[llvm-commits] [llvm] r83705 - in /llvm/trunk: include/llvm/Transforms/Utils/SSAUpdater.h lib/Transforms/Utils/CMakeLists.txt lib/Transforms/Utils/SSAUpdater.cpp
Chris Lattner
sabre at nondot.org
Sat Oct 10 02:04:28 PDT 2009
Author: lattner
Date: Sat Oct 10 04:04:27 2009
New Revision: 83705
URL: http://llvm.org/viewvc/llvm-project?rev=83705&view=rev
Log:
Implement an efficient and fully general SSA update mechanism that
works on unstructured CFGs. This implements PR217, our oldest open PR.
Added:
llvm/trunk/include/llvm/Transforms/Utils/SSAUpdater.h
llvm/trunk/lib/Transforms/Utils/SSAUpdater.cpp
Modified:
llvm/trunk/lib/Transforms/Utils/CMakeLists.txt
Added: llvm/trunk/include/llvm/Transforms/Utils/SSAUpdater.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Utils/SSAUpdater.h?rev=83705&view=auto
==============================================================================
--- llvm/trunk/include/llvm/Transforms/Utils/SSAUpdater.h (added)
+++ llvm/trunk/include/llvm/Transforms/Utils/SSAUpdater.h Sat Oct 10 04:04:27 2009
@@ -0,0 +1,71 @@
+//===-- SSAUpdater.h - Unstructured SSA Update Tool -------------*- C++ -*-===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares the SSAUpdater class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_UTILS_SSAUPDATER_H
+#define LLVM_TRANSFORMS_UTILS_SSAUPDATER_H
+
+namespace llvm {
+ class Value;
+ class BasicBlock;
+ class Use;
+
+/// SSAUpdater - This class updates SSA form for a set of values defined in
+/// multiple blocks. This is used when code duplication or another unstructured
+/// transformation wants to rewrite a set of uses of one value with uses of a
+/// set of values.
+class SSAUpdater {
+ /// AvailableVals - This keeps track of which value to use on a per-block
+ /// basis. When we insert PHI nodes, we keep track of them here. We use
+ /// WeakVH's for the value of the map because we RAUW PHI nodes when we
+ /// eliminate them, and want the WeakVH to track this.
+ //typedef DenseMap<BasicBlock*, TrackingVH<Value> > AvailableValsTy;
+ void *AV;
+
+ /// PrototypeValue is an arbitrary representative value, which we derive names
+ /// and a type for PHI nodes.
+ Value *PrototypeValue;
+
+ /// IncomingPredInfo - We use this as scratch space when doing our recursive
+ /// walk. This should only be used in GetValueInBlockInternal, normally it
+ /// should be empty.
+ //std::vector<std::pair<BasicBlock*, TrackingVH<Value> > > IncomingPredInfo;
+ void *IPI;
+public:
+ SSAUpdater();
+ ~SSAUpdater();
+
+ /// Initialize - Reset this object to get ready for a new set of SSA
+ /// updates. ProtoValue is the value used to name PHI nodes.
+ void Initialize(Value *ProtoValue);
+
+ /// AddAvailableValue - Indicate that a rewritten value is available in the
+ /// specified block with the specified value.
+ void AddAvailableValue(BasicBlock *BB, Value *V);
+
+ /// GetValueInBlock - Construct SSA form, materializing a value in the
+ /// specified block.
+ Value *GetValueInBlock(BasicBlock *BB);
+
+ /// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
+ /// which use their value in the corresponding predecessor.
+ void RewriteUse(Use &U);
+
+private:
+ Value *GetValueInBlockInternal(BasicBlock *BB);
+ void operator=(const SSAUpdater&); // DO NOT IMPLEMENT
+ SSAUpdater(const SSAUpdater&); // DO NOT IMPLEMENT
+};
+
+} // End llvm namespace
+
+#endif
Modified: llvm/trunk/lib/Transforms/Utils/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/CMakeLists.txt?rev=83705&r1=83704&r2=83705&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/CMakeLists.txt (original)
+++ llvm/trunk/lib/Transforms/Utils/CMakeLists.txt Sat Oct 10 04:04:27 2009
@@ -19,6 +19,7 @@
LowerSwitch.cpp
Mem2Reg.cpp
PromoteMemoryToRegister.cpp
+ SSAUpdater.cpp
SSI.cpp
SimplifyCFG.cpp
UnifyFunctionExitNodes.cpp
Added: llvm/trunk/lib/Transforms/Utils/SSAUpdater.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SSAUpdater.cpp?rev=83705&view=auto
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SSAUpdater.cpp (added)
+++ llvm/trunk/lib/Transforms/Utils/SSAUpdater.cpp Sat Oct 10 04:04:27 2009
@@ -0,0 +1,232 @@
+//===- SSAUpdater.cpp - Unstructured SSA Update Tool ----------------------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the SSAUpdater class.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/SSAUpdater.h"
+#include "llvm/Instructions.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ValueHandle.h"
+#include "llvm/Support/raw_ostream.h"
+using namespace llvm;
+
+typedef DenseMap<BasicBlock*, TrackingVH<Value> > AvailableValsTy;
+typedef std::vector<std::pair<BasicBlock*, TrackingVH<Value> > >
+ IncomingPredInfoTy;
+
+static AvailableValsTy &getAvailableVals(void *AV) {
+ return *static_cast<AvailableValsTy*>(AV);
+}
+
+static IncomingPredInfoTy &getIncomingPredInfo(void *IPI) {
+ return *static_cast<IncomingPredInfoTy*>(IPI);
+}
+
+
+SSAUpdater::SSAUpdater() : AV(0), PrototypeValue(0), IPI(0) {}
+
+SSAUpdater::~SSAUpdater() {
+ delete &getAvailableVals(AV);
+ delete &getIncomingPredInfo(IPI);
+}
+
+/// Initialize - Reset this object to get ready for a new set of SSA
+/// updates. ProtoValue is the value used to name PHI nodes.
+void SSAUpdater::Initialize(Value *ProtoValue) {
+ if (AV == 0)
+ AV = new AvailableValsTy();
+ else
+ getAvailableVals(AV).clear();
+
+ if (IPI == 0)
+ IPI = new IncomingPredInfoTy();
+ else
+ getIncomingPredInfo(IPI).clear();
+ PrototypeValue = ProtoValue;
+}
+
+/// AddAvailableValue - Indicate that a rewritten value is available in the
+/// specified block with the specified value.
+void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
+ assert(PrototypeValue != 0 && "Need to initialize SSAUpdater");
+ assert(PrototypeValue->getType() == V->getType() &&
+ "All rewritten values must have the same type");
+ getAvailableVals(AV)[BB] = V;
+}
+
+/// GetValueInBlock - Construct SSA form, materializing a value in the
+/// specified block.
+Value *SSAUpdater::GetValueInBlock(BasicBlock *BB) {
+ assert(getIncomingPredInfo(IPI).empty() && "Unexpected Internal State");
+ Value *Res = GetValueInBlockInternal(BB);
+ assert(getIncomingPredInfo(IPI).empty() && "Unexpected Internal State");
+ return Res;
+}
+
+/// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
+/// which use their value in the corresponding predecessor.
+void SSAUpdater::RewriteUse(Use &U) {
+ Instruction *User = cast<Instruction>(U.getUser());
+ BasicBlock *UseBB = User->getParent();
+ if (PHINode *UserPN = dyn_cast<PHINode>(User))
+ UseBB = UserPN->getIncomingBlock(U);
+
+ U.set(GetValueInBlock(UseBB));
+}
+
+
+/// GetValueInBlock - Check to see if AvailableVals has an entry for the
+/// specified BB and if so, return it. If not, construct SSA form by walking
+/// predecessors inserting PHI nodes as needed until we get to a block where the
+/// value is available.
+///
+Value *SSAUpdater::GetValueInBlockInternal(BasicBlock *BB) {
+ AvailableValsTy &AvailableVals = getAvailableVals(AV);
+
+ // Query AvailableVals by doing an insertion of null.
+ std::pair<AvailableValsTy::iterator, bool> InsertRes =
+ AvailableVals.insert(std::make_pair(BB, WeakVH()));
+
+ // Handle the case when the insertion fails because we have already seen BB.
+ if (!InsertRes.second) {
+ // If the insertion failed, there are two cases. The first case is that the
+ // value is already available for the specified block. If we get this, just
+ // return the value.
+ if (InsertRes.first->second != 0)
+ return InsertRes.first->second;
+
+ // Otherwise, if the value we find is null, then this is the value is not
+ // known but it is being computed elsewhere in our recursion. This means
+ // that we have a cycle. Handle this by inserting a PHI node and returning
+ // it. When we get back to the first instance of the recursion we will fill
+ // in the PHI node.
+ return InsertRes.first->second =
+ PHINode::Create(PrototypeValue->getType(), PrototypeValue->getName(),
+ &BB->front());
+ }
+
+ // Okay, the value isn't in the map and we just inserted a null in the entry
+ // to indicate that we're processing the block. Since we have no idea what
+ // value is in this block, we have to recurse through our predecessors.
+ //
+ // While we're walking our predecessors, we keep track of them in a vector,
+ // then insert a PHI node in the end if we actually need one. We could use a
+ // smallvector here, but that would take a lot of stack space for every level
+ // of the recursion, just use IncomingPredInfo as an explicit stack.
+ IncomingPredInfoTy &IncomingPredInfo = getIncomingPredInfo(IPI);
+ unsigned FirstPredInfoEntry = IncomingPredInfo.size();
+
+ // As we're walking the predecessors, keep track of whether they are all
+ // producing the same value. If so, this value will capture it, if not, it
+ // will get reset to null. We distinguish the no-predecessor case explicitly
+ // below.
+ TrackingVH<Value> SingularValue;
+
+ // We can get our predecessor info by walking the pred_iterator list, but it
+ // is relatively slow. If we already have PHI nodes in this block, walk one
+ // of them to get the predecessor list instead.
+ if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
+ for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
+ BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
+ Value *PredVal = GetValueInBlockInternal(PredBB);
+ IncomingPredInfo.push_back(std::make_pair(PredBB, PredVal));
+
+ // Compute SingularValue.
+ if (i == 0)
+ SingularValue = PredVal;
+ else if (PredVal != SingularValue)
+ SingularValue = 0;
+ }
+ } else {
+ bool isFirstPred = true;
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+ BasicBlock *PredBB = *PI;
+ Value *PredVal = GetValueInBlockInternal(PredBB);
+ IncomingPredInfo.push_back(std::make_pair(PredBB, PredVal));
+
+ // Compute SingularValue.
+ if (isFirstPred) {
+ SingularValue = PredVal;
+ isFirstPred = false;
+ } else if (PredVal != SingularValue)
+ SingularValue = 0;
+ }
+ }
+
+ // If there are no predecessors, then we must have found an unreachable block
+ // just return 'undef'. Since there are no predecessors, InsertRes must not
+ // be invalidated.
+ if (IncomingPredInfo.size() == FirstPredInfoEntry)
+ return InsertRes.first->second = UndefValue::get(PrototypeValue->getType());
+
+ /// Look up BB's entry in AvailableVals. 'InsertRes' may be invalidated. If
+ /// this block is involved in a loop, a no-entry PHI node will have been
+ /// inserted as InsertedVal. Otherwise, we'll still have the null we inserted
+ /// above.
+ TrackingVH<Value> &InsertedVal = AvailableVals[BB];
+
+ // If all the predecessor values are the same then we don't need to insert a
+ // PHI. This is the simple and common case.
+ if (SingularValue) {
+ // If a PHI node got inserted, replace it with the singlar value and delete
+ // it.
+ if (InsertedVal) {
+ PHINode *OldVal = cast<PHINode>(InsertedVal);
+ // Be careful about dead loops. These RAUW's also update InsertedVal.
+ if (InsertedVal != SingularValue)
+ OldVal->replaceAllUsesWith(SingularValue);
+ else
+ OldVal->replaceAllUsesWith(UndefValue::get(InsertedVal->getType()));
+ OldVal->eraseFromParent();
+ } else {
+ InsertedVal = SingularValue;
+ }
+
+ // Drop the entries we added in IncomingPredInfo to restore the stack.
+ IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry,
+ IncomingPredInfo.end());
+ return InsertedVal;
+ }
+
+ // Otherwise, we do need a PHI: insert one now if we don't already have one.
+ if (InsertedVal == 0)
+ InsertedVal = PHINode::Create(PrototypeValue->getType(),
+ PrototypeValue->getName(), &BB->front());
+
+ PHINode *InsertedPHI = cast<PHINode>(InsertedVal);
+ InsertedPHI->reserveOperandSpace(IncomingPredInfo.size()-FirstPredInfoEntry);
+
+ // Fill in all the predecessors of the PHI.
+ for (std::vector<std::pair<BasicBlock*, TrackingVH<Value> > >::iterator I =
+ IncomingPredInfo.begin()+FirstPredInfoEntry, E = IncomingPredInfo.end();
+ I != E; ++I)
+ InsertedPHI->addIncoming(I->second, I->first);
+
+ // Drop the entries we added in IncomingPredInfo to restore the stack.
+ IncomingPredInfo.erase(IncomingPredInfo.begin()+FirstPredInfoEntry,
+ IncomingPredInfo.end());
+
+ // See if the PHI node can be merged to a single value. This can happen in
+ // loop cases when we get a PHI of itself and one other value.
+ if (Value *ConstVal = InsertedPHI->hasConstantValue()) {
+ InsertedPHI->replaceAllUsesWith(ConstVal);
+ InsertedPHI->eraseFromParent();
+ InsertedVal = ConstVal;
+ } else {
+ DEBUG(errs() << " Inserted PHI: " << *InsertedPHI << "\n");
+ }
+
+ return InsertedVal;
+}
+
+
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