// 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/Pass.h"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
-#include "llvm/ADT/SetVector.h"
-#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolution.h"
-#include "llvm/Support/CFG.h"
-#include "llvm/Support/Compiler.h"
-#include <algorithm>
-#include <map>
+#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 VISIBILITY_HIDDEN LCSSA : public LoopPass {
+ struct LCSSA : public LoopPass {
static char ID; // Pass identification, replacement for typeid
- LCSSA() : LoopPass((intptr_t)&ID) {}
+ LCSSA() : LoopPass(&ID) {}
// Cached analysis information for the current function.
- LoopInfo *LI;
DominatorTree *DT;
std::vector<BasicBlock*> LoopBlocks;
+ PredIteratorCache PredCache;
+ Loop *L;
virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
- void ProcessInstruction(Instruction* Instr,
- const SmallVector<BasicBlock*, 8>& 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.
AU.setPreservesCFG();
AU.addRequiredID(LoopSimplifyID);
AU.addPreservedID(LoopSimplifyID);
- AU.addRequired<LoopInfo>();
+ AU.addRequiredTransitive<LoopInfo>();
AU.addPreserved<LoopInfo>();
- AU.addRequired<DominatorTree>();
+ AU.addRequiredTransitive<DominatorTree>();
AU.addPreserved<ScalarEvolution>();
AU.addPreserved<DominatorTree>();
AU.addPreserved<DominanceFrontier>();
}
private:
- void getLoopValuesUsedOutsideLoop(Loop *L,
- SetVector<Instruction*> &AffectedValues);
-
- Value *GetValueForBlock(DomTreeNode *BB, Instruction *OrigInst,
- std::map<DomTreeNode*, Value*> &Phis);
+ 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() && "LCSSA form not preserved!");
+ }
/// inLoop - returns true if the given block is within the current loop
- bool inLoop(BasicBlock* B) {
+ 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");
-LoopPass *llvm::createLCSSAPass() { return new LCSSA(); }
+Pass *llvm::createLCSSAPass() { return new LCSSA(); }
const PassInfo *const llvm::LCSSAID = &X;
+
+/// 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 *L, LPPassManager &LPM) {
+bool LCSSA::runOnLoop(Loop *TheLoop, LPPassManager &LPM) {
+ L = TheLoop;
- LI = &LPM.getAnalysis<LoopInfo>();
DT = &getAnalysis<DominatorTree>();
- // 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, AffectedValues);
+ // Get the set of exiting blocks.
+ SmallVector<BasicBlock*, 8> ExitBlocks;
+ L->getExitBlocks(ExitBlocks);
- // If no values are affected, we can save a lot of work, since we know that
- // nothing will be changed.
- if (AffectedValues.empty())
+ if (ExitBlocks.empty())
return false;
- SmallVector<BasicBlock*, 8> exitBlocks;
- L->getExitBlocks(exitBlocks);
+ // 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());
- // Iterate over all affected values for this loop and insert Phi nodes
- // for them in the appropriate exit blocks
+ // 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 (SetVector<Instruction*>::iterator I = AffectedValues.begin(),
- E = AffectedValues.end(); I != E; ++I)
- ProcessInstruction(*I, exitBlocks);
+ 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());
-
- return true;
-}
-
-/// processInstruction - Given a live-out instruction, insert LCSSA Phi nodes,
-/// eliminate all out-of-loop uses.
-void LCSSA::ProcessInstruction(Instruction *Instr,
- const SmallVector<BasicBlock*, 8>& exitBlocks) {
- ++NumLCSSA; // We are applying the transformation
-
- // Keep track of the blocks that have the value available already.
- std::map<DomTreeNode*, Value*> Phis;
+ PredCache.clear();
- DomTreeNode *InstrNode = DT->getNode(Instr->getParent());
-
- // Insert the LCSSA phi's into the exit blocks (dominated by the value), and
- // add them to the Phi's map.
- for (SmallVector<BasicBlock*, 8>::const_iterator BBI = exitBlocks.begin(),
- BBE = exitBlocks.end(); BBI != BBE; ++BBI) {
- BasicBlock *BB = *BBI;
- DomTreeNode *ExitBBNode = DT->getNode(BB);
- Value *&Phi = Phis[ExitBBNode];
- if (!Phi && DT->dominates(InstrNode, ExitBBNode)) {
- PHINode *PN = PHINode::Create(Instr->getType(), Instr->getName()+".lcssa",
- BB->begin());
- PN->reserveOperandSpace(std::distance(pred_begin(BB), pred_end(BB)));
+ return MadeChange;
+}
- // Remember that this phi makes the value alive in this block.
- Phi = PN;
+/// 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;
+}
- // Add inputs from inside the loop for this PHI.
- for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
- PN->addIncoming(Instr, *PI);
- }
- }
+/// 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();
- // 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;) {
+ for (Value::use_iterator UI = Inst->use_begin(), E = Inst->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 (PHINode *PN = dyn_cast<PHINode>(*UI))
+ UserBB = PN->getIncomingBlock(UI);
- // If the user is in the loop, don't rewrite it!
- if (UserBB == Instr->getParent() || inLoop(UserBB)) {
- ++UI;
- 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);
+ if (InstBB != UserBB && !inLoop(UserBB))
+ UsesToRewrite.push_back(&UI.getUse());
}
-}
+
+ // If there are no uses outside the loop, exit with no change.
+ if (UsesToRewrite.empty()) return false;
+
+ ++NumLCSSA; // We are applying the transformation
-/// getLoopValuesUsedOutsideLoop - Return any values defined in the loop that
-/// are used by instructions outside of it.
-void LCSSA::getLoopValuesUsedOutsideLoop(Loop *L,
- SetVector<Instruction*> &AffectedValues) {
- // 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.
- 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 (*BB != UserBB && !inLoop(UserBB)) {
- const StructType *STy = dyn_cast<StructType>(I->getType());
- if (STy) {
- // I is a call or an invoke that returns multiple values.
- // These values are accessible through getresult only.
- // If the getresult value is not in the BB then move it
- // immediately here. It will be processed in next iteration.
- BasicBlock::iterator InsertPoint;
- if (InvokeInst *II = dyn_cast<InvokeInst>(I)) {
- InsertPoint = II->getNormalDest()->begin();
- while (isa<PHINode>(InsertPoint))
- ++InsertPoint;
- } else {
- InsertPoint = I;
- InsertPoint++;
- }
- for (Value::use_iterator TmpI = I->use_begin(),
- TmpE = I->use_end(); TmpI != TmpE; ++TmpI) {
- GetResultInst *GR = cast<GetResultInst>(TmpI);
- if (GR->getParent() != *BB)
- GR->moveBefore(InsertPoint);
- }
- } else
- AffectedValues.insert(I);
- break;
- }
- }
- }
-}
+ // 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();
-/// GetValueForBlock - Get the value to use within the specified basic block.
-/// available values are in Phis.
-Value *LCSSA::GetValueForBlock(DomTreeNode *BB, Instruction *OrigInst,
- std::map<DomTreeNode*, Value*> &Phis) {
- // If there is no dominator info for this BB, it is unreachable.
- if (BB == 0)
- return UndefValue::get(OrigInst->getType());
-
- // If we have already computed this value, return the previously computed val.
- Value *&V = Phis[BB];
- if (V) return V;
+ DomTreeNode *DomNode = DT->getNode(DomBB);
- DomTreeNode *IDom = BB->getIDom();
+ SSAUpdater SSAUpdate;
+ SSAUpdate.Initialize(Inst);
+
+ // 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(), Inst->getName()+".lcssa",
+ ExitBB->begin());
+ PN->reserveOperandSpace(PredCache.GetNumPreds(ExitBB));
- // 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);
+ // Add inputs from inside the loop for this PHI.
+ for (BasicBlock **PI = PredCache.GetPreds(ExitBB); *PI; ++PI)
+ PN->addIncoming(Inst, *PI);
+
+ // Remember that this phi makes the value alive in this block.
+ SSAUpdate.AddAvailableValue(ExitBB, PN);
}
- BasicBlock *BBN = BB->getBlock();
+ // 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)) {
+ UsesToRewrite[i]->set(UserBB->begin());
+ continue;
+ }
+
+ // Otherwise, do full PHI insertion.
+ SSAUpdate.RewriteUse(*UsesToRewrite[i]);
+ }
- // 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.
- PHINode *PN = PHINode::Create(OrigInst->getType(),
- OrigInst->getName() + ".lcssa", BBN->begin());
- PN->reserveOperandSpace(std::distance(pred_begin(BBN), pred_end(BBN)));
- V = PN;
-
- // Fill in the incoming values for the block.
- for (pred_iterator PI = pred_begin(BBN), E = pred_end(BBN); PI != E; ++PI)
- PN->addIncoming(GetValueForBlock(DT->getNode(*PI), OrigInst, Phis), *PI);
- return PN;
+ return true;
}
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