-//===- PromoteMemoryToRegister.cpp - Convert memory refs to regs ----------===//
+//===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===//
+//
+// The LLVM Compiler Infrastructure
//
-// This file is used to promote memory references to be register references. A
-// simple example of the transformation performed by this function is:
-//
-// FROM CODE TO CODE
-// %X = alloca int, uint 1 ret int 42
-// store int 42, int *%X
-// %Y = load int* %X
-// ret int %Y
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
//
-// The code is transformed by looping over all of the alloca instruction,
-// calculating dominator frontiers, then inserting phi-nodes following the usual
-// SSA construction algorithm. This code does not modify the CFG of the
-// function.
+// This file promote memory references to be register references. It promotes
+// alloca instructions which only have loads and stores as uses (or that have
+// PHI nodes which are only loaded from). An alloca is transformed by using
+// dominator frontiers to place PHI nodes, then traversing the function in
+// depth-first order to rewrite loads and stores as appropriate. This is just
+// the standard SSA construction algorithm to construct "pruned" SSA form.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/Dominators.h"
#include "llvm/iMemory.h"
#include "llvm/iPHINode.h"
-#include "llvm/iTerminators.h"
+#include "llvm/iOther.h"
#include "llvm/Function.h"
#include "llvm/Constant.h"
-#include "llvm/Type.h"
#include "llvm/Support/CFG.h"
#include "Support/StringExtras.h"
+using namespace llvm;
/// isAllocaPromotable - Return true if this alloca is legal for promotion.
-/// This is true if there are only loads and stores to the alloca...
+/// This is true if there are only loads and stores to the alloca... of if there
+/// is a PHI node using the address which can be trivially transformed.
///
-bool isAllocaPromotable(const AllocaInst *AI, const TargetData &TD) {
+bool llvm::isAllocaPromotable(const AllocaInst *AI, const TargetData &TD) {
// FIXME: If the memory unit is of pointer or integer type, we can permit
// assignments to subsections of the memory unit.
// Only allow direct loads and stores...
for (Value::use_const_iterator UI = AI->use_begin(), UE = AI->use_end();
UI != UE; ++UI) // Loop over all of the uses of the alloca
- if (!isa<LoadInst>(*UI))
- if (const StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
- if (SI->getOperand(0) == AI)
- return false; // Don't allow a store of the AI, only INTO the AI.
- } else {
- return false; // Not a load or store?
- }
+ if (isa<LoadInst>(*UI)) {
+ // noop
+ } else if (const StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
+ if (SI->getOperand(0) == AI)
+ return false; // Don't allow a store OF the AI, only INTO the AI.
+ } else if (const PHINode *PN = dyn_cast<PHINode>(*UI)) {
+ // We only support PHI nodes in a few simple cases. The PHI node is only
+ // allowed to have one use, which must be a load instruction, and can only
+ // use alloca instructions (no random pointers). Also, there cannot be
+ // any accesses to AI between the PHI node and the use of the PHI.
+ if (!PN->hasOneUse()) return false;
+
+ // Our transformation causes the unconditional loading of all pointer
+ // operands to the PHI node. Because this could cause a fault if there is
+ // a critical edge in the CFG and if one of the pointers is illegal, we
+ // refuse to promote PHI nodes unless they are obviously safe. For now,
+ // obviously safe means that all of the operands are allocas.
+ //
+ // If we wanted to extend this code to break critical edges, this
+ // restriction could be relaxed, and we could even handle uses of the PHI
+ // node that are volatile loads or stores.
+ //
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (!isa<AllocaInst>(PN->getIncomingValue(i)))
+ return false;
+
+ // Now make sure the one user instruction is in the same basic block as
+ // the PHI, and that there are no loads or stores between the PHI node and
+ // the access.
+ BasicBlock::const_iterator UI = cast<Instruction>(PN->use_back());
+ if (!isa<LoadInst>(UI) || cast<LoadInst>(UI)->isVolatile()) return false;
+
+ // Scan looking for memory accesses.
+ // FIXME: this should REALLY use alias analysis.
+ for (--UI; !isa<PHINode>(UI); --UI)
+ if (isa<LoadInst>(UI) || isa<StoreInst>(UI) || isa<CallInst>(UI))
+ return false;
+
+ // If we got this far, we can promote the PHI use.
+ } else if (const SelectInst *SI = dyn_cast<SelectInst>(*UI)) {
+ // We only support selects in a few simple cases. The select is only
+ // allowed to have one use, which must be a load instruction, and can only
+ // use alloca instructions (no random pointers). Also, there cannot be
+ // any accesses to AI between the PHI node and the use of the PHI.
+ if (!SI->hasOneUse()) return false;
+
+ // Our transformation causes the unconditional loading of all pointer
+ // operands of the select. Because this could cause a fault if there is a
+ // critical edge in the CFG and if one of the pointers is illegal, we
+ // refuse to promote the select unless it is obviously safe. For now,
+ // obviously safe means that all of the operands are allocas.
+ //
+ if (!isa<AllocaInst>(SI->getOperand(1)) ||
+ !isa<AllocaInst>(SI->getOperand(2)))
+ return false;
+
+ // Now make sure the one user instruction is in the same basic block as
+ // the PHI, and that there are no loads or stores between the PHI node and
+ // the access.
+ BasicBlock::const_iterator UI = cast<Instruction>(SI->use_back());
+ if (!isa<LoadInst>(UI) || cast<LoadInst>(UI)->isVolatile()) return false;
+
+ // Scan looking for memory accesses.
+ // FIXME: this should REALLY use alias analysis.
+ for (--UI; &*UI != SI; --UI)
+ if (isa<LoadInst>(UI) || isa<StoreInst>(UI) || isa<CallInst>(UI))
+ return false;
+
+ // If we got this far, we can promote the select use.
+ } else {
+ return false; // Not a load, store, or promotable PHI?
+ }
return true;
}
-
namespace {
struct PromoteMem2Reg {
- const std::vector<AllocaInst*> &Allocas; // the alloca instructions..
- std::vector<unsigned> VersionNumbers; // Current version counters
+ // Allocas - The alloca instructions being promoted
+ std::vector<AllocaInst*> Allocas;
+ DominatorTree &DT;
DominanceFrontier &DF;
const TargetData &TD;
- std::map<Instruction*, unsigned> AllocaLookup; // reverse mapping of above
-
- std::vector<std::vector<BasicBlock*> > PhiNodes;// Idx corresponds 2 Allocas
-
- // List of instructions to remove at end of pass
- std::vector<Instruction *> KillList;
-
- std::map<BasicBlock*,
- std::vector<PHINode*> > NewPhiNodes; // the PhiNodes we're adding
+ // AllocaLookup - Reverse mapping of Allocas
+ std::map<AllocaInst*, unsigned> AllocaLookup;
+
+ // NewPhiNodes - The PhiNodes we're adding.
+ std::map<BasicBlock*, std::vector<PHINode*> > NewPhiNodes;
+
+ // Visited - The set of basic blocks the renamer has already visited.
+ std::set<BasicBlock*> Visited;
public:
- PromoteMem2Reg(const std::vector<AllocaInst*> &A, DominanceFrontier &df,
- const TargetData &td)
- : Allocas(A), DF(df), TD(td) {}
+ PromoteMem2Reg(const std::vector<AllocaInst*> &A, DominatorTree &dt,
+ DominanceFrontier &df, const TargetData &td)
+ : Allocas(A), DT(dt), DF(df), TD(td) {}
void run();
private:
+ void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
+ std::set<PHINode*> &DeadPHINodes);
+ void PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI);
+ void PromoteLocallyUsedAllocas(BasicBlock *BB,
+ const std::vector<AllocaInst*> &AIs);
+
void RenamePass(BasicBlock *BB, BasicBlock *Pred,
- std::vector<Value*> &IncVals,
- std::set<BasicBlock*> &Visited);
- bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx);
+ std::vector<Value*> &IncVals);
+ bool QueuePhiNode(BasicBlock *BB, unsigned AllocaIdx, unsigned &Version,
+ std::set<PHINode*> &InsertedPHINodes);
};
} // end of anonymous namespace
-
void PromoteMem2Reg::run() {
- // If there is nothing to do, bail out...
- if (Allocas.empty()) return;
-
Function &F = *DF.getRoot()->getParent();
- VersionNumbers.resize(Allocas.size());
- for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
- assert(isAllocaPromotable(Allocas[i], TD) &&
+ // LocallyUsedAllocas - Keep track of all of the alloca instructions which are
+ // only used in a single basic block. These instructions can be efficiently
+ // promoted by performing a single linear scan over that one block. Since
+ // individual basic blocks are sometimes large, we group together all allocas
+ // that are live in a single basic block by the basic block they are live in.
+ std::map<BasicBlock*, std::vector<AllocaInst*> > LocallyUsedAllocas;
+
+ for (unsigned AllocaNum = 0; AllocaNum != Allocas.size(); ++AllocaNum) {
+ AllocaInst *AI = Allocas[AllocaNum];
+
+ assert(isAllocaPromotable(AI, TD) &&
"Cannot promote non-promotable alloca!");
- assert(Allocas[i]->getParent()->getParent() == &F &&
+ assert(AI->getParent()->getParent() == &F &&
"All allocas should be in the same function, which is same as DF!");
- AllocaLookup[Allocas[i]] = i;
- }
+ if (AI->use_empty()) {
+ // If there are no uses of the alloca, just delete it now.
+ AI->getParent()->getInstList().erase(AI);
- // Add each alloca to the KillList. Note: KillList is destroyed MOST recently
- // added to least recently.
- KillList.assign(Allocas.begin(), Allocas.end());
-
- // Calculate the set of write-locations for each alloca. This is analogous to
- // counting the number of 'redefinitions' of each variable.
- std::vector<std::vector<BasicBlock*> > WriteSets;// Idx corresponds to Allocas
- WriteSets.resize(Allocas.size());
- for (unsigned i = 0; i != Allocas.size(); ++i) {
- AllocaInst *AI = Allocas[i];
- for (Value::use_iterator U =AI->use_begin(), E = AI->use_end(); U != E; ++U)
- if (StoreInst *SI = dyn_cast<StoreInst>(*U))
- // jot down the basic-block it came from
- WriteSets[i].push_back(SI->getParent());
- }
+ // Remove the alloca from the Allocas list, since it has been processed
+ Allocas[AllocaNum] = Allocas.back();
+ Allocas.pop_back();
+ --AllocaNum;
+ continue;
+ }
+
+ // Calculate the set of read and write-locations for each alloca. This is
+ // analogous to finding the 'uses' and 'definitions' of each variable.
+ std::vector<BasicBlock*> DefiningBlocks;
+ std::vector<BasicBlock*> UsingBlocks;
+
+ BasicBlock *OnlyBlock = 0;
+ bool OnlyUsedInOneBlock = true;
+
+ // As we scan the uses of the alloca instruction, keep track of stores, and
+ // decide whether all of the loads and stores to the alloca are within the
+ // same basic block.
+ RestartUseScan:
+ for (Value::use_iterator U =AI->use_begin(), E = AI->use_end(); U != E;++U){
+ Instruction *User = cast<Instruction>(*U);
+ if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
+ // Remember the basic blocks which define new values for the alloca
+ DefiningBlocks.push_back(SI->getParent());
+ } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
+ // Otherwise it must be a load instruction, keep track of variable reads
+ UsingBlocks.push_back(LI->getParent());
+ } else if (SelectInst *SI = dyn_cast<SelectInst>(User)) {
+ // Because of the restrictions we placed on Select instruction uses
+ // above things are very simple. Transform the PHI of addresses into a
+ // select of loaded values.
+ LoadInst *Load = cast<LoadInst>(SI->use_back());
+ std::string LoadName = Load->getName(); Load->setName("");
+
+ Value *TrueVal = new LoadInst(SI->getOperand(1),
+ SI->getOperand(1)->getName()+".val", SI);
+ Value *FalseVal = new LoadInst(SI->getOperand(2),
+ SI->getOperand(2)->getName()+".val", SI);
+
+ Value *NewSI = new SelectInst(SI->getOperand(0), TrueVal,
+ FalseVal, Load->getName(), SI);
+ Load->replaceAllUsesWith(NewSI);
+ Load->getParent()->getInstList().erase(Load);
+ SI->getParent()->getInstList().erase(SI);
+
+ // Restart our scan of uses...
+ DefiningBlocks.clear();
+ UsingBlocks.clear();
+ goto RestartUseScan;
+ } else {
+ // Because of the restrictions we placed on PHI node uses above, the PHI
+ // node reads the block in any using predecessors. Transform the PHI of
+ // addresses into a PHI of loaded values.
+ PHINode *PN = cast<PHINode>(User);
+ assert(PN->hasOneUse() && "Cannot handle PHI Node with != 1 use!");
+ LoadInst *PNUser = cast<LoadInst>(PN->use_back());
+ std::string PNUserName = PNUser->getName(); PNUser->setName("");
+
+ // Create the new PHI node and insert load instructions as appropriate.
+ PHINode *NewPN = new PHINode(AI->getAllocatedType(), PNUserName, PN);
+ std::map<BasicBlock*, LoadInst*> NewLoads;
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ BasicBlock *Pred = PN->getIncomingBlock(i);
+ LoadInst *&NewLoad = NewLoads[Pred];
+ if (NewLoad == 0) // Insert the new load in the predecessor
+ NewLoad = new LoadInst(PN->getIncomingValue(i),
+ PN->getIncomingValue(i)->getName()+".val",
+ Pred->getTerminator());
+ NewPN->addIncoming(NewLoad, Pred);
+ }
+
+ // Remove the old load.
+ PNUser->replaceAllUsesWith(NewPN);
+ PNUser->getParent()->getInstList().erase(PNUser);
+
+ // Remove the old PHI node.
+ PN->getParent()->getInstList().erase(PN);
+
+ // Restart our scan of uses...
+ DefiningBlocks.clear();
+ UsingBlocks.clear();
+ goto RestartUseScan;
+ }
+
+ if (OnlyUsedInOneBlock) {
+ if (OnlyBlock == 0)
+ OnlyBlock = User->getParent();
+ else if (OnlyBlock != User->getParent())
+ OnlyUsedInOneBlock = false;
+ }
+ }
+
+ // If the alloca is only read and written in one basic block, just perform a
+ // linear sweep over the block to eliminate it.
+ if (OnlyUsedInOneBlock) {
+ LocallyUsedAllocas[OnlyBlock].push_back(AI);
+
+ // Remove the alloca from the Allocas list, since it will be processed.
+ Allocas[AllocaNum] = Allocas.back();
+ Allocas.pop_back();
+ --AllocaNum;
+ continue;
+ }
+
+ // Compute the locations where PhiNodes need to be inserted. Look at the
+ // dominance frontier of EACH basic-block we have a write in.
+ //
+ unsigned CurrentVersion = 0;
+ std::set<PHINode*> InsertedPHINodes;
+ while (!DefiningBlocks.empty()) {
+ BasicBlock *BB = DefiningBlocks.back();
+ DefiningBlocks.pop_back();
- // Compute the locations where PhiNodes need to be inserted. Look at the
- // dominance frontier of EACH basic-block we have a write in
- //
- PhiNodes.resize(Allocas.size());
- for (unsigned i = 0; i != Allocas.size(); ++i) {
- for (unsigned j = 0; j != WriteSets[i].size(); j++) {
// Look up the DF for this write, add it to PhiNodes
- DominanceFrontier::const_iterator it = DF.find(WriteSets[i][j]);
+ DominanceFrontier::const_iterator it = DF.find(BB);
if (it != DF.end()) {
const DominanceFrontier::DomSetType &S = it->second;
for (DominanceFrontier::DomSetType::iterator P = S.begin(),PE = S.end();
P != PE; ++P)
- QueuePhiNode(*P, i);
+ if (QueuePhiNode(*P, AllocaNum, CurrentVersion, InsertedPHINodes))
+ DefiningBlocks.push_back(*P);
}
}
-
- // Perform iterative step
- for (unsigned k = 0; k != PhiNodes[i].size(); k++) {
- DominanceFrontier::const_iterator it = DF.find(PhiNodes[i][k]);
- if (it != DF.end()) {
- const DominanceFrontier::DomSetType &S = it->second;
- for (DominanceFrontier::DomSetType::iterator P = S.begin(),PE = S.end();
- P != PE; ++P)
- QueuePhiNode(*P, i);
- }
+
+ // Now that we have inserted PHI nodes along the Iterated Dominance Frontier
+ // of the writes to the variable, scan through the reads of the variable,
+ // marking PHI nodes which are actually necessary as alive (by removing them
+ // from the InsertedPHINodes set). This is not perfect: there may PHI
+ // marked alive because of loads which are dominated by stores, but there
+ // will be no unmarked PHI nodes which are actually used.
+ //
+ for (unsigned i = 0, e = UsingBlocks.size(); i != e; ++i)
+ MarkDominatingPHILive(UsingBlocks[i], AllocaNum, InsertedPHINodes);
+ UsingBlocks.clear();
+
+ // If there are any PHI nodes which are now known to be dead, remove them!
+ for (std::set<PHINode*>::iterator I = InsertedPHINodes.begin(),
+ E = InsertedPHINodes.end(); I != E; ++I) {
+ PHINode *PN = *I;
+ std::vector<PHINode*> &BBPNs = NewPhiNodes[PN->getParent()];
+ BBPNs[AllocaNum] = 0;
+
+ // Check to see if we just removed the last inserted PHI node from this
+ // basic block. If so, remove the entry for the basic block.
+ bool HasOtherPHIs = false;
+ for (unsigned i = 0, e = BBPNs.size(); i != e; ++i)
+ if (BBPNs[i]) {
+ HasOtherPHIs = true;
+ break;
+ }
+ if (!HasOtherPHIs)
+ NewPhiNodes.erase(PN->getParent());
+
+ PN->getParent()->getInstList().erase(PN);
}
+
+ // Keep the reverse mapping of the 'Allocas' array.
+ AllocaLookup[Allocas[AllocaNum]] = AllocaNum;
}
+
+ // Process all allocas which are only used in a single basic block.
+ for (std::map<BasicBlock*, std::vector<AllocaInst*> >::iterator I =
+ LocallyUsedAllocas.begin(), E = LocallyUsedAllocas.end(); I != E; ++I){
+ const std::vector<AllocaInst*> &Allocas = I->second;
+ assert(!Allocas.empty() && "empty alloca list??");
+
+ // It's common for there to only be one alloca in the list. Handle it
+ // efficiently.
+ if (Allocas.size() == 1)
+ PromoteLocallyUsedAlloca(I->first, Allocas[0]);
+ else
+ PromoteLocallyUsedAllocas(I->first, Allocas);
+ }
+
+ if (Allocas.empty())
+ return; // All of the allocas must have been trivial!
// Set the incoming values for the basic block to be null values for all of
// the alloca's. We do this in case there is a load of a value that has not
// Walks all basic blocks in the function performing the SSA rename algorithm
// and inserting the phi nodes we marked as necessary
//
- std::set<BasicBlock*> Visited; // The basic blocks we've already visited
- RenamePass(F.begin(), 0, Values, Visited);
+ RenamePass(F.begin(), 0, Values);
- // Remove all instructions marked by being placed in the KillList...
- //
- while (!KillList.empty()) {
- Instruction *I = KillList.back();
- KillList.pop_back();
+ // The renamer uses the Visited set to avoid infinite loops. Clear it now.
+ Visited.clear();
+
+ // Remove the allocas themselves from the function...
+ for (unsigned i = 0, e = Allocas.size(); i != e; ++i) {
+ Instruction *A = Allocas[i];
- // If there are any uses of these instructions left, they must be in
+ // If there are any uses of the alloca instructions left, they must be in
// sections of dead code that were not processed on the dominance frontier.
// Just delete the users now.
//
- while (!I->use_empty()) {
- Instruction *U = cast<Instruction>(I->use_back());
- if (!U->use_empty()) // If uses remain in dead code segment...
- U->replaceAllUsesWith(Constant::getNullValue(U->getType()));
- U->getParent()->getInstList().erase(U);
+ if (!A->use_empty())
+ A->replaceAllUsesWith(Constant::getNullValue(A->getType()));
+ A->getParent()->getInstList().erase(A);
+ }
+
+ // At this point, the renamer has added entries to PHI nodes for all reachable
+ // code. Unfortunately, there may be blocks which are not reachable, which
+ // the renamer hasn't traversed. If this is the case, the PHI nodes may not
+ // have incoming values for all predecessors. Loop over all PHI nodes we have
+ // created, inserting null constants if they are missing any incoming values.
+ //
+ for (std::map<BasicBlock*, std::vector<PHINode *> >::iterator I =
+ NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) {
+
+ std::vector<BasicBlock*> Preds(pred_begin(I->first), pred_end(I->first));
+ std::vector<PHINode*> &PNs = I->second;
+ assert(!PNs.empty() && "Empty PHI node list??");
+
+ // Only do work here if there the PHI nodes are missing incoming values. We
+ // know that all PHI nodes that were inserted in a block will have the same
+ // number of incoming values, so we can just check any PHI node.
+ PHINode *FirstPHI;
+ for (unsigned i = 0; (FirstPHI = PNs[i]) == 0; ++i)
+ /*empty*/;
+
+ if (Preds.size() != FirstPHI->getNumIncomingValues()) {
+ // Ok, now we know that all of the PHI nodes are missing entries for some
+ // basic blocks. Start by sorting the incoming predecessors for efficient
+ // access.
+ std::sort(Preds.begin(), Preds.end());
+
+ // Now we loop through all BB's which have entries in FirstPHI and remove
+ // them from the Preds list.
+ for (unsigned i = 0, e = FirstPHI->getNumIncomingValues(); i != e; ++i) {
+ // Do a log(n) search of the Preds list for the entry we want.
+ std::vector<BasicBlock*>::iterator EntIt =
+ std::lower_bound(Preds.begin(), Preds.end(),
+ FirstPHI->getIncomingBlock(i));
+ assert(EntIt != Preds.end() && *EntIt == FirstPHI->getIncomingBlock(i)&&
+ "PHI node has entry for a block which is not a predecessor!");
+
+ // Remove the entry
+ Preds.erase(EntIt);
+ }
+
+ // At this point, the blocks left in the preds list must have dummy
+ // entries inserted into every PHI nodes for the block.
+ for (unsigned i = 0, e = PNs.size(); i != e; ++i)
+ if (PHINode *PN = PNs[i]) {
+ Value *NullVal = Constant::getNullValue(PN->getType());
+ for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred)
+ PN->addIncoming(NullVal, Preds[pred]);
+ }
}
+ }
+}
- I->getParent()->getInstList().erase(I);
+// MarkDominatingPHILive - Mem2Reg wants to construct "pruned" SSA form, not
+// "minimal" SSA form. To do this, it inserts all of the PHI nodes on the IDF
+// as usual (inserting the PHI nodes in the DeadPHINodes set), then processes
+// each read of the variable. For each block that reads the variable, this
+// function is called, which removes used PHI nodes from the DeadPHINodes set.
+// After all of the reads have been processed, any PHI nodes left in the
+// DeadPHINodes set are removed.
+//
+void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
+ std::set<PHINode*> &DeadPHINodes) {
+ // Scan the immediate dominators of this block looking for a block which has a
+ // PHI node for Alloca num. If we find it, mark the PHI node as being alive!
+ for (DominatorTree::Node *N = DT[BB]; N; N = N->getIDom()) {
+ BasicBlock *DomBB = N->getBlock();
+ std::map<BasicBlock*, std::vector<PHINode*> >::iterator
+ I = NewPhiNodes.find(DomBB);
+ if (I != NewPhiNodes.end() && I->second[AllocaNum]) {
+ // Ok, we found an inserted PHI node which dominates this value.
+ PHINode *DominatingPHI = I->second[AllocaNum];
+
+ // Find out if we previously thought it was dead.
+ std::set<PHINode*>::iterator DPNI = DeadPHINodes.find(DominatingPHI);
+ if (DPNI != DeadPHINodes.end()) {
+ // Ok, until now, we thought this PHI node was dead. Mark it as being
+ // alive/needed.
+ DeadPHINodes.erase(DPNI);
+
+ // Now that we have marked the PHI node alive, also mark any PHI nodes
+ // which it might use as being alive as well.
+ for (pred_iterator PI = pred_begin(DomBB), PE = pred_end(DomBB);
+ PI != PE; ++PI)
+ MarkDominatingPHILive(*PI, AllocaNum, DeadPHINodes);
+ }
+ }
+ }
+}
+
+/// PromoteLocallyUsedAlloca - Many allocas are only used within a single basic
+/// block. If this is the case, avoid traversing the CFG and inserting a lot of
+/// potentially useless PHI nodes by just performing a single linear pass over
+/// the basic block using the Alloca.
+///
+void PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) {
+ assert(!AI->use_empty() && "There are no uses of the alloca!");
+
+ // Handle degenerate cases quickly.
+ if (AI->hasOneUse()) {
+ Instruction *U = cast<Instruction>(AI->use_back());
+ if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
+ // Must be a load of uninitialized value.
+ LI->replaceAllUsesWith(Constant::getNullValue(AI->getAllocatedType()));
+ } else {
+ // Otherwise it must be a store which is never read.
+ assert(isa<StoreInst>(U));
+ }
+ BB->getInstList().erase(U);
+ } else {
+ // Uses of the uninitialized memory location shall get zero...
+ Value *CurVal = Constant::getNullValue(AI->getAllocatedType());
+
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
+ Instruction *Inst = I++;
+ if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
+ if (LI->getOperand(0) == AI) {
+ // Loads just returns the "current value"...
+ LI->replaceAllUsesWith(CurVal);
+ BB->getInstList().erase(LI);
+ }
+ } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
+ if (SI->getOperand(1) == AI) {
+ // Store updates the "current value"...
+ CurVal = SI->getOperand(0);
+ BB->getInstList().erase(SI);
+ }
+ }
+ }
+ }
+
+ // After traversing the basic block, there should be no more uses of the
+ // alloca, remove it now.
+ assert(AI->use_empty() && "Uses of alloca from more than one BB??");
+ AI->getParent()->getInstList().erase(AI);
+}
+
+/// PromoteLocallyUsedAllocas - This method is just like
+/// PromoteLocallyUsedAlloca, except that it processes multiple alloca
+/// instructions in parallel. This is important in cases where we have large
+/// basic blocks, as we don't want to rescan the entire basic block for each
+/// alloca which is locally used in it (which might be a lot).
+void PromoteMem2Reg::
+PromoteLocallyUsedAllocas(BasicBlock *BB, const std::vector<AllocaInst*> &AIs) {
+ std::map<AllocaInst*, Value*> CurValues;
+ for (unsigned i = 0, e = AIs.size(); i != e; ++i)
+ CurValues[AIs[i]] = 0; // Insert with null value
+
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
+ Instruction *Inst = I++;
+ if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
+ // Is this a load of an alloca we are tracking?
+ if (AllocaInst *AI = dyn_cast<AllocaInst>(LI->getOperand(0))) {
+ std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
+ if (AIt != CurValues.end()) {
+ // Loads just returns the "current value"...
+ if (AIt->second == 0) // Uninitialized value??
+ AIt->second =Constant::getNullValue(AIt->first->getAllocatedType());
+ LI->replaceAllUsesWith(AIt->second);
+ BB->getInstList().erase(LI);
+ }
+ }
+ } else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
+ if (AllocaInst *AI = dyn_cast<AllocaInst>(SI->getOperand(1))) {
+ std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
+ if (AIt != CurValues.end()) {
+ // Store updates the "current value"...
+ AIt->second = SI->getOperand(0);
+ BB->getInstList().erase(SI);
+ }
+ }
+ }
}
}
+
// QueuePhiNode - queues a phi-node to be added to a basic-block for a specific
// Alloca returns true if there wasn't already a phi-node for that variable
//
-bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo) {
+bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo,
+ unsigned &Version,
+ std::set<PHINode*> &InsertedPHINodes) {
// Look up the basic-block in question
std::vector<PHINode*> &BBPNs = NewPhiNodes[BB];
if (BBPNs.empty()) BBPNs.resize(Allocas.size());
// Create a PhiNode using the dereferenced type... and add the phi-node to the
// BasicBlock.
- PHINode *PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(),
- Allocas[AllocaNo]->getName() + "." +
- utostr(VersionNumbers[AllocaNo]++),
- BB->begin());
-
- // Add null incoming values for all predecessors. This ensures that if one of
- // the predecessors is not found in the depth-first traversal of the CFG (ie,
- // because it is an unreachable predecessor), that all PHI nodes will have the
- // correct number of entries for their predecessors.
- Value *NullVal = Constant::getNullValue(PN->getType());
-
- // This is necessary because adding incoming values to the PHI node adds uses
- // to the basic blocks being used, which can invalidate the predecessor
- // iterator!
- std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
- for (unsigned i = 0, e = Preds.size(); i != e; ++i)
- PN->addIncoming(NullVal, Preds[i]);
-
- BBPNs[AllocaNo] = PN;
- PhiNodes[AllocaNo].push_back(BB);
+ BBPNs[AllocaNo] = new PHINode(Allocas[AllocaNo]->getAllocatedType(),
+ Allocas[AllocaNo]->getName() + "." +
+ utostr(Version++), BB->begin());
+ InsertedPHINodes.insert(BBPNs[AllocaNo]);
return true;
}
+
+// RenamePass - Recursively traverse the CFG of the function, renaming loads and
+// stores to the allocas which we are promoting. IncomingVals indicates what
+// value each Alloca contains on exit from the predecessor block Pred.
+//
void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred,
- std::vector<Value*> &IncomingVals,
- std::set<BasicBlock*> &Visited) {
- // If this is a BB needing a phi node, lookup/create the phinode for each
- // variable we need phinodes for.
- std::vector<PHINode *> &BBPNs = NewPhiNodes[BB];
- for (unsigned k = 0; k != BBPNs.size(); ++k)
- if (PHINode *PN = BBPNs[k]) {
- // The PHI node may have multiple entries for this predecessor. We must
- // make sure we update all of them.
- for (unsigned i = 0, e = PN->getNumOperands(); i != e; i += 2) {
- if (PN->getOperand(i+1) == Pred)
- // At this point we can assume that the array has phi nodes.. let's
- // update the incoming data.
- PN->setOperand(i, IncomingVals[k]);
+ std::vector<Value*> &IncomingVals) {
+
+ // If this BB needs a PHI node, update the PHI node for each variable we need
+ // PHI nodes for.
+ std::map<BasicBlock*, std::vector<PHINode *> >::iterator
+ BBPNI = NewPhiNodes.find(BB);
+ if (BBPNI != NewPhiNodes.end()) {
+ std::vector<PHINode *> &BBPNs = BBPNI->second;
+ for (unsigned k = 0; k != BBPNs.size(); ++k)
+ if (PHINode *PN = BBPNs[k]) {
+ // Add this incoming value to the PHI node.
+ PN->addIncoming(IncomingVals[k], Pred);
+
+ // The currently active variable for this block is now the PHI.
+ IncomingVals[k] = PN;
}
- // also note that the active variable IS designated by the phi node
- IncomingVals[k] = PN;
- }
+ }
// don't revisit nodes
if (Visited.count(BB)) return;
// mark as visited
Visited.insert(BB);
- // keep track of the value of each variable we're watching.. how?
- for (BasicBlock::iterator II = BB->begin(); II != BB->end(); ++II) {
- Instruction *I = II; // get the instruction
+ for (BasicBlock::iterator II = BB->begin(); !isa<TerminatorInst>(II); ) {
+ Instruction *I = II++; // get the instruction, increment iterator
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
if (AllocaInst *Src = dyn_cast<AllocaInst>(LI->getPointerOperand())) {
- std::map<Instruction*, unsigned>::iterator AI = AllocaLookup.find(Src);
+ std::map<AllocaInst*, unsigned>::iterator AI = AllocaLookup.find(Src);
if (AI != AllocaLookup.end()) {
Value *V = IncomingVals[AI->second];
// walk the use list of this load and replace all uses with r
LI->replaceAllUsesWith(V);
- KillList.push_back(LI); // Mark the load to be deleted
+ BB->getInstList().erase(LI);
}
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
// Delete this instruction and mark the name as the current holder of the
// value
if (AllocaInst *Dest = dyn_cast<AllocaInst>(SI->getPointerOperand())) {
- std::map<Instruction *, unsigned>::iterator ai =AllocaLookup.find(Dest);
+ std::map<AllocaInst *, unsigned>::iterator ai = AllocaLookup.find(Dest);
if (ai != AllocaLookup.end()) {
// what value were we writing?
IncomingVals[ai->second] = SI->getOperand(0);
- KillList.push_back(SI); // Mark the store to be deleted
+ BB->getInstList().erase(SI);
}
}
-
- } else if (TerminatorInst *TI = dyn_cast<TerminatorInst>(I)) {
- // Recurse across our successors
- for (unsigned i = 0; i != TI->getNumSuccessors(); i++) {
- std::vector<Value*> OutgoingVals(IncomingVals);
- RenamePass(TI->getSuccessor(i), BB, OutgoingVals, Visited);
- }
}
}
+
+ // Recurse to our successors.
+ TerminatorInst *TI = BB->getTerminator();
+ for (unsigned i = 0; i != TI->getNumSuccessors(); i++) {
+ std::vector<Value*> OutgoingVals(IncomingVals);
+ RenamePass(TI->getSuccessor(i), BB, OutgoingVals);
+ }
}
/// PromoteMemToReg - Promote the specified list of alloca instructions into
/// use of DominanceFrontier information. This function does not modify the CFG
/// of the function at all. All allocas must be from the same function.
///
-void PromoteMemToReg(const std::vector<AllocaInst*> &Allocas,
- DominanceFrontier &DF, const TargetData &TD) {
- PromoteMem2Reg(Allocas, DF, TD).run();
+void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas,
+ DominatorTree &DT, DominanceFrontier &DF,
+ const TargetData &TD) {
+ // If there is nothing to do, bail out...
+ if (Allocas.empty()) return;
+ PromoteMem2Reg(Allocas, DT, DF, TD).run();
}
projects / oota-llvm.git / blobdiff