//
// 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
//
//===----------------------------------------------------------------------===//
+#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/ADT/SetVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/Dominators.h"
-#include "llvm/Analysis/LoopInfo.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 <vector>
-
using namespace llvm;
+STATISTIC(NumLCSSA, "Number of live out of a loop variables");
+
namespace {
- static Statistic<> NumLCSSA("lcssa",
- "Number of live out of a loop variables");
-
- class LCSSA : public FunctionPass {
- public:
-
-
- LoopInfo *LI; // Loop information
- DominatorTree *DT; // Dominator Tree for the current Loop...
- DominanceFrontier *DF; // Current Dominance Frontier
+ struct VISIBILITY_HIDDEN LCSSA : public LoopPass {
+ static char ID; // Pass identification, replacement for typeid
+ LCSSA() : LoopPass(&ID) {}
+
+ // Cached analysis information for the current function.
+ LoopInfo *LI;
+ DominatorTree *DT;
+ std::vector<BasicBlock*> LoopBlocks;
- virtual bool runOnFunction(Function &F);
- bool visitSubloop(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,
AU.addRequired<LoopInfo>();
AU.addPreserved<LoopInfo>();
AU.addRequired<DominatorTree>();
- AU.addRequired<DominanceFrontier>();
+ AU.addPreserved<ScalarEvolution>();
+ AU.addPreserved<DominatorTree>();
+
+ // Request DominanceFrontier now, even though LCSSA does
+ // not use it. This allows Pass Manager to schedule Dominance
+ // Frontier early enough such that one LPPassManager can handle
+ // multiple loop transformation passes.
+ AU.addRequired<DominanceFrontier>();
+ AU.addPreserved<DominanceFrontier>();
}
private:
- std::set<Instruction*> getLoopValuesUsedOutsideLoop(Loop *L,
- std::vector<BasicBlock*> LoopBlocks);
+ void getLoopValuesUsedOutsideLoop(Loop *L,
+ SetVector<Instruction*> &AffectedValues);
+
+ Value *GetValueForBlock(DomTreeNode *BB, Instruction *OrigInst,
+ DenseMap<DomTreeNode*, Value*> &Phis);
+
+ /// inLoop - returns true if the given block is within the current loop
+ bool inLoop(BasicBlock* B) {
+ return std::binary_search(LoopBlocks.begin(), LoopBlocks.end(), B);
+ }
};
-
- RegisterOpt<LCSSA> X("lcssa", "Loop-Closed SSA Form Pass");
}
+
+char LCSSA::ID = 0;
+static RegisterPass<LCSSA> X("lcssa", "Loop-Closed SSA Form Pass");
-FunctionPass *llvm::createLCSSAPass() { return new LCSSA(); }
+Pass *llvm::createLCSSAPass() { return new LCSSA(); }
+const PassInfo *const llvm::LCSSAID = &X;
-bool LCSSA::runOnFunction(Function &F) {
- bool changed = false;
- LI = &getAnalysis<LoopInfo>();
- DF = &getAnalysis<DominanceFrontier>();
+/// runOnFunction - Process all loops in the function, inner-most out.
+bool LCSSA::runOnLoop(Loop *L, LPPassManager &LPM) {
+
+ LI = &LPM.getAnalysis<LoopInfo>();
DT = &getAnalysis<DominatorTree>();
-
- for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I) {
- changed |= visitSubloop(*I);
- }
-
- return changed;
-}
-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
- std::vector<BasicBlock*> LoopBlocks(L->block_begin(), L->block_end());
+ LoopBlocks.clear();
+ LoopBlocks.insert(LoopBlocks.end(), L->block_begin(), L->block_end());
std::sort(LoopBlocks.begin(), LoopBlocks.end());
- std::set<Instruction*> AffectedValues = getLoopValuesUsedOutsideLoop(L,
- LoopBlocks);
+ SetVector<Instruction*> AffectedValues;
+ getLoopValuesUsedOutsideLoop(L, AffectedValues);
- std::vector<BasicBlock*> 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())
+ return false;
- // Phi nodes that need to be IDF-processed
- std::vector<PHINode*> workList;
+ SmallVector<BasicBlock*, 8> exitBlocks;
+ L->getExitBlocks(exitBlocks);
// Iterate over all affected values for this loop and insert Phi nodes
// for them in the appropriate exit blocks
- std::map<BasicBlock*, PHINode*> ExitPhis;
- for (std::set<Instruction*>::iterator I = AffectedValues.begin(),
- E = AffectedValues.end(); I != E; ++I) {
- ++NumLCSSA; // We are applying the transformation
- for (std::vector<BasicBlock*>::iterator BBI = exitBlocks.begin(),
- BBE = exitBlocks.end(); BBI != BBE; ++BBI) {
- PHINode *phi = new PHINode((*I)->getType(), "lcssa");
- (*BBI)->getInstList().insert((*BBI)->front(), phi);
- workList.push_back(phi);
- ExitPhis[*BBI] = phi;
-
- // Since LoopSimplify has been run, we know that all of these predecessors
- // are in the loop, so just hook them up in the obvious manner.
- for (pred_iterator PI = pred_begin(*BBI), PE = pred_end(*BBI); PI != PE;
- ++PI)
- phi->addIncoming(*I, *PI);
+
+ 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 SmallVector<BasicBlock*, 8>& exitBlocks) {
+ ++NumLCSSA; // We are applying the transformation
+
+ // Keep track of the blocks that have the value available already.
+ DenseMap<DomTreeNode*, Value*> Phis;
+
+ 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)));
+
+ // Remember that this phi makes the value alive in this block.
+ Phi = PN;
+
+ // 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);
}
+ }
- // Calculate the IDF of these LCSSA Phi nodes, inserting new Phi's where
- // necessary. Keep track of these new Phi's in DFPhis.
- std::map<BasicBlock*, PHINode*> DFPhis;
- for (std::vector<PHINode*>::iterator DFI = workList.begin(),
- E = workList.end(); DFI != E; ++DFI) {
-
- // Get the current Phi's DF, and insert Phi nodes. Add these new
- // nodes to our worklist.
- DominanceFrontier::const_iterator it = DF->find((*DFI)->getParent());
- if (it != DF->end()) {
- const DominanceFrontier::DomSetType &S = it->second;
- for (DominanceFrontier::DomSetType::const_iterator P = S.begin(),
- PE = S.end(); P != PE; ++P) {
- if (DFPhis[*P] == 0) {
- // Still doesn't have operands...
- PHINode *phi = new PHINode((*DFI)->getType(), "lcssa");
- (*P)->getInstList().insert((*P)->front(), phi);
- DFPhis[*P] = phi;
-
- workList.push_back(phi);
- }
- }
- }
-
- // Get the predecessor blocks of the current Phi, and use them to hook up
- // the operands of the current Phi to any members of DFPhis that dominate
- // it. This is a nop for the Phis inserted directly in the exit blocks,
- // since they are not dominated by any members of DFPhis.
- for (pred_iterator PI = pred_begin((*DFI)->getParent()),
- E = pred_end((*DFI)->getParent()); PI != E; ++PI)
- for (std::map<BasicBlock*, PHINode*>::iterator MI = DFPhis.begin(),
- ME = DFPhis.end(); MI != ME; ++MI)
- if (DT->getNode((*MI).first)->dominates(DT->getNode(*PI))) {
- (*DFI)->addIncoming((*MI).second, *PI);
-
- // Since dominate() is not cheap, don't do it more than we have to.
- break;
- }
+
+ // 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)) {
+ UserBB = P->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);
- // Find all uses of the affected value, and replace them with the
- // appropriate Phi.
- for (Instruction::use_iterator UI = (*I)->use_begin(), UE=(*I)->use_end();
- UI != UE; ++UI) {
- Instruction* use = cast<Instruction>(*UI);
-
- // Don't need to update uses within the loop body
- if (!std::binary_search(LoopBlocks.begin(), LoopBlocks.end(),
- use->getParent())) {
-
- for (std::map<BasicBlock*, PHINode*>::iterator DI = ExitPhis.begin(),
- DE = ExitPhis.end(); DI != DE; ++DI) {
- if (DT->getNode((*DI).first)->dominates( \
- DT->getNode(use->getParent())) && use != (*DI).second) {
- use->replaceUsesOfWith(*I, (*DI).second);
- break;
- }
- }
-
- for (std::map<BasicBlock*, PHINode*>::iterator DI = DFPhis.begin(),
- DE = DFPhis.end(); DI != DE; ++DI) {
- if (DT->getNode((*DI).first)->dominates( \
- DT->getNode(use->getParent()))) {
- use->replaceUsesOfWith(*I, (*DI).second);
- break;
- }
- }
- }
- }
+ // Preincrement the iterator to avoid invalidating it when we change the
+ // value.
+ Use &U = UI.getUse();
+ ++UI;
+ U.set(Val);
}
-
- return true; // FIXME: Should be more intelligent in our return value.
}
/// getLoopValuesUsedOutsideLoop - Return any values defined in the loop that
/// are used by instructions outside of it.
-std::set<Instruction*> LCSSA::getLoopValuesUsedOutsideLoop(Loop *L,
- std::vector<BasicBlock*> LoopBlocks) {
-
- std::set<Instruction*> AffectedValues;
+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 (!std::binary_search(LoopBlocks.begin(), LoopBlocks.end(), UserBB))
+ if (PHINode* p = dyn_cast<PHINode>(*UI)) {
+ UserBB = p->getIncomingBlock(UI);
+ }
+
+ if (*BB != UserBB && !inLoop(UserBB)) {
AffectedValues.insert(I);
+ break;
+ }
}
}
- return AffectedValues;
}
+
+/// GetValueForBlock - Get the value to use within the specified basic block.
+/// available values are in Phis.
+Value *LCSSA::GetValueForBlock(DomTreeNode *BB, Instruction *OrigInst,
+ DenseMap<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.
+ if (Phis.count(BB)) return Phis[BB];
+
+ DomTreeNode *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.
+ Value* val = GetValueForBlock(IDom, OrigInst, Phis);
+ Phis.insert(std::make_pair(BB, val));
+ return val;
+ }
+
+ 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.
+ PHINode *PN = PHINode::Create(OrigInst->getType(),
+ OrigInst->getName() + ".lcssa", BBN->begin());
+ PN->reserveOperandSpace(std::distance(pred_begin(BBN), pred_end(BBN)));
+ Phis.insert(std::make_pair(BB, 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;
+}
+
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