From 98a37c2b9c9c7f2791e0a8abda33b9a2eb36ad8e Mon Sep 17 00:00:00 2001
From: Cameron Buschardt <buschard@uiuc.edu>
Date: Wed, 27 Mar 2002 23:17:37 +0000
Subject: [PATCH] Implemented promote mem->reg pass.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2005 91177308-0d34-0410-b5e6-96231b3b80d8
---
.../Utils/PromoteMemoryToRegister.cpp | 344 ++++++++++++++----
1 file changed, 283 insertions(+), 61 deletions(-)
diff --git a/lib/Transforms/Utils/PromoteMemoryToRegister.cpp b/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
index 47fe38f2a67..74ac04c8edf 100644
--- a/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
+++ b/lib/Transforms/Utils/PromoteMemoryToRegister.cpp
@@ -13,7 +13,7 @@
// Currently this just loops over all alloca instructions, looking for
// instructions that are only used in simple load and stores.
//
-// After this, the code is transformed by...
+// After this, the code is transformed by...something magical :)
//
//===----------------------------------------------------------------------===//
@@ -24,90 +24,312 @@
#include "llvm/Method.h"
#include "llvm/BasicBlock.h"
#include "llvm/Assembly/Writer.h" // For debugging
+#include "llvm/iPHINode.h"
+#include "llvm/iTerminators.h"
+
+using namespace std;
+
+
using cfg::DominanceFrontier;
-// PromotePass - This class is implements the PromoteMemoryToRegister pass
-//
+
+//instance of the promoter -- to keep all the local method data.
+// gets re-created for each method processed
+class PromoteInstance
+{
+ protected:
+ vector<AllocaInst*> Allocas; // the alloca instruction..
+ map<Instruction *, int> AllocaLookup; //reverse mapping of above
+
+ vector<vector<BasicBlock *> > WriteSets; // index corresponds to Allocas
+ vector<vector<BasicBlock *> > PhiNodes; // index corresponds to Allocas
+ vector<vector<Value *> > CurrentValue; //the current value stack
+
+ //list of instructions to remove at end of pass :)
+ vector<Instruction *> killlist;
+
+ set<BasicBlock *> visited; //the basic blocks we've already visited
+ map<BasicBlock *, vector<PHINode *> > new_phinodes; //the phinodes we're adding
+
+
+ void traverse(BasicBlock *f, BasicBlock * predecessor);
+ bool PromoteMethod(Method *M, DominanceFrontier & DF);
+ bool queuePhiNode(BasicBlock *bb, int alloca_index);
+ void findSafeAllocas(Method *M);
+ bool didchange;
+ public:
+ // I do this so that I can force the deconstruction of the local variables
+ PromoteInstance(Method *M, DominanceFrontier & DF)
+ {
+ didchange=PromoteMethod(M, DF);
+ }
+ //This returns whether the pass changes anything
+ operator bool () { return didchange; }
+};
+
class PromotePass : public MethodPass {
-public:
- // runOnMethod - To run this pass, first we calculate the alloca instructions
- // that are safe for promotion, then we promote each one.
- //
- virtual bool runOnMethod(Method *M) {
- std::vector<AllocaInst*> Allocas;
- findSafeAllocas(M, Allocas); // Calculate safe allocas
+ public:
- // Get dominance frontier information...
- DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
-
- // Transform each alloca in turn...
- for (std::vector<AllocaInst*>::iterator I = Allocas.begin(),
- E = Allocas.end(); I != E; ++I)
- promoteAlloca(*I, DF);
-
- return !Allocas.empty();
- }
+ // runOnMethod - To run this pass, first we calculate the alloca instructions
+ // that are safe for promotion, then we promote each one.
+ //
+ virtual bool runOnMethod(Method *M)
+ {
+ PromoteInstance inst(M, getAnalysis<DominanceFrontier>());
+ return (bool)inst;
+ }
- // getAnalysisUsageInfo - We need dominance frontiers
- //
- virtual void getAnalysisUsageInfo(Pass::AnalysisSet &Requires,
- Pass::AnalysisSet &Destroyed,
- Pass::AnalysisSet &Provided) {
- Requires.push_back(DominanceFrontier::ID);
- }
-
-private:
- // findSafeAllocas - Find allocas that are safe to promote
- //
- void findSafeAllocas(Method *M, std::vector<AllocaInst*> &Allocas) const;
-
- // promoteAlloca - Convert the use chain of an alloca instruction into
- // register references.
- //
- void promoteAlloca(AllocaInst *AI, DominanceFrontier &DF);
+ // getAnalysisUsageInfo - We need dominance frontiers
+ //
+ virtual void getAnalysisUsageInfo(Pass::AnalysisSet &Requires,
+ Pass::AnalysisSet &Destroyed,
+ Pass::AnalysisSet &Provided) {
+ Requires.push_back(DominanceFrontier::ID);
+ }
};
// findSafeAllocas - Find allocas that are safe to promote
//
-void PromotePass::findSafeAllocas(Method *M,
- std::vector<AllocaInst*> &Allocas) const {
+void PromoteInstance::findSafeAllocas(Method *M)
+{
BasicBlock *BB = M->front(); // Get the entry node for the method
// Look at all instructions in the entry node
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
if (AllocaInst *AI = dyn_cast<AllocaInst>(*I)) // Is it an alloca?
if (!AI->isArrayAllocation()) {
- bool isSafe = true;
- for (Value::use_iterator UI = AI->use_begin(), UE = AI->use_end();
- UI != UE; ++UI) { // Loop over all of the uses of the alloca
- // Only allow nonindexed memory access instructions...
- if (MemAccessInst *MAI = dyn_cast<MemAccessInst>(*UI)) {
- if (MAI->hasIndices()) { isSafe = false; break; } // indexed?
- } else {
- isSafe = false; break; // Not a load or store?
- }
- }
+ bool isSafe = true;
+ for (Value::use_iterator UI = AI->use_begin(), UE = AI->use_end();
+ UI != UE; ++UI) { // Loop over all of the uses of the alloca
- if (isSafe) // If all checks pass, add alloca to safe list
- Allocas.push_back(AI);
+ // Only allow nonindexed memory access instructions...
+ if (MemAccessInst *MAI = dyn_cast<MemAccessInst>(*UI)) {
+ if (MAI->hasIndices()) { // indexed?
+ // Allow the access if there is only one index and the index is zero.
+ if (*MAI->idx_begin() != ConstantUInt::get(Type::UIntTy, 0) ||
+ MAI->idx_begin()+1 != MAI->idx_end()) {
+ isSafe = false; break;
+ }
+ }
+ } else {
+ isSafe = false; break; // Not a load or store?
+ }
+ }
+ if (isSafe) // If all checks pass, add alloca to safe list
+ {
+ AllocaLookup[AI]=Allocas.size();
+ Allocas.push_back(AI);
+ }
}
-
}
-// promoteAlloca - Convert the use chain of an alloca instruction into
-// register references.
-//
-void PromotePass::promoteAlloca(AllocaInst *AI, DominanceFrontier &DFInfo) {
- std::cerr << "TODO: Should process: " << AI;
-}
-
-
// newPromoteMemoryToRegister - Provide an entry point to create this pass.
//
Pass *newPromoteMemoryToRegister() {
- return new PromotePass();
+ return new PromotePass();
+}
+
+
+bool PromoteInstance::PromoteMethod(Method *M, DominanceFrontier & DF) {
+ // Calculate the set of safe allocas
+ findSafeAllocas(M);
+
+ // 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.
+ for (unsigned i = 0; i<Allocas.size(); ++i)
+ {
+ AllocaInst * AI = Allocas[i];
+ WriteSets.push_back(std::vector<BasicBlock *>()); //add a new set
+ for (Value::use_iterator U = AI->use_begin();U!=AI->use_end();++U)
+ {
+ if (MemAccessInst *MAI = dyn_cast<StoreInst>(*U)) {
+ WriteSets[i].push_back(MAI->getParent()); // jot down the basic-block it came from
+ }
+ }
+ }
+
+ // 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::DomSetType s = (*it).second;
+ for (DominanceFrontier::DomSetType::iterator p = s.begin();p!=s.end(); ++p)
+ {
+ if (queuePhiNode((BasicBlock *)*p, i))
+ PhiNodes[i].push_back((BasicBlock *)*p);
+ }
+ }
+ // perform iterative step
+ for (unsigned k = 0; k<PhiNodes[i].size(); k++)
+ {
+ DominanceFrontier::const_iterator it = DF.find(PhiNodes[i][k]);
+ DominanceFrontier::DomSetType s = it->second;
+ for (DominanceFrontier::DomSetType::iterator p = s.begin(); p!=s.end(); ++p)
+ {
+ if (queuePhiNode((BasicBlock *)*p,i))
+ PhiNodes[i].push_back((BasicBlock*)*p);
+ }
+ }
+ }
+
+ // Walks all basic blocks in the method
+ // performing the SSA rename algorithm
+ // and inserting the phi nodes we marked as necessary
+ BasicBlock * f = M->front(); //get root basic-block
+
+ CurrentValue.push_back(vector<Value *>(Allocas.size()));
+
+ traverse(f, NULL); // there is no predecessor of the root node
+
+
+ // ** REMOVE EVERYTHING IN THE KILL-LIST **
+ // we need to kill 'uses' before root values
+ // so we should probably run through in reverse
+ for (vector<Instruction *>::reverse_iterator i = killlist.rbegin(); i!=killlist.rend(); ++i)
+ {
+ Instruction * r = *i;
+ BasicBlock * o = r->getParent();
+ //now go find..
+
+ BasicBlock::InstListType & l = o->getInstList();
+ o->getInstList().remove(r);
+ delete r;
+ }
+
+ return !Allocas.empty();
+}
+
+
+
+void PromoteInstance::traverse(BasicBlock *f, BasicBlock * predecessor)
+{
+ vector<Value *> * tos = &CurrentValue.back(); //look at top-
+
+ //if this is a BB needing a phi node, lookup/create the phinode for
+ // each variable we need phinodes for.
+ map<BasicBlock *, vector<PHINode *> >::iterator nd = new_phinodes.find(f);
+ if (nd!=new_phinodes.end())
+ {
+ for (unsigned k = 0; k!=nd->second.size(); ++k)
+ if (nd->second[k])
+ {
+ //at this point we can assume that the array has phi nodes.. let's
+ // add the incoming data
+ if ((*tos)[k])
+ nd->second[k]->addIncoming((*tos)[k],predecessor);
+ //also note that the active variable IS designated by the phi node
+ (*tos)[k] = nd->second[k];
+ }
+ }
+
+ //don't revisit nodes
+ if (visited.find(f)!=visited.end())
+ return;
+ //mark as visited
+ visited.insert(f);
+
+ BasicBlock::iterator i = f->begin();
+ //keep track of the value of each variable we're watching.. how?
+ while(i!=f->end())
+ {
+ Instruction * inst = *i; //get the instruction
+ //is this a write/read?
+ if (LoadInst * LI = dyn_cast<LoadInst>(inst))
+ {
+ // This is a bit weird...
+ Value * ptr = LI->getPointerOperand(); //of type value
+ if (AllocaInst * srcinstr = dyn_cast<AllocaInst>(ptr))
+ {
+ map<Instruction *, int>::iterator ai = AllocaLookup.find(srcinstr);
+ if (ai!=AllocaLookup.end())
+ {
+ if (Value *r = (*tos)[ai->second])
+ {
+ //walk the use list of this load and replace
+ // all uses with r
+ LI->replaceAllUsesWith(r);
+ //now delete the instruction.. somehow..
+ killlist.push_back((Instruction *)LI);
+ }
+ }
+ }
+ }
+ else if (StoreInst * SI = dyn_cast<StoreInst>(inst))
+ {
+ // delete this instruction and mark the name as the
+ // current holder of the value
+ Value * ptr = SI->getPointerOperand(); //of type value
+ if (Instruction * srcinstr = dyn_cast<Instruction>(ptr))
+ {
+ map<Instruction *, int>::iterator ai = AllocaLookup.find(srcinstr);
+ if (ai!=AllocaLookup.end())
+ {
+ //what value were we writing?
+ Value * writeval = SI->getOperand(0);
+ //write down...
+ (*tos)[ai->second] = writeval;
+ //now delete it.. somehow?
+ killlist.push_back((Instruction *)SI);
+ }
+ }
+
+ }
+ else if (TerminatorInst * TI = dyn_cast<TerminatorInst>(inst))
+ {
+ // Recurse across our sucessors
+ for (unsigned i = 0; i!=TI->getNumSuccessors(); i++)
+ {
+ CurrentValue.push_back(CurrentValue.back());
+ traverse(TI->getSuccessor(i),f); //this node IS the predecessor
+ CurrentValue.pop_back();
+ }
+ }
+ i++;
+ }
+}
+
+// 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 PromoteInstance::queuePhiNode(BasicBlock *bb, int i /*the alloca*/)
+{
+ map<BasicBlock *, vector<PHINode *> >::iterator nd;
+ //look up the basic-block in question
+ nd = new_phinodes.find(bb);
+ //if the basic-block has no phi-nodes added, or at least none
+ //for the i'th alloca. then add.
+ if (nd==new_phinodes.end() || nd->second[i]==NULL)
+ {
+ //we're not added any phi nodes to this basicblock yet
+ // create the phi-node array.
+ if (nd==new_phinodes.end())
+ {
+ new_phinodes[bb] = vector<PHINode *>(Allocas.size());
+ nd = new_phinodes.find(bb);
+ }
+
+ //find the type the alloca returns
+ const PointerType * pt = Allocas[i]->getType();
+ //create a phi-node using the DEREFERENCED type
+ PHINode * ph = new PHINode(pt->getElementType(), Allocas[i]->getName()+".mem2reg");
+ nd->second[i] = ph;
+ //add the phi-node to the basic-block
+ bb->getInstList().push_front(ph);
+ return true;
+ }
+ return false;
}