/// ProcessInstruction - Given an instruction in the loop, check to see if it /// has any uses that are outside the current loop. If so, insert LCSSA PHI /// nodes and rewrite the uses. bool LCSSA::ProcessInstruction(Instruction *Inst, const SmallVectorImpl<BasicBlock*> &ExitBlocks) { SmallVector<Use*, 16> UsesToRewrite; BasicBlock *InstBB = Inst->getParent(); for (Value::use_iterator UI = Inst->use_begin(), E = Inst->use_end(); UI != E; ++UI) { User *U = *UI; BasicBlock *UserBB = cast<Instruction>(U)->getParent(); if (PHINode *PN = dyn_cast<PHINode>(U)) UserBB = PN->getIncomingBlock(UI); if (InstBB != UserBB && !inLoop(UserBB)) UsesToRewrite.push_back(&UI.getUse()); } // If there are no uses outside the loop, exit with no change. if (UsesToRewrite.empty()) return false; ++NumLCSSA; // We are applying the transformation // Invoke instructions are special in that their result value is not available // along their unwind edge. The code below tests to see whether DomBB dominates // the value, so adjust DomBB to the normal destination block, which is // effectively where the value is first usable. BasicBlock *DomBB = Inst->getParent(); if (InvokeInst *Inv = dyn_cast<InvokeInst>(Inst)) DomBB = Inv->getNormalDest(); DomTreeNode *DomNode = DT->getNode(DomBB); SSAUpdater SSAUpdate; SSAUpdate.Initialize(Inst->getType(), Inst->getName()); // Insert the LCSSA phi's into all of the exit blocks dominated by the // value, and add them to the Phi's map. for (SmallVectorImpl<BasicBlock*>::const_iterator BBI = ExitBlocks.begin(), BBE = ExitBlocks.end(); BBI != BBE; ++BBI) { BasicBlock *ExitBB = *BBI; if (!DT->dominates(DomNode, DT->getNode(ExitBB))) continue; // If we already inserted something for this BB, don't reprocess it. if (SSAUpdate.HasValueForBlock(ExitBB)) continue; PHINode *PN = PHINode::Create(Inst->getType(), Inst->getName()+".lcssa", ExitBB->begin()); PN->reserveOperandSpace(PredCache.GetNumPreds(ExitBB)); // Add inputs from inside the loop for this PHI. for (BasicBlock **PI = PredCache.GetPreds(ExitBB); *PI; ++PI) { PN->addIncoming(Inst, *PI); // If the exit block has a predecessor not within the loop, arrange for // the incoming value use corresponding to that predecessor to be // rewritten in terms of a different LCSSA PHI. if (!inLoop(*PI)) UsesToRewrite.push_back( &PN->getOperandUse( PN->getOperandNumForIncomingValue(PN->getNumIncomingValues()-1))); } // Remember that this phi makes the value alive in this block. SSAUpdate.AddAvailableValue(ExitBB, PN); } // Rewrite all uses outside the loop in terms of the new PHIs we just // inserted. for (unsigned i = 0, e = UsesToRewrite.size(); i != e; ++i) { // If this use is in an exit block, rewrite to use the newly inserted PHI. // This is required for correctness because SSAUpdate doesn't handle uses in // the same block. It assumes the PHI we inserted is at the end of the // block. Instruction *User = cast<Instruction>(UsesToRewrite[i]->getUser()); BasicBlock *UserBB = User->getParent(); if (PHINode *PN = dyn_cast<PHINode>(User)) UserBB = PN->getIncomingBlock(*UsesToRewrite[i]); if (isa<PHINode>(UserBB->begin()) && isExitBlock(UserBB, ExitBlocks)) { UsesToRewrite[i]->set(UserBB->begin()); continue; } // Otherwise, do full PHI insertion. SSAUpdate.RewriteUse(*UsesToRewrite[i]); } return true; }
/// For every instruction from the worklist, check to see if it has any uses /// that are outside the current loop. If so, insert LCSSA PHI nodes and /// rewrite the uses. bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist, DominatorTree &DT, LoopInfo &LI) { SmallVector<Use *, 16> UsesToRewrite; SmallSetVector<PHINode *, 16> PHIsToRemove; PredIteratorCache PredCache; bool Changed = false; // Cache the Loop ExitBlocks across this loop. We expect to get a lot of // instructions within the same loops, computing the exit blocks is // expensive, and we're not mutating the loop structure. SmallDenseMap<Loop*, SmallVector<BasicBlock *,1>> LoopExitBlocks; while (!Worklist.empty()) { UsesToRewrite.clear(); Instruction *I = Worklist.pop_back_val(); BasicBlock *InstBB = I->getParent(); Loop *L = LI.getLoopFor(InstBB); if (!LoopExitBlocks.count(L)) L->getExitBlocks(LoopExitBlocks[L]); assert(LoopExitBlocks.count(L)); const SmallVectorImpl<BasicBlock *> &ExitBlocks = LoopExitBlocks[L]; if (ExitBlocks.empty()) continue; // Tokens cannot be used in PHI nodes, so we skip over them. // We can run into tokens which are live out of a loop with catchswitch // instructions in Windows EH if the catchswitch has one catchpad which // is inside the loop and another which is not. if (I->getType()->isTokenTy()) continue; for (Use &U : I->uses()) { Instruction *User = cast<Instruction>(U.getUser()); BasicBlock *UserBB = User->getParent(); if (PHINode *PN = dyn_cast<PHINode>(User)) UserBB = PN->getIncomingBlock(U); if (InstBB != UserBB && !L->contains(UserBB)) UsesToRewrite.push_back(&U); } // If there are no uses outside the loop, exit with no change. if (UsesToRewrite.empty()) continue; ++NumLCSSA; // We are applying the transformation // Invoke instructions are special in that their result value is not // available along their unwind edge. The code below tests to see whether // DomBB dominates the value, so adjust DomBB to the normal destination // block, which is effectively where the value is first usable. BasicBlock *DomBB = InstBB; if (InvokeInst *Inv = dyn_cast<InvokeInst>(I)) DomBB = Inv->getNormalDest(); DomTreeNode *DomNode = DT.getNode(DomBB); SmallVector<PHINode *, 16> AddedPHIs; SmallVector<PHINode *, 8> PostProcessPHIs; SmallVector<PHINode *, 4> InsertedPHIs; SSAUpdater SSAUpdate(&InsertedPHIs); SSAUpdate.Initialize(I->getType(), I->getName()); // Insert the LCSSA phi's into all of the exit blocks dominated by the // value, and add them to the Phi's map. for (BasicBlock *ExitBB : ExitBlocks) { if (!DT.dominates(DomNode, DT.getNode(ExitBB))) continue; // If we already inserted something for this BB, don't reprocess it. if (SSAUpdate.HasValueForBlock(ExitBB)) continue; PHINode *PN = PHINode::Create(I->getType(), PredCache.size(ExitBB), I->getName() + ".lcssa", &ExitBB->front()); // Add inputs from inside the loop for this PHI. for (BasicBlock *Pred : PredCache.get(ExitBB)) { PN->addIncoming(I, Pred); // If the exit block has a predecessor not within the loop, arrange for // the incoming value use corresponding to that predecessor to be // rewritten in terms of a different LCSSA PHI. if (!L->contains(Pred)) UsesToRewrite.push_back( &PN->getOperandUse(PN->getOperandNumForIncomingValue( PN->getNumIncomingValues() - 1))); } AddedPHIs.push_back(PN); // Remember that this phi makes the value alive in this block. SSAUpdate.AddAvailableValue(ExitBB, PN); // LoopSimplify might fail to simplify some loops (e.g. when indirect // branches are involved). In such situations, it might happen that an // exit for Loop L1 is the header of a disjoint Loop L2. Thus, when we // create PHIs in such an exit block, we are also inserting PHIs into L2's // header. This could break LCSSA form for L2 because these inserted PHIs // can also have uses outside of L2. Remember all PHIs in such situation // as to revisit than later on. FIXME: Remove this if indirectbr support // into LoopSimplify gets improved. if (auto *OtherLoop = LI.getLoopFor(ExitBB)) if (!L->contains(OtherLoop)) PostProcessPHIs.push_back(PN); } // Rewrite all uses outside the loop in terms of the new PHIs we just // inserted. for (Use *UseToRewrite : UsesToRewrite) { // If this use is in an exit block, rewrite to use the newly inserted PHI. // This is required for correctness because SSAUpdate doesn't handle uses // in the same block. It assumes the PHI we inserted is at the end of the // block. Instruction *User = cast<Instruction>(UseToRewrite->getUser()); BasicBlock *UserBB = User->getParent(); if (PHINode *PN = dyn_cast<PHINode>(User)) UserBB = PN->getIncomingBlock(*UseToRewrite); if (isa<PHINode>(UserBB->begin()) && isExitBlock(UserBB, ExitBlocks)) { // Tell the VHs that the uses changed. This updates SCEV's caches. if (UseToRewrite->get()->hasValueHandle()) ValueHandleBase::ValueIsRAUWd(*UseToRewrite, &UserBB->front()); UseToRewrite->set(&UserBB->front()); continue; } // Otherwise, do full PHI insertion. SSAUpdate.RewriteUse(*UseToRewrite); } // SSAUpdater might have inserted phi-nodes inside other loops. We'll need // to post-process them to keep LCSSA form. for (PHINode *InsertedPN : InsertedPHIs) { if (auto *OtherLoop = LI.getLoopFor(InsertedPN->getParent())) if (!L->contains(OtherLoop)) PostProcessPHIs.push_back(InsertedPN); } // Post process PHI instructions that were inserted into another disjoint // loop and update their exits properly. for (auto *PostProcessPN : PostProcessPHIs) { if (PostProcessPN->use_empty()) continue; // Reprocess each PHI instruction. Worklist.push_back(PostProcessPN); } // Keep track of PHI nodes that we want to remove because they did not have // any uses rewritten. for (PHINode *PN : AddedPHIs) if (PN->use_empty()) PHIsToRemove.insert(PN); Changed = true; } // Remove PHI nodes that did not have any uses rewritten. for (PHINode *PN : PHIsToRemove) { assert (PN->use_empty() && "Trying to remove a phi with uses."); PN->eraseFromParent(); } return Changed; }
/// Given an instruction in the loop, check to see if it has any uses that are /// outside the current loop. If so, insert LCSSA PHI nodes and rewrite the /// uses. static bool processInstruction(Loop &L, Instruction &Inst, DominatorTree &DT, const SmallVectorImpl<BasicBlock *> &ExitBlocks, PredIteratorCache &PredCache, LoopInfo *LI) { SmallVector<Use *, 16> UsesToRewrite; // Tokens cannot be used in PHI nodes, so we skip over them. // We can run into tokens which are live out of a loop with catchswitch // instructions in Windows EH if the catchswitch has one catchpad which // is inside the loop and another which is not. if (Inst.getType()->isTokenTy()) return false; BasicBlock *InstBB = Inst.getParent(); for (Use &U : Inst.uses()) { Instruction *User = cast<Instruction>(U.getUser()); BasicBlock *UserBB = User->getParent(); if (PHINode *PN = dyn_cast<PHINode>(User)) UserBB = PN->getIncomingBlock(U); if (InstBB != UserBB && !L.contains(UserBB)) UsesToRewrite.push_back(&U); } // If there are no uses outside the loop, exit with no change. if (UsesToRewrite.empty()) return false; ++NumLCSSA; // We are applying the transformation // Invoke instructions are special in that their result value is not available // along their unwind edge. The code below tests to see whether DomBB // dominates the value, so adjust DomBB to the normal destination block, // which is effectively where the value is first usable. BasicBlock *DomBB = Inst.getParent(); if (InvokeInst *Inv = dyn_cast<InvokeInst>(&Inst)) DomBB = Inv->getNormalDest(); DomTreeNode *DomNode = DT.getNode(DomBB); SmallVector<PHINode *, 16> AddedPHIs; SmallVector<PHINode *, 8> PostProcessPHIs; SSAUpdater SSAUpdate; SSAUpdate.Initialize(Inst.getType(), Inst.getName()); // Insert the LCSSA phi's into all of the exit blocks dominated by the // value, and add them to the Phi's map. for (BasicBlock *ExitBB : ExitBlocks) { if (!DT.dominates(DomNode, DT.getNode(ExitBB))) continue; // If we already inserted something for this BB, don't reprocess it. if (SSAUpdate.HasValueForBlock(ExitBB)) continue; PHINode *PN = PHINode::Create(Inst.getType(), PredCache.size(ExitBB), Inst.getName() + ".lcssa", &ExitBB->front()); // Add inputs from inside the loop for this PHI. for (BasicBlock *Pred : PredCache.get(ExitBB)) { PN->addIncoming(&Inst, Pred); // If the exit block has a predecessor not within the loop, arrange for // the incoming value use corresponding to that predecessor to be // rewritten in terms of a different LCSSA PHI. if (!L.contains(Pred)) UsesToRewrite.push_back( &PN->getOperandUse(PN->getOperandNumForIncomingValue( PN->getNumIncomingValues() - 1))); } AddedPHIs.push_back(PN); // Remember that this phi makes the value alive in this block. SSAUpdate.AddAvailableValue(ExitBB, PN); // LoopSimplify might fail to simplify some loops (e.g. when indirect // branches are involved). In such situations, it might happen that an exit // for Loop L1 is the header of a disjoint Loop L2. Thus, when we create // PHIs in such an exit block, we are also inserting PHIs into L2's header. // This could break LCSSA form for L2 because these inserted PHIs can also // have uses outside of L2. Remember all PHIs in such situation as to // revisit than later on. FIXME: Remove this if indirectbr support into // LoopSimplify gets improved. if (auto *OtherLoop = LI->getLoopFor(ExitBB)) if (!L.contains(OtherLoop)) PostProcessPHIs.push_back(PN); } // Rewrite all uses outside the loop in terms of the new PHIs we just // inserted. for (Use *UseToRewrite : UsesToRewrite) { // If this use is in an exit block, rewrite to use the newly inserted PHI. // This is required for correctness because SSAUpdate doesn't handle uses in // the same block. It assumes the PHI we inserted is at the end of the // block. Instruction *User = cast<Instruction>(UseToRewrite->getUser()); BasicBlock *UserBB = User->getParent(); if (PHINode *PN = dyn_cast<PHINode>(User)) UserBB = PN->getIncomingBlock(*UseToRewrite); if (isa<PHINode>(UserBB->begin()) && isExitBlock(UserBB, ExitBlocks)) { // Tell the VHs that the uses changed. This updates SCEV's caches. if (UseToRewrite->get()->hasValueHandle()) ValueHandleBase::ValueIsRAUWd(*UseToRewrite, &UserBB->front()); UseToRewrite->set(&UserBB->front()); continue; } // Otherwise, do full PHI insertion. SSAUpdate.RewriteUse(*UseToRewrite); } // Post process PHI instructions that were inserted into another disjoint loop // and update their exits properly. for (auto *I : PostProcessPHIs) { if (I->use_empty()) continue; BasicBlock *PHIBB = I->getParent(); Loop *OtherLoop = LI->getLoopFor(PHIBB); SmallVector<BasicBlock *, 8> EBs; OtherLoop->getExitBlocks(EBs); if (EBs.empty()) continue; // Recurse and re-process each PHI instruction. FIXME: we should really // convert this entire thing to a worklist approach where we process a // vector of instructions... processInstruction(*OtherLoop, *I, DT, EBs, PredCache, LI); } // Remove PHI nodes that did not have any uses rewritten. for (PHINode *PN : AddedPHIs) if (PN->use_empty()) PN->eraseFromParent(); return true; }