#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/CodeMetrics.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolution.h"
#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Analysis/BlockFrequencyInfoImpl.h"
+#include "llvm/Analysis/BlockFrequencyInfo.h"
+#include "llvm/Analysis/BranchProbabilityInfo.h"
+#include "llvm/Support/BranchProbability.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/MDBuilder.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
cl::init(100), cl::Hidden);
+static cl::opt<bool>
+LoopUnswitchWithBlockFrequency("loop-unswitch-with-block-frequency",
+ cl::init(false), cl::Hidden,
+ cl::desc("Enable the use of the block frequency analysis to access PGO "
+ "heuristics to minimize code growth in cold regions."));
+
+static cl::opt<unsigned>
+ColdnessThreshold("loop-unswitch-coldness-threshold", cl::init(1), cl::Hidden,
+ cl::desc("Coldness threshold in percentage. The loop header frequency "
+ "(relative to the entry frequency) is compared with this "
+ "threshold to determine if non-trivial unswitching should be "
+ "enabled."));
+
namespace {
class LUAnalysisCache {
struct LoopProperties {
unsigned CanBeUnswitchedCount;
+ unsigned WasUnswitchedCount;
unsigned SizeEstimation;
UnswitchedValsMap UnswitchedVals;
};
UnswitchedValsMap *CurLoopInstructions;
LoopProperties *CurrentLoopProperties;
- // Max size of code we can produce on remained iterations.
+ // A loop unswitching with an estimated cost above this threshold
+ // is not performed. MaxSize is turned into unswitching quota for
+ // the current loop, and reduced correspondingly, though note that
+ // the quota is returned by releaseMemory() when the loop has been
+ // processed, so that MaxSize will return to its previous
+ // value. So in most cases MaxSize will equal the Threshold flag
+ // when a new loop is processed. An exception to that is that
+ // MaxSize will have a smaller value while processing nested loops
+ // that were introduced due to loop unswitching of an outer loop.
+ //
+ // FIXME: The way that MaxSize works is subtle and depends on the
+ // pass manager processing loops and calling releaseMemory() in a
+ // specific order. It would be good to find a more straightforward
+ // way of doing what MaxSize does.
unsigned MaxSize;
- public:
-
- LUAnalysisCache() :
- CurLoopInstructions(nullptr), CurrentLoopProperties(nullptr),
- MaxSize(Threshold)
- {}
-
- // Analyze loop. Check its size, calculate is it possible to unswitch
- // it. Returns true if we can unswitch this loop.
- bool countLoop(const Loop *L, const TargetTransformInfo &TTI,
- AssumptionCache *AC);
-
- // Clean all data related to given loop.
- void forgetLoop(const Loop *L);
-
- // Mark case value as unswitched.
- // Since SI instruction can be partly unswitched, in order to avoid
- // extra unswitching in cloned loops keep track all unswitched values.
- void setUnswitched(const SwitchInst *SI, const Value *V);
-
- // Check was this case value unswitched before or not.
- bool isUnswitched(const SwitchInst *SI, const Value *V);
-
- // Clone all loop-unswitch related loop properties.
- // Redistribute unswitching quotas.
- // Note, that new loop data is stored inside the VMap.
- void cloneData(const Loop *NewLoop, const Loop *OldLoop,
- const ValueToValueMapTy &VMap);
+ public:
+ LUAnalysisCache()
+ : CurLoopInstructions(nullptr), CurrentLoopProperties(nullptr),
+ MaxSize(Threshold) {}
+
+ // Analyze loop. Check its size, calculate is it possible to unswitch
+ // it. Returns true if we can unswitch this loop.
+ bool countLoop(const Loop *L, const TargetTransformInfo &TTI,
+ AssumptionCache *AC);
+
+ // Clean all data related to given loop.
+ void forgetLoop(const Loop *L);
+
+ // Mark case value as unswitched.
+ // Since SI instruction can be partly unswitched, in order to avoid
+ // extra unswitching in cloned loops keep track all unswitched values.
+ void setUnswitched(const SwitchInst *SI, const Value *V);
+
+ // Check was this case value unswitched before or not.
+ bool isUnswitched(const SwitchInst *SI, const Value *V);
+
+ // Returns true if another unswitching could be done within the cost
+ // threshold.
+ bool CostAllowsUnswitching();
+
+ // Clone all loop-unswitch related loop properties.
+ // Redistribute unswitching quotas.
+ // Note, that new loop data is stored inside the VMap.
+ void cloneData(const Loop *NewLoop, const Loop *OldLoop,
+ const ValueToValueMapTy &VMap);
};
class LoopUnswitch : public LoopPass {
LPPassManager *LPM;
AssumptionCache *AC;
- // LoopProcessWorklist - Used to check if second loop needs processing
- // after RewriteLoopBodyWithConditionConstant rewrites first loop.
+ // Used to check if second loop needs processing after
+ // RewriteLoopBodyWithConditionConstant rewrites first loop.
std::vector<Loop*> LoopProcessWorklist;
LUAnalysisCache BranchesInfo;
+ bool EnabledPGO;
+
+ // BFI and ColdEntryFreq are only used when PGO and
+ // LoopUnswitchWithBlockFrequency are enabled.
+ BlockFrequencyInfo BFI;
+ BlockFrequency ColdEntryFreq;
+
bool OptimizeForSize;
bool redoLoop;
AU.addPreserved<LoopInfoWrapperPass>();
AU.addRequiredID(LCSSAID);
AU.addPreservedID(LCSSAID);
+ AU.addRequired<DominatorTreeWrapperPass>();
AU.addPreserved<DominatorTreeWrapperPass>();
- AU.addPreserved<ScalarEvolution>();
- AU.addRequired<TargetTransformInfo>();
+ AU.addPreserved<ScalarEvolutionWrapperPass>();
+ AU.addRequired<TargetTransformInfoWrapperPass>();
+ AU.addPreserved<GlobalsAAWrapperPass>();
}
private:
/// Split all of the edges from inside the loop to their exit blocks.
/// Update the appropriate Phi nodes as we do so.
- void SplitExitEdges(Loop *L, const SmallVectorImpl<BasicBlock *> &ExitBlocks);
+ void SplitExitEdges(Loop *L,
+ const SmallVectorImpl<BasicBlock *> &ExitBlocks);
+
+ bool TryTrivialLoopUnswitch(bool &Changed);
- bool UnswitchIfProfitable(Value *LoopCond, Constant *Val);
+ bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,
+ TerminatorInst *TI = nullptr);
void UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
- BasicBlock *ExitBlock);
- void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L);
+ BasicBlock *ExitBlock, TerminatorInst *TI);
+ void UnswitchNontrivialCondition(Value *LIC, Constant *OnVal, Loop *L,
+ TerminatorInst *TI);
void RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
Constant *Val, bool isEqual);
void EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
BasicBlock *TrueDest,
BasicBlock *FalseDest,
- Instruction *InsertPt);
+ Instruction *InsertPt,
+ TerminatorInst *TI);
void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L);
- bool IsTrivialUnswitchCondition(Value *Cond, Constant **Val = nullptr,
- BasicBlock **LoopExit = nullptr);
-
};
}
// consideration code simplification opportunities and code that can
// be shared by the resultant unswitched loops.
CodeMetrics Metrics;
- for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
- I != E; ++I)
+ for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); I != E;
+ ++I)
Metrics.analyzeBasicBlock(*I, TTI, EphValues);
- Props.SizeEstimation = std::min(Metrics.NumInsts, Metrics.NumBlocks * 5);
+ Props.SizeEstimation = Metrics.NumInsts;
Props.CanBeUnswitchedCount = MaxSize / (Props.SizeEstimation);
+ Props.WasUnswitchedCount = 0;
MaxSize -= Props.SizeEstimation * Props.CanBeUnswitchedCount;
if (Metrics.notDuplicatable) {
}
}
- if (!Props.CanBeUnswitchedCount) {
- DEBUG(dbgs() << "NOT unswitching loop %"
- << L->getHeader()->getName() << ", cost too high: "
- << L->getBlocks().size() << "\n");
- return false;
- }
-
// Be careful. This links are good only before new loop addition.
CurrentLoopProperties = &Props;
CurLoopInstructions = &Props.UnswitchedVals;
if (LIt != LoopsProperties.end()) {
LoopProperties &Props = LIt->second;
- MaxSize += Props.CanBeUnswitchedCount * Props.SizeEstimation;
+ MaxSize += (Props.CanBeUnswitchedCount + Props.WasUnswitchedCount) *
+ Props.SizeEstimation;
LoopsProperties.erase(LIt);
}
return (*CurLoopInstructions)[SI].count(V);
}
+bool LUAnalysisCache::CostAllowsUnswitching() {
+ return CurrentLoopProperties->CanBeUnswitchedCount > 0;
+}
+
// Clone all loop-unswitch related loop properties.
// Redistribute unswitching quotas.
// Note, that new loop data is stored inside the VMap.
// Reallocate "can-be-unswitched quota"
--OldLoopProps.CanBeUnswitchedCount;
+ ++OldLoopProps.WasUnswitchedCount;
+ NewLoopProps.WasUnswitchedCount = 0;
unsigned Quota = OldLoopProps.CanBeUnswitchedCount;
NewLoopProps.CanBeUnswitchedCount = Quota / 2;
OldLoopProps.CanBeUnswitchedCount = Quota - Quota / 2;
char LoopUnswitch::ID = 0;
INITIALIZE_PASS_BEGIN(LoopUnswitch, "loop-unswitch", "Unswitch loops",
false, false)
-INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
return new LoopUnswitch(Os);
}
-/// FindLIVLoopCondition - Cond is a condition that occurs in L. If it is
-/// invariant in the loop, or has an invariant piece, return the invariant.
-/// Otherwise, return null.
+/// Cond is a condition that occurs in L. If it is invariant in the loop, or has
+/// an invariant piece, return the invariant. Otherwise, return null.
static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
// We started analyze new instruction, increment scanned instructions counter.
*L->getHeader()->getParent());
LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
LPM = &LPM_Ref;
- DominatorTreeWrapperPass *DTWP =
- getAnalysisIfAvailable<DominatorTreeWrapperPass>();
- DT = DTWP ? &DTWP->getDomTree() : nullptr;
+ DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
currentLoop = L;
Function *F = currentLoop->getHeader()->getParent();
+
+ EnabledPGO = F->getEntryCount().hasValue();
+
+ if (LoopUnswitchWithBlockFrequency && EnabledPGO) {
+ BranchProbabilityInfo BPI(*F, *LI);
+ BFI.calculate(*L->getHeader()->getParent(), BPI, *LI);
+
+ // Use BranchProbability to compute a minimum frequency based on
+ // function entry baseline frequency. Loops with headers below this
+ // frequency are considered as cold.
+ const BranchProbability ColdProb(ColdnessThreshold, 100);
+ ColdEntryFreq = BlockFrequency(BFI.getEntryFreq()) * ColdProb;
+ }
+
bool Changed = false;
do {
assert(currentLoop->isLCSSAForm(*DT));
Changed |= processCurrentLoop();
} while(redoLoop);
- if (Changed) {
- // FIXME: Reconstruct dom info, because it is not preserved properly.
- if (DT)
- DT->recalculate(*F);
- }
+ // FIXME: Reconstruct dom info, because it is not preserved properly.
+ if (Changed)
+ DT->recalculate(*F);
return Changed;
}
-/// processCurrentLoop - Do actual work and unswitch loop if possible
-/// and profitable.
+/// Do actual work and unswitch loop if possible and profitable.
bool LoopUnswitch::processCurrentLoop() {
bool Changed = false;
LLVMContext &Context = loopHeader->getContext();
- // Probably we reach the quota of branches for this loop. If so
- // stop unswitching.
- if (!BranchesInfo.countLoop(currentLoop, getAnalysis<TargetTransformInfo>(),
- AC))
+ // Analyze loop cost, and stop unswitching if loop content can not be duplicated.
+ if (!BranchesInfo.countLoop(
+ currentLoop, getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
+ *currentLoop->getHeader()->getParent()),
+ AC))
return false;
+ // Try trivial unswitch first before loop over other basic blocks in the loop.
+ if (TryTrivialLoopUnswitch(Changed)) {
+ return true;
+ }
+
+ // Do not unswitch loops containing convergent operations, as we might be
+ // making them control dependent on the unswitch value when they were not
+ // before.
+ // FIXME: This could be refined to only bail if the convergent operation is
+ // not already control-dependent on the unswitch value.
+ for (const auto BB : currentLoop->blocks()) {
+ for (auto &I : *BB) {
+ auto CS = CallSite(&I);
+ if (!CS) continue;
+ if (CS.hasFnAttr(Attribute::Convergent))
+ return false;
+ }
+ }
+
+ // Do not do non-trivial unswitch while optimizing for size.
+ // FIXME: Use Function::optForSize().
+ if (OptimizeForSize ||
+ loopHeader->getParent()->hasFnAttribute(Attribute::OptimizeForSize))
+ return false;
+
+ if (LoopUnswitchWithBlockFrequency && EnabledPGO) {
+ // Compute the weighted frequency of the hottest block in the
+ // loop (loopHeader in this case since inner loops should be
+ // processed before outer loop). If it is less than ColdFrequency,
+ // we should not unswitch.
+ BlockFrequency LoopEntryFreq = BFI.getBlockFreq(loopHeader);
+ if (LoopEntryFreq < ColdEntryFreq)
+ return false;
+ }
+
// Loop over all of the basic blocks in the loop. If we find an interior
// block that is branching on a loop-invariant condition, we can unswitch this
// loop.
// unswitch on it if we desire.
Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
currentLoop, Changed);
- if (LoopCond && UnswitchIfProfitable(LoopCond,
- ConstantInt::getTrue(Context))) {
+ if (LoopCond &&
+ UnswitchIfProfitable(LoopCond, ConstantInt::getTrue(Context), TI)) {
++NumBranches;
return true;
}
return Changed;
}
-/// isTrivialLoopExitBlock - Check to see if all paths from BB exit the
-/// loop with no side effects (including infinite loops).
+/// Check to see if all paths from BB exit the loop with no side effects
+/// (including infinite loops).
///
/// If true, we return true and set ExitBB to the block we
/// exit through.
return true;
}
-/// isTrivialLoopExitBlock - Return true if the specified block unconditionally
-/// leads to an exit from the specified loop, and has no side-effects in the
-/// process. If so, return the block that is exited to, otherwise return null.
+/// Return true if the specified block unconditionally leads to an exit from
+/// the specified loop, and has no side-effects in the process. If so, return
+/// the block that is exited to, otherwise return null.
static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
std::set<BasicBlock*> Visited;
Visited.insert(L->getHeader()); // Branches to header make infinite loops.
return nullptr;
}
-/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
-/// trivial: that is, that the condition controls whether or not the loop does
-/// anything at all. If this is a trivial condition, unswitching produces no
-/// code duplications (equivalently, it produces a simpler loop and a new empty
-/// loop, which gets deleted).
-///
-/// If this is a trivial condition, return true, otherwise return false. When
-/// returning true, this sets Cond and Val to the condition that controls the
-/// trivial condition: when Cond dynamically equals Val, the loop is known to
-/// exit. Finally, this sets LoopExit to the BB that the loop exits to when
-/// Cond == Val.
-///
-bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
- BasicBlock **LoopExit) {
- BasicBlock *Header = currentLoop->getHeader();
- TerminatorInst *HeaderTerm = Header->getTerminator();
- LLVMContext &Context = Header->getContext();
-
- BasicBlock *LoopExitBB = nullptr;
- if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
- // If the header block doesn't end with a conditional branch on Cond, we
- // can't handle it.
- if (!BI->isConditional() || BI->getCondition() != Cond)
- return false;
-
- // Check to see if a successor of the branch is guaranteed to
- // exit through a unique exit block without having any
- // side-effects. If so, determine the value of Cond that causes it to do
- // this.
- if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
- BI->getSuccessor(0)))) {
- if (Val) *Val = ConstantInt::getTrue(Context);
- } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
- BI->getSuccessor(1)))) {
- if (Val) *Val = ConstantInt::getFalse(Context);
- }
- } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
- // If this isn't a switch on Cond, we can't handle it.
- if (SI->getCondition() != Cond) return false;
-
- // Check to see if a successor of the switch is guaranteed to go to the
- // latch block or exit through a one exit block without having any
- // side-effects. If so, determine the value of Cond that causes it to do
- // this.
- // Note that we can't trivially unswitch on the default case or
- // on already unswitched cases.
- for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
- i != e; ++i) {
- BasicBlock *LoopExitCandidate;
- if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
- i.getCaseSuccessor()))) {
- // Okay, we found a trivial case, remember the value that is trivial.
- ConstantInt *CaseVal = i.getCaseValue();
-
- // Check that it was not unswitched before, since already unswitched
- // trivial vals are looks trivial too.
- if (BranchesInfo.isUnswitched(SI, CaseVal))
- continue;
- LoopExitBB = LoopExitCandidate;
- if (Val) *Val = CaseVal;
- break;
- }
- }
- }
-
- // If we didn't find a single unique LoopExit block, or if the loop exit block
- // contains phi nodes, this isn't trivial.
- if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
- return false; // Can't handle this.
-
- if (LoopExit) *LoopExit = LoopExitBB;
-
- // We already know that nothing uses any scalar values defined inside of this
- // loop. As such, we just have to check to see if this loop will execute any
- // side-effecting instructions (e.g. stores, calls, volatile loads) in the
- // part of the loop that the code *would* execute. We already checked the
- // tail, check the header now.
- for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
- if (I->mayHaveSideEffects())
- return false;
- return true;
-}
-
-/// UnswitchIfProfitable - We have found that we can unswitch currentLoop when
-/// LoopCond == Val to simplify the loop. If we decide that this is profitable,
+/// We have found that we can unswitch currentLoop when LoopCond == Val to
+/// simplify the loop. If we decide that this is profitable,
/// unswitch the loop, reprocess the pieces, then return true.
-bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val) {
- Function *F = loopHeader->getParent();
- Constant *CondVal = nullptr;
- BasicBlock *ExitBlock = nullptr;
-
- if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) {
- // If the condition is trivial, always unswitch. There is no code growth
- // for this case.
- UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock);
- return true;
- }
-
+bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,
+ TerminatorInst *TI) {
// Check to see if it would be profitable to unswitch current loop.
-
- // Do not do non-trivial unswitch while optimizing for size.
- if (OptimizeForSize ||
- F->getAttributes().hasAttribute(AttributeSet::FunctionIndex,
- Attribute::OptimizeForSize))
+ if (!BranchesInfo.CostAllowsUnswitching()) {
+ DEBUG(dbgs() << "NOT unswitching loop %"
+ << currentLoop->getHeader()->getName()
+ << " at non-trivial condition '" << *Val
+ << "' == " << *LoopCond << "\n"
+ << ". Cost too high.\n");
return false;
+ }
- UnswitchNontrivialCondition(LoopCond, Val, currentLoop);
+ UnswitchNontrivialCondition(LoopCond, Val, currentLoop, TI);
return true;
}
-/// CloneLoop - Recursively clone the specified loop and all of its children,
+/// Recursively clone the specified loop and all of its children,
/// mapping the blocks with the specified map.
static Loop *CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM,
LoopInfo *LI, LPPassManager *LPM) {
- Loop *New = new Loop();
- LPM->insertLoop(New, PL);
+ Loop &New = LPM->addLoop(PL);
// Add all of the blocks in L to the new loop.
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
I != E; ++I)
if (LI->getLoopFor(*I) == L)
- New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), *LI);
+ New.addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), *LI);
// Add all of the subloops to the new loop.
for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
- CloneLoop(*I, New, VM, LI, LPM);
+ CloneLoop(*I, &New, VM, LI, LPM);
- return New;
+ return &New;
+}
+
+static void copyMetadata(Instruction *DstInst, const Instruction *SrcInst,
+ bool Swapped) {
+ if (!SrcInst || !SrcInst->hasMetadata())
+ return;
+
+ SmallVector<std::pair<unsigned, MDNode *>, 4> MDs;
+ SrcInst->getAllMetadata(MDs);
+ for (auto &MD : MDs) {
+ switch (MD.first) {
+ default:
+ break;
+ case LLVMContext::MD_prof:
+ if (Swapped && MD.second->getNumOperands() == 3 &&
+ isa<MDString>(MD.second->getOperand(0))) {
+ MDString *MDName = cast<MDString>(MD.second->getOperand(0));
+ if (MDName->getString() == "branch_weights") {
+ auto *ValT = cast_or_null<ConstantAsMetadata>(
+ MD.second->getOperand(1))->getValue();
+ auto *ValF = cast_or_null<ConstantAsMetadata>(
+ MD.second->getOperand(2))->getValue();
+ assert(ValT && ValF && "Invalid Operands of branch_weights");
+ auto NewMD =
+ MDBuilder(DstInst->getParent()->getContext())
+ .createBranchWeights(cast<ConstantInt>(ValF)->getZExtValue(),
+ cast<ConstantInt>(ValT)->getZExtValue());
+ MD.second = NewMD;
+ }
+ }
+ // fallthrough.
+ case LLVMContext::MD_make_implicit:
+ case LLVMContext::MD_dbg:
+ DstInst->setMetadata(MD.first, MD.second);
+ }
+ }
}
-/// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
-/// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest. Insert the
-/// code immediately before InsertPt.
+/// Emit a conditional branch on two values if LIC == Val, branch to TrueDst,
+/// otherwise branch to FalseDest. Insert the code immediately before InsertPt.
void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
BasicBlock *TrueDest,
BasicBlock *FalseDest,
- Instruction *InsertPt) {
+ Instruction *InsertPt,
+ TerminatorInst *TI) {
// Insert a conditional branch on LIC to the two preheaders. The original
// code is the true version and the new code is the false version.
Value *BranchVal = LIC;
+ bool Swapped = false;
if (!isa<ConstantInt>(Val) ||
Val->getType() != Type::getInt1Ty(LIC->getContext()))
BranchVal = new ICmpInst(InsertPt, ICmpInst::ICMP_EQ, LIC, Val);
- else if (Val != ConstantInt::getTrue(Val->getContext()))
+ else if (Val != ConstantInt::getTrue(Val->getContext())) {
// We want to enter the new loop when the condition is true.
std::swap(TrueDest, FalseDest);
+ Swapped = true;
+ }
// Insert the new branch.
BranchInst *BI = BranchInst::Create(TrueDest, FalseDest, BranchVal, InsertPt);
+ copyMetadata(BI, TI, Swapped);
// If either edge is critical, split it. This helps preserve LoopSimplify
// form for enclosing loops.
- SplitCriticalEdge(BI, 0, this, false, false, true);
- SplitCriticalEdge(BI, 1, this, false, false, true);
+ auto Options = CriticalEdgeSplittingOptions(DT, LI).setPreserveLCSSA();
+ SplitCriticalEdge(BI, 0, Options);
+ SplitCriticalEdge(BI, 1, Options);
}
-/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
-/// condition in it (a cond branch from its header block to its latch block,
-/// where the path through the loop that doesn't execute its body has no
-/// side-effects), unswitch it. This doesn't involve any code duplication, just
-/// moving the conditional branch outside of the loop and updating loop info.
-void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond,
- Constant *Val,
- BasicBlock *ExitBlock) {
+/// Given a loop that has a trivial unswitchable condition in it (a cond branch
+/// from its header block to its latch block, where the path through the loop
+/// that doesn't execute its body has no side-effects), unswitch it. This
+/// doesn't involve any code duplication, just moving the conditional branch
+/// outside of the loop and updating loop info.
+void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
+ BasicBlock *ExitBlock,
+ TerminatorInst *TI) {
DEBUG(dbgs() << "loop-unswitch: Trivial-Unswitch loop %"
- << loopHeader->getName() << " [" << L->getBlocks().size()
- << " blocks] in Function " << L->getHeader()->getParent()->getName()
- << " on cond: " << *Val << " == " << *Cond << "\n");
+ << loopHeader->getName() << " [" << L->getBlocks().size()
+ << " blocks] in Function "
+ << L->getHeader()->getParent()->getName() << " on cond: " << *Val
+ << " == " << *Cond << "\n");
// First step, split the preheader, so that we know that there is a safe place
// to insert the conditional branch. We will change loopPreheader to have a
// conditional branch on Cond.
- BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, this);
+ BasicBlock *NewPH = SplitEdge(loopPreheader, loopHeader, DT, LI);
// Now that we have a place to insert the conditional branch, create a place
// to branch to: this is the exit block out of the loop that we should
// without actually branching to it (the exit block should be dominated by the
// loop header, not the preheader).
assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
- BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), this);
+ BasicBlock *NewExit = SplitBlock(ExitBlock, &ExitBlock->front(), DT, LI);
// Okay, now we have a position to branch from and a position to branch to,
// insert the new conditional branch.
EmitPreheaderBranchOnCondition(Cond, Val, NewExit, NewPH,
- loopPreheader->getTerminator());
+ loopPreheader->getTerminator(), TI);
LPM->deleteSimpleAnalysisValue(loopPreheader->getTerminator(), L);
loopPreheader->getTerminator()->eraseFromParent();
++NumTrivial;
}
-/// SplitExitEdges - Split all of the edges from inside the loop to their exit
-/// blocks. Update the appropriate Phi nodes as we do so.
+/// Check if the first non-constant condition starting from the loop header is
+/// a trivial unswitch condition: that is, a condition controls whether or not
+/// the loop does anything at all. If it is a trivial condition, unswitching
+/// produces no code duplications (equivalently, it produces a simpler loop and
+/// a new empty loop, which gets deleted). Therefore always unswitch trivial
+/// condition.
+bool LoopUnswitch::TryTrivialLoopUnswitch(bool &Changed) {
+ BasicBlock *CurrentBB = currentLoop->getHeader();
+ TerminatorInst *CurrentTerm = CurrentBB->getTerminator();
+ LLVMContext &Context = CurrentBB->getContext();
+
+ // If loop header has only one reachable successor (currently via an
+ // unconditional branch or constant foldable conditional branch, but
+ // should also consider adding constant foldable switch instruction in
+ // future), we should keep looking for trivial condition candidates in
+ // the successor as well. An alternative is to constant fold conditions
+ // and merge successors into loop header (then we only need to check header's
+ // terminator). The reason for not doing this in LoopUnswitch pass is that
+ // it could potentially break LoopPassManager's invariants. Folding dead
+ // branches could either eliminate the current loop or make other loops
+ // unreachable. LCSSA form might also not be preserved after deleting
+ // branches. The following code keeps traversing loop header's successors
+ // until it finds the trivial condition candidate (condition that is not a
+ // constant). Since unswitching generates branches with constant conditions,
+ // this scenario could be very common in practice.
+ SmallSet<BasicBlock*, 8> Visited;
+
+ while (true) {
+ // If we exit loop or reach a previous visited block, then
+ // we can not reach any trivial condition candidates (unfoldable
+ // branch instructions or switch instructions) and no unswitch
+ // can happen. Exit and return false.
+ if (!currentLoop->contains(CurrentBB) || !Visited.insert(CurrentBB).second)
+ return false;
+
+ // Check if this loop will execute any side-effecting instructions (e.g.
+ // stores, calls, volatile loads) in the part of the loop that the code
+ // *would* execute. Check the header first.
+ for (Instruction &I : *CurrentBB)
+ if (I.mayHaveSideEffects())
+ return false;
+
+ // FIXME: add check for constant foldable switch instructions.
+ if (BranchInst *BI = dyn_cast<BranchInst>(CurrentTerm)) {
+ if (BI->isUnconditional()) {
+ CurrentBB = BI->getSuccessor(0);
+ } else if (BI->getCondition() == ConstantInt::getTrue(Context)) {
+ CurrentBB = BI->getSuccessor(0);
+ } else if (BI->getCondition() == ConstantInt::getFalse(Context)) {
+ CurrentBB = BI->getSuccessor(1);
+ } else {
+ // Found a trivial condition candidate: non-foldable conditional branch.
+ break;
+ }
+ } else {
+ break;
+ }
+
+ CurrentTerm = CurrentBB->getTerminator();
+ }
+
+ // CondVal is the condition that controls the trivial condition.
+ // LoopExitBB is the BasicBlock that loop exits when meets trivial condition.
+ Constant *CondVal = nullptr;
+ BasicBlock *LoopExitBB = nullptr;
+
+ if (BranchInst *BI = dyn_cast<BranchInst>(CurrentTerm)) {
+ // If this isn't branching on an invariant condition, we can't unswitch it.
+ if (!BI->isConditional())
+ return false;
+
+ Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
+ currentLoop, Changed);
+
+ // Unswitch only if the trivial condition itself is an LIV (not
+ // partial LIV which could occur in and/or)
+ if (!LoopCond || LoopCond != BI->getCondition())
+ return false;
+
+ // Check to see if a successor of the branch is guaranteed to
+ // exit through a unique exit block without having any
+ // side-effects. If so, determine the value of Cond that causes
+ // it to do this.
+ if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
+ BI->getSuccessor(0)))) {
+ CondVal = ConstantInt::getTrue(Context);
+ } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
+ BI->getSuccessor(1)))) {
+ CondVal = ConstantInt::getFalse(Context);
+ }
+
+ // If we didn't find a single unique LoopExit block, or if the loop exit
+ // block contains phi nodes, this isn't trivial.
+ if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
+ return false; // Can't handle this.
+
+ UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, LoopExitBB,
+ CurrentTerm);
+ ++NumBranches;
+ return true;
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurrentTerm)) {
+ // If this isn't switching on an invariant condition, we can't unswitch it.
+ Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
+ currentLoop, Changed);
+
+ // Unswitch only if the trivial condition itself is an LIV (not
+ // partial LIV which could occur in and/or)
+ if (!LoopCond || LoopCond != SI->getCondition())
+ return false;
+
+ // Check to see if a successor of the switch is guaranteed to go to the
+ // latch block or exit through a one exit block without having any
+ // side-effects. If so, determine the value of Cond that causes it to do
+ // this.
+ // Note that we can't trivially unswitch on the default case or
+ // on already unswitched cases.
+ for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
+ i != e; ++i) {
+ BasicBlock *LoopExitCandidate;
+ if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
+ i.getCaseSuccessor()))) {
+ // Okay, we found a trivial case, remember the value that is trivial.
+ ConstantInt *CaseVal = i.getCaseValue();
+
+ // Check that it was not unswitched before, since already unswitched
+ // trivial vals are looks trivial too.
+ if (BranchesInfo.isUnswitched(SI, CaseVal))
+ continue;
+ LoopExitBB = LoopExitCandidate;
+ CondVal = CaseVal;
+ break;
+ }
+ }
+
+ // If we didn't find a single unique LoopExit block, or if the loop exit
+ // block contains phi nodes, this isn't trivial.
+ if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
+ return false; // Can't handle this.
+
+ UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, LoopExitBB,
+ nullptr);
+ ++NumSwitches;
+ return true;
+ }
+ return false;
+}
+
+/// Split all of the edges from inside the loop to their exit blocks.
+/// Update the appropriate Phi nodes as we do so.
void LoopUnswitch::SplitExitEdges(Loop *L,
const SmallVectorImpl<BasicBlock *> &ExitBlocks){
// Although SplitBlockPredecessors doesn't preserve loop-simplify in
// general, if we call it on all predecessors of all exits then it does.
- if (!ExitBlock->isLandingPad()) {
- SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", this);
- } else {
- SmallVector<BasicBlock*, 2> NewBBs;
- SplitLandingPadPredecessors(ExitBlock, Preds, ".us-lcssa", ".us-lcssa",
- this, NewBBs);
- }
+ SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", DT, LI,
+ /*PreserveLCSSA*/ true);
}
}
-/// UnswitchNontrivialCondition - We determined that the loop is profitable
-/// to unswitch when LIC equal Val. Split it into loop versions and test the
-/// condition outside of either loop. Return the loops created as Out1/Out2.
+/// We determined that the loop is profitable to unswitch when LIC equal Val.
+/// Split it into loop versions and test the condition outside of either loop.
+/// Return the loops created as Out1/Out2.
void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
- Loop *L) {
+ Loop *L, TerminatorInst *TI) {
Function *F = loopHeader->getParent();
DEBUG(dbgs() << "loop-unswitch: Unswitching loop %"
<< loopHeader->getName() << " [" << L->getBlocks().size()
<< " blocks] in Function " << F->getName()
<< " when '" << *Val << "' == " << *LIC << "\n");
- if (ScalarEvolution *SE = getAnalysisIfAvailable<ScalarEvolution>())
- SE->forgetLoop(L);
+ if (auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>())
+ SEWP->getSE().forgetLoop(L);
LoopBlocks.clear();
NewBlocks.clear();
// First step, split the preheader and exit blocks, and add these blocks to
// the LoopBlocks list.
- BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, this);
+ BasicBlock *NewPreheader = SplitEdge(loopPreheader, loopHeader, DT, LI);
LoopBlocks.push_back(NewPreheader);
// We want the loop to come after the preheader, but before the exit blocks.
// Splice the newly inserted blocks into the function right before the
// original preheader.
- F->getBasicBlockList().splice(NewPreheader, F->getBasicBlockList(),
- NewBlocks[0], F->end());
+ F->getBasicBlockList().splice(NewPreheader->getIterator(),
+ F->getBasicBlockList(),
+ NewBlocks[0]->getIterator(), F->end());
// FIXME: We could register any cloned assumptions instead of clearing the
// whole function's cache.
if (LandingPadInst *LPad = NewExit->getLandingPadInst()) {
PHINode *PN = PHINode::Create(LPad->getType(), 0, "",
- ExitSucc->getFirstInsertionPt());
+ &*ExitSucc->getFirstInsertionPt());
for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc);
I != E; ++I) {
for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
for (BasicBlock::iterator I = NewBlocks[i]->begin(),
E = NewBlocks[i]->end(); I != E; ++I)
- RemapInstruction(I, VMap,RF_NoModuleLevelChanges|RF_IgnoreMissingEntries);
+ RemapInstruction(&*I, VMap,
+ RF_NoModuleLevelChanges | RF_IgnoreMissingEntries);
// Rewrite the original preheader to select between versions of the loop.
BranchInst *OldBR = cast<BranchInst>(loopPreheader->getTerminator());
"Preheader splitting did not work correctly!");
// Emit the new branch that selects between the two versions of this loop.
- EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR);
+ EmitPreheaderBranchOnCondition(LIC, Val, NewBlocks[0], LoopBlocks[0], OldBR,
+ TI);
LPM->deleteSimpleAnalysisValue(OldBR, L);
OldBR->eraseFromParent();
RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true);
}
-/// RemoveFromWorklist - Remove all instances of I from the worklist vector
-/// specified.
+/// Remove all instances of I from the worklist vector specified.
static void RemoveFromWorklist(Instruction *I,
std::vector<Instruction*> &Worklist) {
Worklist.end());
}
-/// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
+/// When we find that I really equals V, remove I from the
/// program, replacing all uses with V and update the worklist.
static void ReplaceUsesOfWith(Instruction *I, Value *V,
std::vector<Instruction*> &Worklist,
++NumSimplify;
}
-// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
-// the value specified by Val in the specified loop, or we know it does NOT have
-// that value. Rewrite any uses of LIC or of properties correlated to it.
+/// We know either that the value LIC has the value specified by Val in the
+/// specified loop, or we know it does NOT have that value.
+/// Rewrite any uses of LIC or of properties correlated to it.
void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
Constant *Val,
bool IsEqual) {
// and hooked up so as to preserve the loop structure, because
// trying to update it is complicated. So instead we preserve the
// loop structure and put the block on a dead code path.
- SplitEdge(Switch, SISucc, this);
+ SplitEdge(Switch, SISucc, DT, LI);
// Compute the successors instead of relying on the return value
// of SplitEdge, since it may have split the switch successor
// after PHI nodes.
// domtree here -- instead we force it to do a full recomputation
// after the pass is complete -- but we do need to inform it of
// new blocks.
- if (DT)
- DT->addNewBlock(Abort, NewSISucc);
+ DT->addNewBlock(Abort, NewSISucc);
}
SimplifyCode(Worklist, L);
}
-/// SimplifyCode - Okay, now that we have simplified some instructions in the
-/// loop, walk over it and constant prop, dce, and fold control flow where
-/// possible. Note that this is effectively a very simple loop-structure-aware
-/// optimizer. During processing of this loop, L could very well be deleted, so
-/// it must not be used.
+/// Now that we have simplified some instructions in the loop, walk over it and
+/// constant prop, dce, and fold control flow where possible. Note that this is
+/// effectively a very simple loop-structure-aware optimizer. During processing
+/// of this loop, L could very well be deleted, so it must not be used.
///
/// FIXME: When the loop optimizer is more mature, separate this out to a new
/// pass.
///
void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
+ const DataLayout &DL = L->getHeader()->getModule()->getDataLayout();
while (!Worklist.empty()) {
Instruction *I = Worklist.back();
Worklist.pop_back();
// See if instruction simplification can hack this up. This is common for
// things like "select false, X, Y" after unswitching made the condition be
// 'false'. TODO: update the domtree properly so we can pass it here.
- if (Value *V = SimplifyInstruction(I))
+ if (Value *V = SimplifyInstruction(I, DL))
if (LI->replacementPreservesLCSSAForm(I, V)) {
ReplaceUsesOfWith(I, V, Worklist, L, LPM);
continue;
Succ->replaceAllUsesWith(Pred);
// Move all of the successor contents from Succ to Pred.
- Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
- Succ->end());
+ Pred->getInstList().splice(BI->getIterator(), Succ->getInstList(),
+ Succ->begin(), Succ->end());
LPM->deleteSimpleAnalysisValue(BI, L);
BI->eraseFromParent();
RemoveFromWorklist(BI, Worklist);
projects / oota-llvm.git / blobdiff