BasicBlockUtils.cpp revision 841a14753175bb9a02a8f5286ffe03d050b0da26
16acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn//===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==// 26acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn// 36acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn// The LLVM Compiler Infrastructure 46acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn// 56acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn// This file is distributed under the University of Illinois Open Source 66acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn// License. See LICENSE.TXT for details. 76acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn// 86acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn//===----------------------------------------------------------------------===// 96acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn// 106acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn// This family of functions perform manipulations on basic blocks, and 116acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn// instructions contained within basic blocks. 126acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn// 136acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn//===----------------------------------------------------------------------===// 146acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 156acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/Transforms/Utils/BasicBlockUtils.h" 166acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/Function.h" 176acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/Instructions.h" 186acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/IntrinsicInst.h" 196acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/LLVMContext.h" 206acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/Constant.h" 216acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/Type.h" 226acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/Analysis/AliasAnalysis.h" 236acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/Analysis/LoopInfo.h" 246acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/Analysis/Dominators.h" 256acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/Target/TargetData.h" 266acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/Transforms/Utils/Local.h" 276acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/Transforms/Scalar.h" 286acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/Support/ErrorHandling.h" 296acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include "llvm/Support/ValueHandle.h" 306acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#include <algorithm> 316acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Rennusing namespace llvm; 326acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 336acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// DeleteDeadBlock - Delete the specified block, which must have no 346acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// predecessors. 356acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Rennvoid llvm::DeleteDeadBlock(BasicBlock *BB) { 366acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn assert((pred_begin(BB) == pred_end(BB) || 376acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Can delete self loop. 386acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BB->getSinglePredecessor() == BB) && "Block is not dead!"); 396acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn TerminatorInst *BBTerm = BB->getTerminator(); 406acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 416acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Loop through all of our successors and make sure they know that one 426acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // of their predecessors is going away. 436acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) 446acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BBTerm->getSuccessor(i)->removePredecessor(BB); 456acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 466acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Zap all the instructions in the block. 476acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn while (!BB->empty()) { 486acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn Instruction &I = BB->back(); 496acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // If this instruction is used, replace uses with an arbitrary value. 506acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Because control flow can't get here, we don't care what we replace the 516acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // value with. Note that since this block is unreachable, and all values 526acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // contained within it must dominate their uses, that all uses will 536acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // eventually be removed (they are themselves dead). 546acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (!I.use_empty()) 556acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn I.replaceAllUsesWith(UndefValue::get(I.getType())); 566acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BB->getInstList().pop_back(); 576acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 586acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 596acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Zap the block! 606acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BB->eraseFromParent(); 616acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn} 626acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 636acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// FoldSingleEntryPHINodes - We know that BB has one predecessor. If there are 646acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// any single-entry PHI nodes in it, fold them away. This handles the case 656acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// when all entries to the PHI nodes in a block are guaranteed equal, such as 666acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// when the block has exactly one predecessor. 676acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Rennvoid llvm::FoldSingleEntryPHINodes(BasicBlock *BB) { 686acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (!isa<PHINode>(BB->begin())) 696acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn return; 706acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 716acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { 726acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (PN->getIncomingValue(0) != PN) 736acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn PN->replaceAllUsesWith(PN->getIncomingValue(0)); 746acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn else 756acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn PN->replaceAllUsesWith(UndefValue::get(PN->getType())); 766acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn PN->eraseFromParent(); 776acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 786acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn} 796acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 806acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 816acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it 826acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// is dead. Also recursively delete any operands that become dead as 836acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// a result. This includes tracing the def-use list from the PHI to see if 846acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// it is ultimately unused or if it reaches an unused cycle. 856acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Rennvoid llvm::DeleteDeadPHIs(BasicBlock *BB) { 866acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Recursively deleting a PHI may cause multiple PHIs to be deleted 876acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // or RAUW'd undef, so use an array of WeakVH for the PHIs to delete. 886acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn SmallVector<WeakVH, 8> PHIs; 896acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn for (BasicBlock::iterator I = BB->begin(); 906acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn PHINode *PN = dyn_cast<PHINode>(I); ++I) 916acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn PHIs.push_back(PN); 926acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 936acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn for (unsigned i = 0, e = PHIs.size(); i != e; ++i) 946acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*())) 956acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn RecursivelyDeleteDeadPHINode(PN); 966acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn} 976acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 986acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor, 996acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// if possible. The return value indicates success or failure. 1006acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Rennbool llvm::MergeBlockIntoPredecessor(BasicBlock* BB, Pass* P) { 1016acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn pred_iterator PI(pred_begin(BB)), PE(pred_end(BB)); 1026acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Can't merge the entry block. 1036acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (pred_begin(BB) == pred_end(BB)) return false; 1046acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1056acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BasicBlock *PredBB = *PI++; 1066acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn for (; PI != PE; ++PI) // Search all predecessors, see if they are all same 1076acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (*PI != PredBB) { 1086acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn PredBB = 0; // There are multiple different predecessors... 1096acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn break; 1106acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 1116acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1126acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Can't merge if there are multiple predecessors. 1136acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (!PredBB) return false; 1146acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Don't break self-loops. 1156acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (PredBB == BB) return false; 1166acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Don't break invokes. 1176acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (isa<InvokeInst>(PredBB->getTerminator())) return false; 1186acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1196acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB)); 1206acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BasicBlock* OnlySucc = BB; 1216acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn for (; SI != SE; ++SI) 1226acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (*SI != OnlySucc) { 1236acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn OnlySucc = 0; // There are multiple distinct successors! 1246acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn break; 1256acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 1266acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1276acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Can't merge if there are multiple successors. 1286acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (!OnlySucc) return false; 1296acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1306acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Can't merge if there is PHI loop. 1316acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) { 1326acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (PHINode *PN = dyn_cast<PHINode>(BI)) { 1336acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) 1346acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (PN->getIncomingValue(i) == PN) 1356acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn return false; 1366acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } else 1376acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn break; 1386acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 1396acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1406acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Begin by getting rid of unneeded PHIs. 1416acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { 1426acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn PN->replaceAllUsesWith(PN->getIncomingValue(0)); 1436acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BB->getInstList().pop_front(); // Delete the phi node... 1446acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 1456acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1466acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Delete the unconditional branch from the predecessor... 1476acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn PredBB->getInstList().pop_back(); 1486acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1496acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Move all definitions in the successor to the predecessor... 1506acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn PredBB->getInstList().splice(PredBB->end(), BB->getInstList()); 1516acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1526acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Make all PHI nodes that referred to BB now refer to Pred as their 1536acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // source... 1546acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BB->replaceAllUsesWith(PredBB); 1556acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1566acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Inherit predecessors name if it exists. 1576acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (!PredBB->hasName()) 1586acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn PredBB->takeName(BB); 1596acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1606acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Finally, erase the old block and update dominator info. 1616acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (P) { 1626acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (DominatorTree* DT = P->getAnalysisIfAvailable<DominatorTree>()) { 1636acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn DomTreeNode* DTN = DT->getNode(BB); 1646acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn DomTreeNode* PredDTN = DT->getNode(PredBB); 1656acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1666acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (DTN) { 1676acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn SmallPtrSet<DomTreeNode*, 8> Children(DTN->begin(), DTN->end()); 1686acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn for (SmallPtrSet<DomTreeNode*, 8>::iterator DI = Children.begin(), 1696acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn DE = Children.end(); DI != DE; ++DI) 1706acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn DT->changeImmediateDominator(*DI, PredDTN); 1716acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1726acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn DT->eraseNode(BB); 1736acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 1746acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 1756acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 1766acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1776acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BB->eraseFromParent(); 1786acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1796acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1806acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn return true; 1816acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn} 1826acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1836acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI) 1846acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// with a value, then remove and delete the original instruction. 1856acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// 1866acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Rennvoid llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL, 1876acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BasicBlock::iterator &BI, Value *V) { 1886acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn Instruction &I = *BI; 1896acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Replaces all of the uses of the instruction with uses of the value 1906acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn I.replaceAllUsesWith(V); 1916acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1926acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Make sure to propagate a name if there is one already. 1936acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (I.hasName() && !V->hasName()) 1946acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn V->takeName(&I); 1956acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 1966acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Delete the unnecessary instruction now... 1976acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BI = BIL.erase(BI); 1986acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn} 1996acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2006acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2016acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// ReplaceInstWithInst - Replace the instruction specified by BI with the 2026acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// instruction specified by I. The original instruction is deleted and BI is 2036acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// updated to point to the new instruction. 2046acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// 2056acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Rennvoid llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL, 2066acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BasicBlock::iterator &BI, Instruction *I) { 2076acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn assert(I->getParent() == 0 && 2086acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn "ReplaceInstWithInst: Instruction already inserted into basic block!"); 2096acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2106acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Insert the new instruction into the basic block... 2116acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BasicBlock::iterator New = BIL.insert(BI, I); 2126acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2136acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Replace all uses of the old instruction, and delete it. 2146acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn ReplaceInstWithValue(BIL, BI, I); 2156acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2166acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Move BI back to point to the newly inserted instruction 2176acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BI = New; 2186acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn} 2196acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2206acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// ReplaceInstWithInst - Replace the instruction specified by From with the 2216acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// instruction specified by To. 2226acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// 2236acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Rennvoid llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) { 2246acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BasicBlock::iterator BI(From); 2256acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn ReplaceInstWithInst(From->getParent()->getInstList(), BI, To); 2266acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn} 2276acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2286acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// RemoveSuccessor - Change the specified terminator instruction such that its 2296acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// successor SuccNum no longer exists. Because this reduces the outgoing 2306acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// degree of the current basic block, the actual terminator instruction itself 2316acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// may have to be changed. In the case where the last successor of the block 2326acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// is deleted, a return instruction is inserted in its place which can cause a 2336acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// surprising change in program behavior if it is not expected. 2346acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// 2356acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Rennvoid llvm::RemoveSuccessor(TerminatorInst *TI, unsigned SuccNum) { 2366acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn assert(SuccNum < TI->getNumSuccessors() && 2376acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn "Trying to remove a nonexistant successor!"); 2386acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2396acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // If our old successor block contains any PHI nodes, remove the entry in the 2406acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // PHI nodes that comes from this branch... 2416acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // 2426acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BasicBlock *BB = TI->getParent(); 2436acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn TI->getSuccessor(SuccNum)->removePredecessor(BB); 2446acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2456acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn TerminatorInst *NewTI = 0; 2466acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn switch (TI->getOpcode()) { 2476acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn case Instruction::Br: 2486acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // If this is a conditional branch... convert to unconditional branch. 2496acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (TI->getNumSuccessors() == 2) { 2506acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn cast<BranchInst>(TI)->setUnconditionalDest(TI->getSuccessor(1-SuccNum)); 2516acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } else { // Otherwise convert to a return instruction... 2526acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn Value *RetVal = 0; 2536acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2546acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Create a value to return... if the function doesn't return null... 2556acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (BB->getParent()->getReturnType() != Type::getVoidTy(TI->getContext())) 2566acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn RetVal = Constant::getNullValue(BB->getParent()->getReturnType()); 2576acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2586acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Create the return... 2596acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn NewTI = ReturnInst::Create(TI->getContext(), RetVal); 2606acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 2616acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn break; 2626acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2636acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn case Instruction::Invoke: // Should convert to call 2646acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn case Instruction::Switch: // Should remove entry 2656acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn default: 2666acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn case Instruction::Ret: // Cannot happen, has no successors! 2676acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn llvm_unreachable("Unhandled terminator instruction type in RemoveSuccessor!"); 2686acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 2696acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2706acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (NewTI) // If it's a different instruction, replace. 2716acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn ReplaceInstWithInst(TI, NewTI); 2726acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn} 2736acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2746acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// SplitEdge - Split the edge connecting specified block. Pass P must 2756acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// not be NULL. 2766acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius RennBasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) { 2776acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn TerminatorInst *LatchTerm = BB->getTerminator(); 2786acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn unsigned SuccNum = 0; 2796acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#ifndef NDEBUG 2806acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn unsigned e = LatchTerm->getNumSuccessors(); 2816acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn#endif 2826acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn for (unsigned i = 0; ; ++i) { 2836acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn assert(i != e && "Didn't find edge?"); 2846acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (LatchTerm->getSuccessor(i) == Succ) { 2856acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn SuccNum = i; 2866acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn break; 2876acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 2886acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 2896acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2906acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // If this is a critical edge, let SplitCriticalEdge do it. 2916acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (SplitCriticalEdge(BB->getTerminator(), SuccNum, P)) 2926acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn return LatchTerm->getSuccessor(SuccNum); 2936acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 2946acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // If the edge isn't critical, then BB has a single successor or Succ has a 2956acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // single pred. Split the block. 2966acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BasicBlock::iterator SplitPoint; 2976acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (BasicBlock *SP = Succ->getSinglePredecessor()) { 2986acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // If the successor only has a single pred, split the top of the successor 2996acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // block. 3006acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn assert(SP == BB && "CFG broken"); 3016acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn SP = NULL; 3026acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn return SplitBlock(Succ, Succ->begin(), P); 3036acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } else { 3046acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Otherwise, if BB has a single successor, split it at the bottom of the 3056acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // block. 3066acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn assert(BB->getTerminator()->getNumSuccessors() == 1 && 3076acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn "Should have a single succ!"); 3086acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn return SplitBlock(BB, BB->getTerminator(), P); 3096acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 3106acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn} 3116acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 3126acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// SplitBlock - Split the specified block at the specified instruction - every 3136acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// thing before SplitPt stays in Old and everything starting with SplitPt moves 3146acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// to a new block. The two blocks are joined by an unconditional branch and 3156acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// the loop info is updated. 3166acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn/// 3176acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius RennBasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) { 3186acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BasicBlock::iterator SplitIt = SplitPt; 3196acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn while (isa<PHINode>(SplitIt)) 3206acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn ++SplitIt; 3216acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split"); 3226acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 3236acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // The new block lives in whichever loop the old one did. This preserves 3246acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // LCSSA as well, because we force the split point to be after any PHI nodes. 3256acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (LoopInfo* LI = P->getAnalysisIfAvailable<LoopInfo>()) 3266acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (Loop *L = LI->getLoopFor(Old)) 3276acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn L->addBasicBlockToLoop(New, LI->getBase()); 3286acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 3296acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>()) 3306acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn { 3316acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn // Old dominates New. New node domiantes all other nodes dominated by Old. 3326acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn DomTreeNode *OldNode = DT->getNode(Old); 3336acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn std::vector<DomTreeNode *> Children; 3346acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end(); 3356acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn I != E; ++I) 3366acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn Children.push_back(*I); 3376acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 3386acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn DomTreeNode *NewNode = DT->addNewBlock(New,Old); 3396acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 3406acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn for (std::vector<DomTreeNode *>::iterator I = Children.begin(), 3416acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn E = Children.end(); I != E; ++I) 3426acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn DT->changeImmediateDominator(*I, NewNode); 3436acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn } 3446acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn 3456acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn if (DominanceFrontier *DF = P->getAnalysisIfAvailable<DominanceFrontier>()) 3466acb9a7ea3d7564944e12cbc73a857b88c1301eeMarius Renn DF->splitBlock(Old); 347 348 return New; 349} 350 351 352/// SplitBlockPredecessors - This method transforms BB by introducing a new 353/// basic block into the function, and moving some of the predecessors of BB to 354/// be predecessors of the new block. The new predecessors are indicated by the 355/// Preds array, which has NumPreds elements in it. The new block is given a 356/// suffix of 'Suffix'. 357/// 358/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree, 359/// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. 360/// In particular, it does not preserve LoopSimplify (because it's 361/// complicated to handle the case where one of the edges being split 362/// is an exit of a loop with other exits). 363/// 364BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB, 365 BasicBlock *const *Preds, 366 unsigned NumPreds, const char *Suffix, 367 Pass *P) { 368 // Create new basic block, insert right before the original block. 369 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), BB->getName()+Suffix, 370 BB->getParent(), BB); 371 372 // The new block unconditionally branches to the old block. 373 BranchInst *BI = BranchInst::Create(BB, NewBB); 374 375 LoopInfo *LI = P ? P->getAnalysisIfAvailable<LoopInfo>() : 0; 376 Loop *L = LI ? LI->getLoopFor(BB) : 0; 377 bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID); 378 379 // Move the edges from Preds to point to NewBB instead of BB. 380 // While here, if we need to preserve loop analyses, collect 381 // some information about how this split will affect loops. 382 bool HasLoopExit = false; 383 bool IsLoopEntry = !!L; 384 bool SplitMakesNewLoopHeader = false; 385 for (unsigned i = 0; i != NumPreds; ++i) { 386 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB); 387 388 if (LI) { 389 // If we need to preserve LCSSA, determine if any of 390 // the preds is a loop exit. 391 if (PreserveLCSSA) 392 if (Loop *PL = LI->getLoopFor(Preds[i])) 393 if (!PL->contains(BB)) 394 HasLoopExit = true; 395 // If we need to preserve LoopInfo, note whether any of the 396 // preds crosses an interesting loop boundary. 397 if (L) { 398 if (L->contains(Preds[i])) 399 IsLoopEntry = false; 400 else 401 SplitMakesNewLoopHeader = true; 402 } 403 } 404 } 405 406 // Update dominator tree and dominator frontier if available. 407 DominatorTree *DT = P ? P->getAnalysisIfAvailable<DominatorTree>() : 0; 408 if (DT) 409 DT->splitBlock(NewBB); 410 if (DominanceFrontier *DF = P ? P->getAnalysisIfAvailable<DominanceFrontier>():0) 411 DF->splitBlock(NewBB); 412 413 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI 414 // node becomes an incoming value for BB's phi node. However, if the Preds 415 // list is empty, we need to insert dummy entries into the PHI nodes in BB to 416 // account for the newly created predecessor. 417 if (NumPreds == 0) { 418 // Insert dummy values as the incoming value. 419 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) 420 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB); 421 return NewBB; 422 } 423 424 AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0; 425 426 if (L) { 427 if (IsLoopEntry) { 428 // Add the new block to the nearest enclosing loop (and not an 429 // adjacent loop). To find this, examine each of the predecessors and 430 // determine which loops enclose them, and select the most-nested loop 431 // which contains the loop containing the block being split. 432 Loop *InnermostPredLoop = 0; 433 for (unsigned i = 0; i != NumPreds; ++i) 434 if (Loop *PredLoop = LI->getLoopFor(Preds[i])) { 435 // Seek a loop which actually contains the block being split (to 436 // avoid adjacent loops). 437 while (PredLoop && !PredLoop->contains(BB)) 438 PredLoop = PredLoop->getParentLoop(); 439 // Select the most-nested of these loops which contains the block. 440 if (PredLoop && 441 PredLoop->contains(BB) && 442 (!InnermostPredLoop || 443 InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth())) 444 InnermostPredLoop = PredLoop; 445 } 446 if (InnermostPredLoop) 447 InnermostPredLoop->addBasicBlockToLoop(NewBB, LI->getBase()); 448 } else { 449 L->addBasicBlockToLoop(NewBB, LI->getBase()); 450 if (SplitMakesNewLoopHeader) 451 L->moveToHeader(NewBB); 452 } 453 } 454 455 // Otherwise, create a new PHI node in NewBB for each PHI node in BB. 456 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) { 457 PHINode *PN = cast<PHINode>(I++); 458 459 // Check to see if all of the values coming in are the same. If so, we 460 // don't need to create a new PHI node, unless it's needed for LCSSA. 461 Value *InVal = 0; 462 if (!HasLoopExit) { 463 InVal = PN->getIncomingValueForBlock(Preds[0]); 464 for (unsigned i = 1; i != NumPreds; ++i) 465 if (InVal != PN->getIncomingValueForBlock(Preds[i])) { 466 InVal = 0; 467 break; 468 } 469 } 470 471 if (InVal) { 472 // If all incoming values for the new PHI would be the same, just don't 473 // make a new PHI. Instead, just remove the incoming values from the old 474 // PHI. 475 for (unsigned i = 0; i != NumPreds; ++i) 476 PN->removeIncomingValue(Preds[i], false); 477 } else { 478 // If the values coming into the block are not the same, we need a PHI. 479 // Create the new PHI node, insert it into NewBB at the end of the block 480 PHINode *NewPHI = 481 PHINode::Create(PN->getType(), PN->getName()+".ph", BI); 482 if (AA) AA->copyValue(PN, NewPHI); 483 484 // Move all of the PHI values for 'Preds' to the new PHI. 485 for (unsigned i = 0; i != NumPreds; ++i) { 486 Value *V = PN->removeIncomingValue(Preds[i], false); 487 NewPHI->addIncoming(V, Preds[i]); 488 } 489 InVal = NewPHI; 490 } 491 492 // Add an incoming value to the PHI node in the loop for the preheader 493 // edge. 494 PN->addIncoming(InVal, NewBB); 495 } 496 497 return NewBB; 498} 499 500/// FindFunctionBackedges - Analyze the specified function to find all of the 501/// loop backedges in the function and return them. This is a relatively cheap 502/// (compared to computing dominators and loop info) analysis. 503/// 504/// The output is added to Result, as pairs of <from,to> edge info. 505void llvm::FindFunctionBackedges(const Function &F, 506 SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) { 507 const BasicBlock *BB = &F.getEntryBlock(); 508 if (succ_begin(BB) == succ_end(BB)) 509 return; 510 511 SmallPtrSet<const BasicBlock*, 8> Visited; 512 SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack; 513 SmallPtrSet<const BasicBlock*, 8> InStack; 514 515 Visited.insert(BB); 516 VisitStack.push_back(std::make_pair(BB, succ_begin(BB))); 517 InStack.insert(BB); 518 do { 519 std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back(); 520 const BasicBlock *ParentBB = Top.first; 521 succ_const_iterator &I = Top.second; 522 523 bool FoundNew = false; 524 while (I != succ_end(ParentBB)) { 525 BB = *I++; 526 if (Visited.insert(BB)) { 527 FoundNew = true; 528 break; 529 } 530 // Successor is in VisitStack, it's a back edge. 531 if (InStack.count(BB)) 532 Result.push_back(std::make_pair(ParentBB, BB)); 533 } 534 535 if (FoundNew) { 536 // Go down one level if there is a unvisited successor. 537 InStack.insert(BB); 538 VisitStack.push_back(std::make_pair(BB, succ_begin(BB))); 539 } else { 540 // Go up one level. 541 InStack.erase(VisitStack.pop_back_val().first); 542 } 543 } while (!VisitStack.empty()); 544 545 546} 547 548 549 550/// AreEquivalentAddressValues - Test if A and B will obviously have the same 551/// value. This includes recognizing that %t0 and %t1 will have the same 552/// value in code like this: 553/// %t0 = getelementptr \@a, 0, 3 554/// store i32 0, i32* %t0 555/// %t1 = getelementptr \@a, 0, 3 556/// %t2 = load i32* %t1 557/// 558static bool AreEquivalentAddressValues(const Value *A, const Value *B) { 559 // Test if the values are trivially equivalent. 560 if (A == B) return true; 561 562 // Test if the values come from identical arithmetic instructions. 563 // Use isIdenticalToWhenDefined instead of isIdenticalTo because 564 // this function is only used when one address use dominates the 565 // other, which means that they'll always either have the same 566 // value or one of them will have an undefined value. 567 if (isa<BinaryOperator>(A) || isa<CastInst>(A) || 568 isa<PHINode>(A) || isa<GetElementPtrInst>(A)) 569 if (const Instruction *BI = dyn_cast<Instruction>(B)) 570 if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI)) 571 return true; 572 573 // Otherwise they may not be equivalent. 574 return false; 575} 576 577/// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at the 578/// instruction before ScanFrom) checking to see if we have the value at the 579/// memory address *Ptr locally available within a small number of instructions. 580/// If the value is available, return it. 581/// 582/// If not, return the iterator for the last validated instruction that the 583/// value would be live through. If we scanned the entire block and didn't find 584/// something that invalidates *Ptr or provides it, ScanFrom would be left at 585/// begin() and this returns null. ScanFrom could also be left 586/// 587/// MaxInstsToScan specifies the maximum instructions to scan in the block. If 588/// it is set to 0, it will scan the whole block. You can also optionally 589/// specify an alias analysis implementation, which makes this more precise. 590Value *llvm::FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB, 591 BasicBlock::iterator &ScanFrom, 592 unsigned MaxInstsToScan, 593 AliasAnalysis *AA) { 594 if (MaxInstsToScan == 0) MaxInstsToScan = ~0U; 595 596 // If we're using alias analysis to disambiguate get the size of *Ptr. 597 unsigned AccessSize = 0; 598 if (AA) { 599 const Type *AccessTy = cast<PointerType>(Ptr->getType())->getElementType(); 600 AccessSize = AA->getTypeStoreSize(AccessTy); 601 } 602 603 while (ScanFrom != ScanBB->begin()) { 604 // We must ignore debug info directives when counting (otherwise they 605 // would affect codegen). 606 Instruction *Inst = --ScanFrom; 607 if (isa<DbgInfoIntrinsic>(Inst)) 608 continue; 609 // We skip pointer-to-pointer bitcasts, which are NOPs. 610 // It is necessary for correctness to skip those that feed into a 611 // llvm.dbg.declare, as these are not present when debugging is off. 612 if (isa<BitCastInst>(Inst) && isa<PointerType>(Inst->getType())) 613 continue; 614 615 // Restore ScanFrom to expected value in case next test succeeds 616 ScanFrom++; 617 618 // Don't scan huge blocks. 619 if (MaxInstsToScan-- == 0) return 0; 620 621 --ScanFrom; 622 // If this is a load of Ptr, the loaded value is available. 623 if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) 624 if (AreEquivalentAddressValues(LI->getOperand(0), Ptr)) 625 return LI; 626 627 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { 628 // If this is a store through Ptr, the value is available! 629 if (AreEquivalentAddressValues(SI->getOperand(1), Ptr)) 630 return SI->getOperand(0); 631 632 // If Ptr is an alloca and this is a store to a different alloca, ignore 633 // the store. This is a trivial form of alias analysis that is important 634 // for reg2mem'd code. 635 if ((isa<AllocaInst>(Ptr) || isa<GlobalVariable>(Ptr)) && 636 (isa<AllocaInst>(SI->getOperand(1)) || 637 isa<GlobalVariable>(SI->getOperand(1)))) 638 continue; 639 640 // If we have alias analysis and it says the store won't modify the loaded 641 // value, ignore the store. 642 if (AA && 643 (AA->getModRefInfo(SI, Ptr, AccessSize) & AliasAnalysis::Mod) == 0) 644 continue; 645 646 // Otherwise the store that may or may not alias the pointer, bail out. 647 ++ScanFrom; 648 return 0; 649 } 650 651 // If this is some other instruction that may clobber Ptr, bail out. 652 if (Inst->mayWriteToMemory()) { 653 // If alias analysis claims that it really won't modify the load, 654 // ignore it. 655 if (AA && 656 (AA->getModRefInfo(Inst, Ptr, AccessSize) & AliasAnalysis::Mod) == 0) 657 continue; 658 659 // May modify the pointer, bail out. 660 ++ScanFrom; 661 return 0; 662 } 663 } 664 665 // Got to the start of the block, we didn't find it, but are done for this 666 // block. 667 return 0; 668} 669 670/// CopyPrecedingStopPoint - If I is immediately preceded by a StopPoint, 671/// make a copy of the stoppoint before InsertPos (presumably before copying 672/// or moving I). 673void llvm::CopyPrecedingStopPoint(Instruction *I, 674 BasicBlock::iterator InsertPos) { 675 if (I != I->getParent()->begin()) { 676 BasicBlock::iterator BBI = I; --BBI; 677 if (DbgStopPointInst *DSPI = dyn_cast<DbgStopPointInst>(BBI)) { 678 CallInst *newDSPI = DSPI->clone(); 679 newDSPI->insertBefore(InsertPos); 680 } 681 } 682} 683