize), LI(LI), TTI(TTI), AC(AC), DT(DT), SE(SE),
- SQ(SQ) {}
- bool processLoop(Loop *L);
-
-private:
- bool rotateLoop(Loop *L, bool SimplifiedLatch);
- bool simplifyLoopLatch(Loop *L);
-};
-} // end anonymous namespace
-
-/// RewriteUsesOfClonedInstructions - We just cloned the instructions from the
-/// old header into the preheader. If there were uses of the values produced by
-/// these instruction that were outside of the loop, we have to insert PHI nodes
-/// to merge the two values. Do this now.
-static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
- BasicBlock *OrigPreheader,
- ValueToValueMapTy &ValueMap,
- SmallVectorImpl<PHINode*> *InsertedPHIs) {
- // Remove PHI node entries that are no longer live.
- BasicBlock::iterator I, E = OrigHeader->end();
- for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I)
- PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreheader));
-
- // Now fix up users of the instructions in OrigHeader, inserting PHI nodes
- // as necessary.
- SSAUpdater SSA(InsertedPHIs);
- for (I = OrigHeader->begin(); I != E; ++I) {
- Value *OrigHeaderVal = &*I;
-
- // If there are no uses of the value (e.g. because it returns void), there
- // is nothing to rewrite.
- if (OrigHeaderVal->use_empty())
- continue;
-
- Value *OrigPreHeaderVal = ValueMap.lookup(OrigHeaderVal);
-
- // The value now exits in two versions: the initial value in the preheader
- // and the loop "next" value in the original header.
- SSA.Initialize(OrigHeaderVal->getType(), OrigHeaderVal->getName());
- SSA.AddAvailableValue(OrigHeader, OrigHeaderVal);
- SSA.AddAvailableValue(OrigPreheader, OrigPreHeaderVal);
-
- // Visit each use of the OrigHeader instruction.
- for (Value::use_iterator UI = OrigHeaderVal->use_begin(),
- UE = OrigHeaderVal->use_end();
- UI != UE;) {
- // Grab the use before incrementing the iterator.
- Use &U = *UI;
-
- // Increment the iterator before removing the use from the list.
- ++UI;
-
- // SSAUpdater can't handle a non-PHI use in the same block as an
- // earlier def. We can easily handle those cases manually.
- Instruction *UserInst = cast<Instruction>(U.getUser());
- if (!isa<PHINode>(UserInst)) {
- BasicBlock *UserBB = UserInst->getParent();
-
- // The original users in the OrigHeader are already using the
- // original definitions.
- if (UserBB == OrigHeader)
- continue;
-
- // Users in the OrigPreHeader need to use the value to which the
- // original definitions are mapped.
- if (UserBB == OrigPreheader) {
- U = OrigPreHeaderVal;
- continue;
- }
- }
-
- // Anything else can be handled by SSAUpdater.
- SSA.RewriteUse(U);
- }
-
- // Replace MetadataAsValue(ValueAsMetadata(OrigHeaderVal)) uses in debug
- // intrinsics.
- SmallVector<DbgValueInst *, 1> DbgValues;
- llvm::findDbgValues(DbgValues, OrigHeaderVal);
- for (auto &DbgValue : DbgValues) {
- // The original users in the OrigHeader are already using the original
- // definitions.
- BasicBlock *UserBB = DbgValue->getParent();
- if (UserBB == OrigHeader)
- continue;
-
- // Users in the OrigPreHeader need to use the value to which the
- // original definitions are mapped and anything else can be handled by
- // the SSAUpdater. To avoid adding PHINodes, check if the value is
- // available in UserBB, if not substitute undef.
- Value *NewVal;
- if (UserBB == OrigPreheader)
- NewVal = OrigPreHeaderVal;
- else if (SSA.HasValueForBlock(UserBB))
- NewVal = SSA.GetValueInMiddleOfBlock(UserBB);
- else
- NewVal = UndefValue::get(OrigHeaderVal->getType());
- DbgValue->setOperand(0,
- MetadataAsValue::get(OrigHeaderVal->getContext(),
- ValueAsMetadata::get(NewVal)));
- }
- }
-}
-
-/// Rotate loop LP. Return true if the loop is rotated.
-///
-/// \param SimplifiedLatch is true if the latch was just folded into the final
-/// loop exit. In this case we may want to rotate even though the new latch is
-/// now an exiting branch. This rotation would have happened had the latch not
-/// been simplified. However, if SimplifiedLatch is false, then we avoid
-/// rotating loops in which the latch exits to avoid excessive or endless
-/// rotation. LoopRotate should be repeatable and converge to a canonical
-/// form. This property is satisfied because simplifying the loop latch can only
-/// happen once across multiple invocations of the LoopRotate pass.
-bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
- // If the loop has only one block then there is not much to rotate.
- if (L->getBlocks().size() == 1)
- return false;
-
- BasicBlock *OrigHeader = L->getHeader();
- BasicBlock *OrigLatch = L->getLoopLatch();
-
- BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
- if (!BI || BI->isUnconditional())
- return false;
-
- // If the loop header is not one of the loop exiting blocks then
- // either this loop is already rotated or it is not
- // suitable for loop rotation transformations.
- if (!L->isLoopExiting(OrigHeader))
- return false;
-
- // If the loop latch already contains a branch that leaves the loop then the
- // loop is already rotated.
- if (!OrigLatch)
- return false;
-
- // Rotate if either the loop latch does *not* exit the loop, or if the loop
- // latch was just simplified.
- if (L->isLoopExiting(OrigLatch) && !SimplifiedLatch)
- return false;
-
- // Check size of original header and reject loop if it is very big or we can't
- // duplicate blocks inside it.
- {
- SmallPtrSet<const Value *, 32> EphValues;
- CodeMetrics::collectEphemeralValues(L, AC, EphValues);
-
- CodeMetrics Metrics;
- Metrics.analyzeBasicBlock(OrigHeader, *TTI, EphValues);
- if (Metrics.notDuplicatable) {
- DEBUG(dbgs() << "LoopRotation: NOT rotating - contains non-duplicatable"
- << " instructions: ";
- L->dump());
- return false;
- }
- if (Metrics.convergent) {
- DEBUG(dbgs() << "LoopRotation: NOT rotating - contains convergent "
- "instructions: ";
- L->dump());
- return false;
- }
- if (Metrics.NumInsts > MaxHeaderSize)
- return false;
- }
-
- // Now, this loop is suitable for rotation.
- BasicBlock *OrigPreheader = L->getLoopPreheader();
-
- // If the loop could not be converted to canonical form, it must have an
- // indirectbr in it, just give up.
- if (!OrigPreheader || !L->hasDedicatedExits())
- return false;
-
- // Anything ScalarEvolution may know about this loop or the PHI nodes
- // in its header will soon be invalidated.
- if (SE)
- SE->forgetLoop(L);
-
- DEBUG(dbgs() << "LoopRotation: rotating "; L->dump());
-
- // Find new Loop header. NewHeader is a Header's one and only successor
- // that is inside loop. Header's other successor is outside the
- // loop. Otherwise loop is not suitable for rotation.
- BasicBlock *Exit = BI->getSuccessor(0);
- BasicBlock *NewHeader = BI->getSuccessor(1);
- if (L->contains(Exit))
- std::swap(Exit, NewHeader);
- assert(NewHeader && "Unable to determine new loop header");
- assert(L->contains(NewHeader) && !L->contains(Exit) &&
- "Unable to determine loop header and exit blocks");
-
- // This code assumes that the new header has exactly one predecessor.
- // Remove any single-entry PHI nodes in it.
- assert(NewHeader->getSinglePredecessor() &&
- "New header doesn't have one pred!");
- FoldSingleEntryPHINodes(NewHeader);
-
- // Begin by walking OrigHeader and populating ValueMap with an entry for
- // each Instruction.
- BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
- ValueToValueMapTy ValueMap;
-
- // For PHI nodes, the value available in OldPreHeader is just the
- // incoming value from OldPreHeader.
- for (; PHINode *PN = dyn_cast<PHINode>(I); ++I)
- ValueMap[PN] = PN->getIncomingValueForBlock(OrigPreheader);
-
- // For the rest of the instructions, either hoist to the OrigPreheader if
- // possible or create a clone in the OldPreHeader if not.
- TerminatorInst *LoopEntryBranch = OrigPreheader->getTerminator();
-
- // Record all debug intrinsics preceding LoopEntryBranch to avoid duplication.
- using DbgIntrinsicHash =
- std::pair<std::pair<Value *, DILocalVariable *>, DIExpression *>;
- auto makeHash = [](DbgInfoIntrinsic *D) -> DbgIntrinsicHash {
- return {{D->getVariableLocation(), D->getVariable()}, D->getExpression()};
- };
- SmallDenseSet<DbgIntrinsicHash, 8> DbgIntrinsics;
- for (auto I = std::next(OrigPreheader->rbegin()), E = OrigPreheader->rend();
- I != E; ++I) {
- if (auto *DII = dyn_cast<DbgInfoIntrinsic>(&*I))
- DbgIntrinsics.insert(makeHash(DII));
- else
- break;
- }
-
- while (I != E) {
- Instruction *Inst = &*I++;
-
- // If the instruction's operands are invariant and it doesn't read or write
- // memory, then it is safe to hoist. Doing this doesn't change the order of
- // execution in the preheader, but does prevent the instruction from
- // executing in each iteration of the loop. This means it is safe to hoist
- // something that might trap, but isn't safe to hoist something that reads
- // memory (without proving that the loop doesn't write).
- if (L->hasLoopInvariantOperands(Inst) && !Inst->mayReadFromMemory() &&
- !Inst->mayWriteToMemory() && !isa<TerminatorInst>(Inst) &&
- !isa<DbgInfoIntrinsic>(Inst) && !isa<AllocaInst>(Inst)) {
- Inst->moveBefore(LoopEntryBranch);
- continue;
- }
-
- // Otherwise, create a duplicate of the instruction.
- Instruction *C = Inst->clone();
-
- // Eagerly remap the operands of the instruction.
- RemapInstruction(C, ValueMap,
- RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
-
- // Avoid inserting the same intrinsic twice.
- if (auto *DII = dyn_cast<DbgInfoIntrinsic>(C))
- if (DbgIntrinsics.count(makeHash(DII))) {
- C->deleteValue();
- continue;
- }
-
- // With the operands remapped, see if the instruction constant folds or is
- // otherwise simplifyable. This commonly occurs because the entry from PHI
- // nodes allows icmps and other instructions to fold.
- Value *V = SimplifyInstruction(C, SQ);
- if (V && LI->replacementPreservesLCSSAForm(C, V)) {
- // If so, then delete the temporary instruction and stick the folded value
- // in the map.
- ValueMap[Inst] = V;
- if (!C->mayHaveSideEffects()) {
- C->deleteValue();
- C = nullptr;
- }
- } else {
- ValueMap[Inst] = C;
- }
- if (C) {
- // Otherwise, stick the new instruction into the new block!
- C->setName(Inst->getName());
- C->insertBefore(LoopEntryBranch);
-
- if (auto *II = dyn_cast<IntrinsicInst>(C))
- if (II->getIntrinsicID() == Intrinsic::assume)
- AC->registerAssumption(II);
- }
- }
-
- // Along with all the other instructions, we just cloned OrigHeader's
- // terminator into OrigPreHeader. Fix up the PHI nodes in each of OrigHeader's
- // successors by duplicating their incoming values for OrigHeader.
- TerminatorInst *TI = OrigHeader->getTerminator();
- for (BasicBlock *SuccBB : TI->successors())
- for (BasicBlock::iterator BI = SuccBB->begin();
- PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
- PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreheader);
-
- // Now that OrigPreHeader has a clone of OrigHeader's terminator, remove
- // OrigPreHeader's old terminator (the original branch into the loop), and
- // remove the corresponding incoming values from the PHI nodes in OrigHeader.
- LoopEntryBranch->eraseFromParent();
-
-
- SmallVector<PHINode*, 2> InsertedPHIs;
- // If there were any uses of instructions in the duplicated block outside the
- // loop, update them, inserting PHI nodes as required
- RewriteUsesOfClonedInstructions(OrigHeader, OrigPreheader, ValueMap,
- &InsertedPHIs);
-
- // Attach dbg.value intrinsics to the new phis if that phi uses a value that
- // previously had debug metadata attached. This keeps the debug info
- // up-to-date in the loop body.
- if (!InsertedPHIs.empty())
- insertDebugValuesForPHIs(OrigHeader, InsertedPHIs);
-
- // NewHeader is now the header of the loop.
- L->moveToHeader(NewHeader);
- assert(L->getHeader() == NewHeader && "Latch block is our new header");
-
- // Inform DT about changes to the CFG.
- if (DT) {
- // The OrigPreheader branches to the NewHeader and Exit now. Then, inform
- // the DT about the removed edge to the OrigHeader (that got removed).
- SmallVector<DominatorTree::UpdateType, 3> Updates;
- Updates.push_back({DominatorTree::Insert, OrigPreheader, Exit});
- Updates.push_back({DominatorTree::Insert, OrigPreheader, NewHeader});
- Updates.push_back({DominatorTree::Delete, OrigPreheader, OrigHeader});
- DT->applyUpdates(Updates);
- }
-
- // At this point, we've finished our major CFG changes. As part of cloning
- // the loop into the preheader we've simplified instructions and the
- // duplicated conditional branch may now be branching on a constant. If it is
- // branching on a constant and if that constant means that we enter the loop,
- // then we fold away the cond branch to an uncond branch. This simplifies the
- // loop in cases important for nested loops, and it also means we don't have
- // to split as many edges.
- BranchInst *PHBI = cast<BranchInst>(OrigPreheader->getTerminator());
- assert(PHBI->isConditional() && "Should be clone of BI condbr!");
- if (!isa<ConstantInt>(PHBI->getCondition()) ||
- PHBI->getSuccessor(cast<ConstantInt>(PHBI->getCondition())->isZero()) !=
- NewHeader) {
- // The conditional branch can't be folded, handle the general case.
- // Split edges as necessary to preserve LoopSimplify form.
-
- // Right now OrigPreHeader has two successors, NewHeader and ExitBlock, and
- // thus is not a preheader anymore.
- // Split the edge to form a real preheader.
- BasicBlock *NewPH = SplitCriticalEdge(
- OrigPreheader, NewHeader,
- CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA());
- NewPH->setName(NewHeader->getName() + ".lr.ph");
-
- // Preserve canonical loop form, which means that 'Exit' should have only
- // one predecessor. Note that Exit could be an exit block for multiple
- // nested loops, causing both of the edges to now be critical and need to
- // be split.
- SmallVector<BasicBlock *, 4> ExitPreds(pred_begin(Exit), pred_end(Exit));
- bool SplitLatchEdge = false;
- for (BasicBlock *ExitPred : ExitPreds) {
- // We only need to split loop exit edges.
- Loop *PredLoop = LI->getLoopFor(ExitPred);
- if (!PredLoop || PredLoop->contains(Exit))
- continue;
- if (isa<IndirectBrInst>(ExitPred->getTerminator()))
- continue;
- SplitLatchEdge |= L->getLoopLatch() == ExitPred;
- BasicBlock *ExitSplit = SplitCriticalEdge(
- ExitPred, Exit,
- CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA());
- ExitSplit->moveBefore(Exit);
- }
- assert(SplitLatchEdge &&
- "Despite splitting all preds, failed to split latch exit?");
- } else {
- // We can fold the conditional branch in the preheader, this makes things
- // simpler. The first step is to remove the extra edge to the Exit block.
- Exit->removePredecessor(OrigPreheader, true /*preserve LCSSA*/);
- BranchInst *NewBI = BranchInst::Create(NewHeader, PHBI);
- NewBI->setDebugLoc(PHBI->getDebugLoc());
- PHBI->eraseFromParent();
-
- // With our CFG finalized, update DomTree if it is available.
- if (DT) DT->deleteEdge(OrigPreheader, Exit);
- }
-
- assert(L->getLoopPreheader() && "Invalid loop preheader after loop rotation");
- assert(L->getLoopLatch() && "Invalid loop latch after loop rotation");
-
- // Now that the CFG and DomTree are in a consistent state again, try to merge
- // the OrigHeader block into OrigLatch. This will succeed if they are
- // connected by an unconditional branch. This is just a cleanup so the
- // emitted code isn't too gross in this common case.
- MergeBlockIntoPredecessor(OrigHeader, DT, LI);
-
- DEBUG(dbgs() << "LoopRotation: into "; L->dump());
-
- ++NumRotated;
- return true;
-}
-
-/// Determine whether the instructions in this range may be safely and cheaply
-/// speculated. This is not an important enough situation to develop complex
-/// heuristics. We handle a single arithmetic instruction along with any type
-/// conversions.
-static bool shouldSpeculateInstrs(BasicBlock::iterator Begin,
- BasicBlock::iterator End, Loop *L) {
- bool seenIncrement = false;
- bool MultiExitLoop = false;
-
- if (!L->getExitingBlock())
- MultiExitLoop = true;
-
- for (BasicBlock::iterator I = Begin; I != End; ++I) {
-
- if (!isSafeToSpeculativelyExecute(&*I))
- return false;
-
- if (isa<DbgInfoIntrinsic>(I))
- continue;
-
- switch (I->getOpcode()) {
- default:
- return false;
- case Instruction::GetElementPtr:
- // GEPs are cheap if all indices are constant.
- if (!cast<GEPOperator>(I)->hasAllConstantIndices())
- return false;
- // fall-thru to increment case
- LLVM_FALLTHROUGH;
- case Instruction::Add:
- case Instruction::Sub:
- case Instruction::And:
- case Instruction::Or:
- case Instruction::Xor:
- case Instruction::Shl:
- case Instruction::LShr:
- case Instruction::AShr: {
- Value *IVOpnd =
- !isa<Constant>(I->getOperand(0))
- ? I->getOperand(0)
- : !isa<Constant>(I->getOperand(1)) ? I->getOperand(1) : nullptr;
- if (!IVOpnd)
- return false;
-
- // If increment operand is used outside of the loop, this speculation
- // could cause extra live range interference.
- if (MultiExitLoop) {
- for (User *UseI : IVOpnd->users()) {
- auto *UserInst = cast<Instruction>(UseI);
- if (!L->contains(UserInst))
- return false;
- }
- }
-
- if (seenIncrement)
- return false;
- seenIncrement = true;
- break;
- }
- case Instruction::Trunc:
- case Instruction::ZExt:
- case Instruction::SExt:
- // ignore type conversions
- break;
- }
- }
- return true;
-}
-
-/// Fold the loop tail into the loop exit by speculating the loop tail
-/// instructions. Typically, this is a single post-increment. In the case of a
-/// simple 2-block loop, hoisting the increment can be much better than
-/// duplicating the entire loop header. In the case of loops with early exits,
-/// rotation will not work anyway, but simplifyLoopLatch will put the loop in
-/// canonical form so downstream passes can handle it.
-///
-/// I don't believe this invalidates SCEV.
-bool LoopRotate::simplifyLoopLatch(Loop *L) {
- BasicBlock *Latch = L->getLoopLatch();
- if (!Latch || Latch->hasAddressTaken())
- return false;
-
- BranchInst *Jmp = dyn_cast<BranchInst>(Latch->getTerminator());
- if (!Jmp || !Jmp->isUnconditional())
- return false;
-
- BasicBlock *LastExit = Latch->getSinglePredecessor();
- if (!LastExit || !L->isLoopExiting(LastExit))
- return false;
-
- BranchInst *BI = dyn_cast<BranchInst>(LastExit->getTerminator());
- if (!BI)
- return false;
-
- if (!shouldSpeculateInstrs(Latch->begin(), Jmp->getIterator(), L))
- return false;
-
- DEBUG(dbgs() << "Folding loop latch " << Latch->getName() << " into "
- << LastExit->getName() << "\n");
-
- // Hoist the instructions from Latch into LastExit.
- LastExit->getInstList().splice(BI->getIterator(), Latch->getInstList(),
- Latch->begin(), Jmp->getIterator());
-
- unsigned FallThruPath = BI->getSuccessor(0) == Latch ? 0 : 1;
- BasicBlock *Header = Jmp->getSuccessor(0);
- assert(Header == L->getHeader() && "expected a backward branch");
-
- // Remove Latch from the CFG so that LastExit becomes the new Latch.
- BI->setSuccessor(FallThruPath, Header);
- Latch->replaceSuccessorsPhiUsesWith(LastExit);
- Jmp->eraseFromParent();
-
- // Nuke the Latch block.
- assert(Latch->empty() && "unable to evacuate Latch");
- LI->removeBlock(Latch);
- if (DT)
- DT->eraseNode(Latch);
- Latch->eraseFromParent();
- return true;
-}
-
-/// Rotate \c L, and return true if any modification was made.
-bool LoopRotate::processLoop(Loop *L) {
- // Save the loop metadata.
- MDNode *LoopMD = L->getLoopID();
-
- // Simplify the loop latch before attempting to rotate the header
- // upward. Rotation may not be needed if the loop tail can be folded into the
- // loop exit.
- bool SimplifiedLatch = simplifyLoopLatch(L);
-
- bool MadeChange = rotateLoop(L, SimplifiedLatch);
- assert((!MadeChange || L->isLoopExiting(L->getLoopLatch())) &&
- "Loop latch should be exiting after loop-rotate.");
-
- // Restore the loop metadata.
- // NB! We presume LoopRotation DOESN'T ADD its own metadata.
- if ((MadeChange || SimplifiedLatch) && LoopMD)
- L->setLoopID(LoopMD);
-
- return MadeChange || SimplifiedLatch;
-}
-
LoopRotatePass::LoopRotatePass(bool EnableHeaderDuplication)
: EnableHeaderDuplication(EnableHeaderDuplication) {}
@@ -614,10 +39,10 @@ PreservedAnalyses LoopRotatePass::run(Lo
int Threshold = EnableHeaderDuplication ? DefaultRotationThreshold : 0;
const DataLayout &DL = L.getHeader()->getModule()->getDataLayout();
const SimplifyQuery SQ = getBestSimplifyQuery(AR, DL);
- LoopRotate LR(Threshold, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE,
- SQ);
- bool Changed = LR.processLoop(&L);
+ bool Changed =
+ LoopRotation(&L, Threshold, &AR.LI, &AR.TTI, &AR.AC, &AR.DT, &AR.SE, SQ);
+
if (!Changed)
return PreservedAnalyses::all();
@@ -659,8 +84,7 @@ public:
auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
auto *SE = SEWP ? &SEWP->getSE() : nullptr;
const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
- LoopRotate LR(MaxHeaderSize, LI, TTI, AC, DT, SE, SQ);
- return LR.processLoop(L);
+ return LoopRotation(L, MaxHeaderSize, LI, TTI, AC, DT, SE, SQ);
}
};
}
Modified: llvm/trunk/lib/Transforms/Utils/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/CMakeLists.txt?rev=328766&r1=328765&r2=328766&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/CMakeLists.txt (original)
+++ llvm/trunk/lib/Transforms/Utils/CMakeLists.txt Thu Mar 29 01:48:15 2018
@@ -25,6 +25,7 @@ add_llvm_library(LLVMTransformUtils
LCSSA.cpp
LibCallsShrinkWrap.cpp
Local.cpp
+ LoopRotationUtils.cpp
LoopSimplify.cpp
LoopUnroll.cpp
LoopUnrollPeel.cpp
Added: llvm/trunk/lib/Transforms/Utils/LoopRotationUtils.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopRotationUtils.cpp?rev=328766&view=auto
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/LoopRotationUtils.cpp (added)
+++ llvm/trunk/lib/Transforms/Utils/LoopRotationUtils.cpp Thu Mar 29 01:48:15 2018
@@ -0,0 +1,613 @@
+//===----------------- LoopRotationUtils.cpp -----------------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file provides utilities to convert a loop into a loop with bottom test.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/LoopRotationUtils.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/AssumptionCache.h"
+#include "llvm/Analysis/BasicAliasAnalysis.h"
+#include "llvm/Analysis/CodeMetrics.h"
+#include "llvm/Analysis/GlobalsModRef.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Analysis/Utils/Local.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/DebugInfoMetadata.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Scalar/LoopPassManager.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
+#include "llvm/Transforms/Utils/SSAUpdater.h"
+#include "llvm/Transforms/Utils/ValueMapper.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "loop-rotate"
+
+STATISTIC(NumRotated, "Number of loops rotated");
+
+namespace {
+/// A simple loop rotation transformation.
+class LoopRotate {
+ const unsigned MaxHeaderSize;
+ LoopInfo *LI;
+ const TargetTransformInfo *TTI;
+ AssumptionCache *AC;
+ DominatorTree *DT;
+ ScalarEvolution *SE;
+ const SimplifyQuery &SQ;
+
+public:
+ LoopRotate(unsigned MaxHeaderSize, LoopInfo *LI,
+ const TargetTransformInfo *TTI, AssumptionCache *AC,
+ DominatorTree *DT, ScalarEvolution *SE, const SimplifyQuery &SQ)
+ : MaxHeaderSize(MaxHeaderSize), LI(LI), TTI(TTI), AC(AC), DT(DT), SE(SE),
+ SQ(SQ) {}
+ bool processLoop(Loop *L);
+
+private:
+ bool rotateLoop(Loop *L, bool SimplifiedLatch);
+ bool simplifyLoopLatch(Loop *L);
+};
+} // end anonymous namespace
+
+/// RewriteUsesOfClonedInstructions - We just cloned the instructions from the
+/// old header into the preheader. If there were uses of the values produced by
+/// these instruction that were outside of the loop, we have to insert PHI nodes
+/// to merge the two values. Do this now.
+static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
+ BasicBlock *OrigPreheader,
+ ValueToValueMapTy &ValueMap,
+ SmallVectorImpl<PHINode*> *InsertedPHIs) {
+ // Remove PHI node entries that are no longer live.
+ BasicBlock::iterator I, E = OrigHeader->end();
+ for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I)
+ PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreheader));
+
+ // Now fix up users of the instructions in OrigHeader, inserting PHI nodes
+ // as necessary.
+ SSAUpdater SSA(InsertedPHIs);
+ for (I = OrigHeader->begin(); I != E; ++I) {
+ Value *OrigHeaderVal = &*I;
+
+ // If there are no uses of the value (e.g. because it returns void), there
+ // is nothing to rewrite.
+ if (OrigHeaderVal->use_empty())
+ continue;
+
+ Value *OrigPreHeaderVal = ValueMap.lookup(OrigHeaderVal);
+
+ // The value now exits in two versions: the initial value in the preheader
+ // and the loop "next" value in the original header.
+ SSA.Initialize(OrigHeaderVal->getType(), OrigHeaderVal->getName());
+ SSA.AddAvailableValue(OrigHeader, OrigHeaderVal);
+ SSA.AddAvailableValue(OrigPreheader, OrigPreHeaderVal);
+
+ // Visit each use of the OrigHeader instruction.
+ for (Value::use_iterator UI = OrigHeaderVal->use_begin(),
+ UE = OrigHeaderVal->use_end();
+ UI != UE;) {
+ // Grab the use before incrementing the iterator.
+ Use &U = *UI;
+
+ // Increment the iterator before removing the use from the list.
+ ++UI;
+
+ // SSAUpdater can't handle a non-PHI use in the same block as an
+ // earlier def. We can easily handle those cases manually.
+ Instruction *UserInst = cast<Instruction>(U.getUser());
+ if (!isa<PHINode>(UserInst)) {
+ BasicBlock *UserBB = UserInst->getParent();
+
+ // The original users in the OrigHeader are already using the
+ // original definitions.
+ if (UserBB == OrigHeader)
+ continue;
+
+ // Users in the OrigPreHeader need to use the value to which the
+ // original definitions are mapped.
+ if (UserBB == OrigPreheader) {
+ U = OrigPreHeaderVal;
+ continue;
+ }
+ }
+
+ // Anything else can be handled by SSAUpdater.
+ SSA.RewriteUse(U);
+ }
+
+ // Replace MetadataAsValue(ValueAsMetadata(OrigHeaderVal)) uses in debug
+ // intrinsics.
+ SmallVector<DbgValueInst *, 1> DbgValues;
+ llvm::findDbgValues(DbgValues, OrigHeaderVal);
+ for (auto &DbgValue : DbgValues) {
+ // The original users in the OrigHeader are already using the original
+ // definitions.
+ BasicBlock *UserBB = DbgValue->getParent();
+ if (UserBB == OrigHeader)
+ continue;
+
+ // Users in the OrigPreHeader need to use the value to which the
+ // original definitions are mapped and anything else can be handled by
+ // the SSAUpdater. To avoid adding PHINodes, check if the value is
+ // available in UserBB, if not substitute undef.
+ Value *NewVal;
+ if (UserBB == OrigPreheader)
+ NewVal = OrigPreHeaderVal;
+ else if (SSA.HasValueForBlock(UserBB))
+ NewVal = SSA.GetValueInMiddleOfBlock(UserBB);
+ else
+ NewVal = UndefValue::get(OrigHeaderVal->getType());
+ DbgValue->setOperand(0,
+ MetadataAsValue::get(OrigHeaderVal->getContext(),
+ ValueAsMetadata::get(NewVal)));
+ }
+ }
+}
+
+/// Rotate loop LP. Return true if the loop is rotated.
+///
+/// \param SimplifiedLatch is true if the latch was just folded into the final
+/// loop exit. In this case we may want to rotate even though the new latch is
+/// now an exiting branch. This rotation would have happened had the latch not
+/// been simplified. However, if SimplifiedLatch is false, then we avoid
+/// rotating loops in which the latch exits to avoid excessive or endless
+/// rotation. LoopRotate should be repeatable and converge to a canonical
+/// form. This property is satisfied because simplifying the loop latch can only
+/// happen once across multiple invocations of the LoopRotate pass.
+bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
+ // If the loop has only one block then there is not much to rotate.
+ if (L->getBlocks().size() == 1)
+ return false;
+
+ BasicBlock *OrigHeader = L->getHeader();
+ BasicBlock *OrigLatch = L->getLoopLatch();
+
+ BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
+ if (!BI || BI->isUnconditional())
+ return false;
+
+ // If the loop header is not one of the loop exiting blocks then
+ // either this loop is already rotated or it is not
+ // suitable for loop rotation transformations.
+ if (!L->isLoopExiting(OrigHeader))
+ return false;
+
+ // If the loop latch already contains a branch that leaves the loop then the
+ // loop is already rotated.
+ if (!OrigLatch)
+ return false;
+
+ // Rotate if either the loop latch does *not* exit the loop, or if the loop
+ // latch was just simplified.
+ if (L->isLoopExiting(OrigLatch) && !SimplifiedLatch)
+ return false;
+
+ // Check size of original header and reject loop if it is very big or we can't
+ // duplicate blocks inside it.
+ {
+ SmallPtrSet<const Value *, 32> EphValues;
+ CodeMetrics::collectEphemeralValues(L, AC, EphValues);
+
+ CodeMetrics Metrics;
+ Metrics.analyzeBasicBlock(OrigHeader, *TTI, EphValues);
+ if (Metrics.notDuplicatable) {
+ DEBUG(dbgs() << "LoopRotation: NOT rotating - contains non-duplicatable"
+ << " instructions: ";
+ L->dump());
+ return false;
+ }
+ if (Metrics.convergent) {
+ DEBUG(dbgs() << "LoopRotation: NOT rotating - contains convergent "
+ "instructions: ";
+ L->dump());
+ return false;
+ }
+ if (Metrics.NumInsts > MaxHeaderSize)
+ return false;
+ }
+
+ // Now, this loop is suitable for rotation.
+ BasicBlock *OrigPreheader = L->getLoopPreheader();
+
+ // If the loop could not be converted to canonical form, it must have an
+ // indirectbr in it, just give up.
+ if (!OrigPreheader || !L->hasDedicatedExits())
+ return false;
+
+ // Anything ScalarEvolution may know about this loop or the PHI nodes
+ // in its header will soon be invalidated.
+ if (SE)
+ SE->forgetLoop(L);
+
+ DEBUG(dbgs() << "LoopRotation: rotating "; L->dump());
+
+ // Find new Loop header. NewHeader is a Header's one and only successor
+ // that is inside loop. Header's other successor is outside the
+ // loop. Otherwise loop is not suitable for rotation.
+ BasicBlock *Exit = BI->getSuccessor(0);
+ BasicBlock *NewHeader = BI->getSuccessor(1);
+ if (L->contains(Exit))
+ std::swap(Exit, NewHeader);
+ assert(NewHeader && "Unable to determine new loop header");
+ assert(L->contains(NewHeader) && !L->contains(Exit) &&
+ "Unable to determine loop header and exit blocks");
+
+ // This code assumes that the new header has exactly one predecessor.
+ // Remove any single-entry PHI nodes in it.
+ assert(NewHeader->getSinglePredecessor() &&
+ "New header doesn't have one pred!");
+ FoldSingleEntryPHINodes(NewHeader);
+
+ // Begin by walking OrigHeader and populating ValueMap with an entry for
+ // each Instruction.
+ BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
+ ValueToValueMapTy ValueMap;
+
+ // For PHI nodes, the value available in OldPreHeader is just the
+ // incoming value from OldPreHeader.
+ for (; PHINode *PN = dyn_cast<PHINode>(I); ++I)
+ ValueMap[PN] = PN->getIncomingValueForBlock(OrigPreheader);
+
+ // For the rest of the instructions, either hoist to the OrigPreheader if
+ // possible or create a clone in the OldPreHeader if not.
+ TerminatorInst *LoopEntryBranch = OrigPreheader->getTerminator();
+
+ // Record all debug intrinsics preceding LoopEntryBranch to avoid duplication.
+ using DbgIntrinsicHash =
+ std::pair<std::pair<Value *, DILocalVariable *>, DIExpression *>;
+ auto makeHash = [](DbgInfoIntrinsic *D) -> DbgIntrinsicHash {
+ return {{D->getVariableLocation(), D->getVariable()}, D->getExpression()};
+ };
+ SmallDenseSet<DbgIntrinsicHash, 8> DbgIntrinsics;
+ for (auto I = std::next(OrigPreheader->rbegin()), E = OrigPreheader->rend();
+ I != E; ++I) {
+ if (auto *DII = dyn_cast<DbgInfoIntrinsic>(&*I))
+ DbgIntrinsics.insert(makeHash(DII));
+ else
+ break;
+ }
+
+ while (I != E) {
+ Instruction *Inst = &*I++;
+
+ // If the instruction's operands are invariant and it doesn't read or write
+ // memory, then it is safe to hoist. Doing this doesn't change the order of
+ // execution in the preheader, but does prevent the instruction from
+ // executing in each iteration of the loop. This means it is safe to hoist
+ // something that might trap, but isn't safe to hoist something that reads
+ // memory (without proving that the loop doesn't write).
+ if (L->hasLoopInvariantOperands(Inst) && !Inst->mayReadFromMemory() &&
+ !Inst->mayWriteToMemory() && !isa<TerminatorInst>(Inst) &&
+ !isa<DbgInfoIntrinsic>(Inst) && !isa<AllocaInst>(Inst)) {
+ Inst->moveBefore(LoopEntryBranch);
+ continue;
+ }
+
+ // Otherwise, create a duplicate of the instruction.
+ Instruction *C = Inst->clone();
+
+ // Eagerly remap the operands of the instruction.
+ RemapInstruction(C, ValueMap,
+ RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
+
+ // Avoid inserting the same intrinsic twice.
+ if (auto *DII = dyn_cast<DbgInfoIntrinsic>(C))
+ if (DbgIntrinsics.count(makeHash(DII))) {
+ C->deleteValue();
+ continue;
+ }
+
+ // With the operands remapped, see if the instruction constant folds or is
+ // otherwise simplifyable. This commonly occurs because the entry from PHI
+ // nodes allows icmps and other instructions to fold.
+ Value *V = SimplifyInstruction(C, SQ);
+ if (V && LI->replacementPreservesLCSSAForm(C, V)) {
+ // If so, then delete the temporary instruction and stick the folded value
+ // in the map.
+ ValueMap[Inst] = V;
+ if (!C->mayHaveSideEffects()) {
+ C->deleteValue();
+ C = nullptr;
+ }
+ } else {
+ ValueMap[Inst] = C;
+ }
+ if (C) {
+ // Otherwise, stick the new instruction into the new block!
+ C->setName(Inst->getName());
+ C->insertBefore(LoopEntryBranch);
+
+ if (auto *II = dyn_cast<IntrinsicInst>(C))
+ if (II->getIntrinsicID() == Intrinsic::assume)
+ AC->registerAssumption(II);
+ }
+ }
+
+ // Along with all the other instructions, we just cloned OrigHeader's
+ // terminator into OrigPreHeader. Fix up the PHI nodes in each of OrigHeader's
+ // successors by duplicating their incoming values for OrigHeader.
+ TerminatorInst *TI = OrigHeader->getTerminator();
+ for (BasicBlock *SuccBB : TI->successors())
+ for (BasicBlock::iterator BI = SuccBB->begin();
+ PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
+ PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreheader);
+
+ // Now that OrigPreHeader has a clone of OrigHeader's terminator, remove
+ // OrigPreHeader's old terminator (the original branch into the loop), and
+ // remove the corresponding incoming values from the PHI nodes in OrigHeader.
+ LoopEntryBranch->eraseFromParent();
+
+
+ SmallVector<PHINode*, 2> InsertedPHIs;
+ // If there were any uses of instructions in the duplicated block outside the
+ // loop, update them, inserting PHI nodes as required
+ RewriteUsesOfClonedInstructions(OrigHeader, OrigPreheader, ValueMap,
+ &InsertedPHIs);
+
+ // Attach dbg.value intrinsics to the new phis if that phi uses a value that
+ // previously had debug metadata attached. This keeps the debug info
+ // up-to-date in the loop body.
+ if (!InsertedPHIs.empty())
+ insertDebugValuesForPHIs(OrigHeader, InsertedPHIs);
+
+ // NewHeader is now the header of the loop.
+ L->moveToHeader(NewHeader);
+ assert(L->getHeader() == NewHeader && "Latch block is our new header");
+
+ // Inform DT about changes to the CFG.
+ if (DT) {
+ // The OrigPreheader branches to the NewHeader and Exit now. Then, inform
+ // the DT about the removed edge to the OrigHeader (that got removed).
+ SmallVector<DominatorTree::UpdateType, 3> Updates;
+ Updates.push_back({DominatorTree::Insert, OrigPreheader, Exit});
+ Updates.push_back({DominatorTree::Insert, OrigPreheader, NewHeader});
+ Updates.push_back({DominatorTree::Delete, OrigPreheader, OrigHeader});
+ DT->applyUpdates(Updates);
+ }
+
+ // At this point, we've finished our major CFG changes. As part of cloning
+ // the loop into the preheader we've simplified instructions and the
+ // duplicated conditional branch may now be branching on a constant. If it is
+ // branching on a constant and if that constant means that we enter the loop,
+ // then we fold away the cond branch to an uncond branch. This simplifies the
+ // loop in cases important for nested loops, and it also means we don't have
+ // to split as many edges.
+ BranchInst *PHBI = cast<BranchInst>(OrigPreheader->getTerminator());
+ assert(PHBI->isConditional() && "Should be clone of BI condbr!");
+ if (!isa<ConstantInt>(PHBI->getCondition()) ||
+ PHBI->getSuccessor(cast<ConstantInt>(PHBI->getCondition())->isZero()) !=
+ NewHeader) {
+ // The conditional branch can't be folded, handle the general case.
+ // Split edges as necessary to preserve LoopSimplify form.
+
+ // Right now OrigPreHeader has two successors, NewHeader and ExitBlock, and
+ // thus is not a preheader anymore.
+ // Split the edge to form a real preheader.
+ BasicBlock *NewPH = SplitCriticalEdge(
+ OrigPreheader, NewHeader,
+ CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA());
+ NewPH->setName(NewHeader->getName() + ".lr.ph");
+
+ // Preserve canonical loop form, which means that 'Exit' should have only
+ // one predecessor. Note that Exit could be an exit block for multiple
+ // nested loops, causing both of the edges to now be critical and need to
+ // be split.
+ SmallVector<BasicBlock *, 4> ExitPreds(pred_begin(Exit), pred_end(Exit));
+ bool SplitLatchEdge = false;
+ for (BasicBlock *ExitPred : ExitPreds) {
+ // We only need to split loop exit edges.
+ Loop *PredLoop = LI->getLoopFor(ExitPred);
+ if (!PredLoop || PredLoop->contains(Exit))
+ continue;
+ if (isa<IndirectBrInst>(ExitPred->getTerminator()))
+ continue;
+ SplitLatchEdge |= L->getLoopLatch() == ExitPred;
+ BasicBlock *ExitSplit = SplitCriticalEdge(
+ ExitPred, Exit,
+ CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA());
+ ExitSplit->moveBefore(Exit);
+ }
+ assert(SplitLatchEdge &&
+ "Despite splitting all preds, failed to split latch exit?");
+ } else {
+ // We can fold the conditional branch in the preheader, this makes things
+ // simpler. The first step is to remove the extra edge to the Exit block.
+ Exit->removePredecessor(OrigPreheader, true /*preserve LCSSA*/);
+ BranchInst *NewBI = BranchInst::Create(NewHeader, PHBI);
+ NewBI->setDebugLoc(PHBI->getDebugLoc());
+ PHBI->eraseFromParent();
+
+ // With our CFG finalized, update DomTree if it is available.
+ if (DT) DT->deleteEdge(OrigPreheader, Exit);
+ }
+
+ assert(L->getLoopPreheader() && "Invalid loop preheader after loop rotation");
+ assert(L->getLoopLatch() && "Invalid loop latch after loop rotation");
+
+ // Now that the CFG and DomTree are in a consistent state again, try to merge
+ // the OrigHeader block into OrigLatch. This will succeed if they are
+ // connected by an unconditional branch. This is just a cleanup so the
+ // emitted code isn't too gross in this common case.
+ MergeBlockIntoPredecessor(OrigHeader, DT, LI);
+
+ DEBUG(dbgs() << "LoopRotation: into "; L->dump());
+
+ ++NumRotated;
+ return true;
+}
+
+/// Determine whether the instructions in this range may be safely and cheaply
+/// speculated. This is not an important enough situation to develop complex
+/// heuristics. We handle a single arithmetic instruction along with any type
+/// conversions.
+static bool shouldSpeculateInstrs(BasicBlock::iterator Begin,
+ BasicBlock::iterator End, Loop *L) {
+ bool seenIncrement = false;
+ bool MultiExitLoop = false;
+
+ if (!L->getExitingBlock())
+ MultiExitLoop = true;
+
+ for (BasicBlock::iterator I = Begin; I != End; ++I) {
+
+ if (!isSafeToSpeculativelyExecute(&*I))
+ return false;
+
+ if (isa<DbgInfoIntrinsic>(I))
+ continue;
+
+ switch (I->getOpcode()) {
+ default:
+ return false;
+ case Instruction::GetElementPtr:
+ // GEPs are cheap if all indices are constant.
+ if (!cast<GEPOperator>(I)->hasAllConstantIndices())
+ return false;
+ // fall-thru to increment case
+ LLVM_FALLTHROUGH;
+ case Instruction::Add:
+ case Instruction::Sub:
+ case Instruction::And:
+ case Instruction::Or:
+ case Instruction::Xor:
+ case Instruction::Shl:
+ case Instruction::LShr:
+ case Instruction::AShr: {
+ Value *IVOpnd =
+ !isa<Constant>(I->getOperand(0))
+ ? I->getOperand(0)
+ : !isa<Constant>(I->getOperand(1)) ? I->getOperand(1) : nullptr;
+ if (!IVOpnd)
+ return false;
+
+ // If increment operand is used outside of the loop, this speculation
+ // could cause extra live range interference.
+ if (MultiExitLoop) {
+ for (User *UseI : IVOpnd->users()) {
+ auto *UserInst = cast<Instruction>(UseI);
+ if (!L->contains(UserInst))
+ return false;
+ }
+ }
+
+ if (seenIncrement)
+ return false;
+ seenIncrement = true;
+ break;
+ }
+ case Instruction::Trunc:
+ case Instruction::ZExt:
+ case Instruction::SExt:
+ // ignore type conversions
+ break;
+ }
+ }
+ return true;
+}
+
+/// Fold the loop tail into the loop exit by speculating the loop tail
+/// instructions. Typically, this is a single post-increment. In the case of a
+/// simple 2-block loop, hoisting the increment can be much better than
+/// duplicating the entire loop header. In the case of loops with early exits,
+/// rotation will not work anyway, but simplifyLoopLatch will put the loop in
+/// canonical form so downstream passes can handle it.
+///
+/// I don't believe this invalidates SCEV.
+bool LoopRotate::simplifyLoopLatch(Loop *L) {
+ BasicBlock *Latch = L->getLoopLatch();
+ if (!Latch || Latch->hasAddressTaken())
+ return false;
+
+ BranchInst *Jmp = dyn_cast<BranchInst>(Latch->getTerminator());
+ if (!Jmp || !Jmp->isUnconditional())
+ return false;
+
+ BasicBlock *LastExit = Latch->getSinglePredecessor();
+ if (!LastExit || !L->isLoopExiting(LastExit))
+ return false;
+
+ BranchInst *BI = dyn_cast<BranchInst>(LastExit->getTerminator());
+ if (!BI)
+ return false;
+
+ if (!shouldSpeculateInstrs(Latch->begin(), Jmp->getIterator(), L))
+ return false;
+
+ DEBUG(dbgs() << "Folding loop latch " << Latch->getName() << " into "
+ << LastExit->getName() << "\n");
+
+ // Hoist the instructions from Latch into LastExit.
+ LastExit->getInstList().splice(BI->getIterator(), Latch->getInstList(),
+ Latch->begin(), Jmp->getIterator());
+
+ unsigned FallThruPath = BI->getSuccessor(0) == Latch ? 0 : 1;
+ BasicBlock *Header = Jmp->getSuccessor(0);
+ assert(Header == L->getHeader() && "expected a backward branch");
+
+ // Remove Latch from the CFG so that LastExit becomes the new Latch.
+ BI->setSuccessor(FallThruPath, Header);
+ Latch->replaceSuccessorsPhiUsesWith(LastExit);
+ Jmp->eraseFromParent();
+
+ // Nuke the Latch block.
+ assert(Latch->empty() && "unable to evacuate Latch");
+ LI->removeBlock(Latch);
+ if (DT)
+ DT->eraseNode(Latch);
+ Latch->eraseFromParent();
+ return true;
+}
+
+/// Rotate \c L, and return true if any modification was made.
+bool LoopRotate::processLoop(Loop *L) {
+ // Save the loop metadata.
+ MDNode *LoopMD = L->getLoopID();
+
+ // Simplify the loop latch before attempting to rotate the header
+ // upward. Rotation may not be needed if the loop tail can be folded into the
+ // loop exit.
+ bool SimplifiedLatch = simplifyLoopLatch(L);
+
+ bool MadeChange = rotateLoop(L, SimplifiedLatch);
+ assert((!MadeChange || L->isLoopExiting(L->getLoopLatch())) &&
+ "Loop latch should be exiting after loop-rotate.");
+
+ // Restore the loop metadata.
+ // NB! We presume LoopRotation DOESN'T ADD its own metadata.
+ if ((MadeChange || SimplifiedLatch) && LoopMD)
+ L->setLoopID(LoopMD);
+
+ return MadeChange || SimplifiedLatch;
+}
+
+
+/// The utility to convert a loop into a loop with bottom test.
+bool llvm::LoopRotation(Loop *L, unsigned MaxHeaderSize, LoopInfo *LI,
+ const TargetTransformInfo *TTI, AssumptionCache *AC,
+ DominatorTree *DT, ScalarEvolution *SE,
+ const SimplifyQuery &SQ) {
+ LoopRotate LR(MaxHeaderSize, LI, TTI, AC, DT, SE, SQ);
+
+ return LR.processLoop(L);
+}
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