#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
#include <algorithm>
using namespace llvm;
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<LoopInfo>();
AU.addRequiredID(LoopSimplifyID);
+ AU.addPreservedID(LoopSimplifyID);
+ AU.addRequiredID(LCSSAID);
+ AU.addPreservedID(LCSSAID);
AU.addRequired<AliasAnalysis>();
AU.addPreserved<AliasAnalysis>();
AU.addPreserved<ScalarEvolution>();
- AU.addPreservedID(LoopSimplifyID);
AU.addRequired<TargetLibraryInfo>();
}
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
+INITIALIZE_PASS_DEPENDENCY(LCSSA)
+INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_END(LICM, "licm", "Loop Invariant Code Motion", false, false)
PromoteAliasSet(*I, ExitBlocks, InsertPts);
}
+ // If we have successfully changed the loop, re-form LCSSA and also re-form
+ // LCSSA in the parent loop as hoisting or sinking may have broken it.
+ if (Changed) {
+ formLCSSA(*L, *DT, getAnalysisIfAvailable<ScalarEvolution>());
+ if (Loop *ParentL = L->getParentLoop())
+ formLCSSA(*ParentL, *DT, getAnalysisIfAvailable<ScalarEvolution>());
+ }
+
// Clear out loops state information for the next iteration
CurLoop = 0;
Preheader = 0;
return isSafeToExecuteUnconditionally(I);
}
+/// \brief 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.
+static bool isTriviallyReplacablePHI(PHINode &PN, Instruction &I) {
+ for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
+ if (PN.getIncomingValue(i) != &I)
+ return false;
+
+ 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.
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!
+ // A PHI node where all of the incoming values are this instruction are
+ // special -- they can just be RAUW'ed with the instruction and thus
+ // don't require a use in the predecessor. This is a particular important
+ // special case because it is the pattern found in LCSSA form.
+ if (isTriviallyReplacablePHI(*PN, I)) {
+ if (CurLoop->contains(PN))
+ return false;
+ else
+ continue;
+ }
+
+ // Otherwise, PHI node uses occur in predecessor blocks if the incoming
+ // values. Check for such a use being inside the loop.
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)) {
- return false;
+
+ continue;
}
+
+ if (CurLoop->contains(User))
+ return false;
}
return true;
}
+static BasicBlock::iterator
+replaceTrivialPHIsAndGetInsertionPt(BasicBlock &BB, Instruction &I) {
+ BasicBlock::iterator II = BB.begin();
+ while (PHINode *PN = dyn_cast<PHINode>(II)) {
+ ++II;
+ if (isTriviallyReplacablePHI(*PN, I)) {
+ PN->replaceAllUsesWith(&I);
+ PN->eraseFromParent();
+ }
+ }
+ if (isa<LandingPadInst>(II))
+ ++II;
+
+ return II;
+}
/// 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.
I.replaceAllUsesWith(UndefValue::get(I.getType()));
I.eraseFromParent();
} else {
+ // Look for any LCSSA PHI nodes for this instruction in the exit blocks
+ // and replace them.
+ BasicBlock::iterator II =
+ replaceTrivialPHIsAndGetInsertionPt(*ExitBlocks[0], I);
+
// Move the instruction to the start of the exit block, after any PHI
// nodes in it.
- I.moveBefore(ExitBlocks[0]->getFirstInsertionPt());
+ I.moveBefore(II);
// This instruction is no longer in the AST for the current loop, because
// we just sunk it out of the loop. If we just sunk it into an outer
if (!DT->dominates(InstOrigBB, ExitBlock))
continue;
- // Insert the code after the last PHI node.
- BasicBlock::iterator InsertPt = ExitBlock->getFirstInsertionPt();
+ // Look for any LCSSA PHI nodes for this instruction in the exit blocks
+ // and replace them. Then get the insertion point after the last PHI.
+ BasicBlock::iterator InsertPt =
+ replaceTrivialPHIsAndGetInsertionPt(*ExitBlock, I);
// If this is the first exit block processed, just move the original
// instruction, otherwise clone the original instruction and insert
#include "llvm/IR/Instructions.h"
#include "llvm/Pass.h"
#include "llvm/Support/PredIteratorCache.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
using namespace llvm;
STATISTIC(NumLCSSA, "Number of live out of a loop variables");
-namespace {
- struct LCSSA : public LoopPass {
- static char ID; // Pass identification, replacement for typeid
- LCSSA() : LoopPass(ID) {
- initializeLCSSAPass(*PassRegistry::getPassRegistry());
- }
-
- // Cached analysis information for the current function.
- DominatorTree *DT;
- LoopInfo *LI;
- ScalarEvolution *SE;
- PredIteratorCache PredCache;
- Loop *L;
-
- virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
-
- /// This transformation requires natural loop information & requires that
- /// loop preheaders be inserted into the CFG. It maintains both of these,
- /// as well as the CFG. It also requires dominator information.
- ///
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.setPreservesCFG();
-
- AU.addRequired<DominatorTreeWrapperPass>();
- AU.addRequired<LoopInfo>();
- AU.addPreservedID(LoopSimplifyID);
- AU.addPreserved<ScalarEvolution>();
- }
- private:
- bool ProcessInstruction(Instruction *Inst,
- const SmallVectorImpl<BasicBlock*> &ExitBlocks);
-
- /// verifyAnalysis() - Verify loop nest.
- virtual void verifyAnalysis() const {
- // Check the special guarantees that LCSSA makes.
- assert(L->isLCSSAForm(*DT) && "LCSSA form not preserved!");
- }
- };
-}
-
-char LCSSA::ID = 0;
-INITIALIZE_PASS_BEGIN(LCSSA, "lcssa", "Loop-Closed SSA Form Pass", false, false)
-INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(LoopInfo)
-INITIALIZE_PASS_END(LCSSA, "lcssa", "Loop-Closed SSA Form Pass", false, false)
-
-Pass *llvm::createLCSSAPass() { return new LCSSA(); }
-char &llvm::LCSSAID = LCSSA::ID;
-
-
-/// BlockDominatesAnExit - Return true if the specified block dominates at least
-/// one of the blocks in the specified list.
-static bool BlockDominatesAnExit(BasicBlock *BB,
- const SmallVectorImpl<BasicBlock*> &ExitBlocks,
- DominatorTree *DT) {
- DomTreeNode *DomNode = DT->getNode(BB);
- for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
- if (DT->dominates(DomNode, DT->getNode(ExitBlocks[i])))
- return true;
-
- return false;
-}
-
-
-/// runOnFunction - Process all loops in the function, inner-most out.
-bool LCSSA::runOnLoop(Loop *TheLoop, LPPassManager &LPM) {
- L = TheLoop;
-
- DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
- LI = &getAnalysis<LoopInfo>();
- SE = getAnalysisIfAvailable<ScalarEvolution>();
-
- // Get the set of exiting blocks.
- SmallVector<BasicBlock*, 8> ExitBlocks;
- L->getExitBlocks(ExitBlocks);
-
- if (ExitBlocks.empty())
- return false;
-
- // Look at all the instructions in the loop, checking to see if they have uses
- // outside the loop. If so, rewrite those uses.
- bool MadeChange = false;
-
- for (Loop::block_iterator BBI = L->block_begin(), E = L->block_end();
- BBI != E; ++BBI) {
- BasicBlock *BB = *BBI;
-
- // For large loops, avoid use-scanning by using dominance information: In
- // particular, if a block does not dominate any of the loop exits, then none
- // of the values defined in the block could be used outside the loop.
- if (!BlockDominatesAnExit(BB, ExitBlocks, DT))
- continue;
-
- for (BasicBlock::iterator I = BB->begin(), E = BB->end();
- I != E; ++I) {
- // Reject two common cases fast: instructions with no uses (like stores)
- // and instructions with one use that is in the same block as this.
- if (I->use_empty() ||
- (I->hasOneUse() && I->use_back()->getParent() == BB &&
- !isa<PHINode>(I->use_back())))
- continue;
-
- MadeChange |= ProcessInstruction(I, ExitBlocks);
- }
- }
-
- // If we modified the code, remove any caches about the loop from SCEV to
- // avoid dangling entries.
- // FIXME: This is a big hammer, can we clear the cache more selectively?
- if (SE && MadeChange)
- SE->forgetLoop(L);
-
- assert(L->isLCSSAForm(*DT));
- PredCache.clear();
-
- return MadeChange;
-}
-
-/// isExitBlock - Return true if the specified block is in the list.
+/// Return true if the specified block is in the list.
static bool isExitBlock(BasicBlock *BB,
- const SmallVectorImpl<BasicBlock*> &ExitBlocks) {
+ const SmallVectorImpl<BasicBlock *> &ExitBlocks) {
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
if (ExitBlocks[i] == BB)
return true;
return false;
}
-/// ProcessInstruction - Given an instruction in the loop, check to see if it
-/// has any uses that are outside the current loop. If so, insert LCSSA PHI
-/// nodes and rewrite the uses.
-bool LCSSA::ProcessInstruction(Instruction *Inst,
- const SmallVectorImpl<BasicBlock*> &ExitBlocks) {
- SmallVector<Use*, 16> UsesToRewrite;
-
- BasicBlock *InstBB = Inst->getParent();
-
- for (Value::use_iterator UI = Inst->use_begin(), E = Inst->use_end();
- UI != E; ++UI) {
+/// Given an instruction in the loop, check to see if it has any uses that are
+/// outside the current loop. If so, insert LCSSA PHI nodes and rewrite the
+/// uses.
+static bool processInstruction(Loop &L, Instruction &Inst, DominatorTree &DT,
+ const SmallVectorImpl<BasicBlock *> &ExitBlocks,
+ PredIteratorCache &PredCache) {
+ SmallVector<Use *, 16> UsesToRewrite;
+
+ BasicBlock *InstBB = Inst.getParent();
+
+ for (Value::use_iterator UI = Inst.use_begin(), E = Inst.use_end(); UI != E;
+ ++UI) {
User *U = *UI;
BasicBlock *UserBB = cast<Instruction>(U)->getParent();
if (PHINode *PN = dyn_cast<PHINode>(U))
UserBB = PN->getIncomingBlock(UI);
-
- if (InstBB != UserBB && !L->contains(UserBB))
+
+ if (InstBB != UserBB && !L.contains(UserBB))
UsesToRewrite.push_back(&UI.getUse());
}
// If there are no uses outside the loop, exit with no change.
- if (UsesToRewrite.empty()) return false;
-
+ if (UsesToRewrite.empty())
+ return false;
+
++NumLCSSA; // We are applying the transformation
// Invoke instructions are special in that their result value is not available
- // along their unwind edge. The code below tests to see whether DomBB dominates
+ // along their unwind edge. The code below tests to see whether DomBB
+ // dominates
// the value, so adjust DomBB to the normal destination block, which is
// effectively where the value is first usable.
- BasicBlock *DomBB = Inst->getParent();
- if (InvokeInst *Inv = dyn_cast<InvokeInst>(Inst))
+ BasicBlock *DomBB = Inst.getParent();
+ if (InvokeInst *Inv = dyn_cast<InvokeInst>(&Inst))
DomBB = Inv->getNormalDest();
- DomTreeNode *DomNode = DT->getNode(DomBB);
+ DomTreeNode *DomNode = DT.getNode(DomBB);
- SmallVector<PHINode*, 16> AddedPHIs;
+ SmallVector<PHINode *, 16> AddedPHIs;
SSAUpdater SSAUpdate;
- SSAUpdate.Initialize(Inst->getType(), Inst->getName());
-
+ SSAUpdate.Initialize(Inst.getType(), Inst.getName());
+
// Insert the LCSSA phi's into all of the exit blocks dominated by the
// value, and add them to the Phi's map.
- for (SmallVectorImpl<BasicBlock*>::const_iterator BBI = ExitBlocks.begin(),
- BBE = ExitBlocks.end(); BBI != BBE; ++BBI) {
+ for (SmallVectorImpl<BasicBlock *>::const_iterator BBI = ExitBlocks.begin(),
+ BBE = ExitBlocks.end();
+ BBI != BBE; ++BBI) {
BasicBlock *ExitBB = *BBI;
- if (!DT->dominates(DomNode, DT->getNode(ExitBB))) continue;
-
+ if (!DT.dominates(DomNode, DT.getNode(ExitBB)))
+ continue;
+
// If we already inserted something for this BB, don't reprocess it.
- if (SSAUpdate.HasValueForBlock(ExitBB)) continue;
-
- PHINode *PN = PHINode::Create(Inst->getType(),
- PredCache.GetNumPreds(ExitBB),
- Inst->getName()+".lcssa",
- ExitBB->begin());
+ if (SSAUpdate.HasValueForBlock(ExitBB))
+ continue;
+
+ PHINode *PN = PHINode::Create(Inst.getType(), PredCache.GetNumPreds(ExitBB),
+ Inst.getName() + ".lcssa", ExitBB->begin());
// Add inputs from inside the loop for this PHI.
for (BasicBlock **PI = PredCache.GetPreds(ExitBB); *PI; ++PI) {
- PN->addIncoming(Inst, *PI);
+ PN->addIncoming(&Inst, *PI);
// If the exit block has a predecessor not within the loop, arrange for
// the incoming value use corresponding to that predecessor to be
// rewritten in terms of a different LCSSA PHI.
- if (!L->contains(*PI))
+ if (!L.contains(*PI))
UsesToRewrite.push_back(
- &PN->getOperandUse(
- PN->getOperandNumForIncomingValue(PN->getNumIncomingValues()-1)));
+ &PN->getOperandUse(PN->getOperandNumForIncomingValue(
+ PN->getNumIncomingValues() - 1)));
}
AddedPHIs.push_back(PN);
-
+
// Remember that this phi makes the value alive in this block.
SSAUpdate.AddAvailableValue(ExitBB, PN);
}
if (PHINode *PN = dyn_cast<PHINode>(User))
UserBB = PN->getIncomingBlock(*UsesToRewrite[i]);
- if (isa<PHINode>(UserBB->begin()) &&
- isExitBlock(UserBB, ExitBlocks)) {
+ if (isa<PHINode>(UserBB->begin()) && isExitBlock(UserBB, ExitBlocks)) {
// Tell the VHs that the uses changed. This updates SCEV's caches.
if (UsesToRewrite[i]->get()->hasValueHandle())
ValueHandleBase::ValueIsRAUWd(*UsesToRewrite[i], UserBB->begin());
UsesToRewrite[i]->set(UserBB->begin());
continue;
}
-
+
// Otherwise, do full PHI insertion.
SSAUpdate.RewriteUse(*UsesToRewrite[i]);
}
if (AddedPHIs[i]->use_empty())
AddedPHIs[i]->eraseFromParent();
}
-
+
return true;
}
+/// Return true if the specified block dominates at least
+/// one of the blocks in the specified list.
+static bool
+blockDominatesAnExit(BasicBlock *BB,
+ DominatorTree &DT,
+ const SmallVectorImpl<BasicBlock *> &ExitBlocks) {
+ DomTreeNode *DomNode = DT.getNode(BB);
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
+ if (DT.dominates(DomNode, DT.getNode(ExitBlocks[i])))
+ return true;
+
+ return false;
+}
+
+bool llvm::formLCSSA(Loop &L, DominatorTree &DT, ScalarEvolution *SE) {
+ bool Changed = false;
+
+ // Get the set of exiting blocks.
+ SmallVector<BasicBlock *, 8> ExitBlocks;
+ L.getExitBlocks(ExitBlocks);
+
+ if (ExitBlocks.empty())
+ return false;
+
+ PredIteratorCache PredCache;
+
+ // Look at all the instructions in the loop, checking to see if they have uses
+ // outside the loop. If so, rewrite those uses.
+ for (Loop::block_iterator BBI = L.block_begin(), BBE = L.block_end();
+ BBI != BBE; ++BBI) {
+ BasicBlock *BB = *BBI;
+
+ // For large loops, avoid use-scanning by using dominance information: In
+ // particular, if a block does not dominate any of the loop exits, then none
+ // of the values defined in the block could be used outside the loop.
+ if (!blockDominatesAnExit(BB, DT, ExitBlocks))
+ continue;
+
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
+ // Reject two common cases fast: instructions with no uses (like stores)
+ // and instructions with one use that is in the same block as this.
+ if (I->use_empty() ||
+ (I->hasOneUse() && I->use_back()->getParent() == BB &&
+ !isa<PHINode>(I->use_back())))
+ continue;
+
+ Changed |= processInstruction(L, *I, DT, ExitBlocks, PredCache);
+ }
+ }
+
+ // If we modified the code, remove any caches about the loop from SCEV to
+ // avoid dangling entries.
+ // FIXME: This is a big hammer, can we clear the cache more selectively?
+ if (SE && Changed)
+ SE->forgetLoop(&L);
+
+ assert(L.isLCSSAForm(DT));
+
+ return Changed;
+}
+
+namespace {
+struct LCSSA : public FunctionPass {
+ static char ID; // Pass identification, replacement for typeid
+ LCSSA() : FunctionPass(ID) {
+ initializeLCSSAPass(*PassRegistry::getPassRegistry());
+ }
+
+ // Cached analysis information for the current function.
+ DominatorTree *DT;
+ LoopInfo *LI;
+ ScalarEvolution *SE;
+
+ virtual bool runOnFunction(Function &F);
+
+ /// This transformation requires natural loop information & requires that
+ /// loop preheaders be inserted into the CFG. It maintains both of these,
+ /// as well as the CFG. It also requires dominator information.
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.setPreservesCFG();
+
+ AU.addRequired<DominatorTreeWrapperPass>();
+ AU.addRequired<LoopInfo>();
+ AU.addPreservedID(LoopSimplifyID);
+ AU.addPreserved<ScalarEvolution>();
+ }
+
+private:
+ bool processLoop(Loop &L);
+
+ virtual void verifyAnalysis() const;
+};
+}
+
+char LCSSA::ID = 0;
+INITIALIZE_PASS_BEGIN(LCSSA, "lcssa", "Loop-Closed SSA Form Pass", false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopInfo)
+INITIALIZE_PASS_END(LCSSA, "lcssa", "Loop-Closed SSA Form Pass", false, false)
+
+Pass *llvm::createLCSSAPass() { return new LCSSA(); }
+char &llvm::LCSSAID = LCSSA::ID;
+
+
+/// Process all loops in the function, inner-most out.
+bool LCSSA::runOnFunction(Function &F) {
+ bool Changed = false;
+ LI = &getAnalysis<LoopInfo>();
+ DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ SE = getAnalysisIfAvailable<ScalarEvolution>();
+
+ // Simplify each loop nest in the function.
+ for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
+ Changed |= processLoop(**I);
+
+ return Changed;
+}
+
+/// Process a loop nest depth first.
+bool LCSSA::processLoop(Loop &L) {
+ bool Changed = false;
+
+ // Recurse depth-first through inner loops.
+ for (Loop::iterator LI = L.begin(), LE = L.end(); LI != LE; ++LI)
+ Changed |= processLoop(**LI);
+
+ Changed |= formLCSSA(L, *DT, SE);
+ return Changed;
+}
+
+static void verifyLoop(Loop &L, DominatorTree &DT) {
+ // Recurse depth-first through inner loops.
+ for (Loop::iterator LI = L.begin(), LE = L.end(); LI != LE; ++LI)
+ verifyLoop(**LI, DT);
+
+ // Check the special guarantees that LCSSA makes.
+ //assert(L.isLCSSAForm(DT) && "LCSSA form not preserved!");
+}
+
+void LCSSA::verifyAnalysis() const {
+ // Verify each loop nest in the function, assuming LI still points at that
+ // function's loop info.
+ for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
+ verifyLoop(**I, *DT);
+}
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