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which branch on undef to branch on a boolean constant for the edge exiting the loop. This helps ScalarEvolution compute trip counts for loops. Teach ScalarEvolution to recognize single-value PHIs, when safe, and ForgetSymbolicName to forget such single-value PHI nodes as apprpriate in ForgetSymbolicName. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97126 91177308-0d34-0410-b5e6-96231b3b80d8
704 lines
27 KiB
C++
704 lines
27 KiB
C++
//===- LoopSimplify.cpp - Loop Canonicalization 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 pass performs several transformations to transform natural loops into a
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// simpler form, which makes subsequent analyses and transformations simpler and
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// more effective.
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//
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// Loop pre-header insertion guarantees that there is a single, non-critical
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// entry edge from outside of the loop to the loop header. This simplifies a
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// number of analyses and transformations, such as LICM.
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//
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// Loop exit-block insertion guarantees that all exit blocks from the loop
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// (blocks which are outside of the loop that have predecessors inside of the
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// loop) only have predecessors from inside of the loop (and are thus dominated
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// by the loop header). This simplifies transformations such as store-sinking
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// that are built into LICM.
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//
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// This pass also guarantees that loops will have exactly one backedge.
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//
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// Indirectbr instructions introduce several complications. If the loop
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// contains or is entered by an indirectbr instruction, it may not be possible
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// to transform the loop and make these guarantees. Client code should check
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// that these conditions are true before relying on them.
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//
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// Note that the simplifycfg pass will clean up blocks which are split out but
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// end up being unnecessary, so usage of this pass should not pessimize
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// generated code.
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//
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// This pass obviously modifies the CFG, but updates loop information and
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// dominator information.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "loopsimplify"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Constants.h"
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#include "llvm/Instructions.h"
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#include "llvm/Function.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Type.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/Dominators.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/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/ADT/SetOperations.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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using namespace llvm;
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STATISTIC(NumInserted, "Number of pre-header or exit blocks inserted");
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STATISTIC(NumNested , "Number of nested loops split out");
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namespace {
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struct LoopSimplify : public LoopPass {
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static char ID; // Pass identification, replacement for typeid
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LoopSimplify() : LoopPass(&ID) {}
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// AA - If we have an alias analysis object to update, this is it, otherwise
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// this is null.
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AliasAnalysis *AA;
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LoopInfo *LI;
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DominatorTree *DT;
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Loop *L;
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virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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// We need loop information to identify the loops...
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AU.addRequiredTransitive<LoopInfo>();
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AU.addRequiredTransitive<DominatorTree>();
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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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AU.addPreserved<AliasAnalysis>();
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AU.addPreserved<ScalarEvolution>();
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AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
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}
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/// verifyAnalysis() - Verify LoopSimplifyForm's guarantees.
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void verifyAnalysis() const;
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private:
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bool ProcessLoop(Loop *L, LPPassManager &LPM);
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BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
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BasicBlock *InsertPreheaderForLoop(Loop *L);
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Loop *SeparateNestedLoop(Loop *L, LPPassManager &LPM);
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BasicBlock *InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader);
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void PlaceSplitBlockCarefully(BasicBlock *NewBB,
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SmallVectorImpl<BasicBlock*> &SplitPreds,
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Loop *L);
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};
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}
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char LoopSimplify::ID = 0;
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static RegisterPass<LoopSimplify>
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X("loopsimplify", "Canonicalize natural loops", true);
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// Publically exposed interface to pass...
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const PassInfo *const llvm::LoopSimplifyID = &X;
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Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
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/// runOnLoop - Run down all loops in the CFG (recursively, but we could do
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/// it in any convenient order) inserting preheaders...
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///
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bool LoopSimplify::runOnLoop(Loop *l, LPPassManager &LPM) {
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L = l;
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bool Changed = false;
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LI = &getAnalysis<LoopInfo>();
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AA = getAnalysisIfAvailable<AliasAnalysis>();
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DT = &getAnalysis<DominatorTree>();
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Changed |= ProcessLoop(L, LPM);
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return Changed;
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}
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/// ProcessLoop - Walk the loop structure in depth first order, ensuring that
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/// all loops have preheaders.
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///
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bool LoopSimplify::ProcessLoop(Loop *L, LPPassManager &LPM) {
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bool Changed = false;
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ReprocessLoop:
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// Check to see that no blocks (other than the header) in this loop that has
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// predecessors that are not in the loop. This is not valid for natural
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// loops, but can occur if the blocks are unreachable. Since they are
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// unreachable we can just shamelessly delete those CFG edges!
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for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
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BB != E; ++BB) {
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if (*BB == L->getHeader()) continue;
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SmallPtrSet<BasicBlock *, 4> BadPreds;
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for (pred_iterator PI = pred_begin(*BB), PE = pred_end(*BB); PI != PE; ++PI)
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if (!L->contains(*PI))
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BadPreds.insert(*PI);
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// Delete each unique out-of-loop (and thus dead) predecessor.
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for (SmallPtrSet<BasicBlock *, 4>::iterator I = BadPreds.begin(),
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E = BadPreds.end(); I != E; ++I) {
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// Inform each successor of each dead pred.
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for (succ_iterator SI = succ_begin(*I), SE = succ_end(*I); SI != SE; ++SI)
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(*SI)->removePredecessor(*I);
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// Zap the dead pred's terminator and replace it with unreachable.
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TerminatorInst *TI = (*I)->getTerminator();
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TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
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(*I)->getTerminator()->eraseFromParent();
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new UnreachableInst((*I)->getContext(), *I);
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Changed = true;
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}
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}
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// If there are exiting blocks with branches on undef, resolve the undef in
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// the direction which will exit the loop. This will help simplify loop
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// trip count computations.
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SmallVector<BasicBlock*, 8> ExitingBlocks;
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L->getExitingBlocks(ExitingBlocks);
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for (SmallVectorImpl<BasicBlock *>::iterator I = ExitingBlocks.begin(),
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E = ExitingBlocks.end(); I != E; ++I)
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if (BranchInst *BI = dyn_cast<BranchInst>((*I)->getTerminator()))
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if (BI->isConditional()) {
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if (UndefValue *Cond = dyn_cast<UndefValue>(BI->getCondition())) {
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BI->setCondition(ConstantInt::get(Cond->getType(),
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!L->contains(BI->getSuccessor(0))));
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Changed = true;
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}
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}
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// Does the loop already have a preheader? If so, don't insert one.
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BasicBlock *Preheader = L->getLoopPreheader();
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if (!Preheader) {
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Preheader = InsertPreheaderForLoop(L);
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if (Preheader) {
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NumInserted++;
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Changed = true;
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}
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}
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// Next, check to make sure that all exit nodes of the loop only have
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// predecessors that are inside of the loop. This check guarantees that the
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// loop preheader/header will dominate the exit blocks. If the exit block has
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// predecessors from outside of the loop, split the edge now.
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SmallVector<BasicBlock*, 8> ExitBlocks;
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L->getExitBlocks(ExitBlocks);
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SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(),
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ExitBlocks.end());
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for (SmallSetVector<BasicBlock *, 8>::iterator I = ExitBlockSet.begin(),
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E = ExitBlockSet.end(); I != E; ++I) {
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BasicBlock *ExitBlock = *I;
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for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
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PI != PE; ++PI)
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// Must be exactly this loop: no subloops, parent loops, or non-loop preds
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// allowed.
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if (!L->contains(*PI)) {
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if (RewriteLoopExitBlock(L, ExitBlock)) {
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NumInserted++;
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Changed = true;
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}
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break;
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}
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}
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// If the header has more than two predecessors at this point (from the
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// preheader and from multiple backedges), we must adjust the loop.
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BasicBlock *LoopLatch = L->getLoopLatch();
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if (!LoopLatch) {
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// If this is really a nested loop, rip it out into a child loop. Don't do
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// this for loops with a giant number of backedges, just factor them into a
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// common backedge instead.
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if (L->getNumBackEdges() < 8) {
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if (SeparateNestedLoop(L, LPM)) {
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++NumNested;
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// This is a big restructuring change, reprocess the whole loop.
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Changed = true;
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// GCC doesn't tail recursion eliminate this.
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goto ReprocessLoop;
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}
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}
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// If we either couldn't, or didn't want to, identify nesting of the loops,
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// insert a new block that all backedges target, then make it jump to the
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// loop header.
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LoopLatch = InsertUniqueBackedgeBlock(L, Preheader);
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if (LoopLatch) {
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NumInserted++;
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Changed = true;
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}
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}
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// Scan over the PHI nodes in the loop header. Since they now have only two
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// incoming values (the loop is canonicalized), we may have simplified the PHI
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// down to 'X = phi [X, Y]', which should be replaced with 'Y'.
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PHINode *PN;
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for (BasicBlock::iterator I = L->getHeader()->begin();
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(PN = dyn_cast<PHINode>(I++)); )
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if (Value *V = PN->hasConstantValue(DT)) {
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if (AA) AA->deleteValue(PN);
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PN->replaceAllUsesWith(V);
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PN->eraseFromParent();
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}
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// If this loop has multiple exits and the exits all go to the same
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// block, attempt to merge the exits. This helps several passes, such
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// as LoopRotation, which do not support loops with multiple exits.
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// SimplifyCFG also does this (and this code uses the same utility
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// function), however this code is loop-aware, where SimplifyCFG is
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// not. That gives it the advantage of being able to hoist
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// loop-invariant instructions out of the way to open up more
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// opportunities, and the disadvantage of having the responsibility
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// to preserve dominator information.
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bool UniqueExit = true;
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if (!ExitBlocks.empty())
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for (unsigned i = 1, e = ExitBlocks.size(); i != e; ++i)
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if (ExitBlocks[i] != ExitBlocks[0]) {
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UniqueExit = false;
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break;
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}
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if (UniqueExit) {
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for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
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BasicBlock *ExitingBlock = ExitingBlocks[i];
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if (!ExitingBlock->getSinglePredecessor()) continue;
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BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
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if (!BI || !BI->isConditional()) continue;
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CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition());
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if (!CI || CI->getParent() != ExitingBlock) continue;
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// Attempt to hoist out all instructions except for the
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// comparison and the branch.
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bool AllInvariant = true;
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for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) {
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Instruction *Inst = I++;
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if (Inst == CI)
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continue;
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if (!L->makeLoopInvariant(Inst, Changed,
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Preheader ? Preheader->getTerminator() : 0)) {
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AllInvariant = false;
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break;
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}
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}
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if (!AllInvariant) continue;
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// The block has now been cleared of all instructions except for
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// a comparison and a conditional branch. SimplifyCFG may be able
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// to fold it now.
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if (!FoldBranchToCommonDest(BI)) continue;
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// Success. The block is now dead, so remove it from the loop,
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// update the dominator tree and dominance frontier, and delete it.
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assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock));
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Changed = true;
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LI->removeBlock(ExitingBlock);
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DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>();
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DomTreeNode *Node = DT->getNode(ExitingBlock);
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const std::vector<DomTreeNodeBase<BasicBlock> *> &Children =
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Node->getChildren();
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while (!Children.empty()) {
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DomTreeNode *Child = Children.front();
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DT->changeImmediateDominator(Child, Node->getIDom());
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if (DF) DF->changeImmediateDominator(Child->getBlock(),
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Node->getIDom()->getBlock(),
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DT);
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}
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DT->eraseNode(ExitingBlock);
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if (DF) DF->removeBlock(ExitingBlock);
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BI->getSuccessor(0)->removePredecessor(ExitingBlock);
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BI->getSuccessor(1)->removePredecessor(ExitingBlock);
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ExitingBlock->eraseFromParent();
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}
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}
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return Changed;
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}
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/// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
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/// preheader, this method is called to insert one. This method has two phases:
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/// preheader insertion and analysis updating.
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///
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BasicBlock *LoopSimplify::InsertPreheaderForLoop(Loop *L) {
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BasicBlock *Header = L->getHeader();
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// Compute the set of predecessors of the loop that are not in the loop.
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SmallVector<BasicBlock*, 8> OutsideBlocks;
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for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
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PI != PE; ++PI)
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if (!L->contains(*PI)) { // Coming in from outside the loop?
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// If the loop is branched to from an indirect branch, we won't
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// be able to fully transform the loop, because it prohibits
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// edge splitting.
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if (isa<IndirectBrInst>((*PI)->getTerminator())) return 0;
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// Keep track of it.
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OutsideBlocks.push_back(*PI);
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}
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// Split out the loop pre-header.
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BasicBlock *NewBB =
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SplitBlockPredecessors(Header, &OutsideBlocks[0], OutsideBlocks.size(),
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".preheader", this);
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// Make sure that NewBB is put someplace intelligent, which doesn't mess up
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// code layout too horribly.
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PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L);
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return NewBB;
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}
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/// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
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/// blocks. This method is used to split exit blocks that have predecessors
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/// outside of the loop.
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BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
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SmallVector<BasicBlock*, 8> LoopBlocks;
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for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
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if (L->contains(*I)) {
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// Don't do this if the loop is exited via an indirect branch.
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if (isa<IndirectBrInst>((*I)->getTerminator())) return 0;
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LoopBlocks.push_back(*I);
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}
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assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
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BasicBlock *NewBB = SplitBlockPredecessors(Exit, &LoopBlocks[0],
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LoopBlocks.size(), ".loopexit",
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this);
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return NewBB;
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}
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/// AddBlockAndPredsToSet - Add the specified block, and all of its
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/// predecessors, to the specified set, if it's not already in there. Stop
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/// predecessor traversal when we reach StopBlock.
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static void AddBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock,
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std::set<BasicBlock*> &Blocks) {
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std::vector<BasicBlock *> WorkList;
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WorkList.push_back(InputBB);
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do {
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BasicBlock *BB = WorkList.back(); WorkList.pop_back();
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if (Blocks.insert(BB).second && BB != StopBlock)
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// If BB is not already processed and it is not a stop block then
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// insert its predecessor in the work list
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for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
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BasicBlock *WBB = *I;
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WorkList.push_back(WBB);
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}
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} while(!WorkList.empty());
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}
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/// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
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/// PHI node that tells us how to partition the loops.
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static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT,
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AliasAnalysis *AA) {
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for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
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PHINode *PN = cast<PHINode>(I);
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++I;
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if (Value *V = PN->hasConstantValue(DT)) {
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// This is a degenerate PHI already, don't modify it!
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PN->replaceAllUsesWith(V);
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if (AA) AA->deleteValue(PN);
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PN->eraseFromParent();
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continue;
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}
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// Scan this PHI node looking for a use of the PHI node by itself.
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for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
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if (PN->getIncomingValue(i) == PN &&
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L->contains(PN->getIncomingBlock(i)))
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// We found something tasty to remove.
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return PN;
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}
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return 0;
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}
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// PlaceSplitBlockCarefully - If the block isn't already, move the new block to
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// right after some 'outside block' block. This prevents the preheader from
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// being placed inside the loop body, e.g. when the loop hasn't been rotated.
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void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
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SmallVectorImpl<BasicBlock*> &SplitPreds,
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Loop *L) {
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// Check to see if NewBB is already well placed.
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Function::iterator BBI = NewBB; --BBI;
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for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
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if (&*BBI == SplitPreds[i])
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return;
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}
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// If it isn't already after an outside block, move it after one. This is
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// always good as it makes the uncond branch from the outside block into a
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// fall-through.
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// Figure out *which* outside block to put this after. Prefer an outside
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// block that neighbors a BB actually in the loop.
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BasicBlock *FoundBB = 0;
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for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
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Function::iterator BBI = SplitPreds[i];
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if (++BBI != NewBB->getParent()->end() &&
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L->contains(BBI)) {
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FoundBB = SplitPreds[i];
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break;
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}
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}
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// If our heuristic for a *good* bb to place this after doesn't find
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// anything, just pick something. It's likely better than leaving it within
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// the loop.
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if (!FoundBB)
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FoundBB = SplitPreds[0];
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NewBB->moveAfter(FoundBB);
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}
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/// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
|
|
/// them out into a nested loop. This is important for code that looks like
|
|
/// this:
|
|
///
|
|
/// Loop:
|
|
/// ...
|
|
/// br cond, Loop, Next
|
|
/// ...
|
|
/// br cond2, Loop, Out
|
|
///
|
|
/// To identify this common case, we look at the PHI nodes in the header of the
|
|
/// loop. PHI nodes with unchanging values on one backedge correspond to values
|
|
/// that change in the "outer" loop, but not in the "inner" loop.
|
|
///
|
|
/// If we are able to separate out a loop, return the new outer loop that was
|
|
/// created.
|
|
///
|
|
Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM) {
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|
PHINode *PN = FindPHIToPartitionLoops(L, DT, AA);
|
|
if (PN == 0) return 0; // No known way to partition.
|
|
|
|
// Pull out all predecessors that have varying values in the loop. This
|
|
// handles the case when a PHI node has multiple instances of itself as
|
|
// arguments.
|
|
SmallVector<BasicBlock*, 8> OuterLoopPreds;
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|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
|
|
if (PN->getIncomingValue(i) != PN ||
|
|
!L->contains(PN->getIncomingBlock(i))) {
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|
// We can't split indirectbr edges.
|
|
if (isa<IndirectBrInst>(PN->getIncomingBlock(i)->getTerminator()))
|
|
return 0;
|
|
|
|
OuterLoopPreds.push_back(PN->getIncomingBlock(i));
|
|
}
|
|
|
|
BasicBlock *Header = L->getHeader();
|
|
BasicBlock *NewBB = SplitBlockPredecessors(Header, &OuterLoopPreds[0],
|
|
OuterLoopPreds.size(),
|
|
".outer", this);
|
|
|
|
// Make sure that NewBB is put someplace intelligent, which doesn't mess up
|
|
// code layout too horribly.
|
|
PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L);
|
|
|
|
// Create the new outer loop.
|
|
Loop *NewOuter = new Loop();
|
|
|
|
// Change the parent loop to use the outer loop as its child now.
|
|
if (Loop *Parent = L->getParentLoop())
|
|
Parent->replaceChildLoopWith(L, NewOuter);
|
|
else
|
|
LI->changeTopLevelLoop(L, NewOuter);
|
|
|
|
// L is now a subloop of our outer loop.
|
|
NewOuter->addChildLoop(L);
|
|
|
|
// Add the new loop to the pass manager queue.
|
|
LPM.insertLoopIntoQueue(NewOuter);
|
|
|
|
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
|
|
I != E; ++I)
|
|
NewOuter->addBlockEntry(*I);
|
|
|
|
// Now reset the header in L, which had been moved by
|
|
// SplitBlockPredecessors for the outer loop.
|
|
L->moveToHeader(Header);
|
|
|
|
// Determine which blocks should stay in L and which should be moved out to
|
|
// the Outer loop now.
|
|
std::set<BasicBlock*> BlocksInL;
|
|
for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI)
|
|
if (DT->dominates(Header, *PI))
|
|
AddBlockAndPredsToSet(*PI, Header, BlocksInL);
|
|
|
|
|
|
// Scan all of the loop children of L, moving them to OuterLoop if they are
|
|
// not part of the inner loop.
|
|
const std::vector<Loop*> &SubLoops = L->getSubLoops();
|
|
for (size_t I = 0; I != SubLoops.size(); )
|
|
if (BlocksInL.count(SubLoops[I]->getHeader()))
|
|
++I; // Loop remains in L
|
|
else
|
|
NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I));
|
|
|
|
// Now that we know which blocks are in L and which need to be moved to
|
|
// OuterLoop, move any blocks that need it.
|
|
for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
|
|
BasicBlock *BB = L->getBlocks()[i];
|
|
if (!BlocksInL.count(BB)) {
|
|
// Move this block to the parent, updating the exit blocks sets
|
|
L->removeBlockFromLoop(BB);
|
|
if ((*LI)[BB] == L)
|
|
LI->changeLoopFor(BB, NewOuter);
|
|
--i;
|
|
}
|
|
}
|
|
|
|
return NewOuter;
|
|
}
|
|
|
|
|
|
|
|
/// InsertUniqueBackedgeBlock - This method is called when the specified loop
|
|
/// has more than one backedge in it. If this occurs, revector all of these
|
|
/// backedges to target a new basic block and have that block branch to the loop
|
|
/// header. This ensures that loops have exactly one backedge.
|
|
///
|
|
BasicBlock *
|
|
LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) {
|
|
assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
|
|
|
|
// Get information about the loop
|
|
BasicBlock *Header = L->getHeader();
|
|
Function *F = Header->getParent();
|
|
|
|
// Unique backedge insertion currently depends on having a preheader.
|
|
if (!Preheader)
|
|
return 0;
|
|
|
|
// Figure out which basic blocks contain back-edges to the loop header.
|
|
std::vector<BasicBlock*> BackedgeBlocks;
|
|
for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
|
|
if (*I != Preheader) BackedgeBlocks.push_back(*I);
|
|
|
|
// Create and insert the new backedge block...
|
|
BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
|
|
Header->getName()+".backedge", F);
|
|
BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
|
|
|
|
// Move the new backedge block to right after the last backedge block.
|
|
Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
|
|
F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
|
|
|
|
// Now that the block has been inserted into the function, create PHI nodes in
|
|
// the backedge block which correspond to any PHI nodes in the header block.
|
|
for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
|
|
PHINode *PN = cast<PHINode>(I);
|
|
PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName()+".be",
|
|
BETerminator);
|
|
NewPN->reserveOperandSpace(BackedgeBlocks.size());
|
|
if (AA) AA->copyValue(PN, NewPN);
|
|
|
|
// Loop over the PHI node, moving all entries except the one for the
|
|
// preheader over to the new PHI node.
|
|
unsigned PreheaderIdx = ~0U;
|
|
bool HasUniqueIncomingValue = true;
|
|
Value *UniqueValue = 0;
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
BasicBlock *IBB = PN->getIncomingBlock(i);
|
|
Value *IV = PN->getIncomingValue(i);
|
|
if (IBB == Preheader) {
|
|
PreheaderIdx = i;
|
|
} else {
|
|
NewPN->addIncoming(IV, IBB);
|
|
if (HasUniqueIncomingValue) {
|
|
if (UniqueValue == 0)
|
|
UniqueValue = IV;
|
|
else if (UniqueValue != IV)
|
|
HasUniqueIncomingValue = false;
|
|
}
|
|
}
|
|
}
|
|
|
|
// Delete all of the incoming values from the old PN except the preheader's
|
|
assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
|
|
if (PreheaderIdx != 0) {
|
|
PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
|
|
PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
|
|
}
|
|
// Nuke all entries except the zero'th.
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
|
|
PN->removeIncomingValue(e-i, false);
|
|
|
|
// Finally, add the newly constructed PHI node as the entry for the BEBlock.
|
|
PN->addIncoming(NewPN, BEBlock);
|
|
|
|
// As an optimization, if all incoming values in the new PhiNode (which is a
|
|
// subset of the incoming values of the old PHI node) have the same value,
|
|
// eliminate the PHI Node.
|
|
if (HasUniqueIncomingValue) {
|
|
NewPN->replaceAllUsesWith(UniqueValue);
|
|
if (AA) AA->deleteValue(NewPN);
|
|
BEBlock->getInstList().erase(NewPN);
|
|
}
|
|
}
|
|
|
|
// Now that all of the PHI nodes have been inserted and adjusted, modify the
|
|
// backedge blocks to just to the BEBlock instead of the header.
|
|
for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
|
|
TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
|
|
for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
|
|
if (TI->getSuccessor(Op) == Header)
|
|
TI->setSuccessor(Op, BEBlock);
|
|
}
|
|
|
|
//===--- Update all analyses which we must preserve now -----------------===//
|
|
|
|
// Update Loop Information - we know that this block is now in the current
|
|
// loop and all parent loops.
|
|
L->addBasicBlockToLoop(BEBlock, LI->getBase());
|
|
|
|
// Update dominator information
|
|
DT->splitBlock(BEBlock);
|
|
if (DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>())
|
|
DF->splitBlock(BEBlock);
|
|
|
|
return BEBlock;
|
|
}
|
|
|
|
void LoopSimplify::verifyAnalysis() const {
|
|
// It used to be possible to just assert L->isLoopSimplifyForm(), however
|
|
// with the introduction of indirectbr, there are now cases where it's
|
|
// not possible to transform a loop as necessary. We can at least check
|
|
// that there is an indirectbr near any time there's trouble.
|
|
|
|
// Indirectbr can interfere with preheader and unique backedge insertion.
|
|
if (!L->getLoopPreheader() || !L->getLoopLatch()) {
|
|
bool HasIndBrPred = false;
|
|
for (pred_iterator PI = pred_begin(L->getHeader()),
|
|
PE = pred_end(L->getHeader()); PI != PE; ++PI)
|
|
if (isa<IndirectBrInst>((*PI)->getTerminator())) {
|
|
HasIndBrPred = true;
|
|
break;
|
|
}
|
|
assert(HasIndBrPred &&
|
|
"LoopSimplify has no excuse for missing loop header info!");
|
|
}
|
|
|
|
// Indirectbr can interfere with exit block canonicalization.
|
|
if (!L->hasDedicatedExits()) {
|
|
bool HasIndBrExiting = false;
|
|
SmallVector<BasicBlock*, 8> ExitingBlocks;
|
|
L->getExitingBlocks(ExitingBlocks);
|
|
for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i)
|
|
if (isa<IndirectBrInst>((ExitingBlocks[i])->getTerminator())) {
|
|
HasIndBrExiting = true;
|
|
break;
|
|
}
|
|
assert(HasIndBrExiting &&
|
|
"LoopSimplify has no excuse for missing exit block info!");
|
|
}
|
|
}
|