//===-- LICM.cpp - Loop Invariant Code Motion Pass ------------------------===//
-//
+//
// The LLVM Compiler Infrastructure
//
-// This file was developed by the LLVM research group and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
-//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
//===----------------------------------------------------------------------===//
//
// This pass performs loop invariant code motion, attempting to remove as much
// code from the body of a loop as possible. It does this by either hoisting
// code into the preheader block, or by sinking code to the exit blocks if it is
// safe. This pass also promotes must-aliased memory locations in the loop to
-// live in registers.
+// live in registers, thus hoisting and sinking "invariant" loads and stores.
//
// This pass uses alias analysis for two purposes:
//
-// 1. Moving loop invariant loads out of loops. If we can determine that a
-// load inside of a loop never aliases anything stored to, we can hoist it
-// or sink it like any other instruction.
+// 1. Moving loop invariant loads and calls out of loops. If we can determine
+// that a load or call inside of a loop never aliases anything stored to,
+// we can hoist it or sink it like any other instruction.
// 2. Scalar Promotion of Memory - If there is a store instruction inside of
// the loop, we try to move the store to happen AFTER the loop instead of
// inside of the loop. This can only happen if a few conditions are true:
//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "licm"
#include "llvm/Transforms/Scalar.h"
-#include "llvm/Transforms/Utils/PromoteMemToReg.h"
-#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/Instructions.h"
+#include "llvm/Target/TargetData.h"
#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/AliasSetTracker.h"
#include "llvm/Analysis/Dominators.h"
-#include "llvm/Instructions.h"
-#include "llvm/DerivedTypes.h"
-#include "llvm/Target/TargetData.h"
-#include "llvm/Support/InstVisitor.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include "llvm/Support/CFG.h"
-#include "Support/CommandLine.h"
-#include "Support/Debug.h"
-#include "Support/Statistic.h"
-#include "llvm/Assembly/Writer.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/ADT/Statistic.h"
#include <algorithm>
using namespace llvm;
-namespace {
- cl::opt<bool>
- DisablePromotion("disable-licm-promotion", cl::Hidden,
- cl::desc("Disable memory promotion in LICM pass"));
+STATISTIC(NumSunk , "Number of instructions sunk out of loop");
+STATISTIC(NumHoisted , "Number of instructions hoisted out of loop");
+STATISTIC(NumMovedLoads, "Number of load insts hoisted or sunk");
+STATISTIC(NumMovedCalls, "Number of call insts hoisted or sunk");
+STATISTIC(NumPromoted , "Number of memory locations promoted to registers");
+
+static cl::opt<bool>
+DisablePromotion("disable-licm-promotion", cl::Hidden,
+ cl::desc("Disable memory promotion in LICM pass"));
- Statistic<> NumHoisted("licm", "Number of instructions hoisted out of loop");
- Statistic<> NumHoistedLoads("licm", "Number of load insts hoisted");
- Statistic<> NumPromoted("licm",
- "Number of memory locations promoted to registers");
+namespace {
+ struct VISIBILITY_HIDDEN LICM : public LoopPass {
+ static char ID; // Pass identification, replacement for typeid
+ LICM() : LoopPass((intptr_t)&ID) {}
- struct LICM : public FunctionPass, public InstVisitor<LICM> {
- virtual bool runOnFunction(Function &F);
+ virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
/// This transformation requires natural loop information & requires that
/// loop preheaders be inserted into the CFG...
AU.addRequired<DominatorTree>();
AU.addRequired<DominanceFrontier>(); // For scalar promotion (mem2reg)
AU.addRequired<AliasAnalysis>();
+ AU.addPreserved<ScalarEvolution>();
+ AU.addPreserved<DominanceFrontier>();
+ }
+
+ bool doFinalization() {
+ // Free the values stored in the map
+ for (std::map<Loop *, AliasSetTracker *>::iterator
+ I = LoopToAliasMap.begin(), E = LoopToAliasMap.end(); I != E; ++I)
+ delete I->second;
+
+ LoopToAliasMap.clear();
+ return false;
}
private:
BasicBlock *Preheader; // The preheader block of the current loop...
Loop *CurLoop; // The current loop we are working on...
AliasSetTracker *CurAST; // AliasSet information for the current loop...
+ std::map<Loop *, AliasSetTracker *> LoopToAliasMap;
+
+ /// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
+ void cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L);
- /// visitLoop - Hoist expressions out of the specified loop...
+ /// deleteAnalysisValue - Simple Analysis hook. Delete value V from alias
+ /// set.
+ void deleteAnalysisValue(Value *V, Loop *L);
+
+ /// SinkRegion - Walk the specified region of the CFG (defined by all blocks
+ /// dominated by the specified block, and that are in the current loop) in
+ /// reverse depth first order w.r.t the DominatorTree. This allows us to
+ /// visit uses before definitions, allowing us to sink a loop body in one
+ /// pass without iteration.
///
- void visitLoop(Loop *L, AliasSetTracker &AST);
+ void SinkRegion(DomTreeNode *N);
/// HoistRegion - Walk the specified region of the CFG (defined by all
/// blocks dominated by the specified block, and that are in the current
/// visit definitions before uses, allowing us to hoist a loop body in one
/// pass without iteration.
///
- void HoistRegion(DominatorTree::Node *N);
+ void HoistRegion(DomTreeNode *N);
/// inSubLoop - Little predicate that returns true if the specified basic
/// block is in a subloop of the current one, not the current one itself.
///
bool inSubLoop(BasicBlock *BB) {
assert(CurLoop->contains(BB) && "Only valid if BB is IN the loop");
- for (unsigned i = 0, e = CurLoop->getSubLoops().size(); i != e; ++i)
- if (CurLoop->getSubLoops()[i]->contains(BB))
+ for (Loop::iterator I = CurLoop->begin(), E = CurLoop->end(); I != E; ++I)
+ if ((*I)->contains(BB))
return true; // A subloop actually contains this block!
return false;
}
+ /// isExitBlockDominatedByBlockInLoop - This method checks to see if the
+ /// specified exit block of the loop is dominated by the specified block
+ /// that is in the body of the loop. We use these constraints to
+ /// dramatically limit the amount of the dominator tree that needs to be
+ /// searched.
+ bool isExitBlockDominatedByBlockInLoop(BasicBlock *ExitBlock,
+ BasicBlock *BlockInLoop) const {
+ // If the block in the loop is the loop header, it must be dominated!
+ BasicBlock *LoopHeader = CurLoop->getHeader();
+ if (BlockInLoop == LoopHeader)
+ return true;
+
+ DomTreeNode *BlockInLoopNode = DT->getNode(BlockInLoop);
+ DomTreeNode *IDom = DT->getNode(ExitBlock);
+
+ // Because the exit block is not in the loop, we know we have to get _at
+ // least_ its immediate dominator.
+ do {
+ // Get next Immediate Dominator.
+ IDom = IDom->getIDom();
+
+ // If we have got to the header of the loop, then the instructions block
+ // did not dominate the exit node, so we can't hoist it.
+ if (IDom->getBlock() == LoopHeader)
+ return false;
+
+ } while (IDom != BlockInLoopNode);
+
+ return true;
+ }
+
+ /// sink - When an instruction is found to only be used outside of the loop,
+ /// this function moves it to the exit blocks and patches up SSA form as
+ /// needed.
+ ///
+ void sink(Instruction &I);
+
/// hoist - When an instruction is found to only use loop invariant operands
/// that is safe to hoist, this instruction is called to do the dirty work.
///
void hoist(Instruction &I);
- /// SafeToHoist - Only hoist an instruction if it is not a trapping
- /// instruction or if it is a trapping instruction and is guaranteed to
- /// execute.
+ /// isSafeToExecuteUnconditionally - Only sink or hoist an instruction if it
+ /// is not a trapping instruction or if it is a trapping instruction and is
+ /// guaranteed to execute.
///
- bool SafeToHoist(Instruction &I);
+ bool isSafeToExecuteUnconditionally(Instruction &I);
/// pointerInvalidatedByLoop - Return true if the body of this loop may
/// store into the memory location pointed to by V.
- ///
- bool pointerInvalidatedByLoop(Value *V) {
+ ///
+ bool pointerInvalidatedByLoop(Value *V, unsigned Size) {
// Check to see if any of the basic blocks in CurLoop invalidate *V.
- return CurAST->getAliasSetForPointer(V, 0).isMod();
+ return CurAST->getAliasSetForPointer(V, Size).isMod();
}
- /// isLoopInvariant - Return true if the specified value is loop invariant
- ///
- inline bool isLoopInvariant(Value *V) {
- if (Instruction *I = dyn_cast<Instruction>(V))
- return !CurLoop->contains(I->getParent());
- return true; // All non-instructions are loop invariant
- }
+ bool canSinkOrHoistInst(Instruction &I);
+ bool isLoopInvariantInst(Instruction &I);
+ bool isNotUsedInLoop(Instruction &I);
/// PromoteValuesInLoop - Look at the stores in the loop and promote as many
/// to scalars as we can.
///
void PromoteValuesInLoop();
- /// findPromotableValuesInLoop - Check the current loop for stores to
+ /// FindPromotableValuesInLoop - Check the current loop for stores to
/// definite pointers, which are not loaded and stored through may aliases.
/// If these are found, create an alloca for the value, add it to the
/// PromotedValues list, and keep track of the mapping from value to
/// alloca...
///
- void findPromotableValuesInLoop(
+ void FindPromotableValuesInLoop(
std::vector<std::pair<AllocaInst*, Value*> > &PromotedValues,
std::map<Value*, AllocaInst*> &Val2AlMap);
-
-
- /// Instruction visitation handlers... these basically control whether or
- /// not the specified instruction types are hoisted.
- ///
- friend class InstVisitor<LICM>;
- void visitBinaryOperator(Instruction &I) {
- if (isLoopInvariant(I.getOperand(0)) &&
- isLoopInvariant(I.getOperand(1)) && SafeToHoist(I))
- hoist(I);
- }
- void visitCastInst(CastInst &CI) {
- Instruction &I = (Instruction&)CI;
- if (isLoopInvariant(I.getOperand(0)) && SafeToHoist(CI)) hoist(I);
- }
- void visitShiftInst(ShiftInst &I) { visitBinaryOperator((Instruction&)I); }
-
- void visitLoadInst(LoadInst &LI);
-
- void visitGetElementPtrInst(GetElementPtrInst &GEPI) {
- Instruction &I = (Instruction&)GEPI;
- for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i)
- if (!isLoopInvariant(I.getOperand(i))) return;
- if(SafeToHoist(GEPI))
- hoist(I);
- }
};
-
- RegisterOpt<LICM> X("licm", "Loop Invariant Code Motion");
}
-FunctionPass *llvm::createLICMPass() { return new LICM(); }
+char LICM::ID = 0;
+static RegisterPass<LICM> X("licm", "Loop Invariant Code Motion");
-/// runOnFunction - For LICM, this simply traverses the loop structure of the
-/// function, hoisting expressions out of loops if possible.
+LoopPass *llvm::createLICMPass() { return new LICM(); }
+
+/// Hoist expressions out of the specified loop. Note, alias info for inner
+/// loop is not preserved so it is not a good idea to run LICM multiple
+/// times on one loop.
///
-bool LICM::runOnFunction(Function &) {
+bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
Changed = false;
// Get our Loop and Alias Analysis information...
DF = &getAnalysis<DominanceFrontier>();
DT = &getAnalysis<DominatorTree>();
- // Hoist expressions out of all of the top-level loops.
- const std::vector<Loop*> &TopLevelLoops = LI->getTopLevelLoops();
- for (std::vector<Loop*>::const_iterator I = TopLevelLoops.begin(),
- E = TopLevelLoops.end(); I != E; ++I) {
- AliasSetTracker AST(*AA);
- LICM::visitLoop(*I, AST);
- }
- return Changed;
-}
-
+ CurAST = new AliasSetTracker(*AA);
+ // Collect Alias info from subloops
+ for (Loop::iterator LoopItr = L->begin(), LoopItrE = L->end();
+ LoopItr != LoopItrE; ++LoopItr) {
+ Loop *InnerL = *LoopItr;
+ AliasSetTracker *InnerAST = LoopToAliasMap[InnerL];
+ assert (InnerAST && "Where is my AST?");
-/// visitLoop - Hoist expressions out of the specified loop...
-///
-void LICM::visitLoop(Loop *L, AliasSetTracker &AST) {
- // Recurse through all subloops before we process this loop...
- for (std::vector<Loop*>::const_iterator I = L->getSubLoops().begin(),
- E = L->getSubLoops().end(); I != E; ++I) {
- AliasSetTracker SubAST(*AA);
- LICM::visitLoop(*I, SubAST);
-
- // Incorporate information about the subloops into this loop...
- AST.add(SubAST);
+ // What if InnerLoop was modified by other passes ?
+ CurAST->add(*InnerAST);
}
+
CurLoop = L;
- CurAST = &AST;
// Get the preheader block to move instructions into...
Preheader = L->getLoopPreheader();
// Because subloops have already been incorporated into AST, we skip blocks in
// subloops.
//
- const std::vector<BasicBlock*> &LoopBBs = L->getBlocks();
- for (std::vector<BasicBlock*>::const_iterator I = LoopBBs.begin(),
- E = LoopBBs.end(); I != E; ++I)
+ for (std::vector<BasicBlock*>::const_iterator I = L->getBlocks().begin(),
+ E = L->getBlocks().end(); I != E; ++I)
if (LI->getLoopFor(*I) == L) // Ignore blocks in subloops...
- AST.add(**I); // Incorporate the specified basic block
+ CurAST->add(**I); // Incorporate the specified basic block
// We want to visit all of the instructions in this loop... that are not parts
// of our subloops (they have already had their invariants hoisted out of
//
// Traverse the body of the loop in depth first order on the dominator tree so
// that we are guaranteed to see definitions before we see uses. This allows
- // us to perform the LICM transformation in one pass, without iteration.
+ // us to sink instructions in one pass, without iteration. After sinking
+ // instructions, we perform another pass to hoist them out of the loop.
//
+ SinkRegion(DT->getNode(L->getHeader()));
HoistRegion(DT->getNode(L->getHeader()));
// Now that all loop invariants have been removed from the loop, promote any
// Clear out loops state information for the next iteration
CurLoop = 0;
Preheader = 0;
+
+ LoopToAliasMap[L] = CurAST;
+ return Changed;
}
+/// SinkRegion - Walk the specified region of the CFG (defined by all blocks
+/// dominated by the specified block, and that are in the current loop) in
+/// reverse depth first order w.r.t the DominatorTree. This allows us to visit
+/// uses before definitions, allowing us to sink a loop body in one pass without
+/// iteration.
+///
+void LICM::SinkRegion(DomTreeNode *N) {
+ assert(N != 0 && "Null dominator tree node?");
+ BasicBlock *BB = N->getBlock();
+
+ // If this subregion is not in the top level loop at all, exit.
+ if (!CurLoop->contains(BB)) return;
+
+ // We are processing blocks in reverse dfo, so process children first...
+ const std::vector<DomTreeNode*> &Children = N->getChildren();
+ for (unsigned i = 0, e = Children.size(); i != e; ++i)
+ SinkRegion(Children[i]);
+
+ // Only need to process the contents of this block if it is not part of a
+ // subloop (which would already have been processed).
+ if (inSubLoop(BB)) return;
+
+ for (BasicBlock::iterator II = BB->end(); II != BB->begin(); ) {
+ Instruction &I = *--II;
+
+ // Check to see if we can sink this instruction to the exit blocks
+ // of the loop. We can do this if the all users of the instruction are
+ // outside of the loop. In this case, it doesn't even matter if the
+ // operands of the instruction are loop invariant.
+ //
+ if (isNotUsedInLoop(I) && canSinkOrHoistInst(I)) {
+ ++II;
+ sink(I);
+ }
+ }
+}
+
+
/// HoistRegion - Walk the specified region of the CFG (defined by all blocks
/// dominated by the specified block, and that are in the current loop) in depth
/// first order w.r.t the DominatorTree. This allows us to visit definitions
/// before uses, allowing us to hoist a loop body in one pass without iteration.
///
-void LICM::HoistRegion(DominatorTree::Node *N) {
+void LICM::HoistRegion(DomTreeNode *N) {
assert(N != 0 && "Null dominator tree node?");
+ BasicBlock *BB = N->getBlock();
// If this subregion is not in the top level loop at all, exit.
- if (!CurLoop->contains(N->getBlock())) return;
-
- // Only need to hoist the contents of this block if it is not part of a
- // subloop (which would already have been hoisted)
- if (!inSubLoop(N->getBlock()))
- visit(*N->getBlock());
+ if (!CurLoop->contains(BB)) return;
+
+ // Only need to process the contents of this block if it is not part of a
+ // subloop (which would already have been processed).
+ if (!inSubLoop(BB))
+ for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ) {
+ Instruction &I = *II++;
+
+ // Try hoisting the instruction out to the preheader. We can only do this
+ // if all of the operands of the instruction are loop invariant and if it
+ // is safe to hoist the instruction.
+ //
+ if (isLoopInvariantInst(I) && canSinkOrHoistInst(I) &&
+ isSafeToExecuteUnconditionally(I))
+ hoist(I);
+ }
- const std::vector<DominatorTree::Node*> &Children = N->getChildren();
+ const std::vector<DomTreeNode*> &Children = N->getChildren();
for (unsigned i = 0, e = Children.size(); i != e; ++i)
HoistRegion(Children[i]);
}
+/// canSinkOrHoistInst - Return true if the hoister and sinker can handle this
+/// instruction.
+///
+bool LICM::canSinkOrHoistInst(Instruction &I) {
+ // Loads have extra constraints we have to verify before we can hoist them.
+ if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
+ if (LI->isVolatile())
+ return false; // Don't hoist volatile loads!
+
+ // Don't hoist loads which have may-aliased stores in loop.
+ unsigned Size = 0;
+ if (LI->getType()->isSized())
+ Size = AA->getTargetData().getTypeStoreSize(LI->getType());
+ return !pointerInvalidatedByLoop(LI->getOperand(0), Size);
+ } else if (CallInst *CI = dyn_cast<CallInst>(&I)) {
+ // Handle obvious cases efficiently.
+ AliasAnalysis::ModRefBehavior Behavior = AA->getModRefBehavior(CI);
+ if (Behavior == AliasAnalysis::DoesNotAccessMemory)
+ return true;
+ else if (Behavior == AliasAnalysis::OnlyReadsMemory) {
+ // If this call only reads from memory and there are no writes to memory
+ // in the loop, we can hoist or sink the call as appropriate.
+ bool FoundMod = false;
+ for (AliasSetTracker::iterator I = CurAST->begin(), E = CurAST->end();
+ I != E; ++I) {
+ AliasSet &AS = *I;
+ if (!AS.isForwardingAliasSet() && AS.isMod()) {
+ FoundMod = true;
+ break;
+ }
+ }
+ if (!FoundMod) return true;
+ }
+
+ // FIXME: This should use mod/ref information to see if we can hoist or sink
+ // the call.
+
+ return false;
+ }
+
+ // Otherwise these instructions are hoistable/sinkable
+ return isa<BinaryOperator>(I) || isa<CastInst>(I) ||
+ isa<SelectInst>(I) || isa<GetElementPtrInst>(I) || isa<CmpInst>(I) ||
+ isa<InsertElementInst>(I) || isa<ExtractElementInst>(I) ||
+ isa<ShuffleVectorInst>(I);
+}
+
+/// isNotUsedInLoop - Return true if the only users of this instruction are
+/// outside of the loop. If this is true, we can sink the instruction to the
+/// exit blocks of the loop.
+///
+bool LICM::isNotUsedInLoop(Instruction &I) {
+ for (Value::use_iterator UI = I.use_begin(), E = I.use_end(); UI != E; ++UI) {
+ Instruction *User = cast<Instruction>(*UI);
+ if (PHINode *PN = dyn_cast<PHINode>(User)) {
+ // PHI node uses occur in predecessor blocks!
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (PN->getIncomingValue(i) == &I)
+ if (CurLoop->contains(PN->getIncomingBlock(i)))
+ return false;
+ } else if (CurLoop->contains(User->getParent())) {
+ return false;
+ }
+ }
+ return true;
+}
+
+
+/// isLoopInvariantInst - Return true if all operands of this instruction are
+/// loop invariant. We also filter out non-hoistable instructions here just for
+/// efficiency.
+///
+bool LICM::isLoopInvariantInst(Instruction &I) {
+ // The instruction is loop invariant if all of its operands are loop-invariant
+ for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i)
+ if (!CurLoop->isLoopInvariant(I.getOperand(i)))
+ return false;
+
+ // If we got this far, the instruction is loop invariant!
+ return true;
+}
+
+/// sink - When an instruction is found to only be used outside of the loop,
+/// this function moves it to the exit blocks and patches up SSA form as needed.
+/// This method is guaranteed to remove the original instruction from its
+/// position, and may either delete it or move it to outside of the loop.
+///
+void LICM::sink(Instruction &I) {
+ DOUT << "LICM sinking instruction: " << I;
+
+ SmallVector<BasicBlock*, 8> ExitBlocks;
+ CurLoop->getExitBlocks(ExitBlocks);
+
+ if (isa<LoadInst>(I)) ++NumMovedLoads;
+ else if (isa<CallInst>(I)) ++NumMovedCalls;
+ ++NumSunk;
+ Changed = true;
+
+ // The case where there is only a single exit node of this loop is common
+ // enough that we handle it as a special (more efficient) case. It is more
+ // efficient to handle because there are no PHI nodes that need to be placed.
+ if (ExitBlocks.size() == 1) {
+ if (!isExitBlockDominatedByBlockInLoop(ExitBlocks[0], I.getParent())) {
+ // Instruction is not used, just delete it.
+ CurAST->deleteValue(&I);
+ if (!I.use_empty()) // If I has users in unreachable blocks, eliminate.
+ I.replaceAllUsesWith(UndefValue::get(I.getType()));
+ I.eraseFromParent();
+ } else {
+ // Move the instruction to the start of the exit block, after any PHI
+ // nodes in it.
+ I.removeFromParent();
+
+ BasicBlock::iterator InsertPt = ExitBlocks[0]->begin();
+ while (isa<PHINode>(InsertPt)) ++InsertPt;
+ ExitBlocks[0]->getInstList().insert(InsertPt, &I);
+ }
+ } else if (ExitBlocks.empty()) {
+ // The instruction is actually dead if there ARE NO exit blocks.
+ CurAST->deleteValue(&I);
+ if (!I.use_empty()) // If I has users in unreachable blocks, eliminate.
+ I.replaceAllUsesWith(UndefValue::get(I.getType()));
+ I.eraseFromParent();
+ } else {
+ // Otherwise, if we have multiple exits, use the PromoteMem2Reg function to
+ // do all of the hard work of inserting PHI nodes as necessary. We convert
+ // the value into a stack object to get it to do this.
+
+ // Firstly, we create a stack object to hold the value...
+ AllocaInst *AI = 0;
+
+ if (I.getType() != Type::VoidTy) {
+ AI = new AllocaInst(I.getType(), 0, I.getName(),
+ I.getParent()->getParent()->getEntryBlock().begin());
+ CurAST->add(AI);
+ }
+
+ // Secondly, insert load instructions for each use of the instruction
+ // outside of the loop.
+ while (!I.use_empty()) {
+ Instruction *U = cast<Instruction>(I.use_back());
+
+ // If the user is a PHI Node, we actually have to insert load instructions
+ // in all predecessor blocks, not in the PHI block itself!
+ if (PHINode *UPN = dyn_cast<PHINode>(U)) {
+ // Only insert into each predecessor once, so that we don't have
+ // different incoming values from the same block!
+ std::map<BasicBlock*, Value*> InsertedBlocks;
+ for (unsigned i = 0, e = UPN->getNumIncomingValues(); i != e; ++i)
+ if (UPN->getIncomingValue(i) == &I) {
+ BasicBlock *Pred = UPN->getIncomingBlock(i);
+ Value *&PredVal = InsertedBlocks[Pred];
+ if (!PredVal) {
+ // Insert a new load instruction right before the terminator in
+ // the predecessor block.
+ PredVal = new LoadInst(AI, "", Pred->getTerminator());
+ CurAST->add(cast<LoadInst>(PredVal));
+ }
+
+ UPN->setIncomingValue(i, PredVal);
+ }
+
+ } else {
+ LoadInst *L = new LoadInst(AI, "", U);
+ U->replaceUsesOfWith(&I, L);
+ CurAST->add(L);
+ }
+ }
+
+ // Thirdly, insert a copy of the instruction in each exit block of the loop
+ // that is dominated by the instruction, storing the result into the memory
+ // location. Be careful not to insert the instruction into any particular
+ // basic block more than once.
+ std::set<BasicBlock*> InsertedBlocks;
+ BasicBlock *InstOrigBB = I.getParent();
+
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
+ BasicBlock *ExitBlock = ExitBlocks[i];
+
+ if (isExitBlockDominatedByBlockInLoop(ExitBlock, InstOrigBB)) {
+ // If we haven't already processed this exit block, do so now.
+ if (InsertedBlocks.insert(ExitBlock).second) {
+ // Insert the code after the last PHI node...
+ BasicBlock::iterator InsertPt = ExitBlock->begin();
+ while (isa<PHINode>(InsertPt)) ++InsertPt;
+
+ // If this is the first exit block processed, just move the original
+ // instruction, otherwise clone the original instruction and insert
+ // the copy.
+ Instruction *New;
+ if (InsertedBlocks.size() == 1) {
+ I.removeFromParent();
+ ExitBlock->getInstList().insert(InsertPt, &I);
+ New = &I;
+ } else {
+ New = I.clone();
+ CurAST->copyValue(&I, New);
+ if (!I.getName().empty())
+ New->setName(I.getName()+".le");
+ ExitBlock->getInstList().insert(InsertPt, New);
+ }
+
+ // Now that we have inserted the instruction, store it into the alloca
+ if (AI) new StoreInst(New, AI, InsertPt);
+ }
+ }
+ }
+
+ // If the instruction doesn't dominate any exit blocks, it must be dead.
+ if (InsertedBlocks.empty()) {
+ CurAST->deleteValue(&I);
+ I.eraseFromParent();
+ }
+
+ // Finally, promote the fine value to SSA form.
+ if (AI) {
+ std::vector<AllocaInst*> Allocas;
+ Allocas.push_back(AI);
+ PromoteMemToReg(Allocas, *DT, *DF, CurAST);
+ }
+ }
+}
/// hoist - When an instruction is found to only use loop invariant operands
/// that is safe to hoist, this instruction is called to do the dirty work.
///
-void LICM::hoist(Instruction &Inst) {
- DEBUG(std::cerr << "LICM hoisting to";
- WriteAsOperand(std::cerr, Preheader, false);
- std::cerr << ": " << Inst);
+void LICM::hoist(Instruction &I) {
+ DOUT << "LICM hoisting to " << Preheader->getName() << ": " << I;
// Remove the instruction from its current basic block... but don't delete the
// instruction.
- Inst.getParent()->getInstList().remove(&Inst);
+ I.removeFromParent();
// Insert the new node in Preheader, before the terminator.
- Preheader->getInstList().insert(Preheader->getTerminator(), &Inst);
-
+ Preheader->getInstList().insert(Preheader->getTerminator(), &I);
+
+ if (isa<LoadInst>(I)) ++NumMovedLoads;
+ else if (isa<CallInst>(I)) ++NumMovedCalls;
++NumHoisted;
Changed = true;
}
-/// SafeToHoist - Only hoist an instruction if it is not a trapping instruction
-/// or if it is a trapping instruction and is guaranteed to execute
+/// isSafeToExecuteUnconditionally - Only sink or hoist an instruction if it is
+/// not a trapping instruction or if it is a trapping instruction and is
+/// guaranteed to execute.
///
-bool LICM::SafeToHoist(Instruction &Inst) {
+bool LICM::isSafeToExecuteUnconditionally(Instruction &Inst) {
// If it is not a trapping instruction, it is always safe to hoist.
if (!Inst.isTrapping()) return true;
-
+
// Otherwise we have to check to make sure that the instruction dominates all
// of the exit blocks. If it doesn't, then there is a path out of the loop
// which does not execute this instruction, so we can't hoist it.
// If the instruction is in the header block for the loop (which is very
// common), it is always guaranteed to dominate the exit blocks. Since this
// is a common case, and can save some work, check it now.
- BasicBlock *LoopHeader = CurLoop->getHeader();
- if (Inst.getParent() == LoopHeader)
+ if (Inst.getParent() == CurLoop->getHeader())
return true;
- // Get the Dominator Tree Node for the instruction's basic block.
- DominatorTree::Node *InstDTNode = DT->getNode(Inst.getParent());
-
+ // It's always safe to load from a global or alloca.
+ if (isa<LoadInst>(Inst))
+ if (isa<AllocationInst>(Inst.getOperand(0)) ||
+ isa<GlobalVariable>(Inst.getOperand(0)))
+ return true;
+
// Get the exit blocks for the current loop.
- const std::vector<BasicBlock* > &ExitBlocks = CurLoop->getExitBlocks();
+ SmallVector<BasicBlock*, 8> ExitBlocks;
+ CurLoop->getExitBlocks(ExitBlocks);
// For each exit block, get the DT node and walk up the DT until the
// instruction's basic block is found or we exit the loop.
- for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
- DominatorTree::Node *IDom = DT->getNode(ExitBlocks[i]);
-
- do {
- // Get next Immediate Dominator.
- IDom = IDom->getIDom();
-
- // If we have got to the header of the loop, then the instructions block
- // did not dominate the exit node, so we can't hoist it.
- if (IDom->getBlock() == LoopHeader)
- return false;
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
+ if (!isExitBlockDominatedByBlockInLoop(ExitBlocks[i], Inst.getParent()))
+ return false;
- } while(IDom != InstDTNode);
- }
-
return true;
}
-void LICM::visitLoadInst(LoadInst &LI) {
- if (isLoopInvariant(LI.getOperand(0)) && !LI.isVolatile() &&
- !pointerInvalidatedByLoop(LI.getOperand(0)) && SafeToHoist(LI)) {
- hoist(LI);
- ++NumHoistedLoads;
- }
-}
-
/// PromoteValuesInLoop - Try to promote memory values to scalars by sinking
/// stores out of the loop and moving loads to before the loop. We do this by
/// looping over the stores in the loop, looking for stores to Must pointers
std::vector<std::pair<AllocaInst*, Value*> > PromotedValues;
std::map<Value*, AllocaInst*> ValueToAllocaMap; // Map of ptr to alloca
- findPromotableValuesInLoop(PromotedValues, ValueToAllocaMap);
- if (ValueToAllocaMap.empty()) return; // If there are values to promote...
+ FindPromotableValuesInLoop(PromotedValues, ValueToAllocaMap);
+ if (ValueToAllocaMap.empty()) return; // If there are values to promote.
Changed = true;
NumPromoted += PromotedValues.size();
+ std::vector<Value*> PointerValueNumbers;
+
// Emit a copy from the value into the alloca'd value in the loop preheader
TerminatorInst *LoopPredInst = Preheader->getTerminator();
for (unsigned i = 0, e = PromotedValues.size(); i != e; ++i) {
- // Load from the memory we are promoting...
- LoadInst *LI = new LoadInst(PromotedValues[i].second,
- PromotedValues[i].second->getName()+".promoted",
- LoopPredInst);
- // Store into the temporary alloca...
+ Value *Ptr = PromotedValues[i].second;
+
+ // If we are promoting a pointer value, update alias information for the
+ // inserted load.
+ Value *LoadValue = 0;
+ if (isa<PointerType>(cast<PointerType>(Ptr->getType())->getElementType())) {
+ // Locate a load or store through the pointer, and assign the same value
+ // to LI as we are loading or storing. Since we know that the value is
+ // stored in this loop, this will always succeed.
+ for (Value::use_iterator UI = Ptr->use_begin(), E = Ptr->use_end();
+ UI != E; ++UI)
+ if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
+ LoadValue = LI;
+ break;
+ } else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
+ if (SI->getOperand(1) == Ptr) {
+ LoadValue = SI->getOperand(0);
+ break;
+ }
+ }
+ assert(LoadValue && "No store through the pointer found!");
+ PointerValueNumbers.push_back(LoadValue); // Remember this for later.
+ }
+
+ // Load from the memory we are promoting.
+ LoadInst *LI = new LoadInst(Ptr, Ptr->getName()+".promoted", LoopPredInst);
+
+ if (LoadValue) CurAST->copyValue(LoadValue, LI);
+
+ // Store into the temporary alloca.
new StoreInst(LI, PromotedValues[i].first, LoopPredInst);
}
-
+
// Scan the basic blocks in the loop, replacing uses of our pointers with
- // uses of the allocas in question. If we find a branch that exits the
- // loop, make sure to put reload code into all of the successors of the
- // loop.
+ // uses of the allocas in question.
//
const std::vector<BasicBlock*> &LoopBBs = CurLoop->getBlocks();
for (std::vector<BasicBlock*>::const_iterator I = LoopBBs.begin(),
S->setOperand(1, I->second); // Rewrite store instruction...
}
}
+ }
- // Check to see if any successors of this block are outside of the loop.
- // If so, we need to copy the value from the alloca back into the memory
- // location...
- //
- for (succ_iterator SI = succ_begin(*I), SE = succ_end(*I); SI != SE; ++SI)
- if (!CurLoop->contains(*SI)) {
- // Copy all of the allocas into their memory locations...
- BasicBlock::iterator BI = (*SI)->begin();
- while (isa<PHINode>(*BI))
- ++BI; // Skip over all of the phi nodes in the block...
- Instruction *InsertPos = BI;
- for (unsigned i = 0, e = PromotedValues.size(); i != e; ++i) {
- // Load from the alloca...
- LoadInst *LI = new LoadInst(PromotedValues[i].first, "", InsertPos);
- // Store into the memory we promoted...
- new StoreInst(LI, PromotedValues[i].second, InsertPos);
- }
+ // Now that the body of the loop uses the allocas instead of the original
+ // memory locations, insert code to copy the alloca value back into the
+ // original memory location on all exits from the loop. Note that we only
+ // want to insert one copy of the code in each exit block, though the loop may
+ // exit to the same block more than once.
+ //
+ std::set<BasicBlock*> ProcessedBlocks;
+
+ SmallVector<BasicBlock*, 8> ExitBlocks;
+ CurLoop->getExitBlocks(ExitBlocks);
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
+ if (ProcessedBlocks.insert(ExitBlocks[i]).second) {
+ // Copy all of the allocas into their memory locations.
+ BasicBlock::iterator BI = ExitBlocks[i]->begin();
+ while (isa<PHINode>(*BI))
+ ++BI; // Skip over all of the phi nodes in the block.
+ Instruction *InsertPos = BI;
+ unsigned PVN = 0;
+ for (unsigned i = 0, e = PromotedValues.size(); i != e; ++i) {
+ // Load from the alloca.
+ LoadInst *LI = new LoadInst(PromotedValues[i].first, "", InsertPos);
+
+ // If this is a pointer type, update alias info appropriately.
+ if (isa<PointerType>(LI->getType()))
+ CurAST->copyValue(PointerValueNumbers[PVN++], LI);
+
+ // Store into the memory we promoted.
+ new StoreInst(LI, PromotedValues[i].second, InsertPos);
}
- }
+ }
// Now that we have done the deed, use the mem2reg functionality to promote
- // all of the new allocas we just created into real SSA registers...
+ // all of the new allocas we just created into real SSA registers.
//
std::vector<AllocaInst*> PromotedAllocas;
PromotedAllocas.reserve(PromotedValues.size());
for (unsigned i = 0, e = PromotedValues.size(); i != e; ++i)
PromotedAllocas.push_back(PromotedValues[i].first);
- PromoteMemToReg(PromotedAllocas, *DT, *DF, AA->getTargetData());
+ PromoteMemToReg(PromotedAllocas, *DT, *DF, CurAST);
}
-/// findPromotableValuesInLoop - Check the current loop for stores to definite
-/// pointers, which are not loaded and stored through may aliases. If these are
-/// found, create an alloca for the value, add it to the PromotedValues list,
-/// and keep track of the mapping from value to alloca...
-///
-void LICM::findPromotableValuesInLoop(
+/// FindPromotableValuesInLoop - Check the current loop for stores to definite
+/// pointers, which are not loaded and stored through may aliases and are safe
+/// for promotion. If these are found, create an alloca for the value, add it
+/// to the PromotedValues list, and keep track of the mapping from value to
+/// alloca.
+void LICM::FindPromotableValuesInLoop(
std::vector<std::pair<AllocaInst*, Value*> > &PromotedValues,
std::map<Value*, AllocaInst*> &ValueToAllocaMap) {
Instruction *FnStart = CurLoop->getHeader()->getParent()->begin()->begin();
- // Loop over all of the alias sets in the tracker object...
+ SmallVector<Instruction *, 4> LoopExits;
+ SmallVector<BasicBlock *, 4> Blocks;
+ CurLoop->getExitingBlocks(Blocks);
+ for (SmallVector<BasicBlock *, 4>::iterator BI = Blocks.begin(),
+ BE = Blocks.end(); BI != BE; ++BI) {
+ BasicBlock *BB = *BI;
+ LoopExits.push_back(BB->getTerminator());
+ }
+
+ // Loop over all of the alias sets in the tracker object.
for (AliasSetTracker::iterator I = CurAST->begin(), E = CurAST->end();
I != E; ++I) {
AliasSet &AS = *I;
// We can promote this alias set if it has a store, if it is a "Must" alias
- // set, and if the pointer is loop invariant.
- if (!AS.isForwardingAliasSet() && AS.isMod() && AS.isMustAlias() &&
- isLoopInvariant(AS.begin()->first)) {
- assert(AS.begin() != AS.end() &&
- "Must alias set should have at least one pointer element in it!");
- Value *V = AS.begin()->first;
-
- // Check that all of the pointers in the alias set have the same type. We
- // cannot (yet) promote a memory location that is loaded and stored in
- // different sizes.
+ // set, if the pointer is loop invariant, and if we are not eliminating any
+ // volatile loads or stores.
+ if (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() ||
+ AS.isVolatile() || !CurLoop->isLoopInvariant(AS.begin()->first))
+ continue;
+
+ assert(!AS.empty() &&
+ "Must alias set should have at least one pointer element in it!");
+ Value *V = AS.begin()->first;
+
+ // Check that all of the pointers in the alias set have the same type. We
+ // cannot (yet) promote a memory location that is loaded and stored in
+ // different sizes.
+ {
bool PointerOk = true;
for (AliasSet::iterator I = AS.begin(), E = AS.end(); I != E; ++I)
if (V->getType() != I->first->getType()) {
PointerOk = false;
break;
}
+ if (!PointerOk)
+ continue;
+ }
- if (PointerOk) {
- const Type *Ty = cast<PointerType>(V->getType())->getElementType();
- AllocaInst *AI = new AllocaInst(Ty, 0, V->getName()+".tmp", FnStart);
- PromotedValues.push_back(std::make_pair(AI, V));
-
- for (AliasSet::iterator I = AS.begin(), E = AS.end(); I != E; ++I)
- ValueToAllocaMap.insert(std::make_pair(I->first, AI));
-
- DEBUG(std::cerr << "LICM: Promoting value: " << *V << "\n");
+ // If one use of value V inside the loop is safe then it is OK to promote
+ // this value. On the otherside if there is not any unsafe use inside the
+ // loop then also it is OK to promote this value. Otherwise it is
+ // unsafe to promote this value.
+ bool oneSafeUse = false;
+ bool oneUnsafeUse = false;
+ for(Value::use_iterator UI = V->use_begin(), UE = V->use_end();
+ UI != UE; ++UI) {
+ Instruction *Use = dyn_cast<Instruction>(*UI);
+ if (!Use || !CurLoop->contains(Use->getParent()))
+ continue;
+
+ for (SmallVector<Instruction *, 4>::iterator
+ ExitI = LoopExits.begin(), ExitE = LoopExits.end();
+ ExitI != ExitE; ++ExitI) {
+ Instruction *Ex = *ExitI;
+ if (!isa<PHINode>(Use) && DT->dominates(Use, Ex)) {
+ oneSafeUse = true;
+ break;
+ } else
+ oneUnsafeUse = true;
}
+
+ if (oneSafeUse)
+ break;
}
+
+ if (!oneSafeUse && oneUnsafeUse)
+ continue;
+
+ const Type *Ty = cast<PointerType>(V->getType())->getElementType();
+ AllocaInst *AI = new AllocaInst(Ty, 0, V->getName()+".tmp", FnStart);
+ PromotedValues.push_back(std::make_pair(AI, V));
+
+ // Update the AST and alias analysis.
+ CurAST->copyValue(V, AI);
+
+ for (AliasSet::iterator I = AS.begin(), E = AS.end(); I != E; ++I)
+ ValueToAllocaMap.insert(std::make_pair(I->first, AI));
+
+ DOUT << "LICM: Promoting value: " << *V << "\n";
}
}
+
+/// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
+void LICM::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L) {
+ AliasSetTracker *AST = LoopToAliasMap[L];
+ if (!AST)
+ return;
+
+ AST->copyValue(From, To);
+}
+
+/// deleteAnalysisValue - Simple Analysis hook. Delete value V from alias
+/// set.
+void LICM::deleteAnalysisValue(Value *V, Loop *L) {
+ AliasSetTracker *AST = LoopToAliasMap[L];
+ if (!AST)
+ return;
+
+ AST->deleteValue(V);
+}
projects / oota-llvm.git / blobdiff