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@220872 91177308-0d34-0410-b5e6-96231b3b80d8
604 lines
23 KiB
C++
604 lines
23 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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#include "llvm/Transforms/Scalar.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AssumptionTracker.h"
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#include "llvm/Analysis/CodeMetrics.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/IntrinsicInst.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/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/SSAUpdater.h"
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#include "llvm/Transforms/Utils/ValueMapper.h"
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using namespace llvm;
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#define DEBUG_TYPE "loop-rotate"
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static cl::opt<unsigned>
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DefaultRotationThreshold("rotation-max-header-size", cl::init(16), cl::Hidden,
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cl::desc("The default maximum header size for automatic loop rotation"));
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STATISTIC(NumRotated, "Number of loops rotated");
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namespace {
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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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LoopRotate(int SpecifiedMaxHeaderSize = -1) : LoopPass(ID) {
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initializeLoopRotatePass(*PassRegistry::getPassRegistry());
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if (SpecifiedMaxHeaderSize == -1)
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MaxHeaderSize = DefaultRotationThreshold;
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else
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MaxHeaderSize = unsigned(SpecifiedMaxHeaderSize);
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}
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// LCSSA form makes instruction renaming easier.
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<AssumptionTracker>();
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AU.addPreserved<DominatorTreeWrapperPass>();
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AU.addRequired<LoopInfo>();
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AU.addPreserved<LoopInfo>();
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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.addRequired<TargetTransformInfo>();
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}
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bool runOnLoop(Loop *L, LPPassManager &LPM) override;
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bool simplifyLoopLatch(Loop *L);
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bool rotateLoop(Loop *L, bool SimplifiedLatch);
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private:
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unsigned MaxHeaderSize;
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LoopInfo *LI;
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const TargetTransformInfo *TTI;
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AssumptionTracker *AT;
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};
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}
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char LoopRotate::ID = 0;
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INITIALIZE_PASS_BEGIN(LoopRotate, "loop-rotate", "Rotate Loops", false, false)
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INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)
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INITIALIZE_PASS_DEPENDENCY(AssumptionTracker)
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INITIALIZE_PASS_DEPENDENCY(LoopInfo)
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INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
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INITIALIZE_PASS_DEPENDENCY(LCSSA)
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INITIALIZE_PASS_END(LoopRotate, "loop-rotate", "Rotate Loops", false, false)
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Pass *llvm::createLoopRotatePass(int MaxHeaderSize) {
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return new LoopRotate(MaxHeaderSize);
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}
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/// Rotate Loop L as many times as possible. Return true if
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/// the loop is rotated at least once.
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bool LoopRotate::runOnLoop(Loop *L, LPPassManager &LPM) {
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if (skipOptnoneFunction(L))
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return false;
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// Save the loop metadata.
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MDNode *LoopMD = L->getLoopID();
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LI = &getAnalysis<LoopInfo>();
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TTI = &getAnalysis<TargetTransformInfo>();
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AT = &getAnalysis<AssumptionTracker>();
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// Simplify the loop latch before attempting to rotate the header
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// upward. Rotation may not be needed if the loop tail can be folded into the
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// loop exit.
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bool SimplifiedLatch = simplifyLoopLatch(L);
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// One loop can be rotated multiple times.
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bool MadeChange = false;
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while (rotateLoop(L, SimplifiedLatch)) {
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MadeChange = true;
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SimplifiedLatch = false;
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}
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// Restore the loop metadata.
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// NB! We presume LoopRotation DOESN'T ADD its own metadata.
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if ((MadeChange || SimplifiedLatch) && LoopMD)
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L->setLoopID(LoopMD);
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return MadeChange;
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}
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/// RewriteUsesOfClonedInstructions - We just cloned the instructions from the
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/// old header into the preheader. If there were uses of the values produced by
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/// these instruction that were outside of the loop, we have to insert PHI nodes
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/// to merge the two values. Do this now.
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static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
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BasicBlock *OrigPreheader,
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ValueToValueMapTy &ValueMap) {
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// Remove PHI node entries that are no longer live.
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BasicBlock::iterator I, E = OrigHeader->end();
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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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// Now fix up users of the instructions in OrigHeader, inserting 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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// If there are no uses of the value (e.g. because it returns void), there
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// is nothing to rewrite.
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if (OrigHeaderVal->use_empty())
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continue;
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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->getType(), OrigHeaderVal->getName());
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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;
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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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// 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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}
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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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}
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/// Determine whether the instructions in this range may be safely and cheaply
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/// speculated. This is not an important enough situation to develop complex
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/// heuristics. We handle a single arithmetic instruction along with any type
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/// conversions.
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static bool shouldSpeculateInstrs(BasicBlock::iterator Begin,
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BasicBlock::iterator End, Loop *L) {
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bool seenIncrement = false;
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bool MultiExitLoop = false;
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if (!L->getExitingBlock())
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MultiExitLoop = true;
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for (BasicBlock::iterator I = Begin; I != End; ++I) {
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if (!isSafeToSpeculativelyExecute(I))
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return false;
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if (isa<DbgInfoIntrinsic>(I))
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continue;
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switch (I->getOpcode()) {
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default:
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return false;
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case Instruction::GetElementPtr:
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// GEPs are cheap if all indices are constant.
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if (!cast<GEPOperator>(I)->hasAllConstantIndices())
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return false;
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// fall-thru to increment case
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case Instruction::Add:
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case Instruction::Sub:
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case Instruction::And:
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case Instruction::Or:
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case Instruction::Xor:
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case Instruction::Shl:
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case Instruction::LShr:
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case Instruction::AShr: {
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Value *IVOpnd = nullptr;
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if (isa<ConstantInt>(I->getOperand(0)))
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IVOpnd = I->getOperand(1);
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if (isa<ConstantInt>(I->getOperand(1))) {
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if (IVOpnd)
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return false;
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IVOpnd = I->getOperand(0);
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}
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// If increment operand is used outside of the loop, this speculation
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// could cause extra live range interference.
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if (MultiExitLoop && IVOpnd) {
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for (User *UseI : IVOpnd->users()) {
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auto *UserInst = cast<Instruction>(UseI);
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if (!L->contains(UserInst))
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return false;
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}
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}
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if (seenIncrement)
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return false;
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seenIncrement = true;
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break;
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}
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case Instruction::Trunc:
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case Instruction::ZExt:
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case Instruction::SExt:
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// ignore type conversions
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break;
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}
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}
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return true;
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}
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/// Fold the loop tail into the loop exit by speculating the loop tail
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/// instructions. Typically, this is a single post-increment. In the case of a
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/// simple 2-block loop, hoisting the increment can be much better than
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/// duplicating the entire loop header. In the case of loops with early exits,
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/// rotation will not work anyway, but simplifyLoopLatch will put the loop in
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/// canonical form so downstream passes can handle it.
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///
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/// I don't believe this invalidates SCEV.
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bool LoopRotate::simplifyLoopLatch(Loop *L) {
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BasicBlock *Latch = L->getLoopLatch();
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if (!Latch || Latch->hasAddressTaken())
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return false;
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BranchInst *Jmp = dyn_cast<BranchInst>(Latch->getTerminator());
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if (!Jmp || !Jmp->isUnconditional())
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return false;
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BasicBlock *LastExit = Latch->getSinglePredecessor();
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if (!LastExit || !L->isLoopExiting(LastExit))
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return false;
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BranchInst *BI = dyn_cast<BranchInst>(LastExit->getTerminator());
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if (!BI)
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return false;
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if (!shouldSpeculateInstrs(Latch->begin(), Jmp, L))
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return false;
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DEBUG(dbgs() << "Folding loop latch " << Latch->getName() << " into "
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<< LastExit->getName() << "\n");
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// Hoist the instructions from Latch into LastExit.
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LastExit->getInstList().splice(BI, Latch->getInstList(), Latch->begin(), Jmp);
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unsigned FallThruPath = BI->getSuccessor(0) == Latch ? 0 : 1;
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BasicBlock *Header = Jmp->getSuccessor(0);
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assert(Header == L->getHeader() && "expected a backward branch");
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// Remove Latch from the CFG so that LastExit becomes the new Latch.
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BI->setSuccessor(FallThruPath, Header);
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Latch->replaceSuccessorsPhiUsesWith(LastExit);
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Jmp->eraseFromParent();
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// Nuke the Latch block.
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assert(Latch->empty() && "unable to evacuate Latch");
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LI->removeBlock(Latch);
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if (DominatorTreeWrapperPass *DTWP =
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getAnalysisIfAvailable<DominatorTreeWrapperPass>())
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DTWP->getDomTree().eraseNode(Latch);
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Latch->eraseFromParent();
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return true;
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}
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/// Rotate loop LP. Return true if the loop is rotated.
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///
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/// \param SimplifiedLatch is true if the latch was just folded into the final
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/// loop exit. In this case we may want to rotate even though the new latch is
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/// now an exiting branch. This rotation would have happened had the latch not
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/// been simplified. However, if SimplifiedLatch is false, then we avoid
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/// rotating loops in which the latch exits to avoid excessive or endless
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/// rotation. LoopRotate should be repeatable and converge to a canonical
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/// form. This property is satisfied because simplifying the loop latch can only
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/// happen once across multiple invocations of the LoopRotate pass.
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bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
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// If the 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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BasicBlock *OrigHeader = L->getHeader();
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BasicBlock *OrigLatch = L->getLoopLatch();
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BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
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if (!BI || BI->isUnconditional())
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return false;
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// If the loop header is not one of the loop exiting blocks 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->isLoopExiting(OrigHeader))
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return false;
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// If the loop latch already contains a branch that leaves the loop then the
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// loop is already rotated.
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if (!OrigLatch)
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return false;
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// Rotate if either the loop latch does *not* exit the loop, or if the loop
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// latch was just simplified.
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if (L->isLoopExiting(OrigLatch) && !SimplifiedLatch)
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return false;
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// Check size of original header and reject loop if it is very big or we can't
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// duplicate blocks inside it.
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{
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SmallPtrSet<const Value *, 32> EphValues;
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CodeMetrics::collectEphemeralValues(L, AT, EphValues);
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CodeMetrics Metrics;
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Metrics.analyzeBasicBlock(OrigHeader, *TTI, EphValues);
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if (Metrics.notDuplicatable) {
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DEBUG(dbgs() << "LoopRotation: NOT rotating - contains non-duplicatable"
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<< " instructions: "; L->dump());
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return false;
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}
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if (Metrics.NumInsts > MaxHeaderSize)
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return false;
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}
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// Now, this loop is suitable for rotation.
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BasicBlock *OrigPreheader = L->getLoopPreheader();
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// If the loop could not be converted to canonical form, it must have an
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// indirectbr in it, just give up.
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if (!OrigPreheader)
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return false;
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// Anything ScalarEvolution may know about this loop or the PHI nodes
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// in its header will soon be invalidated.
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if (ScalarEvolution *SE = getAnalysisIfAvailable<ScalarEvolution>())
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SE->forgetLoop(L);
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DEBUG(dbgs() << "LoopRotation: rotating "; L->dump());
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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 outside the
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// loop. Otherwise loop is not suitable for rotation.
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BasicBlock *Exit = BI->getSuccessor(0);
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BasicBlock *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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// This code assumes that the new header has exactly one predecessor.
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// Remove any single-entry PHI nodes in it.
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assert(NewHeader->getSinglePredecessor() &&
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"New header doesn't have one pred!");
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FoldSingleEntryPHINodes(NewHeader);
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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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ValueToValueMapTy ValueMap;
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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->getIncomingValueForBlock(OrigPreheader);
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// For the rest of the instructions, either hoist to the OrigPreheader if
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// possible or create a clone in the OldPreHeader if not.
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TerminatorInst *LoopEntryBranch = OrigPreheader->getTerminator();
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while (I != E) {
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Instruction *Inst = I++;
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// If the instruction's operands are invariant and it doesn't read or write
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// memory, then it is safe to hoist. Doing this doesn't change the order of
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// execution in the preheader, but does prevent the instruction from
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// executing in each iteration of the loop. This means it is safe to hoist
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// something that might trap, but isn't safe to hoist something that reads
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// memory (without proving that the loop doesn't write).
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if (L->hasLoopInvariantOperands(Inst) &&
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!Inst->mayReadFromMemory() && !Inst->mayWriteToMemory() &&
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!isa<TerminatorInst>(Inst) && !isa<DbgInfoIntrinsic>(Inst) &&
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!isa<AllocaInst>(Inst)) {
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Inst->moveBefore(LoopEntryBranch);
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continue;
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}
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// Otherwise, create a duplicate of the instruction.
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Instruction *C = Inst->clone();
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// Eagerly remap the operands of the instruction.
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RemapInstruction(C, ValueMap,
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RF_NoModuleLevelChanges|RF_IgnoreMissingEntries);
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// With the operands remapped, see if the instruction constant folds or is
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// otherwise simplifyable. This commonly occurs because the entry from PHI
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// nodes allows icmps and other instructions to fold.
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// FIXME: Provide DL, TLI, DT, AT to SimplifyInstruction.
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Value *V = SimplifyInstruction(C);
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if (V && LI->replacementPreservesLCSSAForm(C, V)) {
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// If so, then delete the temporary instruction and stick the folded value
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// in the map.
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delete C;
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ValueMap[Inst] = V;
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} else {
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// Otherwise, stick the new instruction into the new block!
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C->setName(Inst->getName());
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C->insertBefore(LoopEntryBranch);
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ValueMap[Inst] = C;
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}
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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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// 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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// If there were any uses of instructions in the duplicated block outside the
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// loop, update them, inserting PHI nodes as required
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RewriteUsesOfClonedInstructions(OrigHeader, OrigPreheader, ValueMap);
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// NewHeader is now the header of the loop.
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L->moveToHeader(NewHeader);
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assert(L->getHeader() == NewHeader && "Latch block is our new header");
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// At this point, we've finished our major CFG changes. As part of cloning
|
|
// the loop into the preheader we've simplified instructions and the
|
|
// duplicated conditional branch may now be branching on a constant. If it is
|
|
// branching on a constant and if that constant means that we enter the loop,
|
|
// then we fold away the cond branch to an uncond branch. This simplifies the
|
|
// loop in cases important for nested loops, and it also means we don't have
|
|
// to split as many edges.
|
|
BranchInst *PHBI = cast<BranchInst>(OrigPreheader->getTerminator());
|
|
assert(PHBI->isConditional() && "Should be clone of BI condbr!");
|
|
if (!isa<ConstantInt>(PHBI->getCondition()) ||
|
|
PHBI->getSuccessor(cast<ConstantInt>(PHBI->getCondition())->isZero())
|
|
!= NewHeader) {
|
|
// The conditional branch can't be folded, handle the general case.
|
|
// Update DominatorTree to reflect the CFG change we just made. Then split
|
|
// edges as necessary to preserve LoopSimplify form.
|
|
if (DominatorTreeWrapperPass *DTWP =
|
|
getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
|
|
DominatorTree &DT = DTWP->getDomTree();
|
|
// Everything that was dominated by the old loop header is now dominated
|
|
// by the original loop preheader. Conceptually the header was merged
|
|
// into the preheader, even though we reuse the actual block as a new
|
|
// loop latch.
|
|
DomTreeNode *OrigHeaderNode = DT.getNode(OrigHeader);
|
|
SmallVector<DomTreeNode *, 8> HeaderChildren(OrigHeaderNode->begin(),
|
|
OrigHeaderNode->end());
|
|
DomTreeNode *OrigPreheaderNode = DT.getNode(OrigPreheader);
|
|
for (unsigned I = 0, E = HeaderChildren.size(); I != E; ++I)
|
|
DT.changeImmediateDominator(HeaderChildren[I], OrigPreheaderNode);
|
|
|
|
assert(DT.getNode(Exit)->getIDom() == OrigPreheaderNode);
|
|
assert(DT.getNode(NewHeader)->getIDom() == OrigPreheaderNode);
|
|
|
|
// Update OrigHeader to be dominated by the new header block.
|
|
DT.changeImmediateDominator(OrigHeader, OrigLatch);
|
|
}
|
|
|
|
// Right now OrigPreHeader has two successors, NewHeader and ExitBlock, and
|
|
// thus is not a preheader anymore.
|
|
// Split the edge to form a real preheader.
|
|
BasicBlock *NewPH = SplitCriticalEdge(OrigPreheader, NewHeader, this);
|
|
NewPH->setName(NewHeader->getName() + ".lr.ph");
|
|
|
|
// Preserve canonical loop form, which means that 'Exit' should have only
|
|
// one predecessor. Note that Exit could be an exit block for multiple
|
|
// nested loops, causing both of the edges to now be critical and need to
|
|
// be split.
|
|
SmallVector<BasicBlock *, 4> ExitPreds(pred_begin(Exit), pred_end(Exit));
|
|
bool SplitLatchEdge = false;
|
|
for (SmallVectorImpl<BasicBlock *>::iterator PI = ExitPreds.begin(),
|
|
PE = ExitPreds.end();
|
|
PI != PE; ++PI) {
|
|
// We only need to split loop exit edges.
|
|
Loop *PredLoop = LI->getLoopFor(*PI);
|
|
if (!PredLoop || PredLoop->contains(Exit))
|
|
continue;
|
|
SplitLatchEdge |= L->getLoopLatch() == *PI;
|
|
BasicBlock *ExitSplit = SplitCriticalEdge(*PI, Exit, this);
|
|
ExitSplit->moveBefore(Exit);
|
|
}
|
|
assert(SplitLatchEdge &&
|
|
"Despite splitting all preds, failed to split latch exit?");
|
|
} else {
|
|
// We can fold the conditional branch in the preheader, this makes things
|
|
// simpler. The first step is to remove the extra edge to the Exit block.
|
|
Exit->removePredecessor(OrigPreheader, true /*preserve LCSSA*/);
|
|
BranchInst *NewBI = BranchInst::Create(NewHeader, PHBI);
|
|
NewBI->setDebugLoc(PHBI->getDebugLoc());
|
|
PHBI->eraseFromParent();
|
|
|
|
// With our CFG finalized, update DomTree if it is available.
|
|
if (DominatorTreeWrapperPass *DTWP =
|
|
getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
|
|
DominatorTree &DT = DTWP->getDomTree();
|
|
// Update OrigHeader to be dominated by the new header block.
|
|
DT.changeImmediateDominator(NewHeader, OrigPreheader);
|
|
DT.changeImmediateDominator(OrigHeader, OrigLatch);
|
|
|
|
// Brute force incremental dominator tree update. Call
|
|
// findNearestCommonDominator on all CFG predecessors of each child of the
|
|
// original header.
|
|
DomTreeNode *OrigHeaderNode = DT.getNode(OrigHeader);
|
|
SmallVector<DomTreeNode *, 8> HeaderChildren(OrigHeaderNode->begin(),
|
|
OrigHeaderNode->end());
|
|
bool Changed;
|
|
do {
|
|
Changed = false;
|
|
for (unsigned I = 0, E = HeaderChildren.size(); I != E; ++I) {
|
|
DomTreeNode *Node = HeaderChildren[I];
|
|
BasicBlock *BB = Node->getBlock();
|
|
|
|
pred_iterator PI = pred_begin(BB);
|
|
BasicBlock *NearestDom = *PI;
|
|
for (pred_iterator PE = pred_end(BB); PI != PE; ++PI)
|
|
NearestDom = DT.findNearestCommonDominator(NearestDom, *PI);
|
|
|
|
// Remember if this changes the DomTree.
|
|
if (Node->getIDom()->getBlock() != NearestDom) {
|
|
DT.changeImmediateDominator(BB, NearestDom);
|
|
Changed = true;
|
|
}
|
|
}
|
|
|
|
// If the dominator changed, this may have an effect on other
|
|
// predecessors, continue until we reach a fixpoint.
|
|
} while (Changed);
|
|
}
|
|
}
|
|
|
|
assert(L->getLoopPreheader() && "Invalid loop preheader after loop rotation");
|
|
assert(L->getLoopLatch() && "Invalid loop latch after loop rotation");
|
|
|
|
// Now that the CFG and DomTree are in a consistent state again, try to merge
|
|
// the OrigHeader block into OrigLatch. This will succeed if they are
|
|
// connected by an unconditional branch. This is just a cleanup so the
|
|
// emitted code isn't too gross in this common case.
|
|
MergeBlockIntoPredecessor(OrigHeader, this);
|
|
|
|
DEBUG(dbgs() << "LoopRotation: into "; L->dump());
|
|
|
|
++NumRotated;
|
|
return true;
|
|
}
|