Example #1
0
File: DIE.cpp Project: smowton/llpe
// VI is an in-loop instruction that uses Visitor.V, a loop invariant. Check whether any
// iteration will require the value. Assume it is used if we're synthesising an unspecialised
// copy of the loop for any reason.
void PeelIteration::visitVariant(ShadowInstructionInvar* VI, DIVisitor& Visitor) {

  const ShadowLoopInvar* immediateChild = immediateChildLoop(L, VI->parent->outerScope);

  PeelAttempt* LPA = getPeelAttempt(immediateChild);
  if(LPA && LPA->isEnabled())
    LPA->visitVariant(VI, Visitor);
  else 
    Visitor.notifyUsersMissed();

}
Example #2
0
File: DIE.cpp Project: smowton/llpe
void IntegrationAttempt::visitUser(ShadowInstIdx& User, DIVisitor& Visitor) {

  // Figure out what context cares about this value. The only possibilities are: this loop iteration, the next iteration of this loop (latch edge of header phi),
  // a child loop (defer to it to decide what to do), or a parent loop (again defer).
  // Note that nested cases (e.g. this is an invariant two children deep) are taken care of in the immediate child or parent's logic.

  if(User.blockIdx == INVALID_BLOCK_IDX || User.instIdx == INVALID_INSTRUCTION_IDX)
    return;

  ShadowInstructionInvar* SII = getInstInvar(User.blockIdx, User.instIdx);
  const ShadowLoopInvar* UserL = SII->parent->outerScope;

  if(UserL == L) {
	  
    if(!visitNextIterationPHI(SII, Visitor)) {

      // Just an ordinary user in the same iteration (or out of any loop!).
      Visitor.visit(getInst(User.blockIdx, User.instIdx), this, User.blockIdx, User.instIdx);

    }

  }
  else {

    if((!L) || L->contains(UserL)) {

      const ShadowLoopInvar* outermostChildLoop = immediateChildLoop(L, UserL);
      // Used in a child loop. Check if that child exists at all and defer to it.

      PeelAttempt* LPA = getPeelAttempt(outermostChildLoop);

      if(LPA && LPA->isEnabled())
	LPA->visitVariant(SII, Visitor);
      else if((!getBB(outermostChildLoop->headerIdx)))
	Visitor.visit(0, this, User.blockIdx, User.instIdx); // Loop not explored, but a failed version may exist
      else
	Visitor.notifyUsersMissed();

    }
    else {

      visitExitPHI(SII, Visitor);

    }

  }

}
Example #3
0
bool IntegrationAttempt::analyseBlock(uint32_t& blockIdx, bool inLoopAnalyser, bool inAnyLoop, bool skipStoreMerge, const ShadowLoopInvar* MyL) {

  ShadowBB* BB = getBB(blockIdx);
  if(!BB)
    return false;

  bool anyChange = false;

  // Use natural scope rather than scope because even if a loop is
  // ignored we want to notice that it exists so we can call analyseLoop
  ShadowBBInvar* BBI = BB->invar;
  const ShadowLoopInvar* BBL = BBI->naturalScope;

  if(BBL != MyL) {

    BB->inAnyLoop = true;
    inAnyLoop = true;

    // By construction of our top-ordering, must be a loop entry block.
    release_assert(BBL && "Walked into root context?");

    // Now explore the loop, if possible.
    // At the moment can't ever happen inside the loop analyser.
    PeelAttempt* LPA = 0;
    if((!inLoopAnalyser) && (LPA = getOrCreatePeelAttempt(BBL))) {

      // Give the preheader an extra reference in case we need that store
      // to calculate a general version of the loop body if it doesn't terminate.
      ShadowBB* PHBB = getBB(LPA->L->preheaderIdx);
      PHBB->refStores();

      bool loopReadsTentativeData, loopContainsCheckedReads;
      LPA->analyse(stack_depth, loopReadsTentativeData, loopContainsCheckedReads);
      readsTentativeData |= loopReadsTentativeData;
      containsCheckedReads |= loopContainsCheckedReads;  

      // We're certainly not in the loop analyser, so pick whether to keep a terminated
      // version of the loop now.

      if(LPA->isTerminated()) {

	LPA->findProfitableIntegration();
	if(!LPA->isEnabled()) {

	  // The preheader already has a copy of the TL and DSE stores
	  // in case the loop didn't terminate -- give it to each exiting block.

	  TLLocalStore* backupTlStore;
	  bool dropTlRef;
	  if(readsTentativeData) {
	    backupTlStore = new TLLocalStore(stack_depth);
	    backupTlStore->allOthersClobbered = true;
	    dropTlRef = true;
	  }
	  else {
	    backupTlStore = PHBB->tlStore;
	    dropTlRef = false;
	  }

	  LPA->Iterations.back()->setExitingStores(backupTlStore, StoreKindTL);
	  
	  if(dropTlRef)
	    backupTlStore->dropReference();

	  DSELocalStore* backupDSEStore = PHBB->dseStore;

	  setAllNeededTop(backupDSEStore);
	  DSELocalStore* emptyStore = new DSELocalStore(stack_depth);
	  emptyStore->allOthersClobbered = true;
	  LPA->Iterations.back()->setExitingStores(emptyStore, StoreKindDSE);
	  emptyStore->dropReference();

	}

      }

      if(LPA->isTerminated() && LPA->isEnabled()) {

	// Committed blocks in the iterations will be used;
	// next parent inherits them.
	inheritCommitBlocksAndFunctions(LPA->CommitBlocks, LPA->CommitFailedBlocks, LPA->CommitFunctions);

      }
      else {

	LPA->releaseCommittedChildren();

      }

    }

    // Analyse for invariants if we didn't establish that the loop terminates.
    if((!LPA) || !LPA->isTerminated()) {

      anyChange |= analyseLoop(BBL, inLoopAnalyser);

      if(!inLoopAnalyser) {

	// Run other passes over the whole loop
	gatherIndirectUsersInLoop(BBL);
	
	findTentativeLoadsInUnboundedLoop(BBL, /* commit disabled here = */ false, /* second pass = */ false);
	tryKillStoresInUnboundedLoop(BBL, /* commit disabled here = */ false, /* disable writes = */ false);

      }
	
    }
    else {

      // The loop preheader's local store was copied by the loop analysis assuming we'd
      // need it to analyse the loop body, but we've found the loop terminates; drop the extra ref.

      // For the common case where the loop has a single known exit point, perform store simplifications.
      // These apply because the store was forked anticipating failure to establish an iteration count.

      ShadowBB* ExitingBlock = LPA->Iterations.back()->getUniqueExitingBlock();

      std::vector<ShadowValue> simplifyStores;
      getBB(BBL->preheaderIdx)->derefStores(ExitingBlock ? &simplifyStores : 0);

      for(std::vector<ShadowValue>::iterator it = simplifyStores.begin(),
	    itend = simplifyStores.end(); it != itend; ++it) {
	  
	if(LocStore* LS = ExitingBlock->getReadableStoreFor(*it))
	  LocStore::simplifyStore(LS);

      }

      // Copy edges found always dead to local scope, to accelerate edgeIsDead queries without
      // checking every iteration every time.
      copyLoopExitingDeadEdges(LPA);

      // Take account of the number of live edges leaving the last iteration
      // when deciding which blocks are certain:
      // The -1 accounts for the header's incoming edge.
      pendingEdges += (LPA->Iterations.back()->pendingEdges - 1);
      LPA->Iterations.back()->pendingEdges = 0;

    }

    // Advance the main loop past this loop. Loop blocks are always contiguous in the topo ordering.
    while(blockIdx < invarInfo->BBs.size() && BBL->contains(getBBInvar(blockIdx)->naturalScope))
      ++blockIdx;
    --blockIdx;
      
    return anyChange;

  }

  BB->inAnyLoop = inAnyLoop;
   
  if(!skipStoreMerge) {

    // Check if the block becomes a certainty (only applicable when not in a loop!)
    checkBlockStatus(BB, inLoopAnalyser);

    // Loop headers and entry blocks are given their stores in other ways
    // If doBlockStoreMerge returned false this block isn't currently reachable.
    // See comments in that function for reasons why that can happen.
    if(!doBlockStoreMerge(BB))
      return false;

    if(!inLoopAnalyser) {

      doTLStoreMerge(BB);
      doDSEStoreMerge(BB);

    }

  }

  // As-expected checks may also be noted duirng analyseBlockInstructions:
  // they are cleared each time around because the flag might not make sense anymore if the instruction's
  // operands have degraded to the point that the instruction will no longer be resolved.
  // The noteAsExpected function here only tags those which are mentioned in path conditions.

  applyMemoryPathConditions(BB, inLoopAnalyser, inAnyLoop);
  clearAsExpectedChecks(BB);
  noteAsExpectedChecks(BB);

  if(!inLoopAnalyser) {

    //TLWalkPathConditions(BB, true, false);
    if(pass->countPathConditionsAtBlockStart(BB->invar, BB->IA)) {
      setAllNeededTop(BB->dseStore);
      BB->dseStore = BB->dseStore->getEmptyMap();
    }
     
  }

  LFV3(errs() << nestingIndent() << "Start block " << BB->invar->BB->getName() << " store " << BB->localStore << " refcount " << BB->localStore->refCount << "\n");

  // Else we should just analyse this block here.
  anyChange |= analyseBlockInstructions(BB, inLoopAnalyser, inAnyLoop);

  LFV3(errs() << nestingIndent() << "End block " << BB->invar->BB->getName() << " store " << BB->localStore << " refcount " << BB->localStore->refCount << "\n");

  return anyChange;

}