//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "lcssa"
#include "llvm/Transforms/Scalar.h"
-#include "llvm/Constants.h"
-#include "llvm/Pass.h"
-#include "llvm/Function.h"
-#include "llvm/Instructions.h"
-#include "llvm/Analysis/Dominators.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/PredIteratorCache.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
-#include "llvm/ADT/Statistic.h"
-#include "llvm/ADT/STLExtras.h"
-#include "llvm/Support/PredIteratorCache.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) {}
-
- // Cached analysis information for the current function.
- DominatorTree *DT;
- std::vector<BasicBlock*> LoopBlocks;
- 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<DominatorTree>();
- AU.addPreserved<DominatorTree>();
- AU.addPreserved<DominanceFrontier>();
- AU.addRequired<LoopInfo>();
- AU.addPreserved<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!");
- }
-
- /// inLoop - returns true if the given block is within the current loop
- bool inLoop(BasicBlock *B) const {
- return std::binary_search(LoopBlocks.begin(), LoopBlocks.end(), B);
- }
- };
-}
-
-char LCSSA::ID = 0;
-static RegisterPass<LCSSA> X("lcssa", "Loop-Closed SSA Form Pass");
-
-Pass *llvm::createLCSSAPass() { return new LCSSA(); }
-const PassInfo *const llvm::LCSSAID = &X;
+#define DEBUG_TYPE "lcssa"
+STATISTIC(NumLCSSA, "Number of live out of a loop variables");
-/// 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);
+/// Return true if the specified block is in the list.
+static bool isExitBlock(BasicBlock *BB,
+ const SmallVectorImpl<BasicBlock *> &ExitBlocks) {
for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
- if (DT->dominates(DomNode, DT->getNode(ExitBlocks[i])))
+ if (ExitBlocks[i] == BB)
return true;
-
return false;
}
+/// 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, LoopInfo *LI) {
+ SmallVector<Use *, 16> UsesToRewrite;
-/// runOnFunction - Process all loops in the function, inner-most out.
-bool LCSSA::runOnLoop(Loop *TheLoop, LPPassManager &LPM) {
- L = TheLoop;
-
- DT = &getAnalysis<DominatorTree>();
-
- // Get the set of exiting blocks.
- SmallVector<BasicBlock*, 8> ExitBlocks;
- L->getExitBlocks(ExitBlocks);
-
- if (ExitBlocks.empty())
- return false;
-
- // Speed up queries by creating a sorted vector of blocks.
- LoopBlocks.clear();
- LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
- array_pod_sort(LoopBlocks.begin(), LoopBlocks.end());
-
- // 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);
- }
- }
-
- assert(L->isLCSSAForm(*DT));
- PredCache.clear();
-
- return MadeChange;
-}
+ BasicBlock *InstBB = Inst.getParent();
-/// isExitBlock - Return true if the specified block is in the list.
-static bool isExitBlock(BasicBlock *BB,
- const SmallVectorImpl<BasicBlock*> &ExitBlocks) {
- for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
- if (ExitBlocks[i] == BB)
- return true;
- return false;
-}
+ for (Use &U : Inst.uses()) {
+ Instruction *User = cast<Instruction>(U.getUser());
+ BasicBlock *UserBB = User->getParent();
+ if (PHINode *PN = dyn_cast<PHINode>(User))
+ UserBB = PN->getIncomingBlock(U);
-/// 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) {
- User *U = *UI;
- BasicBlock *UserBB = cast<Instruction>(U)->getParent();
- if (PHINode *PN = dyn_cast<PHINode>(U))
- UserBB = PN->getIncomingBlock(UI);
-
- if (InstBB != UserBB && !inLoop(UserBB))
- UsesToRewrite.push_back(&UI.getUse());
+ if (InstBB != UserBB && !L.contains(UserBB))
+ UsesToRewrite.push_back(&U);
}
// 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 *, 8> PostProcessPHIs;
SSAUpdater SSAUpdate;
- SSAUpdate.Initialize(Inst);
-
+ 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(), Inst->getName()+".lcssa",
- ExitBB->begin());
- PN->reserveOperandSpace(PredCache.GetNumPreds(ExitBB));
+ 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 (!inLoop(*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);
+
+ // LoopSimplify might fail to simplify some loops (e.g. when indirect
+ // branches are involved). In such situations, it might happen that an exit
+ // for Loop L1 is the header of a disjoint Loop L2. Thus, when we create
+ // PHIs in such an exit block, we are also inserting PHIs into L2's header.
+ // This could break LCSSA form for L2 because these inserted PHIs can also
+ // have uses outside of L2. Remember all PHIs in such situation as to
+ // revisit than later on. FIXME: Remove this if indirectbr support into
+ // LoopSimplify gets improved.
+ if (auto *OtherLoop = LI->getLoopFor(ExitBB))
+ if (!L.contains(OtherLoop))
+ PostProcessPHIs.push_back(PN);
}
-
+
// Rewrite all uses outside the loop in terms of the new PHIs we just
// inserted.
for (unsigned i = 0, e = UsesToRewrite.size(); i != e; ++i) {
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]);
}
-
+
+ // Post process PHI instructions that were inserted into another disjoint loop
+ // and update their exits properly.
+ for (auto *I : PostProcessPHIs) {
+ if (I->use_empty())
+ continue;
+
+ BasicBlock *PHIBB = I->getParent();
+ Loop *OtherLoop = LI->getLoopFor(PHIBB);
+ SmallVector<BasicBlock *, 8> EBs;
+ OtherLoop->getExitBlocks(EBs);
+ if (EBs.empty())
+ continue;
+
+ // Recurse and re-process each PHI instruction. FIXME: we should really
+ // convert this entire thing to a worklist approach where we process a
+ // vector of instructions...
+ processInstruction(*OtherLoop, *I, DT, EBs, PredCache, LI);
+ }
+
+ // Remove PHI nodes that did not have any uses rewritten.
+ for (unsigned i = 0, e = AddedPHIs.size(); i != e; ++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, LoopInfo *LI,
+ 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->user_back()->getParent() == BB &&
+ !isa<PHINode>(I->user_back())))
+ continue;
+
+ Changed |= processInstruction(L, *I, DT, ExitBlocks, PredCache, LI);
+ }
+ }
+
+ // 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;
+}
+
+/// Process a loop nest depth first.
+bool llvm::formLCSSARecursively(Loop &L, DominatorTree &DT, LoopInfo *LI,
+ ScalarEvolution *SE) {
+ bool Changed = false;
+
+ // Recurse depth-first through inner loops.
+ for (Loop::iterator I = L.begin(), E = L.end(); I != E; ++I)
+ Changed |= formLCSSARecursively(**I, DT, LI, SE);
+
+ Changed |= formLCSSA(L, DT, LI, SE);
+ 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;
+
+ bool runOnFunction(Function &F) override;
+
+ /// 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.
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.setPreservesCFG();
+
+ AU.addRequired<DominatorTreeWrapperPass>();
+ AU.addRequired<LoopInfo>();
+ AU.addPreservedID(LoopSimplifyID);
+ AU.addPreserved<AliasAnalysis>();
+ AU.addPreserved<ScalarEvolution>();
+ }
+
+private:
+ void verifyAnalysis() const override;
+};
+}
+
+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 |= formLCSSARecursively(**I, *DT, LI, 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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