//
// The LLVM Compiler Infrastructure
//
-// This file was developed by Owen Anderson 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.
//
//===----------------------------------------------------------------------===//
//
// the left into the right code:
//
// for (...) for (...)
-// if (c) if(c)
+// if (c) if (c)
// X1 = ... X1 = ...
// else else
// X2 = ... X2 = ...
// X3 = phi(X1, X2) X3 = phi(X1, X2)
-// ... = X3 + 4 X4 = phi(X3)
-// ... = X4 + 4
+// ... = X3 + 4 X4 = phi(X3)
+// ... = X4 + 4
//
// This is still valid LLVM; the extra phi nodes are purely redundant, and will
// be trivially eliminated by InstCombine. The major benefit of this
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
-#include "llvm/Constants.h"
-#include "llvm/Pass.h"
-#include "llvm/Function.h"
-#include "llvm/Instructions.h"
-#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/Statistic.h"
-#include "llvm/Analysis/Dominators.h"
-#include "llvm/Analysis/LoopInfo.h"
-#include "llvm/Support/CFG.h"
-#include <algorithm>
-#include <map>
-
+#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"
using namespace llvm;
-namespace {
- static Statistic<> NumLCSSA("lcssa",
- "Number of live out of a loop variables");
-
- struct LCSSA : public FunctionPass {
- // Cached analysis information for the current function.
- LoopInfo *LI;
- DominatorTree *DT;
- std::vector<BasicBlock*> LoopBlocks;
-
- virtual bool runOnFunction(Function &F);
- bool visitSubloop(Loop* L);
- void ProcessInstruction(Instruction* Instr,
- const std::vector<BasicBlock*>& exitBlocks);
-
- /// 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.addRequiredID(LoopSimplifyID);
- AU.addPreservedID(LoopSimplifyID);
- AU.addRequired<LoopInfo>();
- AU.addRequired<DominatorTree>();
- }
- private:
- SetVector<Instruction*> getLoopValuesUsedOutsideLoop(Loop *L);
+#define DEBUG_TYPE "lcssa"
- PHINode *GetValueForBlock(DominatorTree::Node *BB, Instruction *OrigInst,
- std::map<DominatorTree::Node*, PHINode*> &Phis);
+STATISTIC(NumLCSSA, "Number of live out of a loop variables");
- /// inLoop - returns true if the given block is within the current loop
- const bool inLoop(BasicBlock* B) {
- return std::binary_search(LoopBlocks.begin(), LoopBlocks.end(), B);
- }
- };
-
- RegisterOpt<LCSSA> X("lcssa", "Loop-Closed SSA Form Pass");
+/// 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;
}
-FunctionPass *llvm::createLCSSAPass() { return new LCSSA(); }
-const PassInfo *llvm::LCSSAID = X.getPassInfo();
+/// 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::runOnFunction(Function &F) {
- bool changed = false;
-
- LI = &getAnalysis<LoopInfo>();
- DT = &getAnalysis<DominatorTree>();
-
- for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
- changed |= visitSubloop(*I);
-
- return changed;
-}
+ BasicBlock *InstBB = Inst.getParent();
+
+ 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);
-/// visitSubloop - Recursively process all subloops, and then process the given
-/// loop if it has live-out values.
-bool LCSSA::visitSubloop(Loop* L) {
- for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
- visitSubloop(*I);
-
- // Speed up queries by creating a sorted list of blocks
- LoopBlocks.clear();
- LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
- std::sort(LoopBlocks.begin(), LoopBlocks.end());
-
- SetVector<Instruction*> AffectedValues = getLoopValuesUsedOutsideLoop(L);
-
- // If no values are affected, we can save a lot of work, since we know that
- // nothing will be changed.
- if (AffectedValues.empty())
+ 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;
-
- std::vector<BasicBlock*> exitBlocks;
- L->getExitBlocks(exitBlocks);
-
-
- // Iterate over all affected values for this loop and insert Phi nodes
- // for them in the appropriate exit blocks
-
- for (SetVector<Instruction*>::iterator I = AffectedValues.begin(),
- E = AffectedValues.end(); I != E; ++I)
- ProcessInstruction(*I, exitBlocks);
-
- assert(L->isLCSSAForm());
-
- return true;
-}
-/// processInstruction - Given a live-out instruction, insert LCSSA Phi nodes,
-/// eliminate all out-of-loop uses.
-void LCSSA::ProcessInstruction(Instruction *Instr,
- const std::vector<BasicBlock*>& exitBlocks) {
++NumLCSSA; // We are applying the transformation
- // Keep track of the blocks that have the value available already.
- std::map<DominatorTree::Node*, PHINode*> Phis;
+ // 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
+ // 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))
+ DomBB = Inv->getNormalDest();
- DominatorTree::Node *InstrNode = DT->getNode(Instr->getParent());
+ DomTreeNode *DomNode = DT.getNode(DomBB);
- // Insert the LCSSA phi's into the exit blocks (dominated by the value), and
- // add them to the Phi's map.
- for (std::vector<BasicBlock*>::const_iterator BBI = exitBlocks.begin(),
- BBE = exitBlocks.end(); BBI != BBE; ++BBI) {
- BasicBlock *BB = *BBI;
- DominatorTree::Node *ExitBBNode = DT->getNode(BB);
- PHINode *&Phi = Phis[ExitBBNode];
- if (!Phi && InstrNode->dominates(ExitBBNode)) {
- Phi = new PHINode(Instr->getType(), Instr->getName()+".lcssa",
- BB->begin());
- Phi->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB)));
-
- // Add inputs from inside the loop for this PHI.
- for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
- Phi->addIncoming(Instr, *PI);
-
- // Remember that this phi makes the value alive in this block.
- Phis[ExitBBNode] = Phi;
+ SmallVector<PHINode *, 16> AddedPHIs;
+ SmallVector<PHINode *, 8> PostProcessPHIs;
+
+ SSAUpdater SSAUpdate;
+ 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) {
+ BasicBlock *ExitBB = *BBI;
+ 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.size(ExitBB),
+ Inst.getName() + ".lcssa", ExitBB->begin());
+
+ // Add inputs from inside the loop for this PHI.
+ for (BasicBlock *Pred : PredCache.get(ExitBB)) {
+ PN->addIncoming(&Inst, Pred);
+
+ // 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(Pred))
+ UsesToRewrite.push_back(
+ &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);
}
-
-
- // Record all uses of Instr outside the loop. We need to rewrite these. The
- // LCSSA phis won't be included because they use the value in the loop.
- for (Value::use_iterator UI = Instr->use_begin(), E = Instr->use_end();
- UI != E;) {
- BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
- if (PHINode *P = dyn_cast<PHINode>(*UI)) {
- unsigned OperandNo = UI.getOperandNo();
- UserBB = P->getIncomingBlock(OperandNo/2);
- }
-
- // If the user is in the loop, don't rewrite it!
- if (inLoop(UserBB)) {
- ++UI;
+
+ // 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 this use is in an exit block, rewrite to use the newly inserted PHI.
+ // This is required for correctness because SSAUpdate doesn't handle uses in
+ // the same block. It assumes the PHI we inserted is at the end of the
+ // block.
+ Instruction *User = cast<Instruction>(UsesToRewrite[i]->getUser());
+ BasicBlock *UserBB = User->getParent();
+ if (PHINode *PN = dyn_cast<PHINode>(User))
+ UserBB = PN->getIncomingBlock(*UsesToRewrite[i]);
+
+ 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, patch up uses of the value with the appropriate LCSSA Phi,
- // inserting PHI nodes into join points where needed.
- Value *Val = GetValueForBlock(DT->getNode(UserBB), Instr, Phis);
-
- // Preincrement the iterator to avoid invalidating it when we change the
- // value.
- Use &U = UI.getUse();
- ++UI;
- U.set(Val);
+
+ // 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;
}
-/// getLoopValuesUsedOutsideLoop - Return any values defined in the loop that
-/// are used by instructions outside of it.
-SetVector<Instruction*> LCSSA::getLoopValuesUsedOutsideLoop(Loop *L) {
-
- // FIXME: For large loops, we may be able to avoid a lot of 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.
-
- SetVector<Instruction*> AffectedValues;
- for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
- BB != E; ++BB) {
- for (BasicBlock::iterator I = (*BB)->begin(), E = (*BB)->end(); I != E; ++I)
- for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E;
- ++UI) {
- BasicBlock *UserBB = cast<Instruction>(*UI)->getParent();
- if (PHINode* p = dyn_cast<PHINode>(*UI)) {
- unsigned OperandNo = UI.getOperandNo();
- UserBB = p->getIncomingBlock(OperandNo/2);
- }
-
- if (!inLoop(UserBB)) {
- AffectedValues.insert(I);
- break;
- }
- }
+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);
+ }
}
- return AffectedValues;
+
+ // 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;
}
-/// GetValueForBlock - Get the value to use within the specified basic block.
-/// available values are in Phis.
-PHINode *LCSSA::GetValueForBlock(DominatorTree::Node *BB, Instruction *OrigInst,
- std::map<DominatorTree::Node*, PHINode*> &Phis) {
- // If we have already computed this value, return the previously computed val.
- PHINode *&V = Phis[BB];
- if (V) return V;
-
- DominatorTree::Node *IDom = BB->getIDom();
-
- // Otherwise, there are two cases: we either have to insert a PHI node or we
- // don't. We need to insert a PHI node if this block is not dominated by one
- // of the exit nodes from the loop (the loop could have multiple exits, and
- // though the value defined *inside* the loop dominated all its uses, each
- // exit by itself may not dominate all the uses).
- //
- // The simplest way to check for this condition is by checking to see if the
- // idom is in the loop. If so, we *know* that none of the exit blocks
- // dominate this block. Note that we *know* that the block defining the
- // original instruction is in the idom chain, because if it weren't, then the
- // original value didn't dominate this use.
- if (!inLoop(IDom->getBlock())) {
- // Idom is not in the loop, we must still be "below" the exit block and must
- // be fully dominated by the value live in the idom.
- return V = GetValueForBlock(IDom, OrigInst, Phis);
+/// 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<LoopInfoWrapperPass>();
+ AU.addPreservedID(LoopSimplifyID);
+ AU.addPreserved<AliasAnalysis>();
+ AU.addPreserved<ScalarEvolution>();
}
-
- BasicBlock *BBN = BB->getBlock();
-
- // Otherwise, the idom is the loop, so we need to insert a PHI node. Do so
- // now, then get values to fill in the incoming values for the PHI.
- V = new PHINode(OrigInst->getType(), OrigInst->getName()+".lcssa",
- BBN->begin());
- V->reserveOperandSpace(std::distance(pred_begin(BBN), pred_end(BBN)));
-
- // Fill in the incoming values for the block.
- for (pred_iterator PI = pred_begin(BBN), E = pred_end(BBN); PI != E; ++PI)
- V->addIncoming(GetValueForBlock(DT->getNode(*PI), OrigInst, Phis), *PI);
- return V;
+};
+} // namespace
+
+char LCSSA::ID = 0;
+INITIALIZE_PASS_BEGIN(LCSSA, "lcssa", "Loop-Closed SSA Form Pass", false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+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<LoopInfoWrapperPass>().getLoopInfo();
+ 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;
}
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