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https://github.com/c64scene-ar/llvm-6502.git
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b1dbcd886a
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51143 91177308-0d34-0410-b5e6-96231b3b80d8
607 lines
21 KiB
C++
607 lines
21 KiB
C++
//===- LoopRotation.cpp - Loop Rotation Pass ------------------------------===//
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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 Loop Rotation Pass.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "loop-rotate"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Function.h"
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#include "llvm/Instructions.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/Dominators.h"
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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/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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#include "llvm/ADT/SmallVector.h"
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using namespace llvm;
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#define MAX_HEADER_SIZE 16
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STATISTIC(NumRotated, "Number of loops rotated");
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namespace {
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class VISIBILITY_HIDDEN 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 VISIBILITY_HIDDEN LoopRotate : public LoopPass {
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public:
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static char ID; // Pass ID, replacement for typeid
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LoopRotate() : LoopPass((intptr_t)&ID) {}
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// Rotate Loop L as many times as possible. Return true if
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// loop is rotated at least once.
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bool runOnLoop(Loop *L, LPPassManager &LPM);
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// LCSSA form makes instruction renaming easier.
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequiredID(LoopSimplifyID);
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AU.addPreservedID(LoopSimplifyID);
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AU.addRequiredID(LCSSAID);
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AU.addPreservedID(LCSSAID);
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AU.addPreserved<ScalarEvolution>();
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AU.addPreserved<LoopInfo>();
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AU.addPreserved<DominatorTree>();
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AU.addPreserved<DominanceFrontier>();
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}
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// Helper functions
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/// Do actual work
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bool rotateLoop(Loop *L, LPPassManager &LPM);
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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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BasicBlock *OrigLatch;
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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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char LoopRotate::ID = 0;
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static RegisterPass<LoopRotate> X("loop-rotate", "Rotate Loops");
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LoopPass *llvm::createLoopRotatePass() { return new LoopRotate(); }
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/// Rotate Loop L as many times as possible. Return true if
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/// loop is rotated at least once.
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bool LoopRotate::runOnLoop(Loop *Lp, LPPassManager &LPM) {
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bool RotatedOneLoop = false;
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initialize();
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LPM_Ptr = &LPM;
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// One loop can be rotated multiple times.
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while (rotateLoop(Lp,LPM)) {
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RotatedOneLoop = true;
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initialize();
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}
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return RotatedOneLoop;
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}
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/// Rotate loop LP. Return true if the loop is rotated.
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bool LoopRotate::rotateLoop(Loop *Lp, LPPassManager &LPM) {
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L = Lp;
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OrigHeader = L->getHeader();
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OrigPreHeader = L->getLoopPreheader();
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OrigLatch = L->getLoopLatch();
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// If loop has only one block then there is not much to rotate.
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if (L->getBlocks().size() == 1)
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return false;
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assert (OrigHeader && OrigLatch && OrigPreHeader &&
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"Loop is not in canonical form");
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// If loop header is not one of the loop exit block then
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// either this loop is already rotated or it is not
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// suitable for loop rotation transformations.
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if (!L->isLoopExit(OrigHeader))
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return false;
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BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
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if (!BI)
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return false;
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assert (BI->isConditional() && "Branch Instruction is not conditional");
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// Updating PHInodes in loops with multiple exits adds complexity.
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// Keep it simple, and restrict loop rotation to loops with one exit only.
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// In future, lift this restriction and support for multiple exits if
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// required.
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SmallVector<BasicBlock*, 8> ExitBlocks;
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L->getExitBlocks(ExitBlocks);
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if (ExitBlocks.size() > 1)
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return false;
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// Check size of original header and reject
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// loop if it is very big.
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if (OrigHeader->getInstList().size() > MAX_HEADER_SIZE)
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return false;
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// Now, this loop is suitable for rotation.
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// Find new Loop header. NewHeader is a Header's one and only successor
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// that is inside loop. Header's other successor is out side the
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// loop. Otherwise loop is not suitable for rotation.
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Exit = BI->getSuccessor(0);
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NewHeader = BI->getSuccessor(1);
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if (L->contains(Exit))
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std::swap(Exit, NewHeader);
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assert (NewHeader && "Unable to determine new loop header");
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assert(L->contains(NewHeader) && !L->contains(Exit) &&
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"Unable to determine loop header and exit blocks");
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// Copy PHI nodes and other instructions from original header
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// into original pre-header. Unlike original header, original pre-header is
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// not a member of loop.
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//
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// New loop header is 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 original header into 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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BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
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PHINode *PN = NULL;
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for (; (PN = dyn_cast<PHINode>(I)); ++I) {
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Instruction *In = 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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// Create new PHI node with two incoming values for NewHeader.
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// One incoming value is from OrigLatch (through OrigHeader) and
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// second incoming value is from original pre-header.
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PHINode *NH = PHINode::Create(In->getType(), In->getName());
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NH->addIncoming(PN->getIncomingValueForBlock(OrigLatch), OrigHeader);
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NH->addIncoming(NPV, OrigPreHeader);
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NewHeader->getInstList().push_front(NH);
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// "In" can be replaced by NH at various places.
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LoopHeaderInfo.push_back(RenameData(In, NPV, NH));
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}
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// Now, handle non-phi instructions.
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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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if (Instruction *OpPhi = dyn_cast<PHINode>(In->getOperand(opi))) {
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if (const RenameData *D = findReplacementData(OpPhi)) {
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// This is using values from original header PHI node.
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// Here, directly used incoming value from original pre-header.
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C->setOperand(opi, D->PreHeader);
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}
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}
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else if (Instruction *OpInsn =
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dyn_cast<Instruction>(In->getOperand(opi))) {
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if (const RenameData *D = findReplacementData(OpInsn))
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C->setOperand(opi, D->PreHeader);
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}
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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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// FIXME: remove this when we have first-class aggregates.
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if (isa<StructType>(In->getType())) {
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// Can't create PHI nodes for this type. If there are any getResults
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// not defined in this block, move them back to this block. PHI
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// nodes will be created for all getResults later.
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BasicBlock::iterator InsertPoint;
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if (InvokeInst *II = dyn_cast<InvokeInst>(In)) {
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InsertPoint = II->getNormalDest()->begin();
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while (isa<PHINode>(InsertPoint))
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++InsertPoint;
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} else {
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InsertPoint = I; // call
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++InsertPoint;
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}
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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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GetResultInst *InGR = cast<GetResultInst>(UI);
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if (InGR->getParent() != OrigHeader) {
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// Move InGR to immediately after the call or in the normal dest of
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// the invoke. It will be picked up, cloned and PHI'd on the next
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// iteration.
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InGR->moveBefore(InsertPoint);
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}
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}
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} else {
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PHINode *PN = PHINode::Create(In->getType(), In->getName());
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PN->addIncoming(In, OrigHeader);
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PN->addIncoming(C, OrigPreHeader);
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NewHeader->getInstList().push_front(PN);
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NewHeaderReplacement = PN;
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}
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}
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LoopHeaderInfo.push_back(RenameData(In, C, NewHeaderReplacement));
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}
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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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if (!ILoopHeaderInfo.Header)
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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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Instruction *U = cast<Instruction>(UI);
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AllUses.push_back(U);
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}
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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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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 from exit block
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// to receive value from ne new header ane pre header.
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PHINode *PN = PHINode::Create(U->getType(), U->getName());
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PN->addIncoming(ILoopHeaderInfo.PreHeader, OrigPreHeader);
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PN->addIncoming(OldPhi, OrigHeader);
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Exit->getInstList().push_front(PN);
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U->replaceUsesOfWith(OldPhi, PN);
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}
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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(), E = OrigHeader->end();
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I != E; ++I) {
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Instruction *In = I;
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PHINode *PN = dyn_cast<PHINode>(In);
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if (!PN)
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break;
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PN->removeIncomingValue(OrigPreHeader);
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}
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// Make NewHeader as the new header for the loop.
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L->moveToHeader(NewHeader);
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preserveCanonicalLoopForm(LPM);
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NumRotated++;
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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 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 LoopRotate::updateExitBlock() {
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for (BasicBlock::iterator I = Exit->begin(), E = Exit->end();
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I != E; ++I) {
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PHINode *PN = dyn_cast<PHINode>(I);
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if (!PN)
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break;
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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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OrigHeader = NULL;
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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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Instruction *U = cast<Instruction>(UI);
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if (U->getParent() != OrigHeader) {
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if (L->contains(U->getParent()))
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return true;
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}
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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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/// Insert one forwarding basic block to ensure that loop pre-header
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/// has only one successor.
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void LoopRotate::preserveCanonicalLoopForm(LPPassManager &LPM) {
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// Right now original pre-header has two successors, new header and
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// exit block. Insert new block between original pre-header and
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// new header such that loop's new pre-header has only one successor.
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BasicBlock *NewPreHeader = BasicBlock::Create("bb.nph",
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OrigHeader->getParent(),
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NewHeader);
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LoopInfo &LI = LPM.getAnalysis<LoopInfo>();
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if (Loop *PL = LI.getLoopFor(OrigPreHeader))
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PL->addBasicBlockToLoop(NewPreHeader, LI.getBase());
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BranchInst::Create(NewHeader, NewPreHeader);
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BranchInst *OrigPH_BI = cast<BranchInst>(OrigPreHeader->getTerminator());
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if (OrigPH_BI->getSuccessor(0) == NewHeader)
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OrigPH_BI->setSuccessor(0, NewPreHeader);
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else {
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assert (OrigPH_BI->getSuccessor(1) == NewHeader &&
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"Unexpected original pre-header terminator");
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OrigPH_BI->setSuccessor(1, NewPreHeader);
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}
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for (BasicBlock::iterator I = NewHeader->begin(), E = NewHeader->end();
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I != E; ++I) {
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Instruction *In = I;
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PHINode *PN = dyn_cast<PHINode>(In);
|
|
if (!PN)
|
|
break;
|
|
|
|
int index = PN->getBasicBlockIndex(OrigPreHeader);
|
|
assert (index != -1 && "Expected incoming value from Original PreHeader");
|
|
PN->setIncomingBlock(index, NewPreHeader);
|
|
assert (PN->getBasicBlockIndex(OrigPreHeader) == -1 &&
|
|
"Expected only one incoming value from Original PreHeader");
|
|
}
|
|
|
|
if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) {
|
|
DT->addNewBlock(NewPreHeader, OrigPreHeader);
|
|
DT->changeImmediateDominator(L->getHeader(), NewPreHeader);
|
|
DT->changeImmediateDominator(Exit, OrigPreHeader);
|
|
for (Loop::block_iterator BI = L->block_begin(), BE = L->block_end();
|
|
BI != BE; ++BI) {
|
|
BasicBlock *B = *BI;
|
|
if (L->getHeader() != B) {
|
|
DomTreeNode *Node = DT->getNode(B);
|
|
if (Node && Node->getBlock() == OrigHeader)
|
|
DT->changeImmediateDominator(*BI, L->getHeader());
|
|
}
|
|
}
|
|
DT->changeImmediateDominator(OrigHeader, OrigLatch);
|
|
}
|
|
|
|
if(DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {
|
|
|
|
// New Preheader's dominance frontier is Exit block.
|
|
DominanceFrontier::DomSetType NewPHSet;
|
|
NewPHSet.insert(Exit);
|
|
DF->addBasicBlock(NewPreHeader, NewPHSet);
|
|
|
|
// New Header's dominance frontier now includes itself and Exit block
|
|
DominanceFrontier::iterator HeadI = DF->find(L->getHeader());
|
|
if (HeadI != DF->end()) {
|
|
DominanceFrontier::DomSetType & HeaderSet = HeadI->second;
|
|
HeaderSet.clear();
|
|
HeaderSet.insert(L->getHeader());
|
|
HeaderSet.insert(Exit);
|
|
} else {
|
|
DominanceFrontier::DomSetType HeaderSet;
|
|
HeaderSet.insert(L->getHeader());
|
|
HeaderSet.insert(Exit);
|
|
DF->addBasicBlock(L->getHeader(), HeaderSet);
|
|
}
|
|
|
|
// Original header (new Loop Latch)'s dominance frontier is Exit.
|
|
DominanceFrontier::iterator LatchI = DF->find(L->getLoopLatch());
|
|
if (LatchI != DF->end()) {
|
|
DominanceFrontier::DomSetType &LatchSet = LatchI->second;
|
|
LatchSet = LatchI->second;
|
|
LatchSet.clear();
|
|
LatchSet.insert(Exit);
|
|
} else {
|
|
DominanceFrontier::DomSetType LatchSet;
|
|
LatchSet.insert(Exit);
|
|
DF->addBasicBlock(L->getHeader(), LatchSet);
|
|
}
|
|
|
|
// If a loop block dominates new loop latch then its frontier is
|
|
// new header and Exit.
|
|
BasicBlock *NewLatch = L->getLoopLatch();
|
|
DominatorTree *DT = getAnalysisToUpdate<DominatorTree>();
|
|
for (Loop::block_iterator BI = L->block_begin(), BE = L->block_end();
|
|
BI != BE; ++BI) {
|
|
BasicBlock *B = *BI;
|
|
if (DT->dominates(B, NewLatch)) {
|
|
DominanceFrontier::iterator BDFI = DF->find(B);
|
|
if (BDFI != DF->end()) {
|
|
DominanceFrontier::DomSetType &BSet = BDFI->second;
|
|
BSet = BDFI->second;
|
|
BSet.clear();
|
|
BSet.insert(L->getHeader());
|
|
BSet.insert(Exit);
|
|
} else {
|
|
DominanceFrontier::DomSetType BSet;
|
|
BSet.insert(L->getHeader());
|
|
BSet.insert(Exit);
|
|
DF->addBasicBlock(B, BSet);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Preserve canonical loop form, which means Exit block should
|
|
// have only one predecessor.
|
|
BasicBlock *NExit = SplitEdge(L->getLoopLatch(), Exit, this);
|
|
|
|
// Preserve LCSSA.
|
|
BasicBlock::iterator I = Exit->begin(), E = Exit->end();
|
|
PHINode *PN = NULL;
|
|
for (; (PN = dyn_cast<PHINode>(I)); ++I) {
|
|
PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName());
|
|
unsigned N = PN->getNumIncomingValues();
|
|
for (unsigned index = 0; index < N; ++index)
|
|
if (PN->getIncomingBlock(index) == NExit) {
|
|
NewPN->addIncoming(PN->getIncomingValue(index), L->getLoopLatch());
|
|
PN->setIncomingValue(index, NewPN);
|
|
PN->setIncomingBlock(index, NExit);
|
|
NExit->getInstList().push_front(NewPN);
|
|
}
|
|
}
|
|
|
|
assert (NewHeader && L->getHeader() == NewHeader
|
|
&& "Invalid loop header after loop rotation");
|
|
assert (NewPreHeader && L->getLoopPreheader() == NewPreHeader
|
|
&& "Invalid loop preheader after loop rotation");
|
|
assert (L->getLoopLatch()
|
|
&& "Invalid loop latch after loop rotation");
|
|
|
|
}
|