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[LICM] Refactor to expose functionality as utility functions

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This refactors the core functionality of LICM: HoistRegion, SinkRegion and
PromoteAliasSet (renamed to promoteLoopAccessesToScalars) as utility functions
in LoopUtils. This will enable other transformations to make use of them
directly.

Patch by Ashutosh Nema.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230178 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel 2015-02-22 18:35:32 +00:00
parent 66c960350c
commit 67f22b7af9
2 changed files with 255 additions and 173 deletions
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56
include/llvm/Transforms/Utils/LoopUtils.h
View File

@ -24,6 +24,19 @@ class Loop;
class LoopInfo;
class Pass;
class ScalarEvolution;
class AliasSetTracker;
class AliasSet;
class PredIteratorCache;
/// \brief Captures loop safety information.
/// It keep information for loop & its header may throw exception.
struct LICMSafetyInfo {
bool MayThrow; // The current loop contains an instruction which
// may throw.
bool HeaderMayThrow; // Same as previous, but specific to loop header
LICMSafetyInfo() : MayThrow(false), HeaderMayThrow(false)
{}
};
BasicBlock *InsertPreheaderForLoop(Loop *L, Pass *P);
@ -63,6 +76,49 @@ bool formLCSSA(Loop &L, DominatorTree &DT, LoopInfo *LI,
/// Returns true if any modifications are made to the loop.
bool formLCSSARecursively(Loop &L, DominatorTree &DT, LoopInfo *LI,
ScalarEvolution *SE = nullptr);
/// \brief 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. Takes DomTreeNode, AliasAnalysis, LoopInfo, DominatorTree,
/// DataLayout, TargetLibraryInfo, Loop, AliasSet information for all
/// instructions of the loop and loop safety information as arguments.
/// It returns changed status.
bool sinkRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
const DataLayout *, TargetLibraryInfo *, Loop *,
AliasSetTracker *, LICMSafetyInfo *);
/// \brief 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.
/// Takes DomTreeNode, AliasAnalysis, LoopInfo, DominatorTree, DataLayout,
/// TargetLibraryInfo, Loop, AliasSet information for all instructions of the
/// loop and loop safety information as arguments. It returns changed status.
bool hoistRegion(DomTreeNode *, AliasAnalysis *, LoopInfo *, DominatorTree *,
const DataLayout *, TargetLibraryInfo *, Loop *,
AliasSetTracker *, LICMSafetyInfo *);
/// \brief 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 which are
/// loop invariant. It takes AliasSet, Loop exit blocks vector, loop exit blocks
/// insertion point vector, PredIteratorCache, LoopInfo, DominatorTree, Loop,
/// AliasSet information for all instructions of the loop and loop safety
/// information as arguments. It returns changed status.
bool promoteLoopAccessesToScalars(AliasSet &, SmallVectorImpl<BasicBlock*> &,
SmallVectorImpl<Instruction*> &,
PredIteratorCache &, LoopInfo *,
DominatorTree *, Loop *, AliasSetTracker *,
LICMSafetyInfo *);
/// \brief Computes safety information for a loop
/// checks loop body & header for the possiblity of may throw
/// exception, it takes LICMSafetyInfo and loop as argument.
/// Updates safety information in LICMSafetyInfo argument.
void computeLICMSafetyInfo(LICMSafetyInfo *, Loop *);
}
#endif

372
lib/Transforms/Scalar/LICM.cpp
View File

@ -71,6 +71,27 @@ static cl::opt<bool>
DisablePromotion("disable-licm-promotion", cl::Hidden,
cl::desc("Disable memory promotion in LICM pass"));
static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI);
static bool isNotUsedInLoop(Instruction &I, Loop *CurLoop);
static bool hoist(Instruction &I, BasicBlock *Preheader);
static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
Loop *CurLoop, AliasSetTracker *CurAST );
static bool isGuaranteedToExecute(Instruction &Inst, DominatorTree *DT,
Loop *CurLoop, LICMSafetyInfo * SafetyInfo);
static bool isSafeToExecuteUnconditionally(Instruction &Inst,DominatorTree *DT,
const DataLayout *DL, Loop *CurLoop,
LICMSafetyInfo * SafetyInfo);
static bool pointerInvalidatedByLoop(Value *V, uint64_t Size,
const AAMDNodes &AAInfo,
AliasSetTracker *CurAST);
static Instruction *CloneInstructionInExitBlock(Instruction &I,
BasicBlock &ExitBlock,
PHINode &PN, LoopInfo *LI);
static bool canSinkOrHoistInst(Instruction &I, AliasAnalysis *AA,
DominatorTree *DT, const DataLayout *DL,
Loop *CurLoop, AliasSetTracker *CurAST,
LICMSafetyInfo * SafetyInfo);
namespace {
struct LICM : public LoopPass {
static char ID; // Pass identification, replacement for typeid
@ -117,10 +138,6 @@ namespace {
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...
bool MayThrow; // The current loop contains an instruction which
// may throw, thus preventing code motion of
// instructions with side effects.
bool HeaderMayThrow; // Same as previous, but specific to loop header
DenseMap<Loop*, AliasSetTracker*> LoopToAliasSetMap;
/// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
@ -133,77 +150,6 @@ namespace {
/// Simple Analysis hook. Delete loop L from alias set map.
void deleteAnalysisLoop(Loop *L) override;
/// 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 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
/// 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 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");
return LI->getLoopFor(BB) != CurLoop;
}
/// 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);
/// 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 isSafeToExecuteUnconditionally(Instruction &I);
/// isGuaranteedToExecute - Check that the instruction is guaranteed to
/// execute.
///
bool isGuaranteedToExecute(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, uint64_t Size,
const AAMDNodes &AAInfo) {
// Check to see if any of the basic blocks in CurLoop invalidate *V.
return CurAST->getAliasSetForPointer(V, Size, AAInfo).isMod();
}
bool canSinkOrHoistInst(Instruction &I);
bool isNotUsedInLoop(Instruction &I);
void PromoteAliasSet(AliasSet &AS,
SmallVectorImpl<BasicBlock*> &ExitBlocks,
SmallVectorImpl<Instruction*> &InsertPts,
PredIteratorCache &PIC);
/// \brief Create a copy of the instruction in the exit block and patch up
/// SSA.
/// PN is a user of I in ExitBlock that can be used to get the number and
/// list of predecessors fast.
Instruction *CloneInstructionInExitBlock(Instruction &I,
BasicBlock &ExitBlock,
PHINode &PN);
};
}
@ -274,19 +220,9 @@ bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
CurAST->add(*BB); // Incorporate the specified basic block
}
HeaderMayThrow = false;
BasicBlock *Header = L->getHeader();
for (BasicBlock::iterator I = Header->begin(), E = Header->end();
(I != E) && !HeaderMayThrow; ++I)
HeaderMayThrow |= I->mayThrow();
MayThrow = HeaderMayThrow;
// TODO: We've already searched for instructions which may throw in subloops.
// We may want to reuse this information.
for (Loop::block_iterator BB = L->block_begin(), BBE = L->block_end();
(BB != BBE) && !MayThrow ; ++BB)
for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end();
(I != E) && !MayThrow; ++I)
MayThrow |= I->mayThrow();
// Compute loop safety information.
LICMSafetyInfo SafetyInfo;
computeLICMSafetyInfo(&SafetyInfo, CurLoop);
// 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
@ -299,9 +235,11 @@ bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
// instructions, we perform another pass to hoist them out of the loop.
//
if (L->hasDedicatedExits())
SinkRegion(DT->getNode(L->getHeader()));
Changed |= sinkRegion(DT->getNode(L->getHeader()), AA, LI, DT, DL, TLI,
CurLoop, CurAST, &SafetyInfo);
if (Preheader)
HoistRegion(DT->getNode(L->getHeader()));
Changed |= hoistRegion(DT->getNode(L->getHeader()), AA, LI, DT, DL, TLI,
CurLoop, CurAST, &SafetyInfo);
// Now that all loop invariants have been removed from the loop, promote any
// memory references to scalars that we can.
@ -313,7 +251,9 @@ bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
// Loop over all of the alias sets in the tracker object.
for (AliasSetTracker::iterator I = CurAST->begin(), E = CurAST->end();
I != E; ++I)
PromoteAliasSet(*I, ExitBlocks, InsertPts, PIC);
Changed |= promoteLoopAccessesToScalars(*I, ExitBlocks, InsertPts,
PIC, LI, DT, CurLoop,
CurAST, &SafetyInfo);
// Once we have promoted values across the loop body we have to recursively
// reform LCSSA as any nested loop may now have values defined within the
@ -346,27 +286,36 @@ bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
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.
/// 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 != nullptr && "Null dominator tree node?");
BasicBlock *BB = N->getBlock();
bool llvm::sinkRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
DominatorTree *DT, const DataLayout *DL,
TargetLibraryInfo *TLI, Loop *CurLoop,
AliasSetTracker *CurAST, LICMSafetyInfo * SafetyInfo) {
// Verify inputs.
assert(N != nullptr && AA != nullptr && LI != nullptr &&
DT != nullptr && CurLoop != nullptr && CurAST != nullptr &&
SafetyInfo != nullptr && "Unexpected input to sinkRegion");
// Set changed as false.
bool Changed = false;
// Get basic block
BasicBlock *BB = N->getBlock();
// If this subregion is not in the top level loop at all, exit.
if (!CurLoop->contains(BB)) return;
if (!CurLoop->contains(BB)) return Changed;
// 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]);
Changed |= sinkRegion(Children[i], AA, LI, DT, DL, TLI, CurLoop,
CurAST, SafetyInfo);
// 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;
if (inSubLoop(BB,CurLoop,LI)) return Changed;
for (BasicBlock::iterator II = BB->end(); II != BB->begin(); ) {
Instruction &I = *--II;
@ -387,31 +336,39 @@ void LICM::SinkRegion(DomTreeNode *N) {
// 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)) {
if (isNotUsedInLoop(I, CurLoop) &&
canSinkOrHoistInst(I, AA, DT, DL, CurLoop, CurAST, SafetyInfo)) {
++II;
sink(I);
Changed |= sink(I, LI, DT, CurLoop, CurAST);
}
}
return Changed;
}
/// 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.
/// 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(DomTreeNode *N) {
assert(N != nullptr && "Null dominator tree node?");
bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
DominatorTree *DT, const DataLayout *DL,
TargetLibraryInfo *TLI, Loop *CurLoop,
AliasSetTracker *CurAST, LICMSafetyInfo *SafetyInfo) {
// Verify inputs.
assert(N != nullptr && AA != nullptr && LI != nullptr &&
DT != nullptr && CurLoop != nullptr && CurAST != nullptr &&
SafetyInfo != nullptr && "Unexpected input to hoistRegion");
// Set changed as false.
bool Changed = false;
// Get basic block
BasicBlock *BB = N->getBlock();
// If this subregion is not in the top level loop at all, exit.
if (!CurLoop->contains(BB)) return;
if (!CurLoop->contains(BB)) return Changed;
// 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))
if (!inSubLoop(BB, CurLoop, LI))
for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ) {
Instruction &I = *II++;
// Try constant folding this instruction. If all the operands are
// constants, it is technically hoistable, but it would be better to just
// fold it.
@ -428,20 +385,49 @@ void LICM::HoistRegion(DomTreeNode *N) {
// if all of the operands of the instruction are loop invariant and if it
// is safe to hoist the instruction.
//
if (CurLoop->hasLoopInvariantOperands(&I) && canSinkOrHoistInst(I) &&
isSafeToExecuteUnconditionally(I))
hoist(I);
if (CurLoop->hasLoopInvariantOperands(&I) &&
canSinkOrHoistInst(I, AA, DT, DL, CurLoop, CurAST, SafetyInfo) &&
isSafeToExecuteUnconditionally(I, DT, DL, CurLoop, SafetyInfo))
Changed |= hoist(I, CurLoop->getLoopPreheader());
}
const std::vector<DomTreeNode*> &Children = N->getChildren();
for (unsigned i = 0, e = Children.size(); i != e; ++i)
HoistRegion(Children[i]);
Changed |= hoistRegion(Children[i], AA, LI, DT, DL, TLI, CurLoop,
CurAST, SafetyInfo);
return Changed;
}
/// Computes loop safety information, checks loop body & header
/// for the possiblity of may throw exception.
///
void llvm::computeLICMSafetyInfo(LICMSafetyInfo * SafetyInfo, Loop * CurLoop) {
assert(CurLoop != nullptr && "CurLoop cant be null");
BasicBlock *Header = CurLoop->getHeader();
// Setting default safety values.
SafetyInfo->MayThrow = false;
SafetyInfo->HeaderMayThrow = false;
// Iterate over header and compute dafety info.
for (BasicBlock::iterator I = Header->begin(), E = Header->end();
(I != E) && !SafetyInfo->HeaderMayThrow; ++I)
SafetyInfo->HeaderMayThrow |= I->mayThrow();
SafetyInfo->MayThrow = SafetyInfo->HeaderMayThrow;
// Iterate over loop instructions and compute safety info.
for (Loop::block_iterator BB = CurLoop->block_begin(),
BBE = CurLoop->block_end(); (BB != BBE) && !SafetyInfo->MayThrow ; ++BB)
for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end();
(I != E) && !SafetyInfo->MayThrow; ++I)
SafetyInfo->MayThrow |= I->mayThrow();
}
/// canSinkOrHoistInst - Return true if the hoister and sinker can handle this
/// instruction.
///
bool LICM::canSinkOrHoistInst(Instruction &I) {
bool canSinkOrHoistInst(Instruction &I, AliasAnalysis *AA,
DominatorTree *DT, const DataLayout *DL,
Loop *CurLoop, AliasSetTracker *CurAST,
LICMSafetyInfo * SafetyInfo) {
// Loads have extra constraints we have to verify before we can hoist them.
if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
if (!LI->isUnordered())
@ -462,7 +448,7 @@ bool LICM::canSinkOrHoistInst(Instruction &I) {
AAMDNodes AAInfo;
LI->getAAMetadata(AAInfo);
return !pointerInvalidatedByLoop(LI->getOperand(0), Size, AAInfo);
return !pointerInvalidatedByLoop(LI->getOperand(0), Size, AAInfo, CurAST);
} else if (CallInst *CI = dyn_cast<CallInst>(&I)) {
// Don't sink or hoist dbg info; it's legal, but not useful.
if (isa<DbgInfoIntrinsic>(I))
@ -501,14 +487,14 @@ bool LICM::canSinkOrHoistInst(Instruction &I) {
!isa<InsertValueInst>(I))
return false;
return isSafeToExecuteUnconditionally(I);
return isSafeToExecuteUnconditionally(I, DT, DL, CurLoop, SafetyInfo);
}
/// \brief Returns true if a PHINode is a trivially replaceable with an
/// Returns true if a PHINode is a trivially replaceable with an
/// Instruction.
/// This is true when all incoming values are that instruction.
/// This pattern occurs most often with LCSSA PHI nodes.
///
/// This is true when all incoming values are that instruction. This pattern
/// occurs most often with LCSSA PHI nodes.
static bool isTriviallyReplacablePHI(PHINode &PN, Instruction &I) {
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
if (PN.getIncomingValue(i) != &I)
@ -517,11 +503,11 @@ static bool isTriviallyReplacablePHI(PHINode &PN, Instruction &I) {
return true;
}
/// 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.
/// 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) {
static bool isNotUsedInLoop(Instruction &I, Loop *CurLoop) {
for (User *U : I.users()) {
Instruction *UI = cast<Instruction>(U);
if (PHINode *PN = dyn_cast<PHINode>(UI)) {
@ -552,9 +538,9 @@ bool LICM::isNotUsedInLoop(Instruction &I) {
return true;
}
Instruction *LICM::CloneInstructionInExitBlock(Instruction &I,
BasicBlock &ExitBlock,
PHINode &PN) {
static Instruction *CloneInstructionInExitBlock(Instruction &I,
BasicBlock &ExitBlock,
PHINode &PN, LoopInfo *LI) {
Instruction *New = I.clone();
ExitBlock.getInstList().insert(ExitBlock.getFirstInsertionPt(), New);
if (!I.getName().empty()) New->setName(I.getName() + ".le");
@ -581,14 +567,15 @@ Instruction *LICM::CloneInstructionInExitBlock(Instruction &I,
return New;
}
/// 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.
/// 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) {
static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
Loop *CurLoop, AliasSetTracker *CurAST ) {
DEBUG(dbgs() << "LICM sinking instruction: " << I << "\n");
bool Changed = false;
if (isa<LoadInst>(I)) ++NumMovedLoads;
else if (isa<CallInst>(I)) ++NumMovedCalls;
++NumSunk;
@ -597,7 +584,8 @@ void LICM::sink(Instruction &I) {
#ifndef NDEBUG
SmallVector<BasicBlock *, 32> ExitBlocks;
CurLoop->getUniqueExitBlocks(ExitBlocks);
SmallPtrSet<BasicBlock *, 32> ExitBlockSet(ExitBlocks.begin(), ExitBlocks.end());
SmallPtrSet<BasicBlock *, 32> ExitBlockSet(ExitBlocks.begin(),
ExitBlocks.end());
#endif
// Clones of this instruction. Don't create more than one per exit block!
@ -625,7 +613,7 @@ void LICM::sink(Instruction &I) {
New = It->second;
else
New = SunkCopies[ExitBlock] =
CloneInstructionInExitBlock(I, *ExitBlock, *PN);
CloneInstructionInExitBlock(I, *ExitBlock, *PN, LI);
PN->replaceAllUsesWith(New);
PN->eraseFromParent();
@ -633,37 +621,39 @@ void LICM::sink(Instruction &I) {
CurAST->deleteValue(&I);
I.eraseFromParent();
return Changed;
}
/// 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.
/// 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 &I) {
static bool hoist(Instruction &I, BasicBlock *Preheader) {
DEBUG(dbgs() << "LICM hoisting to " << Preheader->getName() << ": "
<< I << "\n");
// Move the new node to the Preheader, before its terminator.
I.moveBefore(Preheader->getTerminator());
if (isa<LoadInst>(I)) ++NumMovedLoads;
else if (isa<CallInst>(I)) ++NumMovedCalls;
++NumHoisted;
Changed = true;
return true;
}
/// 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.
/// 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::isSafeToExecuteUnconditionally(Instruction &Inst) {
static bool isSafeToExecuteUnconditionally(Instruction &Inst, DominatorTree *DT,
const DataLayout *DL, Loop *CurLoop,
LICMSafetyInfo * SafetyInfo) {
// If it is not a trapping instruction, it is always safe to hoist.
if (isSafeToSpeculativelyExecute(&Inst, DL))
return true;
return isGuaranteedToExecute(Inst);
return isGuaranteedToExecute(Inst, DT, CurLoop, SafetyInfo);
}
bool LICM::isGuaranteedToExecute(Instruction &Inst) {
static bool isGuaranteedToExecute(Instruction &Inst, DominatorTree *DT,
Loop *CurLoop, LICMSafetyInfo * SafetyInfo) {
// 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
@ -675,11 +665,11 @@ bool LICM::isGuaranteedToExecute(Instruction &Inst) {
if (Inst.getParent() == CurLoop->getHeader())
// If there's a throw in the header block, we can't guarantee we'll reach
// Inst.
return !HeaderMayThrow;
return !SafetyInfo->HeaderMayThrow;
// Somewhere in this loop there is an instruction which may throw and make us
// exit the loop.
if (MayThrow)
if (SafetyInfo->MayThrow)
return false;
// Get the exit blocks for the current loop.
@ -777,25 +767,37 @@ namespace {
};
} // end anon namespace
/// PromoteAliasSet - 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
/// which are loop invariant.
/// 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 which are
/// loop invariant.
///
void LICM::PromoteAliasSet(AliasSet &AS,
SmallVectorImpl<BasicBlock*> &ExitBlocks,
SmallVectorImpl<Instruction*> &InsertPts,
PredIteratorCache &PIC) {
bool llvm::promoteLoopAccessesToScalars(AliasSet &AS,
SmallVectorImpl<BasicBlock*>&ExitBlocks,
SmallVectorImpl<Instruction*>&InsertPts,
PredIteratorCache &PIC, LoopInfo *LI,
DominatorTree *DT, Loop *CurLoop,
AliasSetTracker *CurAST,
LICMSafetyInfo * SafetyInfo) {
// Verify inputs.
assert(LI != nullptr && DT != nullptr &&
CurLoop != nullptr && CurAST != nullptr &&
SafetyInfo != nullptr &&
"Unexpected Input to promoteLoopAccessesToScalars");
// Initially set Changed status to false.
bool Changed = false;
// We can promote this alias set if it has a store, if it is a "Must" alias
// 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()->getValue()))
return;
return Changed;
assert(!AS.empty() &&
"Must alias set should have at least one pointer element in it!");
Value *SomePtr = AS.begin()->getValue();
BasicBlock * Preheader = CurLoop->getLoopPreheader();
// It isn't safe to promote a load/store from the loop if the load/store is
// conditional. For example, turning:
@ -832,7 +834,7 @@ void LICM::PromoteAliasSet(AliasSet &AS,
// cannot (yet) promote a memory location that is loaded and stored in
// different sizes.
if (SomePtr->getType() != ASIV->getType())
return;
return Changed;
for (User *U : ASIV->users()) {
// Ignore instructions that are outside the loop.
@ -845,7 +847,7 @@ void LICM::PromoteAliasSet(AliasSet &AS,
if (LoadInst *load = dyn_cast<LoadInst>(UI)) {
assert(!load->isVolatile() && "AST broken");
if (!load->isSimple())
return;
return Changed;
} else if (StoreInst *store = dyn_cast<StoreInst>(UI)) {
// Stores *of* the pointer are not interesting, only stores *to* the
// pointer.
@ -853,14 +855,14 @@ void LICM::PromoteAliasSet(AliasSet &AS,
continue;
assert(!store->isVolatile() && "AST broken");
if (!store->isSimple())
return;
return Changed;
// Don't sink stores from loops without dedicated block exits. Exits
// containing indirect branches are not transformed by loop simplify,
// make sure we catch that. An additional load may be generated in the
// preheader for SSA updater, so also avoid sinking when no preheader
// is available.
if (!HasDedicatedExits || !Preheader)
return;
return Changed;
// Note that we only check GuaranteedToExecute inside the store case
// so that we do not introduce stores where they did not exist before
@ -872,16 +874,17 @@ void LICM::PromoteAliasSet(AliasSet &AS,
// Larger is better, with the exception of 0 being the best alignment.
unsigned InstAlignment = store->getAlignment();
if ((InstAlignment > Alignment || InstAlignment == 0) && Alignment != 0)
if (isGuaranteedToExecute(*UI)) {
if (isGuaranteedToExecute(*UI, DT, CurLoop, SafetyInfo)) {
GuaranteedToExecute = true;
Alignment = InstAlignment;
}
if (!GuaranteedToExecute)
GuaranteedToExecute = isGuaranteedToExecute(*UI);
GuaranteedToExecute = isGuaranteedToExecute(*UI, DT,
CurLoop, SafetyInfo);
} else
return; // Not a load or store.
return Changed; // Not a load or store.
// Merge the AA tags.
if (LoopUses.empty()) {
@ -897,7 +900,7 @@ void LICM::PromoteAliasSet(AliasSet &AS,
// If there isn't a guaranteed-to-execute instruction, we can't promote.
if (!GuaranteedToExecute)
return;
return Changed;
// Otherwise, this is safe to promote, lets do it!
DEBUG(dbgs() << "LICM: Promoting value stored to in loop: " <<*SomePtr<<'\n');
@ -942,10 +945,12 @@ void LICM::PromoteAliasSet(AliasSet &AS,
// If the SSAUpdater didn't use the load in the preheader, just zap it now.
if (PreheaderLoad->use_empty())
PreheaderLoad->eraseFromParent();
return Changed;
}
/// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
/// Simple Analysis hook. Clone alias set info.
///
void LICM::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L) {
AliasSetTracker *AST = LoopToAliasSetMap.lookup(L);
if (!AST)
@ -954,8 +959,8 @@ void LICM::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L) {
AST->copyValue(From, To);
}
/// deleteAnalysisValue - Simple Analysis hook. Delete value V from alias
/// set.
/// Simple Analysis hook. Delete value V from alias set
///
void LICM::deleteAnalysisValue(Value *V, Loop *L) {
AliasSetTracker *AST = LoopToAliasSetMap.lookup(L);
if (!AST)
@ -965,6 +970,7 @@ void LICM::deleteAnalysisValue(Value *V, Loop *L) {
}
/// Simple Analysis hook. Delete value L from alias set map.
///
void LICM::deleteAnalysisLoop(Loop *L) {
AliasSetTracker *AST = LoopToAliasSetMap.lookup(L);
if (!AST)
@ -973,3 +979,23 @@ void LICM::deleteAnalysisLoop(Loop *L) {
delete AST;
LoopToAliasSetMap.erase(L);
}
/// Return true if the body of this loop may store into the memory
/// location pointed to by V.
///
static bool pointerInvalidatedByLoop(Value *V, uint64_t Size,
const AAMDNodes &AAInfo,
AliasSetTracker *CurAST) {
// Check to see if any of the basic blocks in CurLoop invalidate *V.
return CurAST->getAliasSetForPointer(V, Size, AAInfo).isMod();
}
/// Little predicate that returns true if the specified basic block is in
/// a subloop of the current one, not the current one itself.
///
static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI) {
assert(CurLoop->contains(BB) && "Only valid if BB is IN the loop");
return LI->getLoopFor(BB) != CurLoop;
}