mirror of
https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100148 91177308-0d34-0410-b5e6-96231b3b80d8
520 lines
18 KiB
C++
520 lines
18 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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#include "llvm/Transforms/Utils/SSAUpdater.h"
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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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using namespace llvm;
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/// BBInfo - Per-basic block information used internally by SSAUpdater.
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/// The predecessors of each block are cached here since pred_iterator is
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/// slow and we need to iterate over the blocks at least a few times.
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class SSAUpdater::BBInfo {
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public:
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Value *AvailableVal; // Value to use in this block.
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BasicBlock *DefBB; // Block that defines the available value.
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unsigned NumPreds; // Number of predecessor blocks.
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BasicBlock **Preds; // Array[NumPreds] of predecessor blocks.
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unsigned Counter; // Marker to identify blocks already visited.
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PHINode *PHITag; // Marker for existing PHIs that match.
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BBInfo(BasicBlock *BB, Value *V, BumpPtrAllocator *Allocator);
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};
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typedef DenseMap<BasicBlock*, SSAUpdater::BBInfo*> BBMapTy;
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SSAUpdater::BBInfo::BBInfo(BasicBlock *BB, Value *V,
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BumpPtrAllocator *Allocator)
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: AvailableVal(V), DefBB(0), NumPreds(0), Preds(0), Counter(0), PHITag(0) {
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// If this block has a known value, don't bother finding its predecessors.
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if (V) {
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DefBB = BB;
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return;
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}
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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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NumPreds = SomePhi->getNumIncomingValues();
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Preds = static_cast<BasicBlock**>
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(Allocator->Allocate(NumPreds * sizeof(BasicBlock*),
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AlignOf<BasicBlock*>::Alignment));
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for (unsigned pi = 0; pi != NumPreds; ++pi)
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Preds[pi] = SomePhi->getIncomingBlock(pi);
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return;
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}
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// Stash the predecessors in a temporary vector until we know how much space
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// to allocate for them.
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SmallVector<BasicBlock*, 10> TmpPreds;
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for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
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TmpPreds.push_back(*PI);
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++NumPreds;
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}
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Preds = static_cast<BasicBlock**>
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(Allocator->Allocate(NumPreds * sizeof(BasicBlock*),
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AlignOf<BasicBlock*>::Alignment));
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memcpy(Preds, TmpPreds.data(), NumPreds * sizeof(BasicBlock*));
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}
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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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static BBMapTy *getBBMap(void *BM) {
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return static_cast<BBMapTy*>(BM);
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}
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static BumpPtrAllocator *getAllocator(void *BPA) {
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return static_cast<BumpPtrAllocator*>(BPA);
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}
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SSAUpdater::SSAUpdater(SmallVectorImpl<PHINode*> *NewPHI)
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: AV(0), PrototypeValue(0), BM(0), BPA(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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assert(BM == 0 && BPA == 0 && "Unexpected Internal State");
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Value *Res = GetValueAtEndOfBlockInternal(BB);
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assert(BM == 0 && BPA == 0 && "Unexpected Internal State");
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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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/// 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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// Pool allocation used internally by GetValueAtEndOfBlock.
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BumpPtrAllocator AllocatorObj;
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BBMapTy BBMapObj;
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BPA = &AllocatorObj;
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BM = &BBMapObj;
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BBInfo *Info = new (AllocatorObj) BBInfo(BB, 0, &AllocatorObj);
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BBMapObj[BB] = Info;
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bool Changed;
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unsigned Counter = 1;
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do {
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Changed = false;
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FindPHIPlacement(BB, Info, Changed, Counter);
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++Counter;
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} while (Changed);
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FindAvailableVal(BB, Info, Counter);
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BPA = 0;
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BM = 0;
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return Info->AvailableVal;
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}
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/// FindPHIPlacement - Recursively visit the predecessors of a block to find
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/// the reaching definition for each predecessor and then determine whether
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/// a PHI is needed in this block.
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void SSAUpdater::FindPHIPlacement(BasicBlock *BB, BBInfo *Info, bool &Changed,
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unsigned Counter) {
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AvailableValsTy &AvailableVals = getAvailableVals(AV);
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BBMapTy *BBMap = getBBMap(BM);
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BumpPtrAllocator *Allocator = getAllocator(BPA);
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bool BBNeedsPHI = false;
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BasicBlock *SamePredDefBB = 0;
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// If there are no predecessors, then we must have found an unreachable
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// block. Treat it as a definition with 'undef'.
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if (Info->NumPreds == 0) {
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Info->AvailableVal = UndefValue::get(PrototypeValue->getType());
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Info->DefBB = BB;
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return;
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}
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Info->Counter = Counter;
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for (unsigned pi = 0; pi != Info->NumPreds; ++pi) {
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BasicBlock *Pred = Info->Preds[pi];
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BBMapTy::value_type &BBMapBucket = BBMap->FindAndConstruct(Pred);
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if (!BBMapBucket.second) {
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Value *PredVal = AvailableVals.lookup(Pred);
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BBMapBucket.second = new (*Allocator) BBInfo(Pred, PredVal, Allocator);
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}
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BBInfo *PredInfo = BBMapBucket.second;
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BasicBlock *DefBB = 0;
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if (!PredInfo->AvailableVal) {
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if (PredInfo->Counter != Counter)
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FindPHIPlacement(Pred, PredInfo, Changed, Counter);
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// Ignore back edges where the value is not yet known.
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if (!PredInfo->DefBB)
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continue;
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}
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DefBB = PredInfo->DefBB;
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if (!SamePredDefBB)
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SamePredDefBB = DefBB;
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else if (DefBB != SamePredDefBB)
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BBNeedsPHI = true;
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}
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BasicBlock *NewDefBB = (BBNeedsPHI ? BB : SamePredDefBB);
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if (Info->DefBB != NewDefBB) {
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Changed = true;
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Info->DefBB = NewDefBB;
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}
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}
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/// FindAvailableVal - If this block requires a PHI, first check if an existing
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/// PHI matches the PHI placement and reaching definitions computed earlier,
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/// and if not, create a new PHI. Visit all the block's predecessors to
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/// calculate the available value for each one and fill in the incoming values
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/// for a new PHI.
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void SSAUpdater::FindAvailableVal(BasicBlock *BB, BBInfo *Info,
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unsigned Counter) {
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if (Info->AvailableVal || Info->Counter == Counter)
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return;
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AvailableValsTy &AvailableVals = getAvailableVals(AV);
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BBMapTy *BBMap = getBBMap(BM);
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// Check if there needs to be a PHI in BB.
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PHINode *NewPHI = 0;
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if (Info->DefBB == BB) {
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// Look for an existing PHI.
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FindExistingPHI(BB);
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if (!Info->AvailableVal) {
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NewPHI = PHINode::Create(PrototypeValue->getType(),
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PrototypeValue->getName(), &BB->front());
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NewPHI->reserveOperandSpace(Info->NumPreds);
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Info->AvailableVal = NewPHI;
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AvailableVals[BB] = NewPHI;
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}
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}
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// Iterate through the block's predecessors.
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Info->Counter = Counter;
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for (unsigned pi = 0; pi != Info->NumPreds; ++pi) {
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BasicBlock *Pred = Info->Preds[pi];
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BBInfo *PredInfo = (*BBMap)[Pred];
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FindAvailableVal(Pred, PredInfo, Counter);
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if (NewPHI) {
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// Skip to the nearest preceding definition.
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if (PredInfo->DefBB != Pred)
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PredInfo = (*BBMap)[PredInfo->DefBB];
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NewPHI->addIncoming(PredInfo->AvailableVal, Pred);
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} else if (!Info->AvailableVal)
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Info->AvailableVal = PredInfo->AvailableVal;
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}
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if (NewPHI) {
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DEBUG(dbgs() << " Inserted PHI: " << *NewPHI << "\n");
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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(NewPHI);
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}
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}
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/// FindExistingPHI - Look through the PHI nodes in a block to see if any of
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/// them match what is needed.
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void SSAUpdater::FindExistingPHI(BasicBlock *BB) {
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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 (CheckIfPHIMatches(SomePHI)) {
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RecordMatchingPHI(SomePHI);
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break;
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}
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ClearPHITags(SomePHI);
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}
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}
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/// CheckIfPHIMatches - Check if a PHI node matches the placement and values
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/// in the BBMap.
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bool SSAUpdater::CheckIfPHIMatches(PHINode *PHI) {
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BBMapTy *BBMap = getBBMap(BM);
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SmallVector<PHINode*, 20> WorkList;
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WorkList.push_back(PHI);
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// Mark that the block containing this PHI has been visited.
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(*BBMap)[PHI->getParent()]->PHITag = PHI;
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while (!WorkList.empty()) {
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PHI = WorkList.pop_back_val();
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// Iterate through the PHI's incoming values.
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for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
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Value *IncomingVal = PHI->getIncomingValue(i);
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BasicBlock *Pred = PHI->getIncomingBlock(i);
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BBInfo *PredInfo = (*BBMap)[Pred];
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// Skip to the nearest preceding definition.
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if (PredInfo->DefBB != Pred) {
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Pred = PredInfo->DefBB;
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PredInfo = (*BBMap)[Pred];
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}
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// Check if it matches the expected value.
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if (PredInfo->AvailableVal) {
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if (IncomingVal == PredInfo->AvailableVal)
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continue;
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return false;
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}
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// Check if the value is a PHI in the correct block.
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PHINode *IncomingPHIVal = dyn_cast<PHINode>(IncomingVal);
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if (!IncomingPHIVal || IncomingPHIVal->getParent() != Pred)
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return false;
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// If this block has already been visited, check if this PHI matches.
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if (PredInfo->PHITag) {
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if (IncomingPHIVal == PredInfo->PHITag)
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continue;
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return false;
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}
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PredInfo->PHITag = IncomingPHIVal;
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WorkList.push_back(IncomingPHIVal);
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}
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}
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return true;
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}
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/// RecordMatchingPHI - For a PHI node that matches, record it and its input
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/// PHIs in both the BBMap and the AvailableVals mapping.
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void SSAUpdater::RecordMatchingPHI(PHINode *PHI) {
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BBMapTy *BBMap = getBBMap(BM);
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AvailableValsTy &AvailableVals = getAvailableVals(AV);
|
|
SmallVector<PHINode*, 20> WorkList;
|
|
WorkList.push_back(PHI);
|
|
|
|
while (!WorkList.empty()) {
|
|
PHI = WorkList.pop_back_val();
|
|
BasicBlock *BB = PHI->getParent();
|
|
BBInfo *Info = (*BBMap)[BB];
|
|
if (!Info || Info->AvailableVal)
|
|
return;
|
|
|
|
// Record the PHI.
|
|
AvailableVals[BB] = PHI;
|
|
Info->AvailableVal = PHI;
|
|
|
|
// Iterate through the PHI's incoming values.
|
|
for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
|
|
PHINode *IncomingVal = dyn_cast<PHINode>(PHI->getIncomingValue(i));
|
|
if (!IncomingVal) continue;
|
|
WorkList.push_back(IncomingVal);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// ClearPHITags - When one of the existing PHI nodes fails to match, clear
|
|
/// the PHITag values that were stored in the BBMap when checking to see if
|
|
/// it matched.
|
|
void SSAUpdater::ClearPHITags(PHINode *PHI) {
|
|
BBMapTy *BBMap = getBBMap(BM);
|
|
SmallVector<PHINode*, 20> WorkList;
|
|
WorkList.push_back(PHI);
|
|
|
|
while (!WorkList.empty()) {
|
|
PHI = WorkList.pop_back_val();
|
|
BasicBlock *BB = PHI->getParent();
|
|
BBInfo *Info = (*BBMap)[BB];
|
|
if (!Info || Info->AvailableVal || !Info->PHITag)
|
|
continue;
|
|
|
|
// Clear the tag.
|
|
Info->PHITag = 0;
|
|
|
|
// Iterate through the PHI's incoming values.
|
|
for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i) {
|
|
PHINode *IncomingVal = dyn_cast<PHINode>(PHI->getIncomingValue(i));
|
|
if (!IncomingVal) continue;
|
|
WorkList.push_back(IncomingVal);
|
|
}
|
|
}
|
|
}
|