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Rewrite LoopRotation's SSA updating code using SSAUpdater.
llvm-svn: 85016
This commit is contained in:
Dan Gohman
parent
e66bb298d4
commit
477456910a
@ -21,6 +21,7 @@
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/SSAUpdater.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/ADT/Statistic.h"
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@ -32,16 +33,6 @@ using namespace llvm;
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STATISTIC(NumRotated, "Number of loops rotated");
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namespace {
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class RenameData {
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public:
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RenameData(Instruction *O, Value *P, Instruction *H)
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: Original(O), PreHeader(P), Header(H) { }
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public:
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Instruction *Original; // Original instruction
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Value *PreHeader; // Original pre-header replacement
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Instruction *Header; // New header replacement
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};
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class LoopRotate : public LoopPass {
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public:
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static char ID; // Pass ID, replacement for typeid
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@ -71,25 +62,12 @@ namespace {
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/// Initialize local data
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void initialize();
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/// Make sure all Exit block PHINodes have required incoming values.
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/// If incoming value is constant or defined outside the loop then
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/// PHINode may not have an entry for original pre-header.
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void updateExitBlock();
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/// Return true if this instruction is used outside original header.
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bool usedOutsideOriginalHeader(Instruction *In);
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/// Find Replacement information for instruction. Return NULL if it is
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/// not available.
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const RenameData *findReplacementData(Instruction *I);
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/// After loop rotation, loop pre-header has multiple sucessors.
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/// Insert one forwarding basic block to ensure that loop pre-header
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/// has only one successor.
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void preserveCanonicalLoopForm(LPPassManager &LPM);
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private:
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Loop *L;
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BasicBlock *OrigHeader;
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BasicBlock *OrigPreHeader;
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@ -97,7 +75,6 @@ namespace {
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BasicBlock *NewHeader;
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BasicBlock *Exit;
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LPPassManager *LPM_Ptr;
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SmallVector<RenameData, MAX_HEADER_SIZE> LoopHeaderInfo;
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};
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}
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@ -199,168 +176,88 @@ bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) {
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"New header doesn't have one pred!");
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FoldSingleEntryPHINodes(NewHeader);
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// Copy PHI nodes and other instructions from the original header
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// into the original pre-header. Unlike the original header, the original
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// pre-header is not a member of the loop.
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//
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// The new loop header is the one and only successor of original header that
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// is inside the loop. All other original header successors are outside
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// the loop. Copy PHI Nodes from the original header into the new loop header.
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// Add second incoming value, from original loop pre-header into these phi
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// nodes. If a value defined in original header is used outside original
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// header then new loop header will need new phi nodes with two incoming
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// values, one definition from original header and second definition is
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// from original loop pre-header.
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// Remove terminator from Original pre-header. Original pre-header will
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// receive a clone of original header terminator as a new terminator.
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OrigPreHeader->getInstList().pop_back();
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// Begin by walking OrigHeader and populating ValueMap with an entry for
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// each Instruction.
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BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
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PHINode *PN = 0;
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for (; (PN = dyn_cast<PHINode>(I)); ++I) {
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// PHI nodes are not copied into original pre-header. Instead their values
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// are directly propagated.
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Value *NPV = PN->getIncomingValueForBlock(OrigPreHeader);
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DenseMap<const Value *, Value *> ValueMap;
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// Create a new PHI node with two incoming values for NewHeader.
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// One incoming value is from OrigLatch (through OrigHeader) and the
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// second incoming value is from original pre-header.
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PHINode *NH = PHINode::Create(PN->getType(), PN->getName(),
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NewHeader->begin());
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NH->addIncoming(PN->getIncomingValueForBlock(OrigLatch), OrigHeader);
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NH->addIncoming(NPV, OrigPreHeader);
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// For PHI nodes, the value available in OldPreHeader is just the
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// incoming value from OldPreHeader.
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for (; PHINode *PN = dyn_cast<PHINode>(I); ++I)
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ValueMap[PN] = PN->getIncomingValue(PN->getBasicBlockIndex(OrigPreHeader));
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// "In" can be replaced by NH at various places.
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LoopHeaderInfo.push_back(RenameData(PN, NPV, NH));
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}
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// Now, handle non-phi instructions.
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// For the rest of the instructions, create a clone in the OldPreHeader.
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TerminatorInst *LoopEntryBranch = OrigPreHeader->getTerminator();
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for (; I != E; ++I) {
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Instruction *In = I;
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assert(!isa<PHINode>(In) && "PHINode is not expected here");
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// This is not a PHI instruction. Insert its clone into original pre-header.
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// If this instruction is using a value from same basic block then
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// update it to use value from cloned instruction.
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Instruction *C = In->clone();
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C->setName(In->getName());
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OrigPreHeader->getInstList().push_back(C);
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for (unsigned opi = 0, e = In->getNumOperands(); opi != e; ++opi) {
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Instruction *OpInsn = dyn_cast<Instruction>(In->getOperand(opi));
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if (!OpInsn) continue; // Ignore non-instruction values.
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if (const RenameData *D = findReplacementData(OpInsn))
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C->setOperand(opi, D->PreHeader);
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Instruction *C = I->clone();
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C->setName(I->getName());
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C->insertBefore(LoopEntryBranch);
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ValueMap[I] = C;
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}
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// If this instruction is used outside this basic block then
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// create new PHINode for this instruction.
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Instruction *NewHeaderReplacement = NULL;
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if (usedOutsideOriginalHeader(In)) {
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PHINode *PN = PHINode::Create(In->getType(), In->getName(),
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NewHeader->begin());
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PN->addIncoming(In, OrigHeader);
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PN->addIncoming(C, OrigPreHeader);
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NewHeaderReplacement = PN;
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}
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LoopHeaderInfo.push_back(RenameData(In, C, NewHeaderReplacement));
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}
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// Along with all the other instructions, we just cloned OrigHeader's
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// terminator into OrigPreHeader. Fix up the PHI nodes in each of OrigHeader's
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// successors by duplicating their incoming values for OrigHeader.
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TerminatorInst *TI = OrigHeader->getTerminator();
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for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
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for (BasicBlock::iterator BI = TI->getSuccessor(i)->begin();
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PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
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PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreHeader);
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// Rename uses of original header instructions to reflect their new
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// definitions (either from original pre-header node or from newly created
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// new header PHINodes.
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//
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// Original header instructions are used in
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// 1) Original header:
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//
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// If instruction is used in non-phi instructions then it is using
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// defintion from original heder iteself. Do not replace this use
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// with definition from new header or original pre-header.
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//
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// If instruction is used in phi node then it is an incoming
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// value. Rename its use to reflect new definition from new-preheader
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// or new header.
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//
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// 2) Inside loop but not in original header
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//
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// Replace this use to reflect definition from new header.
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for (unsigned LHI = 0, LHI_E = LoopHeaderInfo.size(); LHI != LHI_E; ++LHI) {
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const RenameData &ILoopHeaderInfo = LoopHeaderInfo[LHI];
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// Now that OrigPreHeader has a clone of OrigHeader's terminator, remove
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// OrigPreHeader's old terminator (the original branch into the loop), and
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// remove the corresponding incoming values from the PHI nodes in OrigHeader.
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LoopEntryBranch->eraseFromParent();
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for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I)
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PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreHeader));
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if (!ILoopHeaderInfo.Header)
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// Now fix up users of the instructions in OrigHeader, insertting PHI nodes
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// as necessary.
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SSAUpdater SSA;
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for (I = OrigHeader->begin(); I != E; ++I) {
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Value *OrigHeaderVal = I;
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Value *OrigPreHeaderVal = ValueMap[OrigHeaderVal];
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// The value now exits in two versions: the initial value in the preheader
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// and the loop "next" value in the original header.
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SSA.Initialize(OrigHeaderVal);
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SSA.AddAvailableValue(OrigHeader, OrigHeaderVal);
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SSA.AddAvailableValue(OrigPreHeader, OrigPreHeaderVal);
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// Visit each use of the OrigHeader instruction.
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for (Value::use_iterator UI = OrigHeaderVal->use_begin(),
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UE = OrigHeaderVal->use_end(); UI != UE; ) {
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// Grab the use before incrementing the iterator.
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Use &U = UI.getUse();
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// Increment the iterator before removing the use from the list.
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++UI;
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// SSAUpdater can't handle a non-PHI use in the same block as an
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// earlier def. We can easily handle those cases manually.
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Instruction *UserInst = cast<Instruction>(U.getUser());
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if (!isa<PHINode>(UserInst)) {
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BasicBlock *UserBB = UserInst->getParent();
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// The original users in the OrigHeader are already using the
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// original definitions.
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if (UserBB == OrigHeader)
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continue;
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Instruction *OldPhi = ILoopHeaderInfo.Original;
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Instruction *NewPhi = ILoopHeaderInfo.Header;
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// Before replacing uses, collect them first, so that iterator is
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// not invalidated.
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SmallVector<Instruction *, 16> AllUses;
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for (Value::use_iterator UI = OldPhi->use_begin(), UE = OldPhi->use_end();
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UI != UE; ++UI)
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AllUses.push_back(cast<Instruction>(UI));
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for (SmallVector<Instruction *, 16>::iterator UI = AllUses.begin(),
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UE = AllUses.end(); UI != UE; ++UI) {
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Instruction *U = *UI;
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BasicBlock *Parent = U->getParent();
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// Used inside original header
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if (Parent == OrigHeader) {
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// Do not rename uses inside original header non-phi instructions.
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PHINode *PU = dyn_cast<PHINode>(U);
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if (!PU)
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continue;
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// Do not rename uses inside original header phi nodes, if the
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// incoming value is for new header.
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if (PU->getBasicBlockIndex(NewHeader) != -1
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&& PU->getIncomingValueForBlock(NewHeader) == U)
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continue;
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U->replaceUsesOfWith(OldPhi, NewPhi);
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// Users in the OrigPreHeader need to use the value to which the
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// original definitions are mapped.
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if (UserBB == OrigPreHeader) {
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U = OrigPreHeaderVal;
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continue;
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}
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// Used inside loop, but not in original header.
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if (L->contains(U->getParent())) {
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if (U != NewPhi)
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U->replaceUsesOfWith(OldPhi, NewPhi);
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continue;
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}
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// Used inside Exit Block. Since we are in LCSSA form, U must be PHINode.
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if (U->getParent() == Exit) {
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assert(isa<PHINode>(U) && "Use in Exit Block that is not PHINode");
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PHINode *UPhi = cast<PHINode>(U);
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// UPhi already has one incoming argument from original header.
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// Add second incoming argument from new Pre header.
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UPhi->addIncoming(ILoopHeaderInfo.PreHeader, OrigPreHeader);
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} else {
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// Used outside Exit block. Create a new PHI node in the exit block
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// to receive the value from the new header and pre-header.
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PHINode *PN = PHINode::Create(U->getType(), U->getName(),
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Exit->begin());
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PN->addIncoming(ILoopHeaderInfo.PreHeader, OrigPreHeader);
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PN->addIncoming(OldPhi, OrigHeader);
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U->replaceUsesOfWith(OldPhi, PN);
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}
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// Anything else can be handled by SSAUpdater.
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SSA.RewriteUse(U);
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}
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}
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/// Make sure all Exit block PHINodes have required incoming values.
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updateExitBlock();
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// Update CFG
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// Removing incoming branch from loop preheader to original header.
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// Now original header is inside the loop.
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for (BasicBlock::iterator I = OrigHeader->begin();
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(PN = dyn_cast<PHINode>(I)); ++I)
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PN->removeIncomingValue(OrigPreHeader);
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// Make NewHeader as the new header for the loop.
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// NewHeader is now the header of the loop.
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L->moveToHeader(NewHeader);
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preserveCanonicalLoopForm(LPM);
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@ -369,31 +266,6 @@ bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) {
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return true;
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}
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/// Make sure all Exit block PHINodes have required incoming values.
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/// If an incoming value is constant or defined outside the loop then
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/// PHINode may not have an entry for the original pre-header.
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void LoopRotate::updateExitBlock() {
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PHINode *PN;
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for (BasicBlock::iterator I = Exit->begin();
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(PN = dyn_cast<PHINode>(I)); ++I) {
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// There is already one incoming value from original pre-header block.
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if (PN->getBasicBlockIndex(OrigPreHeader) != -1)
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continue;
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const RenameData *ILoopHeaderInfo;
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Value *V = PN->getIncomingValueForBlock(OrigHeader);
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if (isa<Instruction>(V) &&
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(ILoopHeaderInfo = findReplacementData(cast<Instruction>(V)))) {
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assert(ILoopHeaderInfo->PreHeader && "Missing New Preheader Instruction");
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PN->addIncoming(ILoopHeaderInfo->PreHeader, OrigPreHeader);
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} else {
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PN->addIncoming(V, OrigPreHeader);
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}
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}
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}
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/// Initialize local data
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void LoopRotate::initialize() {
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L = NULL;
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@ -401,34 +273,6 @@ void LoopRotate::initialize() {
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OrigPreHeader = NULL;
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NewHeader = NULL;
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Exit = NULL;
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LoopHeaderInfo.clear();
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}
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/// Return true if this instruction is used by any instructions in the loop that
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/// aren't in original header.
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bool LoopRotate::usedOutsideOriginalHeader(Instruction *In) {
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for (Value::use_iterator UI = In->use_begin(), UE = In->use_end();
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UI != UE; ++UI) {
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BasicBlock *UserBB = cast<Instruction>(UI)->getParent();
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if (UserBB != OrigHeader && L->contains(UserBB))
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return true;
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}
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return false;
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}
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/// Find Replacement information for instruction. Return NULL if it is
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/// not available.
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const RenameData *LoopRotate::findReplacementData(Instruction *In) {
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// Since LoopHeaderInfo is small, linear walk is OK.
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for (unsigned LHI = 0, LHI_E = LoopHeaderInfo.size(); LHI != LHI_E; ++LHI) {
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const RenameData &ILoopHeaderInfo = LoopHeaderInfo[LHI];
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if (ILoopHeaderInfo.Original == In)
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return &ILoopHeaderInfo;
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}
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return NULL;
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}
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/// After loop rotation, loop pre-header has multiple sucessors.
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