[llvm] r244851 - [LIR] Remove the dedicated class for popcount recognition and sink the
Chandler Carruth via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 12 17:44:29 PDT 2015
Author: chandlerc
Date: Wed Aug 12 19:44:29 2015
New Revision: 244851
URL: http://llvm.org/viewvc/llvm-project?rev=244851&view=rev
Log:
[LIR] Remove the dedicated class for popcount recognition and sink the
code into methods on LoopIdiomRecognize.
This simplifies the code somewhat and also makes it much easier to move
the analyses around. Ultimately, the separate class wasn't providing
significant value over methods -- it contained the precondition basic
block and the current loop. The current loop is already available and
the precondition block wasn't needed everywhere and is easy to pass
around.
In several cases I just moved things to be static functions because they
already accepted most of their inputs as arguments.
This doesn't fix the way we manage analyses yet, that will be the next
patch, but it already makes the code over 50 lines shorter.
No functionality changed.
Modified:
llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp?rev=244851&r1=244850&r2=244851&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp Wed Aug 12 19:44:29 2015
@@ -67,50 +67,6 @@ STATISTIC(NumMemCpy, "Number of memcpy's
namespace {
-class LoopIdiomRecognize;
-
-/// This class is to recoginize idioms of population-count conducted in
-/// a noncountable loop. Currently it only recognizes this pattern:
-/// \code
-/// while(x) {cnt++; ...; x &= x - 1; ...}
-/// \endcode
-class NclPopcountRecognize {
- LoopIdiomRecognize &LIR;
- Loop *CurLoop;
- BasicBlock *PreCondBB;
-
- typedef IRBuilder<> IRBuilderTy;
-
-public:
- explicit NclPopcountRecognize(LoopIdiomRecognize &TheLIR);
- bool recognize();
-
-private:
- /// Take a glimpse of the loop to see if we need to go ahead recoginizing
- /// the idiom.
- bool preliminaryScreen();
-
- /// Check if the given conditional branch is based on the comparison
- /// between a variable and zero, and if the variable is non-zero, the
- /// control yields to the loop entry. If the branch matches the behavior,
- /// the variable involved in the comparion is returned. This function will
- /// be called to see if the precondition and postcondition of the loop
- /// are in desirable form.
- Value *matchCondition(BranchInst *Br, BasicBlock *NonZeroTarget) const;
-
- /// Return true iff the idiom is detected in the loop. and 1) \p CntInst
- /// is set to the instruction counting the population bit. 2) \p CntPhi
- /// is set to the corresponding phi node. 3) \p Var is set to the value
- /// whose population bits are being counted.
- bool detectIdiom(Instruction *&CntInst, PHINode *&CntPhi, Value *&Var) const;
-
- /// Insert ctpop intrinsic function and some obviously dead instructions.
- void transform(Instruction *CntInst, PHINode *CntPhi, Value *Var);
-
- /// Create llvm.ctpop.* intrinsic function.
- CallInst *createPopcntIntrinsic(IRBuilderTy &IRB, Value *Val, DebugLoc DL);
-};
-
class LoopIdiomRecognize : public LoopPass {
Loop *CurLoop;
DominatorTree *DT;
@@ -200,6 +156,10 @@ private:
bool runOnNoncountableLoop();
+ bool recognizePopcount();
+ void transformLoopToPopcount(BasicBlock *PreCondBB, Instruction *CntInst,
+ PHINode *CntPhi, Value *Var);
+
/// @}
};
@@ -236,838 +196,829 @@ static void deleteDeadInstruction(Instru
//===----------------------------------------------------------------------===//
//
-// Implementation of NclPopcountRecognize
+// Implementation of LoopIdiomRecognize
//
//===----------------------------------------------------------------------===//
-NclPopcountRecognize::NclPopcountRecognize(LoopIdiomRecognize &TheLIR)
- : LIR(TheLIR), CurLoop(TheLIR.getLoop()), PreCondBB(nullptr) {}
-
-bool NclPopcountRecognize::preliminaryScreen() {
- const TargetTransformInfo *TTI = LIR.getTargetTransformInfo();
- if (TTI->getPopcntSupport(32) != TargetTransformInfo::PSK_FastHardware)
- return false;
-
- // Counting population are usually conducted by few arithmetic instructions.
- // Such instructions can be easilly "absorbed" by vacant slots in a
- // non-compact loop. Therefore, recognizing popcount idiom only makes sense
- // in a compact loop.
-
- // Give up if the loop has multiple blocks or multiple backedges.
- if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
+bool LoopIdiomRecognize::runOnLoop(Loop *L, LPPassManager &LPM) {
+ if (skipOptnoneFunction(L))
return false;
- BasicBlock *LoopBody = *(CurLoop->block_begin());
- if (LoopBody->size() >= 20) {
- // The loop is too big, bail out.
- return false;
- }
+ CurLoop = L;
- // It should have a preheader containing nothing but an unconditional branch.
- BasicBlock *PH = CurLoop->getLoopPreheader();
- if (!PH)
- return false;
- if (&PH->front() != PH->getTerminator())
- return false;
- auto *EntryBI = dyn_cast<BranchInst>(PH->getTerminator());
- if (!EntryBI || EntryBI->isConditional())
+ // If the loop could not be converted to canonical form, it must have an
+ // indirectbr in it, just give up.
+ if (!L->getLoopPreheader())
return false;
- // It should have a precondition block where the generated popcount instrinsic
- // function can be inserted.
- PreCondBB = PH->getSinglePredecessor();
- if (!PreCondBB)
- return false;
- auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
- if (!PreCondBI || PreCondBI->isUnconditional())
+ // Disable loop idiom recognition if the function's name is a common idiom.
+ StringRef Name = L->getHeader()->getParent()->getName();
+ if (Name == "memset" || Name == "memcpy")
return false;
- return true;
+ SE = &getAnalysis<ScalarEvolution>();
+ if (SE->hasLoopInvariantBackedgeTakenCount(L))
+ return runOnCountableLoop();
+ return runOnNoncountableLoop();
}
-Value *NclPopcountRecognize::matchCondition(BranchInst *Br,
- BasicBlock *LoopEntry) const {
- if (!Br || !Br->isConditional())
- return nullptr;
+bool LoopIdiomRecognize::runOnCountableLoop() {
+ const SCEV *BECount = SE->getBackedgeTakenCount(CurLoop);
+ assert(!isa<SCEVCouldNotCompute>(BECount) &&
+ "runOnCountableLoop() called on a loop without a predictable"
+ "backedge-taken count");
- ICmpInst *Cond = dyn_cast<ICmpInst>(Br->getCondition());
- if (!Cond)
- return nullptr;
+ // If this loop executes exactly one time, then it should be peeled, not
+ // optimized by this pass.
+ if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
+ if (BECst->getValue()->getValue() == 0)
+ return false;
- ConstantInt *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
- if (!CmpZero || !CmpZero->isZero())
- return nullptr;
+ // set DT
+ (void)getDominatorTree();
- ICmpInst::Predicate Pred = Cond->getPredicate();
- if ((Pred == ICmpInst::ICMP_NE && Br->getSuccessor(0) == LoopEntry) ||
- (Pred == ICmpInst::ICMP_EQ && Br->getSuccessor(1) == LoopEntry))
- return Cond->getOperand(0);
+ LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+ TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
- return nullptr;
-}
+ // set TLI
+ (void)getTargetLibraryInfo();
-bool NclPopcountRecognize::detectIdiom(Instruction *&CntInst, PHINode *&CntPhi,
- Value *&Var) const {
- // Following code tries to detect this idiom:
- //
- // if (x0 != 0)
- // goto loop-exit // the precondition of the loop
- // cnt0 = init-val;
- // do {
- // x1 = phi (x0, x2);
- // cnt1 = phi(cnt0, cnt2);
- //
- // cnt2 = cnt1 + 1;
- // ...
- // x2 = x1 & (x1 - 1);
- // ...
- // } while(x != 0);
- //
- // loop-exit:
- //
+ SmallVector<BasicBlock *, 8> ExitBlocks;
+ CurLoop->getUniqueExitBlocks(ExitBlocks);
- // step 1: Check to see if the look-back branch match this pattern:
- // "if (a!=0) goto loop-entry".
- BasicBlock *LoopEntry;
- Instruction *DefX2, *CountInst;
- Value *VarX1, *VarX0;
- PHINode *PhiX, *CountPhi;
+ DEBUG(dbgs() << "loop-idiom Scanning: F["
+ << CurLoop->getHeader()->getParent()->getName() << "] Loop %"
+ << CurLoop->getHeader()->getName() << "\n");
- DefX2 = CountInst = nullptr;
- VarX1 = VarX0 = nullptr;
- PhiX = CountPhi = nullptr;
- LoopEntry = *(CurLoop->block_begin());
+ bool MadeChange = false;
+ // Scan all the blocks in the loop that are not in subloops.
+ for (auto *BB : CurLoop->getBlocks()) {
+ // Ignore blocks in subloops.
+ if (LI.getLoopFor(BB) != CurLoop)
+ continue;
- // step 1: Check if the loop-back branch is in desirable form.
- {
- if (Value *T = matchCondition(
- dyn_cast<BranchInst>(LoopEntry->getTerminator()), LoopEntry))
- DefX2 = dyn_cast<Instruction>(T);
- else
- return false;
+ MadeChange |= runOnLoopBlock(BB, BECount, ExitBlocks);
}
+ return MadeChange;
+}
- // step 2: detect instructions corresponding to "x2 = x1 & (x1 - 1)"
- {
- if (!DefX2 || DefX2->getOpcode() != Instruction::And)
+/// runOnLoopBlock - Process the specified block, which lives in a counted loop
+/// with the specified backedge count. This block is known to be in the current
+/// loop and not in any subloops.
+bool LoopIdiomRecognize::runOnLoopBlock(
+ BasicBlock *BB, const SCEV *BECount,
+ SmallVectorImpl<BasicBlock *> &ExitBlocks) {
+ // We can only promote stores in this block if they are unconditionally
+ // executed in the loop. For a block to be unconditionally executed, it has
+ // to dominate all the exit blocks of the loop. Verify this now.
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
+ if (!DT->dominates(BB, ExitBlocks[i]))
return false;
- BinaryOperator *SubOneOp;
+ bool MadeChange = false;
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
+ Instruction *Inst = I++;
+ // Look for store instructions, which may be optimized to memset/memcpy.
+ if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
+ WeakVH InstPtr(I);
+ if (!processLoopStore(SI, BECount))
+ continue;
+ MadeChange = true;
- if ((SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(0))))
- VarX1 = DefX2->getOperand(1);
- else {
- VarX1 = DefX2->getOperand(0);
- SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(1));
+ // If processing the store invalidated our iterator, start over from the
+ // top of the block.
+ if (!InstPtr)
+ I = BB->begin();
+ continue;
}
- if (!SubOneOp)
- return false;
- Instruction *SubInst = cast<Instruction>(SubOneOp);
- ConstantInt *Dec = dyn_cast<ConstantInt>(SubInst->getOperand(1));
- if (!Dec ||
- !((SubInst->getOpcode() == Instruction::Sub && Dec->isOne()) ||
- (SubInst->getOpcode() == Instruction::Add &&
- Dec->isAllOnesValue()))) {
- return false;
- }
- }
+ // Look for memset instructions, which may be optimized to a larger memset.
+ if (MemSetInst *MSI = dyn_cast<MemSetInst>(Inst)) {
+ WeakVH InstPtr(I);
+ if (!processLoopMemSet(MSI, BECount))
+ continue;
+ MadeChange = true;
- // step 3: Check the recurrence of variable X
- {
- PhiX = dyn_cast<PHINode>(VarX1);
- if (!PhiX ||
- (PhiX->getOperand(0) != DefX2 && PhiX->getOperand(1) != DefX2)) {
- return false;
+ // If processing the memset invalidated our iterator, start over from the
+ // top of the block.
+ if (!InstPtr)
+ I = BB->begin();
+ continue;
}
}
- // step 4: Find the instruction which count the population: cnt2 = cnt1 + 1
- {
- CountInst = nullptr;
- for (BasicBlock::iterator Iter = LoopEntry->getFirstNonPHI(),
- IterE = LoopEntry->end();
- Iter != IterE; Iter++) {
- Instruction *Inst = Iter;
- if (Inst->getOpcode() != Instruction::Add)
- continue;
+ return MadeChange;
+}
- ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
- if (!Inc || !Inc->isOne())
- continue;
+/// processLoopStore - See if this store can be promoted to a memset or memcpy.
+bool LoopIdiomRecognize::processLoopStore(StoreInst *SI, const SCEV *BECount) {
+ if (!SI->isSimple())
+ return false;
- PHINode *Phi = dyn_cast<PHINode>(Inst->getOperand(0));
- if (!Phi || Phi->getParent() != LoopEntry)
- continue;
+ Value *StoredVal = SI->getValueOperand();
+ Value *StorePtr = SI->getPointerOperand();
- // Check if the result of the instruction is live of the loop.
- bool LiveOutLoop = false;
- for (User *U : Inst->users()) {
- if ((cast<Instruction>(U))->getParent() != LoopEntry) {
- LiveOutLoop = true;
- break;
- }
- }
+ // Reject stores that are so large that they overflow an unsigned.
+ auto &DL = CurLoop->getHeader()->getModule()->getDataLayout();
+ uint64_t SizeInBits = DL.getTypeSizeInBits(StoredVal->getType());
+ if ((SizeInBits & 7) || (SizeInBits >> 32) != 0)
+ return false;
- if (LiveOutLoop) {
- CountInst = Inst;
- CountPhi = Phi;
- break;
- }
+ // See if the pointer expression is an AddRec like {base,+,1} on the current
+ // loop, which indicates a strided store. If we have something else, it's a
+ // random store we can't handle.
+ const SCEVAddRecExpr *StoreEv =
+ dyn_cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
+ if (!StoreEv || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
+ return false;
+
+ // Check to see if the stride matches the size of the store. If so, then we
+ // know that every byte is touched in the loop.
+ unsigned StoreSize = (unsigned)SizeInBits >> 3;
+ const SCEVConstant *Stride = dyn_cast<SCEVConstant>(StoreEv->getOperand(1));
+
+ if (!Stride || StoreSize != Stride->getValue()->getValue()) {
+ // TODO: Could also handle negative stride here someday, that will require
+ // the validity check in mayLoopAccessLocation to be updated though.
+ // Enable this to print exact negative strides.
+ if (0 && Stride && StoreSize == -Stride->getValue()->getValue()) {
+ dbgs() << "NEGATIVE STRIDE: " << *SI << "\n";
+ dbgs() << "BB: " << *SI->getParent();
}
- if (!CountInst)
- return false;
+ return false;
}
- // step 5: check if the precondition is in this form:
- // "if (x != 0) goto loop-head ; else goto somewhere-we-don't-care;"
- {
- auto *PreCondBr = dyn_cast<BranchInst>(PreCondBB->getTerminator());
- Value *T = matchCondition(PreCondBr, CurLoop->getLoopPreheader());
- if (T != PhiX->getOperand(0) && T != PhiX->getOperand(1))
- return false;
-
- CntInst = CountInst;
- CntPhi = CountPhi;
- Var = T;
+ // See if we can optimize just this store in isolation.
+ if (processLoopStridedStore(StorePtr, StoreSize, SI->getAlignment(),
+ StoredVal, SI, StoreEv, BECount))
+ return true;
+
+ // If the stored value is a strided load in the same loop with the same stride
+ // this this may be transformable into a memcpy. This kicks in for stuff like
+ // for (i) A[i] = B[i];
+ if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
+ const SCEVAddRecExpr *LoadEv =
+ dyn_cast<SCEVAddRecExpr>(SE->getSCEV(LI->getOperand(0)));
+ if (LoadEv && LoadEv->getLoop() == CurLoop && LoadEv->isAffine() &&
+ StoreEv->getOperand(1) == LoadEv->getOperand(1) && LI->isSimple())
+ if (processLoopStoreOfLoopLoad(SI, StoreSize, StoreEv, LoadEv, BECount))
+ return true;
}
+ // errs() << "UNHANDLED strided store: " << *StoreEv << " - " << *SI << "\n";
- return true;
+ return false;
}
-void NclPopcountRecognize::transform(Instruction *CntInst, PHINode *CntPhi,
- Value *Var) {
-
- ScalarEvolution *SE = LIR.getScalarEvolution();
- TargetLibraryInfo *TLI = LIR.getTargetLibraryInfo();
- BasicBlock *PreHead = CurLoop->getLoopPreheader();
- auto *PreCondBr = dyn_cast<BranchInst>(PreCondBB->getTerminator());
- const DebugLoc DL = CntInst->getDebugLoc();
+/// processLoopMemSet - See if this memset can be promoted to a large memset.
+bool LoopIdiomRecognize::processLoopMemSet(MemSetInst *MSI,
+ const SCEV *BECount) {
+ // We can only handle non-volatile memsets with a constant size.
+ if (MSI->isVolatile() || !isa<ConstantInt>(MSI->getLength()))
+ return false;
- // Assuming before transformation, the loop is following:
- // if (x) // the precondition
- // do { cnt++; x &= x - 1; } while(x);
+ // If we're not allowed to hack on memset, we fail.
+ if (!TLI->has(LibFunc::memset))
+ return false;
- // Step 1: Insert the ctpop instruction at the end of the precondition block
- IRBuilderTy Builder(PreCondBr);
- Value *PopCnt, *PopCntZext, *NewCount, *TripCnt;
- {
- PopCnt = createPopcntIntrinsic(Builder, Var, DL);
- NewCount = PopCntZext =
- Builder.CreateZExtOrTrunc(PopCnt, cast<IntegerType>(CntPhi->getType()));
+ Value *Pointer = MSI->getDest();
- if (NewCount != PopCnt)
- (cast<Instruction>(NewCount))->setDebugLoc(DL);
+ // See if the pointer expression is an AddRec like {base,+,1} on the current
+ // loop, which indicates a strided store. If we have something else, it's a
+ // random store we can't handle.
+ const SCEVAddRecExpr *Ev = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Pointer));
+ if (!Ev || Ev->getLoop() != CurLoop || !Ev->isAffine())
+ return false;
- // TripCnt is exactly the number of iterations the loop has
- TripCnt = NewCount;
+ // Reject memsets that are so large that they overflow an unsigned.
+ uint64_t SizeInBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
+ if ((SizeInBytes >> 32) != 0)
+ return false;
- // If the population counter's initial value is not zero, insert Add Inst.
- Value *CntInitVal = CntPhi->getIncomingValueForBlock(PreHead);
- ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
- if (!InitConst || !InitConst->isZero()) {
- NewCount = Builder.CreateAdd(NewCount, CntInitVal);
- (cast<Instruction>(NewCount))->setDebugLoc(DL);
- }
- }
+ // Check to see if the stride matches the size of the memset. If so, then we
+ // know that every byte is touched in the loop.
+ const SCEVConstant *Stride = dyn_cast<SCEVConstant>(Ev->getOperand(1));
- // Step 2: Replace the precondition from "if(x == 0) goto loop-exit" to
- // "if(NewCount == 0) loop-exit". Withtout this change, the intrinsic
- // function would be partial dead code, and downstream passes will drag
- // it back from the precondition block to the preheader.
- {
- ICmpInst *PreCond = cast<ICmpInst>(PreCondBr->getCondition());
+ // TODO: Could also handle negative stride here someday, that will require the
+ // validity check in mayLoopAccessLocation to be updated though.
+ if (!Stride || MSI->getLength() != Stride->getValue())
+ return false;
- Value *Opnd0 = PopCntZext;
- Value *Opnd1 = ConstantInt::get(PopCntZext->getType(), 0);
- if (PreCond->getOperand(0) != Var)
- std::swap(Opnd0, Opnd1);
+ return processLoopStridedStore(Pointer, (unsigned)SizeInBytes,
+ MSI->getAlignment(), MSI->getValue(), MSI, Ev,
+ BECount);
+}
- ICmpInst *NewPreCond = cast<ICmpInst>(
- Builder.CreateICmp(PreCond->getPredicate(), Opnd0, Opnd1));
- PreCondBr->setCondition(NewPreCond);
+/// mayLoopAccessLocation - Return true if the specified loop might access the
+/// specified pointer location, which is a loop-strided access. The 'Access'
+/// argument specifies what the verboten forms of access are (read or write).
+static bool mayLoopAccessLocation(Value *Ptr, ModRefInfo Access, Loop *L,
+ const SCEV *BECount, unsigned StoreSize,
+ AliasAnalysis &AA,
+ Instruction *IgnoredStore) {
+ // Get the location that may be stored across the loop. Since the access is
+ // strided positively through memory, we say that the modified location starts
+ // at the pointer and has infinite size.
+ uint64_t AccessSize = MemoryLocation::UnknownSize;
- RecursivelyDeleteTriviallyDeadInstructions(PreCond, TLI);
- }
+ // If the loop iterates a fixed number of times, we can refine the access size
+ // to be exactly the size of the memset, which is (BECount+1)*StoreSize
+ if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
+ AccessSize = (BECst->getValue()->getZExtValue() + 1) * StoreSize;
- // Step 3: Note that the population count is exactly the trip count of the
- // loop in question, which enble us to to convert the loop from noncountable
- // loop into a countable one. The benefit is twofold:
- //
- // - If the loop only counts population, the entire loop become dead after
- // the transformation. It is lots easier to prove a countable loop dead
- // than to prove a noncountable one. (In some C dialects, a infite loop
- // isn't dead even if it computes nothing useful. In general, DCE needs
- // to prove a noncountable loop finite before safely delete it.)
- //
- // - If the loop also performs something else, it remains alive.
- // Since it is transformed to countable form, it can be aggressively
- // optimized by some optimizations which are in general not applicable
- // to a noncountable loop.
- //
- // After this step, this loop (conceptually) would look like following:
- // newcnt = __builtin_ctpop(x);
- // t = newcnt;
- // if (x)
- // do { cnt++; x &= x-1; t--) } while (t > 0);
- BasicBlock *Body = *(CurLoop->block_begin());
- {
- auto *LbBr = dyn_cast<BranchInst>(Body->getTerminator());
- ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
- Type *Ty = TripCnt->getType();
+ // TODO: For this to be really effective, we have to dive into the pointer
+ // operand in the store. Store to &A[i] of 100 will always return may alias
+ // with store of &A[100], we need to StoreLoc to be "A" with size of 100,
+ // which will then no-alias a store to &A[100].
+ MemoryLocation StoreLoc(Ptr, AccessSize);
- PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", Body->begin());
+ for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
+ ++BI)
+ for (BasicBlock::iterator I = (*BI)->begin(), E = (*BI)->end(); I != E; ++I)
+ if (&*I != IgnoredStore && (AA.getModRefInfo(I, StoreLoc) & Access))
+ return true;
- Builder.SetInsertPoint(LbCond);
- Value *Opnd1 = cast<Value>(TcPhi);
- Value *Opnd2 = cast<Value>(ConstantInt::get(Ty, 1));
- Instruction *TcDec = cast<Instruction>(
- Builder.CreateSub(Opnd1, Opnd2, "tcdec", false, true));
+ return false;
+}
- TcPhi->addIncoming(TripCnt, PreHead);
- TcPhi->addIncoming(TcDec, Body);
+/// getMemSetPatternValue - If a strided store of the specified value is safe to
+/// turn into a memset_pattern16, return a ConstantArray of 16 bytes that should
+/// be passed in. Otherwise, return null.
+///
+/// Note that we don't ever attempt to use memset_pattern8 or 4, because these
+/// just replicate their input array and then pass on to memset_pattern16.
+static Constant *getMemSetPatternValue(Value *V, const DataLayout &DL) {
+ // If the value isn't a constant, we can't promote it to being in a constant
+ // array. We could theoretically do a store to an alloca or something, but
+ // that doesn't seem worthwhile.
+ Constant *C = dyn_cast<Constant>(V);
+ if (!C)
+ return nullptr;
- CmpInst::Predicate Pred =
- (LbBr->getSuccessor(0) == Body) ? CmpInst::ICMP_UGT : CmpInst::ICMP_SLE;
- LbCond->setPredicate(Pred);
- LbCond->setOperand(0, TcDec);
- LbCond->setOperand(1, cast<Value>(ConstantInt::get(Ty, 0)));
- }
+ // Only handle simple values that are a power of two bytes in size.
+ uint64_t Size = DL.getTypeSizeInBits(V->getType());
+ if (Size == 0 || (Size & 7) || (Size & (Size - 1)))
+ return nullptr;
- // Step 4: All the references to the original population counter outside
- // the loop are replaced with the NewCount -- the value returned from
- // __builtin_ctpop().
- CntInst->replaceUsesOutsideBlock(NewCount, Body);
+ // Don't care enough about darwin/ppc to implement this.
+ if (DL.isBigEndian())
+ return nullptr;
- // step 5: Forget the "non-computable" trip-count SCEV associated with the
- // loop. The loop would otherwise not be deleted even if it becomes empty.
- SE->forgetLoop(CurLoop);
-}
+ // Convert to size in bytes.
+ Size /= 8;
-CallInst *NclPopcountRecognize::createPopcntIntrinsic(IRBuilderTy &IRBuilder,
- Value *Val, DebugLoc DL) {
- Value *Ops[] = {Val};
- Type *Tys[] = {Val->getType()};
+ // TODO: If CI is larger than 16-bytes, we can try slicing it in half to see
+ // if the top and bottom are the same (e.g. for vectors and large integers).
+ if (Size > 16)
+ return nullptr;
- Module *M = (*(CurLoop->block_begin()))->getParent()->getParent();
- Value *Func = Intrinsic::getDeclaration(M, Intrinsic::ctpop, Tys);
- CallInst *CI = IRBuilder.CreateCall(Func, Ops);
- CI->setDebugLoc(DL);
+ // If the constant is exactly 16 bytes, just use it.
+ if (Size == 16)
+ return C;
- return CI;
+ // Otherwise, we'll use an array of the constants.
+ unsigned ArraySize = 16 / Size;
+ ArrayType *AT = ArrayType::get(V->getType(), ArraySize);
+ return ConstantArray::get(AT, std::vector<Constant *>(ArraySize, C));
}
-/// recognize - detect population count idiom in a non-countable loop. If
-/// detected, transform the relevant code to popcount intrinsic function
-/// call, and return true; otherwise, return false.
-bool NclPopcountRecognize::recognize() {
- if (!LIR.getTargetTransformInfo())
- return false;
-
- LIR.getScalarEvolution();
+/// processLoopStridedStore - We see a strided store of some value. If we can
+/// transform this into a memset or memset_pattern in the loop preheader, do so.
+bool LoopIdiomRecognize::processLoopStridedStore(
+ Value *DestPtr, unsigned StoreSize, unsigned StoreAlignment,
+ Value *StoredVal, Instruction *TheStore, const SCEVAddRecExpr *Ev,
+ const SCEV *BECount) {
- if (!preliminaryScreen())
- return false;
+ // If the stored value is a byte-wise value (like i32 -1), then it may be
+ // turned into a memset of i8 -1, assuming that all the consecutive bytes
+ // are stored. A store of i32 0x01020304 can never be turned into a memset,
+ // but it can be turned into memset_pattern if the target supports it.
+ Value *SplatValue = isBytewiseValue(StoredVal);
+ Constant *PatternValue = nullptr;
+ auto &DL = CurLoop->getHeader()->getModule()->getDataLayout();
+ unsigned DestAS = DestPtr->getType()->getPointerAddressSpace();
- Instruction *CntInst;
- PHINode *CntPhi;
- Value *Val;
- if (!detectIdiom(CntInst, CntPhi, Val))
+ // If we're allowed to form a memset, and the stored value would be acceptable
+ // for memset, use it.
+ if (SplatValue && TLI->has(LibFunc::memset) &&
+ // Verify that the stored value is loop invariant. If not, we can't
+ // promote the memset.
+ CurLoop->isLoopInvariant(SplatValue)) {
+ // Keep and use SplatValue.
+ PatternValue = nullptr;
+ } else if (DestAS == 0 && TLI->has(LibFunc::memset_pattern16) &&
+ (PatternValue = getMemSetPatternValue(StoredVal, DL))) {
+ // Don't create memset_pattern16s with address spaces.
+ // It looks like we can use PatternValue!
+ SplatValue = nullptr;
+ } else {
+ // Otherwise, this isn't an idiom we can transform. For example, we can't
+ // do anything with a 3-byte store.
return false;
+ }
- transform(CntInst, CntPhi, Val);
- return true;
-}
+ // The trip count of the loop and the base pointer of the addrec SCEV is
+ // guaranteed to be loop invariant, which means that it should dominate the
+ // header. This allows us to insert code for it in the preheader.
+ BasicBlock *Preheader = CurLoop->getLoopPreheader();
+ IRBuilder<> Builder(Preheader->getTerminator());
+ SCEVExpander Expander(*SE, DL, "loop-idiom");
-//===----------------------------------------------------------------------===//
-//
-// Implementation of LoopIdiomRecognize
-//
-//===----------------------------------------------------------------------===//
+ Type *DestInt8PtrTy = Builder.getInt8PtrTy(DestAS);
-bool LoopIdiomRecognize::runOnLoop(Loop *L, LPPassManager &LPM) {
- if (skipOptnoneFunction(L))
- return false;
-
- CurLoop = L;
-
- // If the loop could not be converted to canonical form, it must have an
- // indirectbr in it, just give up.
- if (!L->getLoopPreheader())
- return false;
+ // Okay, we have a strided store "p[i]" of a splattable value. We can turn
+ // this into a memset in the loop preheader now if we want. However, this
+ // would be unsafe to do if there is anything else in the loop that may read
+ // or write to the aliased location. Check for any overlap by generating the
+ // base pointer and checking the region.
+ Value *BasePtr = Expander.expandCodeFor(Ev->getStart(), DestInt8PtrTy,
+ Preheader->getTerminator());
- // Disable loop idiom recognition if the function's name is a common idiom.
- StringRef Name = L->getHeader()->getParent()->getName();
- if (Name == "memset" || Name == "memcpy")
+ if (mayLoopAccessLocation(BasePtr, MRI_ModRef, CurLoop, BECount, StoreSize,
+ getAnalysis<AliasAnalysis>(), TheStore)) {
+ Expander.clear();
+ // If we generated new code for the base pointer, clean up.
+ RecursivelyDeleteTriviallyDeadInstructions(BasePtr, TLI);
return false;
+ }
- SE = &getAnalysis<ScalarEvolution>();
- if (SE->hasLoopInvariantBackedgeTakenCount(L))
- return runOnCountableLoop();
- return runOnNoncountableLoop();
-}
-
-bool LoopIdiomRecognize::runOnCountableLoop() {
- const SCEV *BECount = SE->getBackedgeTakenCount(CurLoop);
- assert(!isa<SCEVCouldNotCompute>(BECount) &&
- "runOnCountableLoop() called on a loop without a predictable"
- "backedge-taken count");
+ // Okay, everything looks good, insert the memset.
- // If this loop executes exactly one time, then it should be peeled, not
- // optimized by this pass.
- if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
- if (BECst->getValue()->getValue() == 0)
- return false;
+ // The # stored bytes is (BECount+1)*Size. Expand the trip count out to
+ // pointer size if it isn't already.
+ Type *IntPtr = Builder.getIntPtrTy(DL, DestAS);
+ BECount = SE->getTruncateOrZeroExtend(BECount, IntPtr);
- // set DT
- (void)getDominatorTree();
+ const SCEV *NumBytesS =
+ SE->getAddExpr(BECount, SE->getConstant(IntPtr, 1), SCEV::FlagNUW);
+ if (StoreSize != 1) {
+ NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtr, StoreSize),
+ SCEV::FlagNUW);
+ }
- LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
- TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
+ Value *NumBytes =
+ Expander.expandCodeFor(NumBytesS, IntPtr, Preheader->getTerminator());
- // set TLI
- (void)getTargetLibraryInfo();
+ CallInst *NewCall;
+ if (SplatValue) {
+ NewCall =
+ Builder.CreateMemSet(BasePtr, SplatValue, NumBytes, StoreAlignment);
+ } else {
+ // Everything is emitted in default address space
+ Type *Int8PtrTy = DestInt8PtrTy;
- SmallVector<BasicBlock *, 8> ExitBlocks;
- CurLoop->getUniqueExitBlocks(ExitBlocks);
+ Module *M = TheStore->getParent()->getParent()->getParent();
+ Value *MSP =
+ M->getOrInsertFunction("memset_pattern16", Builder.getVoidTy(),
+ Int8PtrTy, Int8PtrTy, IntPtr, (void *)nullptr);
- DEBUG(dbgs() << "loop-idiom Scanning: F["
- << CurLoop->getHeader()->getParent()->getName() << "] Loop %"
- << CurLoop->getHeader()->getName() << "\n");
+ // Otherwise we should form a memset_pattern16. PatternValue is known to be
+ // an constant array of 16-bytes. Plop the value into a mergable global.
+ GlobalVariable *GV = new GlobalVariable(*M, PatternValue->getType(), true,
+ GlobalValue::PrivateLinkage,
+ PatternValue, ".memset_pattern");
+ GV->setUnnamedAddr(true); // Ok to merge these.
+ GV->setAlignment(16);
+ Value *PatternPtr = ConstantExpr::getBitCast(GV, Int8PtrTy);
+ NewCall = Builder.CreateCall(MSP, {BasePtr, PatternPtr, NumBytes});
+ }
- bool MadeChange = false;
- // Scan all the blocks in the loop that are not in subloops.
- for (auto *BB : CurLoop->getBlocks()) {
- // Ignore blocks in subloops.
- if (LI.getLoopFor(BB) != CurLoop)
- continue;
+ DEBUG(dbgs() << " Formed memset: " << *NewCall << "\n"
+ << " from store to: " << *Ev << " at: " << *TheStore << "\n");
+ NewCall->setDebugLoc(TheStore->getDebugLoc());
- MadeChange |= runOnLoopBlock(BB, BECount, ExitBlocks);
- }
- return MadeChange;
+ // Okay, the memset has been formed. Zap the original store and anything that
+ // feeds into it.
+ deleteDeadInstruction(TheStore, TLI);
+ ++NumMemSet;
+ return true;
}
-/// runOnLoopBlock - Process the specified block, which lives in a counted loop
-/// with the specified backedge count. This block is known to be in the current
-/// loop and not in any subloops.
-bool LoopIdiomRecognize::runOnLoopBlock(
- BasicBlock *BB, const SCEV *BECount,
- SmallVectorImpl<BasicBlock *> &ExitBlocks) {
- // We can only promote stores in this block if they are unconditionally
- // executed in the loop. For a block to be unconditionally executed, it has
- // to dominate all the exit blocks of the loop. Verify this now.
- for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
- if (!DT->dominates(BB, ExitBlocks[i]))
- return false;
+/// processLoopStoreOfLoopLoad - We see a strided store whose value is a
+/// same-strided load.
+bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(
+ StoreInst *SI, unsigned StoreSize, const SCEVAddRecExpr *StoreEv,
+ const SCEVAddRecExpr *LoadEv, const SCEV *BECount) {
+ // If we're not allowed to form memcpy, we fail.
+ if (!TLI->has(LibFunc::memcpy))
+ return false;
- bool MadeChange = false;
- for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
- Instruction *Inst = I++;
- // Look for store instructions, which may be optimized to memset/memcpy.
- if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
- WeakVH InstPtr(I);
- if (!processLoopStore(SI, BECount))
- continue;
- MadeChange = true;
+ LoadInst *LI = cast<LoadInst>(SI->getValueOperand());
- // If processing the store invalidated our iterator, start over from the
- // top of the block.
- if (!InstPtr)
- I = BB->begin();
- continue;
- }
+ // The trip count of the loop and the base pointer of the addrec SCEV is
+ // guaranteed to be loop invariant, which means that it should dominate the
+ // header. This allows us to insert code for it in the preheader.
+ BasicBlock *Preheader = CurLoop->getLoopPreheader();
+ IRBuilder<> Builder(Preheader->getTerminator());
+ const DataLayout &DL = Preheader->getModule()->getDataLayout();
+ SCEVExpander Expander(*SE, DL, "loop-idiom");
- // Look for memset instructions, which may be optimized to a larger memset.
- if (MemSetInst *MSI = dyn_cast<MemSetInst>(Inst)) {
- WeakVH InstPtr(I);
- if (!processLoopMemSet(MSI, BECount))
- continue;
- MadeChange = true;
+ // Okay, we have a strided store "p[i]" of a loaded value. We can turn
+ // this into a memcpy in the loop preheader now if we want. However, this
+ // would be unsafe to do if there is anything else in the loop that may read
+ // or write the memory region we're storing to. This includes the load that
+ // feeds the stores. Check for an alias by generating the base address and
+ // checking everything.
+ Value *StoreBasePtr = Expander.expandCodeFor(
+ StoreEv->getStart(), Builder.getInt8PtrTy(SI->getPointerAddressSpace()),
+ Preheader->getTerminator());
- // If processing the memset invalidated our iterator, start over from the
- // top of the block.
- if (!InstPtr)
- I = BB->begin();
- continue;
- }
+ if (mayLoopAccessLocation(StoreBasePtr, MRI_ModRef, CurLoop, BECount,
+ StoreSize, getAnalysis<AliasAnalysis>(), SI)) {
+ Expander.clear();
+ // If we generated new code for the base pointer, clean up.
+ RecursivelyDeleteTriviallyDeadInstructions(StoreBasePtr, TLI);
+ return false;
}
- return MadeChange;
-}
+ // For a memcpy, we have to make sure that the input array is not being
+ // mutated by the loop.
+ Value *LoadBasePtr = Expander.expandCodeFor(
+ LoadEv->getStart(), Builder.getInt8PtrTy(LI->getPointerAddressSpace()),
+ Preheader->getTerminator());
-/// processLoopStore - See if this store can be promoted to a memset or memcpy.
-bool LoopIdiomRecognize::processLoopStore(StoreInst *SI, const SCEV *BECount) {
- if (!SI->isSimple())
+ if (mayLoopAccessLocation(LoadBasePtr, MRI_Mod, CurLoop, BECount, StoreSize,
+ getAnalysis<AliasAnalysis>(), SI)) {
+ Expander.clear();
+ // If we generated new code for the base pointer, clean up.
+ RecursivelyDeleteTriviallyDeadInstructions(LoadBasePtr, TLI);
+ RecursivelyDeleteTriviallyDeadInstructions(StoreBasePtr, TLI);
return false;
+ }
- Value *StoredVal = SI->getValueOperand();
- Value *StorePtr = SI->getPointerOperand();
+ // Okay, everything is safe, we can transform this!
- // Reject stores that are so large that they overflow an unsigned.
- auto &DL = CurLoop->getHeader()->getModule()->getDataLayout();
- uint64_t SizeInBits = DL.getTypeSizeInBits(StoredVal->getType());
- if ((SizeInBits & 7) || (SizeInBits >> 32) != 0)
- return false;
+ // The # stored bytes is (BECount+1)*Size. Expand the trip count out to
+ // pointer size if it isn't already.
+ Type *IntPtrTy = Builder.getIntPtrTy(DL, SI->getPointerAddressSpace());
+ BECount = SE->getTruncateOrZeroExtend(BECount, IntPtrTy);
- // See if the pointer expression is an AddRec like {base,+,1} on the current
- // loop, which indicates a strided store. If we have something else, it's a
- // random store we can't handle.
- const SCEVAddRecExpr *StoreEv =
- dyn_cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
- if (!StoreEv || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
- return false;
+ const SCEV *NumBytesS =
+ SE->getAddExpr(BECount, SE->getConstant(IntPtrTy, 1), SCEV::FlagNUW);
+ if (StoreSize != 1)
+ NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtrTy, StoreSize),
+ SCEV::FlagNUW);
- // Check to see if the stride matches the size of the store. If so, then we
- // know that every byte is touched in the loop.
- unsigned StoreSize = (unsigned)SizeInBits >> 3;
- const SCEVConstant *Stride = dyn_cast<SCEVConstant>(StoreEv->getOperand(1));
+ Value *NumBytes =
+ Expander.expandCodeFor(NumBytesS, IntPtrTy, Preheader->getTerminator());
- if (!Stride || StoreSize != Stride->getValue()->getValue()) {
- // TODO: Could also handle negative stride here someday, that will require
- // the validity check in mayLoopAccessLocation to be updated though.
- // Enable this to print exact negative strides.
- if (0 && Stride && StoreSize == -Stride->getValue()->getValue()) {
- dbgs() << "NEGATIVE STRIDE: " << *SI << "\n";
- dbgs() << "BB: " << *SI->getParent();
- }
+ CallInst *NewCall =
+ Builder.CreateMemCpy(StoreBasePtr, LoadBasePtr, NumBytes,
+ std::min(SI->getAlignment(), LI->getAlignment()));
+ NewCall->setDebugLoc(SI->getDebugLoc());
- return false;
- }
+ DEBUG(dbgs() << " Formed memcpy: " << *NewCall << "\n"
+ << " from load ptr=" << *LoadEv << " at: " << *LI << "\n"
+ << " from store ptr=" << *StoreEv << " at: " << *SI << "\n");
- // See if we can optimize just this store in isolation.
- if (processLoopStridedStore(StorePtr, StoreSize, SI->getAlignment(),
- StoredVal, SI, StoreEv, BECount))
- return true;
+ // Okay, the memset has been formed. Zap the original store and anything that
+ // feeds into it.
+ deleteDeadInstruction(SI, TLI);
+ ++NumMemCpy;
+ return true;
+}
- // If the stored value is a strided load in the same loop with the same stride
- // this this may be transformable into a memcpy. This kicks in for stuff like
- // for (i) A[i] = B[i];
- if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
- const SCEVAddRecExpr *LoadEv =
- dyn_cast<SCEVAddRecExpr>(SE->getSCEV(LI->getOperand(0)));
- if (LoadEv && LoadEv->getLoop() == CurLoop && LoadEv->isAffine() &&
- StoreEv->getOperand(1) == LoadEv->getOperand(1) && LI->isSimple())
- if (processLoopStoreOfLoopLoad(SI, StoreSize, StoreEv, LoadEv, BECount))
- return true;
- }
- // errs() << "UNHANDLED strided store: " << *StoreEv << " - " << *SI << "\n";
+bool LoopIdiomRecognize::runOnNoncountableLoop() {
+ if (recognizePopcount())
+ return true;
return false;
}
-/// processLoopMemSet - See if this memset can be promoted to a large memset.
-bool LoopIdiomRecognize::processLoopMemSet(MemSetInst *MSI,
- const SCEV *BECount) {
- // We can only handle non-volatile memsets with a constant size.
- if (MSI->isVolatile() || !isa<ConstantInt>(MSI->getLength()))
- return false;
-
- // If we're not allowed to hack on memset, we fail.
- if (!TLI->has(LibFunc::memset))
- return false;
-
- Value *Pointer = MSI->getDest();
-
- // See if the pointer expression is an AddRec like {base,+,1} on the current
- // loop, which indicates a strided store. If we have something else, it's a
- // random store we can't handle.
- const SCEVAddRecExpr *Ev = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Pointer));
- if (!Ev || Ev->getLoop() != CurLoop || !Ev->isAffine())
- return false;
+/// Check if the given conditional branch is based on the comparison between
+/// a variable and zero, and if the variable is non-zero, the control yields to
+/// the loop entry. If the branch matches the behavior, the variable involved
+/// in the comparion is returned. This function will be called to see if the
+/// precondition and postcondition of the loop are in desirable form.
+static Value *matchCondition(BranchInst *BI, BasicBlock *LoopEntry) {
+ if (!BI || !BI->isConditional())
+ return nullptr;
- // Reject memsets that are so large that they overflow an unsigned.
- uint64_t SizeInBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
- if ((SizeInBytes >> 32) != 0)
- return false;
+ ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
+ if (!Cond)
+ return nullptr;
- // Check to see if the stride matches the size of the memset. If so, then we
- // know that every byte is touched in the loop.
- const SCEVConstant *Stride = dyn_cast<SCEVConstant>(Ev->getOperand(1));
+ ConstantInt *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
+ if (!CmpZero || !CmpZero->isZero())
+ return nullptr;
- // TODO: Could also handle negative stride here someday, that will require the
- // validity check in mayLoopAccessLocation to be updated though.
- if (!Stride || MSI->getLength() != Stride->getValue())
- return false;
+ ICmpInst::Predicate Pred = Cond->getPredicate();
+ if ((Pred == ICmpInst::ICMP_NE && BI->getSuccessor(0) == LoopEntry) ||
+ (Pred == ICmpInst::ICMP_EQ && BI->getSuccessor(1) == LoopEntry))
+ return Cond->getOperand(0);
- return processLoopStridedStore(Pointer, (unsigned)SizeInBytes,
- MSI->getAlignment(), MSI->getValue(), MSI, Ev,
- BECount);
+ return nullptr;
}
-/// mayLoopAccessLocation - Return true if the specified loop might access the
-/// specified pointer location, which is a loop-strided access. The 'Access'
-/// argument specifies what the verboten forms of access are (read or write).
-static bool mayLoopAccessLocation(Value *Ptr, ModRefInfo Access, Loop *L,
- const SCEV *BECount, unsigned StoreSize,
- AliasAnalysis &AA,
- Instruction *IgnoredStore) {
- // Get the location that may be stored across the loop. Since the access is
- // strided positively through memory, we say that the modified location starts
- // at the pointer and has infinite size.
- uint64_t AccessSize = MemoryLocation::UnknownSize;
-
- // If the loop iterates a fixed number of times, we can refine the access size
- // to be exactly the size of the memset, which is (BECount+1)*StoreSize
- if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
- AccessSize = (BECst->getValue()->getZExtValue() + 1) * StoreSize;
+/// Return true iff the idiom is detected in the loop.
+///
+/// Additionally:
+/// 1) \p CntInst is set to the instruction counting the population bit.
+/// 2) \p CntPhi is set to the corresponding phi node.
+/// 3) \p Var is set to the value whose population bits are being counted.
+///
+/// The core idiom we are trying to detect is:
+/// \code
+/// if (x0 != 0)
+/// goto loop-exit // the precondition of the loop
+/// cnt0 = init-val;
+/// do {
+/// x1 = phi (x0, x2);
+/// cnt1 = phi(cnt0, cnt2);
+///
+/// cnt2 = cnt1 + 1;
+/// ...
+/// x2 = x1 & (x1 - 1);
+/// ...
+/// } while(x != 0);
+///
+/// loop-exit:
+/// \endcode
+static bool detectPopcountIdiom(Loop *CurLoop, BasicBlock *PreCondBB,
+ Instruction *&CntInst, PHINode *&CntPhi,
+ Value *&Var) {
+ // step 1: Check to see if the look-back branch match this pattern:
+ // "if (a!=0) goto loop-entry".
+ BasicBlock *LoopEntry;
+ Instruction *DefX2, *CountInst;
+ Value *VarX1, *VarX0;
+ PHINode *PhiX, *CountPhi;
- // TODO: For this to be really effective, we have to dive into the pointer
- // operand in the store. Store to &A[i] of 100 will always return may alias
- // with store of &A[100], we need to StoreLoc to be "A" with size of 100,
- // which will then no-alias a store to &A[100].
- MemoryLocation StoreLoc(Ptr, AccessSize);
+ DefX2 = CountInst = nullptr;
+ VarX1 = VarX0 = nullptr;
+ PhiX = CountPhi = nullptr;
+ LoopEntry = *(CurLoop->block_begin());
- for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
- ++BI)
- for (BasicBlock::iterator I = (*BI)->begin(), E = (*BI)->end(); I != E; ++I)
- if (&*I != IgnoredStore && (AA.getModRefInfo(I, StoreLoc) & Access))
- return true;
+ // step 1: Check if the loop-back branch is in desirable form.
+ {
+ if (Value *T = matchCondition(
+ dyn_cast<BranchInst>(LoopEntry->getTerminator()), LoopEntry))
+ DefX2 = dyn_cast<Instruction>(T);
+ else
+ return false;
+ }
- return false;
-}
+ // step 2: detect instructions corresponding to "x2 = x1 & (x1 - 1)"
+ {
+ if (!DefX2 || DefX2->getOpcode() != Instruction::And)
+ return false;
-/// getMemSetPatternValue - If a strided store of the specified value is safe to
-/// turn into a memset_pattern16, return a ConstantArray of 16 bytes that should
-/// be passed in. Otherwise, return null.
-///
-/// Note that we don't ever attempt to use memset_pattern8 or 4, because these
-/// just replicate their input array and then pass on to memset_pattern16.
-static Constant *getMemSetPatternValue(Value *V, const DataLayout &DL) {
- // If the value isn't a constant, we can't promote it to being in a constant
- // array. We could theoretically do a store to an alloca or something, but
- // that doesn't seem worthwhile.
- Constant *C = dyn_cast<Constant>(V);
- if (!C)
- return nullptr;
+ BinaryOperator *SubOneOp;
- // Only handle simple values that are a power of two bytes in size.
- uint64_t Size = DL.getTypeSizeInBits(V->getType());
- if (Size == 0 || (Size & 7) || (Size & (Size - 1)))
- return nullptr;
+ if ((SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(0))))
+ VarX1 = DefX2->getOperand(1);
+ else {
+ VarX1 = DefX2->getOperand(0);
+ SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(1));
+ }
+ if (!SubOneOp)
+ return false;
- // Don't care enough about darwin/ppc to implement this.
- if (DL.isBigEndian())
- return nullptr;
+ Instruction *SubInst = cast<Instruction>(SubOneOp);
+ ConstantInt *Dec = dyn_cast<ConstantInt>(SubInst->getOperand(1));
+ if (!Dec ||
+ !((SubInst->getOpcode() == Instruction::Sub && Dec->isOne()) ||
+ (SubInst->getOpcode() == Instruction::Add &&
+ Dec->isAllOnesValue()))) {
+ return false;
+ }
+ }
- // Convert to size in bytes.
- Size /= 8;
+ // step 3: Check the recurrence of variable X
+ {
+ PhiX = dyn_cast<PHINode>(VarX1);
+ if (!PhiX ||
+ (PhiX->getOperand(0) != DefX2 && PhiX->getOperand(1) != DefX2)) {
+ return false;
+ }
+ }
- // TODO: If CI is larger than 16-bytes, we can try slicing it in half to see
- // if the top and bottom are the same (e.g. for vectors and large integers).
- if (Size > 16)
- return nullptr;
+ // step 4: Find the instruction which count the population: cnt2 = cnt1 + 1
+ {
+ CountInst = nullptr;
+ for (BasicBlock::iterator Iter = LoopEntry->getFirstNonPHI(),
+ IterE = LoopEntry->end();
+ Iter != IterE; Iter++) {
+ Instruction *Inst = Iter;
+ if (Inst->getOpcode() != Instruction::Add)
+ continue;
- // If the constant is exactly 16 bytes, just use it.
- if (Size == 16)
- return C;
+ ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
+ if (!Inc || !Inc->isOne())
+ continue;
- // Otherwise, we'll use an array of the constants.
- unsigned ArraySize = 16 / Size;
- ArrayType *AT = ArrayType::get(V->getType(), ArraySize);
- return ConstantArray::get(AT, std::vector<Constant *>(ArraySize, C));
-}
+ PHINode *Phi = dyn_cast<PHINode>(Inst->getOperand(0));
+ if (!Phi || Phi->getParent() != LoopEntry)
+ continue;
-/// processLoopStridedStore - We see a strided store of some value. If we can
-/// transform this into a memset or memset_pattern in the loop preheader, do so.
-bool LoopIdiomRecognize::processLoopStridedStore(
- Value *DestPtr, unsigned StoreSize, unsigned StoreAlignment,
- Value *StoredVal, Instruction *TheStore, const SCEVAddRecExpr *Ev,
- const SCEV *BECount) {
+ // Check if the result of the instruction is live of the loop.
+ bool LiveOutLoop = false;
+ for (User *U : Inst->users()) {
+ if ((cast<Instruction>(U))->getParent() != LoopEntry) {
+ LiveOutLoop = true;
+ break;
+ }
+ }
- // If the stored value is a byte-wise value (like i32 -1), then it may be
- // turned into a memset of i8 -1, assuming that all the consecutive bytes
- // are stored. A store of i32 0x01020304 can never be turned into a memset,
- // but it can be turned into memset_pattern if the target supports it.
- Value *SplatValue = isBytewiseValue(StoredVal);
- Constant *PatternValue = nullptr;
- auto &DL = CurLoop->getHeader()->getModule()->getDataLayout();
- unsigned DestAS = DestPtr->getType()->getPointerAddressSpace();
+ if (LiveOutLoop) {
+ CountInst = Inst;
+ CountPhi = Phi;
+ break;
+ }
+ }
- // If we're allowed to form a memset, and the stored value would be acceptable
- // for memset, use it.
- if (SplatValue && TLI->has(LibFunc::memset) &&
- // Verify that the stored value is loop invariant. If not, we can't
- // promote the memset.
- CurLoop->isLoopInvariant(SplatValue)) {
- // Keep and use SplatValue.
- PatternValue = nullptr;
- } else if (DestAS == 0 && TLI->has(LibFunc::memset_pattern16) &&
- (PatternValue = getMemSetPatternValue(StoredVal, DL))) {
- // Don't create memset_pattern16s with address spaces.
- // It looks like we can use PatternValue!
- SplatValue = nullptr;
- } else {
- // Otherwise, this isn't an idiom we can transform. For example, we can't
- // do anything with a 3-byte store.
- return false;
+ if (!CountInst)
+ return false;
}
- // The trip count of the loop and the base pointer of the addrec SCEV is
- // guaranteed to be loop invariant, which means that it should dominate the
- // header. This allows us to insert code for it in the preheader.
- BasicBlock *Preheader = CurLoop->getLoopPreheader();
- IRBuilder<> Builder(Preheader->getTerminator());
- SCEVExpander Expander(*SE, DL, "loop-idiom");
+ // step 5: check if the precondition is in this form:
+ // "if (x != 0) goto loop-head ; else goto somewhere-we-don't-care;"
+ {
+ auto *PreCondBr = dyn_cast<BranchInst>(PreCondBB->getTerminator());
+ Value *T = matchCondition(PreCondBr, CurLoop->getLoopPreheader());
+ if (T != PhiX->getOperand(0) && T != PhiX->getOperand(1))
+ return false;
- Type *DestInt8PtrTy = Builder.getInt8PtrTy(DestAS);
+ CntInst = CountInst;
+ CntPhi = CountPhi;
+ Var = T;
+ }
+
+ return true;
+}
- // Okay, we have a strided store "p[i]" of a splattable value. We can turn
- // this into a memset in the loop preheader now if we want. However, this
- // would be unsafe to do if there is anything else in the loop that may read
- // or write to the aliased location. Check for any overlap by generating the
- // base pointer and checking the region.
- Value *BasePtr = Expander.expandCodeFor(Ev->getStart(), DestInt8PtrTy,
- Preheader->getTerminator());
+/// Recognizes a population count idiom in a non-countable loop.
+///
+/// If detected, transforms the relevant code to issue the popcount intrinsic
+/// function call, and returns true; otherwise, returns false.
+bool LoopIdiomRecognize::recognizePopcount() {
+ (void)getScalarEvolution();
+ (void)getTargetLibraryInfo();
+ (void)getTargetTransformInfo();
- if (mayLoopAccessLocation(BasePtr, MRI_ModRef, CurLoop, BECount, StoreSize,
- getAnalysis<AliasAnalysis>(), TheStore)) {
- Expander.clear();
- // If we generated new code for the base pointer, clean up.
- RecursivelyDeleteTriviallyDeadInstructions(BasePtr, TLI);
+ if (TTI->getPopcntSupport(32) != TargetTransformInfo::PSK_FastHardware)
return false;
- }
- // Okay, everything looks good, insert the memset.
+ // Counting population are usually conducted by few arithmetic instructions.
+ // Such instructions can be easilly "absorbed" by vacant slots in a
+ // non-compact loop. Therefore, recognizing popcount idiom only makes sense
+ // in a compact loop.
- // The # stored bytes is (BECount+1)*Size. Expand the trip count out to
- // pointer size if it isn't already.
- Type *IntPtr = Builder.getIntPtrTy(DL, DestAS);
- BECount = SE->getTruncateOrZeroExtend(BECount, IntPtr);
+ // Give up if the loop has multiple blocks or multiple backedges.
+ if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
+ return false;
- const SCEV *NumBytesS =
- SE->getAddExpr(BECount, SE->getConstant(IntPtr, 1), SCEV::FlagNUW);
- if (StoreSize != 1) {
- NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtr, StoreSize),
- SCEV::FlagNUW);
+ BasicBlock *LoopBody = *(CurLoop->block_begin());
+ if (LoopBody->size() >= 20) {
+ // The loop is too big, bail out.
+ return false;
}
- Value *NumBytes =
- Expander.expandCodeFor(NumBytesS, IntPtr, Preheader->getTerminator());
+ // It should have a preheader containing nothing but an unconditional branch.
+ BasicBlock *PH = CurLoop->getLoopPreheader();
+ if (!PH)
+ return false;
+ if (&PH->front() != PH->getTerminator())
+ return false;
+ auto *EntryBI = dyn_cast<BranchInst>(PH->getTerminator());
+ if (!EntryBI || EntryBI->isConditional())
+ return false;
- CallInst *NewCall;
- if (SplatValue) {
- NewCall =
- Builder.CreateMemSet(BasePtr, SplatValue, NumBytes, StoreAlignment);
- } else {
- // Everything is emitted in default address space
- Type *Int8PtrTy = DestInt8PtrTy;
+ // It should have a precondition block where the generated popcount instrinsic
+ // function can be inserted.
+ auto *PreCondBB = PH->getSinglePredecessor();
+ if (!PreCondBB)
+ return false;
+ auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
+ if (!PreCondBI || PreCondBI->isUnconditional())
+ return false;
- Module *M = TheStore->getParent()->getParent()->getParent();
- Value *MSP =
- M->getOrInsertFunction("memset_pattern16", Builder.getVoidTy(),
- Int8PtrTy, Int8PtrTy, IntPtr, (void *)nullptr);
+ Instruction *CntInst;
+ PHINode *CntPhi;
+ Value *Val;
+ if (!detectPopcountIdiom(CurLoop, PreCondBB, CntInst, CntPhi, Val))
+ return false;
- // Otherwise we should form a memset_pattern16. PatternValue is known to be
- // an constant array of 16-bytes. Plop the value into a mergable global.
- GlobalVariable *GV = new GlobalVariable(*M, PatternValue->getType(), true,
- GlobalValue::PrivateLinkage,
- PatternValue, ".memset_pattern");
- GV->setUnnamedAddr(true); // Ok to merge these.
- GV->setAlignment(16);
- Value *PatternPtr = ConstantExpr::getBitCast(GV, Int8PtrTy);
- NewCall = Builder.CreateCall(MSP, {BasePtr, PatternPtr, NumBytes});
- }
+ transformLoopToPopcount(PreCondBB, CntInst, CntPhi, Val);
+ return true;
+}
- DEBUG(dbgs() << " Formed memset: " << *NewCall << "\n"
- << " from store to: " << *Ev << " at: " << *TheStore << "\n");
- NewCall->setDebugLoc(TheStore->getDebugLoc());
+static CallInst *createPopcntIntrinsic(IRBuilder<> &IRBuilder, Value *Val,
+ DebugLoc DL) {
+ Value *Ops[] = {Val};
+ Type *Tys[] = {Val->getType()};
- // Okay, the memset has been formed. Zap the original store and anything that
- // feeds into it.
- deleteDeadInstruction(TheStore, TLI);
- ++NumMemSet;
- return true;
+ Module *M = IRBuilder.GetInsertBlock()->getParent()->getParent();
+ Value *Func = Intrinsic::getDeclaration(M, Intrinsic::ctpop, Tys);
+ CallInst *CI = IRBuilder.CreateCall(Func, Ops);
+ CI->setDebugLoc(DL);
+
+ return CI;
}
-/// processLoopStoreOfLoopLoad - We see a strided store whose value is a
-/// same-strided load.
-bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(
- StoreInst *SI, unsigned StoreSize, const SCEVAddRecExpr *StoreEv,
- const SCEVAddRecExpr *LoadEv, const SCEV *BECount) {
- // If we're not allowed to form memcpy, we fail.
- if (!TLI->has(LibFunc::memcpy))
- return false;
+void LoopIdiomRecognize::transformLoopToPopcount(BasicBlock *PreCondBB,
+ Instruction *CntInst,
+ PHINode *CntPhi, Value *Var) {
+ BasicBlock *PreHead = CurLoop->getLoopPreheader();
+ auto *PreCondBr = dyn_cast<BranchInst>(PreCondBB->getTerminator());
+ const DebugLoc DL = CntInst->getDebugLoc();
- LoadInst *LI = cast<LoadInst>(SI->getValueOperand());
+ // Assuming before transformation, the loop is following:
+ // if (x) // the precondition
+ // do { cnt++; x &= x - 1; } while(x);
- // The trip count of the loop and the base pointer of the addrec SCEV is
- // guaranteed to be loop invariant, which means that it should dominate the
- // header. This allows us to insert code for it in the preheader.
- BasicBlock *Preheader = CurLoop->getLoopPreheader();
- IRBuilder<> Builder(Preheader->getTerminator());
- const DataLayout &DL = Preheader->getModule()->getDataLayout();
- SCEVExpander Expander(*SE, DL, "loop-idiom");
+ // Step 1: Insert the ctpop instruction at the end of the precondition block
+ IRBuilder<> Builder(PreCondBr);
+ Value *PopCnt, *PopCntZext, *NewCount, *TripCnt;
+ {
+ PopCnt = createPopcntIntrinsic(Builder, Var, DL);
+ NewCount = PopCntZext =
+ Builder.CreateZExtOrTrunc(PopCnt, cast<IntegerType>(CntPhi->getType()));
- // Okay, we have a strided store "p[i]" of a loaded value. We can turn
- // this into a memcpy in the loop preheader now if we want. However, this
- // would be unsafe to do if there is anything else in the loop that may read
- // or write the memory region we're storing to. This includes the load that
- // feeds the stores. Check for an alias by generating the base address and
- // checking everything.
- Value *StoreBasePtr = Expander.expandCodeFor(
- StoreEv->getStart(), Builder.getInt8PtrTy(SI->getPointerAddressSpace()),
- Preheader->getTerminator());
+ if (NewCount != PopCnt)
+ (cast<Instruction>(NewCount))->setDebugLoc(DL);
- if (mayLoopAccessLocation(StoreBasePtr, MRI_ModRef, CurLoop, BECount,
- StoreSize, getAnalysis<AliasAnalysis>(), SI)) {
- Expander.clear();
- // If we generated new code for the base pointer, clean up.
- RecursivelyDeleteTriviallyDeadInstructions(StoreBasePtr, TLI);
- return false;
+ // TripCnt is exactly the number of iterations the loop has
+ TripCnt = NewCount;
+
+ // If the population counter's initial value is not zero, insert Add Inst.
+ Value *CntInitVal = CntPhi->getIncomingValueForBlock(PreHead);
+ ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
+ if (!InitConst || !InitConst->isZero()) {
+ NewCount = Builder.CreateAdd(NewCount, CntInitVal);
+ (cast<Instruction>(NewCount))->setDebugLoc(DL);
+ }
}
- // For a memcpy, we have to make sure that the input array is not being
- // mutated by the loop.
- Value *LoadBasePtr = Expander.expandCodeFor(
- LoadEv->getStart(), Builder.getInt8PtrTy(LI->getPointerAddressSpace()),
- Preheader->getTerminator());
+ // Step 2: Replace the precondition from "if(x == 0) goto loop-exit" to
+ // "if(NewCount == 0) loop-exit". Withtout this change, the intrinsic
+ // function would be partial dead code, and downstream passes will drag
+ // it back from the precondition block to the preheader.
+ {
+ ICmpInst *PreCond = cast<ICmpInst>(PreCondBr->getCondition());
- if (mayLoopAccessLocation(LoadBasePtr, MRI_Mod, CurLoop, BECount, StoreSize,
- getAnalysis<AliasAnalysis>(), SI)) {
- Expander.clear();
- // If we generated new code for the base pointer, clean up.
- RecursivelyDeleteTriviallyDeadInstructions(LoadBasePtr, TLI);
- RecursivelyDeleteTriviallyDeadInstructions(StoreBasePtr, TLI);
- return false;
- }
+ Value *Opnd0 = PopCntZext;
+ Value *Opnd1 = ConstantInt::get(PopCntZext->getType(), 0);
+ if (PreCond->getOperand(0) != Var)
+ std::swap(Opnd0, Opnd1);
- // Okay, everything is safe, we can transform this!
+ ICmpInst *NewPreCond = cast<ICmpInst>(
+ Builder.CreateICmp(PreCond->getPredicate(), Opnd0, Opnd1));
+ PreCondBr->setCondition(NewPreCond);
- // The # stored bytes is (BECount+1)*Size. Expand the trip count out to
- // pointer size if it isn't already.
- Type *IntPtrTy = Builder.getIntPtrTy(DL, SI->getPointerAddressSpace());
- BECount = SE->getTruncateOrZeroExtend(BECount, IntPtrTy);
+ RecursivelyDeleteTriviallyDeadInstructions(PreCond, TLI);
+ }
- const SCEV *NumBytesS =
- SE->getAddExpr(BECount, SE->getConstant(IntPtrTy, 1), SCEV::FlagNUW);
- if (StoreSize != 1)
- NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtrTy, StoreSize),
- SCEV::FlagNUW);
+ // Step 3: Note that the population count is exactly the trip count of the
+ // loop in question, which enble us to to convert the loop from noncountable
+ // loop into a countable one. The benefit is twofold:
+ //
+ // - If the loop only counts population, the entire loop become dead after
+ // the transformation. It is lots easier to prove a countable loop dead
+ // than to prove a noncountable one. (In some C dialects, a infite loop
+ // isn't dead even if it computes nothing useful. In general, DCE needs
+ // to prove a noncountable loop finite before safely delete it.)
+ //
+ // - If the loop also performs something else, it remains alive.
+ // Since it is transformed to countable form, it can be aggressively
+ // optimized by some optimizations which are in general not applicable
+ // to a noncountable loop.
+ //
+ // After this step, this loop (conceptually) would look like following:
+ // newcnt = __builtin_ctpop(x);
+ // t = newcnt;
+ // if (x)
+ // do { cnt++; x &= x-1; t--) } while (t > 0);
+ BasicBlock *Body = *(CurLoop->block_begin());
+ {
+ auto *LbBr = dyn_cast<BranchInst>(Body->getTerminator());
+ ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
+ Type *Ty = TripCnt->getType();
- Value *NumBytes =
- Expander.expandCodeFor(NumBytesS, IntPtrTy, Preheader->getTerminator());
+ PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", Body->begin());
- CallInst *NewCall =
- Builder.CreateMemCpy(StoreBasePtr, LoadBasePtr, NumBytes,
- std::min(SI->getAlignment(), LI->getAlignment()));
- NewCall->setDebugLoc(SI->getDebugLoc());
+ Builder.SetInsertPoint(LbCond);
+ Value *Opnd1 = cast<Value>(TcPhi);
+ Value *Opnd2 = cast<Value>(ConstantInt::get(Ty, 1));
+ Instruction *TcDec = cast<Instruction>(
+ Builder.CreateSub(Opnd1, Opnd2, "tcdec", false, true));
- DEBUG(dbgs() << " Formed memcpy: " << *NewCall << "\n"
- << " from load ptr=" << *LoadEv << " at: " << *LI << "\n"
- << " from store ptr=" << *StoreEv << " at: " << *SI << "\n");
+ TcPhi->addIncoming(TripCnt, PreHead);
+ TcPhi->addIncoming(TcDec, Body);
- // Okay, the memset has been formed. Zap the original store and anything that
- // feeds into it.
- deleteDeadInstruction(SI, TLI);
- ++NumMemCpy;
- return true;
-}
+ CmpInst::Predicate Pred =
+ (LbBr->getSuccessor(0) == Body) ? CmpInst::ICMP_UGT : CmpInst::ICMP_SLE;
+ LbCond->setPredicate(Pred);
+ LbCond->setOperand(0, TcDec);
+ LbCond->setOperand(1, cast<Value>(ConstantInt::get(Ty, 0)));
+ }
-bool LoopIdiomRecognize::runOnNoncountableLoop() {
- NclPopcountRecognize Popcount(*this);
- if (Popcount.recognize())
- return true;
+ // Step 4: All the references to the original population counter outside
+ // the loop are replaced with the NewCount -- the value returned from
+ // __builtin_ctpop().
+ CntInst->replaceUsesOutsideBlock(NewCount, Body);
- return false;
+ // step 5: Forget the "non-computable" trip-count SCEV associated with the
+ // loop. The loop would otherwise not be deleted even if it becomes empty.
+ SE->forgetLoop(CurLoop);
}
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