BasicBlockUtils.h revision 327952
1327952Sdim//===- Transform/Utils/BasicBlockUtils.h - BasicBlock Utils -----*- C++ -*-===// 2193323Sed// 3193323Sed// The LLVM Compiler Infrastructure 4193323Sed// 5193323Sed// This file is distributed under the University of Illinois Open Source 6193323Sed// License. See LICENSE.TXT for details. 7193323Sed// 8193323Sed//===----------------------------------------------------------------------===// 9193323Sed// 10193323Sed// This family of functions perform manipulations on basic blocks, and 11193323Sed// instructions contained within basic blocks. 12193323Sed// 13193323Sed//===----------------------------------------------------------------------===// 14193323Sed 15249423Sdim#ifndef LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H 16249423Sdim#define LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H 17193323Sed 18193323Sed// FIXME: Move to this file: BasicBlock::removePredecessor, BB::splitBasicBlock 19193323Sed 20314564Sdim#include "llvm/ADT/ArrayRef.h" 21249423Sdim#include "llvm/IR/BasicBlock.h" 22276479Sdim#include "llvm/IR/CFG.h" 23314564Sdim#include "llvm/IR/InstrTypes.h" 24314564Sdim#include <cassert> 25193323Sed 26193323Sednamespace llvm { 27193323Sed 28327952Sdimclass BlockFrequencyInfo; 29327952Sdimclass BranchProbabilityInfo; 30276479Sdimclass DominatorTree; 31327952Sdimclass Function; 32327952Sdimclass Instruction; 33288943Sdimclass LoopInfo; 34243830Sdimclass MDNode; 35327952Sdimclass MemoryDependenceResults; 36218893Sdimclass ReturnInst; 37243830Sdimclass TargetLibraryInfo; 38327952Sdimclass Value; 39193323Sed 40309124Sdim/// Delete the specified block, which must have no predecessors. 41193323Sedvoid DeleteDeadBlock(BasicBlock *BB); 42226633Sdim 43309124Sdim/// We know that BB has one predecessor. If there are any single-entry PHI nodes 44309124Sdim/// in it, fold them away. This handles the case when all entries to the PHI 45309124Sdim/// nodes in a block are guaranteed equal, such as when the block has exactly 46309124Sdim/// one predecessor. 47296417Sdimvoid FoldSingleEntryPHINodes(BasicBlock *BB, 48309124Sdim MemoryDependenceResults *MemDep = nullptr); 49193323Sed 50309124Sdim/// Examine each PHI in the given block and delete it if it is dead. Also 51309124Sdim/// recursively delete any operands that become dead as a result. This includes 52309124Sdim/// tracing the def-use list from the PHI to see if it is ultimately unused or 53309124Sdim/// if it reaches an unused cycle. Return true if any PHIs were deleted. 54276479Sdimbool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = nullptr); 55193323Sed 56309124Sdim/// Attempts to merge a block into its predecessor, if possible. The return 57309124Sdim/// value indicates success or failure. 58288943Sdimbool MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT = nullptr, 59288943Sdim LoopInfo *LI = nullptr, 60309124Sdim MemoryDependenceResults *MemDep = nullptr); 61193323Sed 62309124Sdim/// Replace all uses of an instruction (specified by BI) with a value, then 63309124Sdim/// remove and delete the original instruction. 64193323Sedvoid ReplaceInstWithValue(BasicBlock::InstListType &BIL, 65193323Sed BasicBlock::iterator &BI, Value *V); 66193323Sed 67309124Sdim/// Replace the instruction specified by BI with the instruction specified by I. 68309124Sdim/// Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc. The 69309124Sdim/// original instruction is deleted and BI is updated to point to the new 70309124Sdim/// instruction. 71193323Sedvoid ReplaceInstWithInst(BasicBlock::InstListType &BIL, 72193323Sed BasicBlock::iterator &BI, Instruction *I); 73193323Sed 74309124Sdim/// Replace the instruction specified by From with the instruction specified by 75309124Sdim/// To. Copies DebugLoc from BI to I, if I doesn't already have a DebugLoc. 76193323Sedvoid ReplaceInstWithInst(Instruction *From, Instruction *To); 77193323Sed 78309124Sdim/// Option class for critical edge splitting. 79288943Sdim/// 80288943Sdim/// This provides a builder interface for overriding the default options used 81288943Sdim/// during critical edge splitting. 82288943Sdimstruct CriticalEdgeSplittingOptions { 83288943Sdim DominatorTree *DT; 84288943Sdim LoopInfo *LI; 85321369Sdim bool MergeIdenticalEdges = false; 86321369Sdim bool DontDeleteUselessPHIs = false; 87321369Sdim bool PreserveLCSSA = false; 88288943Sdim 89296417Sdim CriticalEdgeSplittingOptions(DominatorTree *DT = nullptr, 90288943Sdim LoopInfo *LI = nullptr) 91321369Sdim : DT(DT), LI(LI) {} 92288943Sdim 93288943Sdim CriticalEdgeSplittingOptions &setMergeIdenticalEdges() { 94288943Sdim MergeIdenticalEdges = true; 95288943Sdim return *this; 96288943Sdim } 97288943Sdim 98288943Sdim CriticalEdgeSplittingOptions &setDontDeleteUselessPHIs() { 99288943Sdim DontDeleteUselessPHIs = true; 100288943Sdim return *this; 101288943Sdim } 102288943Sdim 103288943Sdim CriticalEdgeSplittingOptions &setPreserveLCSSA() { 104288943Sdim PreserveLCSSA = true; 105288943Sdim return *this; 106288943Sdim } 107288943Sdim}; 108288943Sdim 109309124Sdim/// If this edge is a critical edge, insert a new node to split the critical 110309124Sdim/// edge. This will update the analyses passed in through the option struct. 111309124Sdim/// This returns the new block if the edge was split, null otherwise. 112193323Sed/// 113288943Sdim/// If MergeIdenticalEdges in the options struct is true (not the default), 114288943Sdim/// *all* edges from TI to the specified successor will be merged into the same 115288943Sdim/// critical edge block. This is most commonly interesting with switch 116288943Sdim/// instructions, which may have many edges to any one destination. This 117288943Sdim/// ensures that all edges to that dest go to one block instead of each going 118288943Sdim/// to a different block, but isn't the standard definition of a "critical 119288943Sdim/// edge". 120193323Sed/// 121198892Srdivacky/// It is invalid to call this function on a critical edge that starts at an 122198892Srdivacky/// IndirectBrInst. Splitting these edges will almost always create an invalid 123198892Srdivacky/// program because the address of the new block won't be the one that is jumped 124198892Srdivacky/// to. 125198090SrdivackyBasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, 126288943Sdim const CriticalEdgeSplittingOptions &Options = 127288943Sdim CriticalEdgeSplittingOptions()); 128193323Sed 129288943Sdiminline BasicBlock * 130288943SdimSplitCriticalEdge(BasicBlock *BB, succ_iterator SI, 131288943Sdim const CriticalEdgeSplittingOptions &Options = 132288943Sdim CriticalEdgeSplittingOptions()) { 133288943Sdim return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(), 134288943Sdim Options); 135193323Sed} 136193323Sed 137309124Sdim/// If the edge from *PI to BB is not critical, return false. Otherwise, split 138309124Sdim/// all edges between the two blocks and return true. This updates all of the 139309124Sdim/// same analyses as the other SplitCriticalEdge function. If P is specified, it 140309124Sdim/// updates the analyses described above. 141276479Sdiminline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI, 142288943Sdim const CriticalEdgeSplittingOptions &Options = 143288943Sdim CriticalEdgeSplittingOptions()) { 144193323Sed bool MadeChange = false; 145193323Sed TerminatorInst *TI = (*PI)->getTerminator(); 146193323Sed for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) 147193323Sed if (TI->getSuccessor(i) == Succ) 148288943Sdim MadeChange |= !!SplitCriticalEdge(TI, i, Options); 149193323Sed return MadeChange; 150193323Sed} 151193323Sed 152309124Sdim/// If an edge from Src to Dst is critical, split the edge and return true, 153309124Sdim/// otherwise return false. This method requires that there be an edge between 154309124Sdim/// the two blocks. It updates the analyses passed in the options struct 155288943Sdiminline BasicBlock * 156288943SdimSplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst, 157288943Sdim const CriticalEdgeSplittingOptions &Options = 158288943Sdim CriticalEdgeSplittingOptions()) { 159193323Sed TerminatorInst *TI = Src->getTerminator(); 160193323Sed unsigned i = 0; 161314564Sdim while (true) { 162193323Sed assert(i != TI->getNumSuccessors() && "Edge doesn't exist!"); 163193323Sed if (TI->getSuccessor(i) == Dst) 164288943Sdim return SplitCriticalEdge(TI, i, Options); 165193323Sed ++i; 166193323Sed } 167193323Sed} 168193323Sed 169309124Sdim/// Loop over all of the edges in the CFG, breaking critical edges as they are 170309124Sdim/// found. Returns the number of broken edges. 171288943Sdimunsigned SplitAllCriticalEdges(Function &F, 172288943Sdim const CriticalEdgeSplittingOptions &Options = 173288943Sdim CriticalEdgeSplittingOptions()); 174280031Sdim 175309124Sdim/// Split the edge connecting specified block. 176288943SdimBasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To, 177288943Sdim DominatorTree *DT = nullptr, LoopInfo *LI = nullptr); 178193323Sed 179309124Sdim/// Split the specified block at the specified instruction - everything before 180309124Sdim/// SplitPt stays in Old and everything starting with SplitPt moves to a new 181309124Sdim/// block. The two blocks are joined by an unconditional branch and the loop 182309124Sdim/// info is updated. 183288943SdimBasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, 184288943Sdim DominatorTree *DT = nullptr, LoopInfo *LI = nullptr); 185226633Sdim 186309124Sdim/// This method introduces at least one new basic block into the function and 187309124Sdim/// moves some of the predecessors of BB to be predecessors of the new block. 188309124Sdim/// The new predecessors are indicated by the Preds array. The new block is 189309124Sdim/// given a suffix of 'Suffix'. Returns new basic block to which predecessors 190309124Sdim/// from Preds are now pointing. 191193323Sed/// 192288943Sdim/// If BB is a landingpad block then additional basicblock might be introduced. 193288943Sdim/// It will have Suffix+".split_lp". See SplitLandingPadPredecessors for more 194288943Sdim/// details on this case. 195288943Sdim/// 196296417Sdim/// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but 197296417Sdim/// no other analyses. In particular, it does not preserve LoopSimplify 198296417Sdim/// (because it's complicated to handle the case where one of the edges being 199296417Sdim/// split is an exit of a loop with other exits). 200288943SdimBasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock *> Preds, 201288943Sdim const char *Suffix, 202288943Sdim DominatorTree *DT = nullptr, 203288943Sdim LoopInfo *LI = nullptr, 204288943Sdim bool PreserveLCSSA = false); 205218893Sdim 206309124Sdim/// This method transforms the landing pad, OrigBB, by introducing two new basic 207309124Sdim/// blocks into the function. One of those new basic blocks gets the 208309124Sdim/// predecessors listed in Preds. The other basic block gets the remaining 209309124Sdim/// predecessors of OrigBB. The landingpad instruction OrigBB is clone into both 210309124Sdim/// of the new basic blocks. The new blocks are given the suffixes 'Suffix1' and 211309124Sdim/// 'Suffix2', and are returned in the NewBBs vector. 212226633Sdim/// 213296417Sdim/// This currently updates the LLVM IR, DominatorTree, LoopInfo, and LCCSA but 214296417Sdim/// no other analyses. In particular, it does not preserve LoopSimplify 215296417Sdim/// (because it's complicated to handle the case where one of the edges being 216296417Sdim/// split is an exit of a loop with other exits). 217288943Sdimvoid SplitLandingPadPredecessors(BasicBlock *OrigBB, 218288943Sdim ArrayRef<BasicBlock *> Preds, 219226633Sdim const char *Suffix, const char *Suffix2, 220288943Sdim SmallVectorImpl<BasicBlock *> &NewBBs, 221288943Sdim DominatorTree *DT = nullptr, 222288943Sdim LoopInfo *LI = nullptr, 223288943Sdim bool PreserveLCSSA = false); 224226633Sdim 225309124Sdim/// This method duplicates the specified return instruction into a predecessor 226309124Sdim/// which ends in an unconditional branch. If the return instruction returns a 227309124Sdim/// value defined by a PHI, propagate the right value into the return. It 228309124Sdim/// returns the new return instruction in the predecessor. 229218893SdimReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB, 230218893Sdim BasicBlock *Pred); 231218893Sdim 232309124Sdim/// Split the containing block at the specified instruction - everything before 233314564Sdim/// SplitBefore stays in the old basic block, and the rest of the instructions 234314564Sdim/// in the BB are moved to a new block. The two blocks are connected by a 235309124Sdim/// conditional branch (with value of Cmp being the condition). 236243830Sdim/// Before: 237243830Sdim/// Head 238276479Sdim/// SplitBefore 239243830Sdim/// Tail 240243830Sdim/// After: 241243830Sdim/// Head 242276479Sdim/// if (Cond) 243243830Sdim/// ThenBlock 244276479Sdim/// SplitBefore 245243830Sdim/// Tail 246243830Sdim/// 247243830Sdim/// If Unreachable is true, then ThenBlock ends with 248243830Sdim/// UnreachableInst, otherwise it branches to Tail. 249243830Sdim/// Returns the NewBasicBlock's terminator. 250276479Sdim/// 251309124Sdim/// Updates DT and LI if given. 252276479SdimTerminatorInst *SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore, 253276479Sdim bool Unreachable, 254276479Sdim MDNode *BranchWeights = nullptr, 255309124Sdim DominatorTree *DT = nullptr, 256309124Sdim LoopInfo *LI = nullptr); 257243830Sdim 258276479Sdim/// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen, 259276479Sdim/// but also creates the ElseBlock. 260276479Sdim/// Before: 261276479Sdim/// Head 262276479Sdim/// SplitBefore 263276479Sdim/// Tail 264276479Sdim/// After: 265276479Sdim/// Head 266276479Sdim/// if (Cond) 267276479Sdim/// ThenBlock 268276479Sdim/// else 269276479Sdim/// ElseBlock 270276479Sdim/// SplitBefore 271276479Sdim/// Tail 272276479Sdimvoid SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore, 273276479Sdim TerminatorInst **ThenTerm, 274276479Sdim TerminatorInst **ElseTerm, 275276479Sdim MDNode *BranchWeights = nullptr); 276243830Sdim 277309124Sdim/// Check whether BB is the merge point of a if-region. 278261991Sdim/// If so, return the boolean condition that determines which entry into 279261991Sdim/// BB will be taken. Also, return by references the block that will be 280261991Sdim/// entered from if the condition is true, and the block that will be 281261991Sdim/// entered if the condition is false. 282309124Sdim/// 283309124Sdim/// This does no checking to see if the true/false blocks have large or unsavory 284309124Sdim/// instructions in them. 285261991SdimValue *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, 286276479Sdim BasicBlock *&IfFalse); 287193323Sed 288327952Sdim// Split critical edges where the source of the edge is an indirectbr 289327952Sdim// instruction. This isn't always possible, but we can handle some easy cases. 290327952Sdim// This is useful because MI is unable to split such critical edges, 291327952Sdim// which means it will not be able to sink instructions along those edges. 292327952Sdim// This is especially painful for indirect branches with many successors, where 293327952Sdim// we end up having to prepare all outgoing values in the origin block. 294327952Sdim// 295327952Sdim// Our normal algorithm for splitting critical edges requires us to update 296327952Sdim// the outgoing edges of the edge origin block, but for an indirectbr this 297327952Sdim// is hard, since it would require finding and updating the block addresses 298327952Sdim// the indirect branch uses. But if a block only has a single indirectbr 299327952Sdim// predecessor, with the others being regular branches, we can do it in a 300327952Sdim// different way. 301327952Sdim// Say we have A -> D, B -> D, I -> D where only I -> D is an indirectbr. 302327952Sdim// We can split D into D0 and D1, where D0 contains only the PHIs from D, 303327952Sdim// and D1 is the D block body. We can then duplicate D0 as D0A and D0B, and 304327952Sdim// create the following structure: 305327952Sdim// A -> D0A, B -> D0A, I -> D0B, D0A -> D1, D0B -> D1 306327952Sdim// If BPI and BFI aren't non-null, BPI/BFI will be updated accordingly. 307327952Sdimbool SplitIndirectBrCriticalEdges(Function &F, 308327952Sdim BranchProbabilityInfo *BPI = nullptr, 309327952Sdim BlockFrequencyInfo *BFI = nullptr); 310327952Sdim 311314564Sdim} // end namespace llvm 312314564Sdim 313314564Sdim#endif // LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H 314