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MachineSSAUpdater to avoid duplicating all the code. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103060 91177308-0d34-0410-b5e6-96231b3b80d8
331 lines
12 KiB
C++
331 lines
12 KiB
C++
//===- SSAUpdater.cpp - Unstructured SSA Update Tool ----------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the SSAUpdater class.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "ssaupdater"
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#include "llvm/Instructions.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/Support/AlignOf.h"
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#include "llvm/Support/Allocator.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Utils/SSAUpdater.h"
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#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
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using namespace llvm;
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typedef DenseMap<BasicBlock*, Value*> AvailableValsTy;
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static AvailableValsTy &getAvailableVals(void *AV) {
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return *static_cast<AvailableValsTy*>(AV);
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}
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SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
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: AV(0), PrototypeValue(0), InsertedPHIs(NewPHI) {}
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SSAUpdater::~SSAUpdater() {
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delete &getAvailableVals(AV);
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}
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/// Initialize - Reset this object to get ready for a new set of SSA
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/// updates. ProtoValue is the value used to name PHI nodes.
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void SSAUpdater::Initialize(Value *ProtoValue) {
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if (AV == 0)
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AV = new AvailableValsTy();
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else
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getAvailableVals(AV).clear();
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PrototypeValue = ProtoValue;
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}
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/// HasValueForBlock - Return true if the SSAUpdater already has a value for
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/// the specified block.
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bool SSAUpdater::HasValueForBlock(BasicBlock *BB) const {
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return getAvailableVals(AV).count(BB);
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}
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/// AddAvailableValue - Indicate that a rewritten value is available in the
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/// specified block with the specified value.
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void SSAUpdater::AddAvailableValue(BasicBlock *BB, Value *V) {
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assert(PrototypeValue != 0 && "Need to initialize SSAUpdater");
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assert(PrototypeValue->getType() == V->getType() &&
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"All rewritten values must have the same type");
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getAvailableVals(AV)[BB] = V;
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}
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/// IsEquivalentPHI - Check if PHI has the same incoming value as specified
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/// in ValueMapping for each predecessor block.
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static bool IsEquivalentPHI(PHINode *PHI,
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DenseMap<BasicBlock*, Value*> &ValueMapping) {
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unsigned PHINumValues = PHI->getNumIncomingValues();
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if (PHINumValues != ValueMapping.size())
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return false;
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// Scan the phi to see if it matches.
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for (unsigned i = 0, e = PHINumValues; i != e; ++i)
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if (ValueMapping[PHI->getIncomingBlock(i)] !=
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PHI->getIncomingValue(i)) {
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return false;
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}
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return true;
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}
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/// GetValueAtEndOfBlock - Construct SSA form, materializing a value that is
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/// live at the end of the specified block.
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Value *SSAUpdater::GetValueAtEndOfBlock(BasicBlock *BB) {
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Value *Res = GetValueAtEndOfBlockInternal(BB);
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return Res;
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}
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/// GetValueInMiddleOfBlock - Construct SSA form, materializing a value that
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/// is live in the middle of the specified block.
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///
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/// GetValueInMiddleOfBlock is the same as GetValueAtEndOfBlock except in one
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/// important case: if there is a definition of the rewritten value after the
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/// 'use' in BB. Consider code like this:
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///
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/// X1 = ...
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/// SomeBB:
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/// use(X)
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/// X2 = ...
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/// br Cond, SomeBB, OutBB
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///
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/// In this case, there are two values (X1 and X2) added to the AvailableVals
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/// set by the client of the rewriter, and those values are both live out of
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/// their respective blocks. However, the use of X happens in the *middle* of
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/// a block. Because of this, we need to insert a new PHI node in SomeBB to
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/// merge the appropriate values, and this value isn't live out of the block.
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///
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Value *SSAUpdater::GetValueInMiddleOfBlock(BasicBlock *BB) {
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// If there is no definition of the renamed variable in this block, just use
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// GetValueAtEndOfBlock to do our work.
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if (!HasValueForBlock(BB))
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return GetValueAtEndOfBlock(BB);
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// Otherwise, we have the hard case. Get the live-in values for each
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// predecessor.
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SmallVector<std::pair<BasicBlock*, Value*>, 8> PredValues;
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Value *SingularValue = 0;
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// We can get our predecessor info by walking the pred_iterator list, but it
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// is relatively slow. If we already have PHI nodes in this block, walk one
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// of them to get the predecessor list instead.
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if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
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for (unsigned i = 0, e = SomePhi->getNumIncomingValues(); i != e; ++i) {
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BasicBlock *PredBB = SomePhi->getIncomingBlock(i);
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Value *PredVal = GetValueAtEndOfBlock(PredBB);
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PredValues.push_back(std::make_pair(PredBB, PredVal));
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// Compute SingularValue.
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if (i == 0)
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SingularValue = PredVal;
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else if (PredVal != SingularValue)
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SingularValue = 0;
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}
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} else {
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bool isFirstPred = true;
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for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
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BasicBlock *PredBB = *PI;
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Value *PredVal = GetValueAtEndOfBlock(PredBB);
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PredValues.push_back(std::make_pair(PredBB, PredVal));
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// Compute SingularValue.
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if (isFirstPred) {
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SingularValue = PredVal;
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isFirstPred = false;
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} else if (PredVal != SingularValue)
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SingularValue = 0;
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}
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}
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// If there are no predecessors, just return undef.
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if (PredValues.empty())
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return UndefValue::get(PrototypeValue->getType());
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// Otherwise, if all the merged values are the same, just use it.
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if (SingularValue != 0)
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return SingularValue;
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// Otherwise, we do need a PHI: check to see if we already have one available
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// in this block that produces the right value.
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if (isa<PHINode>(BB->begin())) {
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DenseMap<BasicBlock*, Value*> ValueMapping(PredValues.begin(),
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PredValues.end());
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PHINode *SomePHI;
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for (BasicBlock::iterator It = BB->begin();
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(SomePHI = dyn_cast<PHINode>(It)); ++It) {
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if (IsEquivalentPHI(SomePHI, ValueMapping))
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return SomePHI;
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}
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}
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// Ok, we have no way out, insert a new one now.
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PHINode *InsertedPHI = PHINode::Create(PrototypeValue->getType(),
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PrototypeValue->getName(),
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&BB->front());
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InsertedPHI->reserveOperandSpace(PredValues.size());
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// Fill in all the predecessors of the PHI.
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for (unsigned i = 0, e = PredValues.size(); i != e; ++i)
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InsertedPHI->addIncoming(PredValues[i].second, PredValues[i].first);
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// See if the PHI node can be merged to a single value. This can happen in
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// loop cases when we get a PHI of itself and one other value.
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if (Value *ConstVal = InsertedPHI->hasConstantValue()) {
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InsertedPHI->eraseFromParent();
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return ConstVal;
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}
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// If the client wants to know about all new instructions, tell it.
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if (InsertedPHIs) InsertedPHIs->push_back(InsertedPHI);
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DEBUG(dbgs() << " Inserted PHI: " << *InsertedPHI << "\n");
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return InsertedPHI;
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}
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/// RewriteUse - Rewrite a use of the symbolic value. This handles PHI nodes,
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/// which use their value in the corresponding predecessor.
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void SSAUpdater::RewriteUse(Use &U) {
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Instruction *User = cast<Instruction>(U.getUser());
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Value *V;
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if (PHINode *UserPN = dyn_cast<PHINode>(User))
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V = GetValueAtEndOfBlock(UserPN->getIncomingBlock(U));
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else
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V = GetValueInMiddleOfBlock(User->getParent());
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U.set(V);
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}
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/// PHIiter - Iterator for PHI operands. This is used for the PHI_iterator
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/// in the SSAUpdaterImpl template.
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namespace {
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class PHIiter {
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private:
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PHINode *PHI;
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unsigned idx;
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public:
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explicit PHIiter(PHINode *P) // begin iterator
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: PHI(P), idx(0) {}
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PHIiter(PHINode *P, bool) // end iterator
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: PHI(P), idx(PHI->getNumIncomingValues()) {}
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PHIiter &operator++() { ++idx; return *this; }
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bool operator==(const PHIiter& x) const { return idx == x.idx; }
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bool operator!=(const PHIiter& x) const { return !operator==(x); }
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Value *getIncomingValue() { return PHI->getIncomingValue(idx); }
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BasicBlock *getIncomingBlock() { return PHI->getIncomingBlock(idx); }
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};
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}
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/// SSAUpdaterTraits<SSAUpdater> - Traits for the SSAUpdaterImpl template,
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/// specialized for SSAUpdater.
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namespace llvm {
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template<>
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class SSAUpdaterTraits<SSAUpdater> {
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public:
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typedef BasicBlock BlkT;
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typedef Value *ValT;
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typedef PHINode PhiT;
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typedef succ_iterator BlkSucc_iterator;
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static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
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static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
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typedef PHIiter PHI_iterator;
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static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
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static inline PHI_iterator PHI_end(PhiT *PHI) {
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return PHI_iterator(PHI, true);
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}
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/// FindPredecessorBlocks - Put the predecessors of Info->BB into the Preds
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/// vector, set Info->NumPreds, and allocate space in Info->Preds.
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static void FindPredecessorBlocks(BasicBlock *BB,
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SmallVectorImpl<BasicBlock*> *Preds) {
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// We can get our predecessor info by walking the pred_iterator list,
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// but it is relatively slow. If we already have PHI nodes in this
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// block, walk one of them to get the predecessor list instead.
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if (PHINode *SomePhi = dyn_cast<PHINode>(BB->begin())) {
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for (unsigned PI = 0, E = SomePhi->getNumIncomingValues(); PI != E; ++PI)
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Preds->push_back(SomePhi->getIncomingBlock(PI));
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} else {
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for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
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Preds->push_back(*PI);
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}
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}
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/// GetUndefVal - Get an undefined value of the same type as the value
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/// being handled.
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static Value *GetUndefVal(BasicBlock *BB, SSAUpdater *Updater) {
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return UndefValue::get(Updater->PrototypeValue->getType());
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}
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/// CreateEmptyPHI - Create a new PHI instruction in the specified block.
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/// Reserve space for the operands but do not fill them in yet.
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static Value *CreateEmptyPHI(BasicBlock *BB, unsigned NumPreds,
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SSAUpdater *Updater) {
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PHINode *PHI = PHINode::Create(Updater->PrototypeValue->getType(),
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Updater->PrototypeValue->getName(),
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&BB->front());
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PHI->reserveOperandSpace(NumPreds);
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return PHI;
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}
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/// AddPHIOperand - Add the specified value as an operand of the PHI for
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/// the specified predecessor block.
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static void AddPHIOperand(PHINode *PHI, Value *Val, BasicBlock *Pred) {
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PHI->addIncoming(Val, Pred);
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}
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/// InstrIsPHI - Check if an instruction is a PHI.
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///
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static PHINode *InstrIsPHI(Instruction *I) {
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return dyn_cast<PHINode>(I);
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}
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/// ValueIsPHI - Check if a value is a PHI.
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///
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static PHINode *ValueIsPHI(Value *Val, SSAUpdater *Updater) {
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return dyn_cast<PHINode>(Val);
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}
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/// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
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/// operands, i.e., it was just added.
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static PHINode *ValueIsNewPHI(Value *Val, SSAUpdater *Updater) {
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PHINode *PHI = ValueIsPHI(Val, Updater);
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if (PHI && PHI->getNumIncomingValues() == 0)
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return PHI;
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return 0;
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}
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/// GetPHIValue - For the specified PHI instruction, return the value
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/// that it defines.
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static Value *GetPHIValue(PHINode *PHI) {
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return PHI;
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}
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};
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} // End llvm namespace
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/// GetValueAtEndOfBlockInternal - Check to see if AvailableVals has an entry
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/// for the specified BB and if so, return it. If not, construct SSA form by
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/// first calculating the required placement of PHIs and then inserting new
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/// PHIs where needed.
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Value *SSAUpdater::GetValueAtEndOfBlockInternal(BasicBlock *BB) {
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AvailableValsTy &AvailableVals = getAvailableVals(AV);
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if (Value *V = AvailableVals[BB])
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return V;
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SSAUpdaterImpl<SSAUpdater> Impl(this, &AvailableVals, InsertedPHIs);
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return Impl.GetValue(BB);
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}
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