1//===-- Transform/Utils/BasicBlockUtils.h - BasicBlock Utils ----*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This family of functions perform manipulations on basic blocks, and
11// instructions contained within basic blocks.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H
16#define LLVM_TRANSFORMS_UTILS_BASICBLOCKUTILS_H
17
18// FIXME: Move to this file: BasicBlock::removePredecessor, BB::splitBasicBlock
19
20#include "llvm/IR/BasicBlock.h"
21#include "llvm/Support/CFG.h"
22
23namespace llvm {
24
25class AliasAnalysis;
26class Instruction;
27class MDNode;
28class Pass;
29class ReturnInst;
30class TargetLibraryInfo;
31class TerminatorInst;
32
33/// DeleteDeadBlock - Delete the specified block, which must have no
34/// predecessors.
35void DeleteDeadBlock(BasicBlock *BB);
36
37
38/// FoldSingleEntryPHINodes - We know that BB has one predecessor.  If there are
39/// any single-entry PHI nodes in it, fold them away.  This handles the case
40/// when all entries to the PHI nodes in a block are guaranteed equal, such as
41/// when the block has exactly one predecessor.
42void FoldSingleEntryPHINodes(BasicBlock *BB, Pass *P = 0);
43
44/// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
45/// is dead. Also recursively delete any operands that become dead as
46/// a result. This includes tracing the def-use list from the PHI to see if
47/// it is ultimately unused or if it reaches an unused cycle. Return true
48/// if any PHIs were deleted.
49bool DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI = 0);
50
51/// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
52/// if possible.  The return value indicates success or failure.
53bool MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P = 0);
54
55// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
56// with a value, then remove and delete the original instruction.
57//
58void ReplaceInstWithValue(BasicBlock::InstListType &BIL,
59                          BasicBlock::iterator &BI, Value *V);
60
61// ReplaceInstWithInst - Replace the instruction specified by BI with the
62// instruction specified by I.  The original instruction is deleted and BI is
63// updated to point to the new instruction.
64//
65void ReplaceInstWithInst(BasicBlock::InstListType &BIL,
66                         BasicBlock::iterator &BI, Instruction *I);
67
68// ReplaceInstWithInst - Replace the instruction specified by From with the
69// instruction specified by To.
70//
71void ReplaceInstWithInst(Instruction *From, Instruction *To);
72
73/// SplitCriticalEdge - If this edge is a critical edge, insert a new node to
74/// split the critical edge.  This will update DominatorTree and
75/// DominatorFrontier information if it is available, thus calling this pass
76/// will not invalidate either of them. This returns the new block if the edge
77/// was split, null otherwise.
78///
79/// If MergeIdenticalEdges is true (not the default), *all* edges from TI to the
80/// specified successor will be merged into the same critical edge block.
81/// This is most commonly interesting with switch instructions, which may
82/// have many edges to any one destination.  This ensures that all edges to that
83/// dest go to one block instead of each going to a different block, but isn't
84/// the standard definition of a "critical edge".
85///
86/// It is invalid to call this function on a critical edge that starts at an
87/// IndirectBrInst.  Splitting these edges will almost always create an invalid
88/// program because the address of the new block won't be the one that is jumped
89/// to.
90///
91BasicBlock *SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
92                              Pass *P = 0, bool MergeIdenticalEdges = false,
93                              bool DontDeleteUselessPHIs = false,
94                              bool SplitLandingPads = false);
95
96inline BasicBlock *SplitCriticalEdge(BasicBlock *BB, succ_iterator SI,
97                                     Pass *P = 0) {
98  return SplitCriticalEdge(BB->getTerminator(), SI.getSuccessorIndex(), P);
99}
100
101/// SplitCriticalEdge - If the edge from *PI to BB is not critical, return
102/// false.  Otherwise, split all edges between the two blocks and return true.
103/// This updates all of the same analyses as the other SplitCriticalEdge
104/// function.  If P is specified, it updates the analyses
105/// described above.
106inline bool SplitCriticalEdge(BasicBlock *Succ, pred_iterator PI, Pass *P = 0) {
107  bool MadeChange = false;
108  TerminatorInst *TI = (*PI)->getTerminator();
109  for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
110    if (TI->getSuccessor(i) == Succ)
111      MadeChange |= !!SplitCriticalEdge(TI, i, P);
112  return MadeChange;
113}
114
115/// SplitCriticalEdge - If an edge from Src to Dst is critical, split the edge
116/// and return true, otherwise return false.  This method requires that there be
117/// an edge between the two blocks.  If P is specified, it updates the analyses
118/// described above.
119inline BasicBlock *SplitCriticalEdge(BasicBlock *Src, BasicBlock *Dst,
120                                     Pass *P = 0,
121                                     bool MergeIdenticalEdges = false,
122                                     bool DontDeleteUselessPHIs = false) {
123  TerminatorInst *TI = Src->getTerminator();
124  unsigned i = 0;
125  while (1) {
126    assert(i != TI->getNumSuccessors() && "Edge doesn't exist!");
127    if (TI->getSuccessor(i) == Dst)
128      return SplitCriticalEdge(TI, i, P, MergeIdenticalEdges,
129                               DontDeleteUselessPHIs);
130    ++i;
131  }
132}
133
134/// SplitEdge -  Split the edge connecting specified block. Pass P must
135/// not be NULL.
136BasicBlock *SplitEdge(BasicBlock *From, BasicBlock *To, Pass *P);
137
138/// SplitBlock - Split the specified block at the specified instruction - every
139/// thing before SplitPt stays in Old and everything starting with SplitPt moves
140/// to a new block.  The two blocks are joined by an unconditional branch and
141/// the loop info is updated.
142///
143BasicBlock *SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P);
144
145/// SplitBlockPredecessors - This method transforms BB by introducing a new
146/// basic block into the function, and moving some of the predecessors of BB to
147/// be predecessors of the new block.  The new predecessors are indicated by the
148/// Preds array, which has NumPreds elements in it.  The new block is given a
149/// suffix of 'Suffix'.  This function returns the new block.
150///
151/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
152/// DominanceFrontier, LoopInfo, and LCCSA but no other analyses.
153/// In particular, it does not preserve LoopSimplify (because it's
154/// complicated to handle the case where one of the edges being split
155/// is an exit of a loop with other exits).
156///
157BasicBlock *SplitBlockPredecessors(BasicBlock *BB, ArrayRef<BasicBlock*> Preds,
158                                   const char *Suffix, Pass *P = 0);
159
160/// SplitLandingPadPredecessors - This method transforms the landing pad,
161/// OrigBB, by introducing two new basic blocks into the function. One of those
162/// new basic blocks gets the predecessors listed in Preds. The other basic
163/// block gets the remaining predecessors of OrigBB. The landingpad instruction
164/// OrigBB is clone into both of the new basic blocks. The new blocks are given
165/// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector.
166///
167/// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
168/// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular,
169/// it does not preserve LoopSimplify (because it's complicated to handle the
170/// case where one of the edges being split is an exit of a loop with other
171/// exits).
172///
173void SplitLandingPadPredecessors(BasicBlock *OrigBB,ArrayRef<BasicBlock*> Preds,
174                                 const char *Suffix, const char *Suffix2,
175                                 Pass *P, SmallVectorImpl<BasicBlock*> &NewBBs);
176
177/// FoldReturnIntoUncondBranch - This method duplicates the specified return
178/// instruction into a predecessor which ends in an unconditional branch. If
179/// the return instruction returns a value defined by a PHI, propagate the
180/// right value into the return. It returns the new return instruction in the
181/// predecessor.
182ReturnInst *FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
183                                       BasicBlock *Pred);
184
185/// SplitBlockAndInsertIfThen - Split the containing block at the
186/// specified instruction - everything before and including Cmp stays
187/// in the old basic block, and everything after Cmp is moved to a
188/// new block. The two blocks are connected by a conditional branch
189/// (with value of Cmp being the condition).
190/// Before:
191///   Head
192///   Cmp
193///   Tail
194/// After:
195///   Head
196///   Cmp
197///   if (Cmp)
198///     ThenBlock
199///   Tail
200///
201/// If Unreachable is true, then ThenBlock ends with
202/// UnreachableInst, otherwise it branches to Tail.
203/// Returns the NewBasicBlock's terminator.
204
205TerminatorInst *SplitBlockAndInsertIfThen(Instruction *Cmp,
206    bool Unreachable, MDNode *BranchWeights = 0);
207
208///
209/// GetIfCondition - Check whether BB is the merge point of a if-region.
210/// If so, return the boolean condition that determines which entry into
211/// BB will be taken.  Also, return by references the block that will be
212/// entered from if the condition is true, and the block that will be
213/// entered if the condition is false.
214
215Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
216		      BasicBlock *&IfFalse);
217} // End llvm namespace
218
219#endif
220