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Chris Lattner184b2982002-09-08 18:59:35 +00001//===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===//
Misha Brukmanb1c93172005-04-21 23:48:37 +00002//
John Criswell482202a2003-10-20 19:43:21 +00003// The LLVM Compiler Infrastructure
4//
Chris Lattnerf3ebc3f2007-12-29 20:36:04 +00005// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
Misha Brukmanb1c93172005-04-21 23:48:37 +00007//
John Criswell482202a2003-10-20 19:43:21 +00008//===----------------------------------------------------------------------===//
Chris Lattner2f7c9632001-06-06 20:29:01 +00009//
Chris Lattnerf739fa82002-04-08 22:03:57 +000010// This file implements the BasicBlock class for the VMCore library.
Chris Lattner2f7c9632001-06-06 20:29:01 +000011//
12//===----------------------------------------------------------------------===//
13
Gabor Greifa3de9e42008-05-27 17:26:02 +000014#include "llvm/BasicBlock.h"
Chris Lattner9daef352005-04-12 18:52:14 +000015#include "llvm/Constants.h"
Misha Brukman2d3fa9e2004-07-29 16:53:53 +000016#include "llvm/Instructions.h"
Chris Lattner2f7c9632001-06-06 20:29:01 +000017#include "llvm/Type.h"
Dan Gohman804c95d2008-07-28 21:51:04 +000018#include "llvm/ADT/STLExtras.h"
Chris Lattner83d485b2002-02-12 22:39:50 +000019#include "llvm/Support/CFG.h"
Reid Spencer7c16caa2004-09-01 22:55:40 +000020#include "llvm/Support/LeakDetector.h"
Chris Lattner3d27be12006-08-27 12:54:02 +000021#include "llvm/Support/Compiler.h"
Chris Lattner113f4f42002-06-25 16:13:24 +000022#include "SymbolTableListTraitsImpl.h"
23#include <algorithm>
Chris Lattnera2960002003-11-21 16:52:05 +000024using namespace llvm;
Chris Lattner2f7c9632001-06-06 20:29:01 +000025
Chris Lattnerb47aa542007-04-17 03:26:42 +000026inline ValueSymbolTable *
27ilist_traits<Instruction>::getSymTab(BasicBlock *BB) {
28 if (BB)
29 if (Function *F = BB->getParent())
30 return &F->getValueSymbolTable();
31 return 0;
32}
33
Gordon Henriksen14a55692007-12-10 02:14:30 +000034
35namespace {
36 /// DummyInst - An instance of this class is used to mark the end of the
37 /// instruction list. This is not a real instruction.
38 struct VISIBILITY_HIDDEN DummyInst : public Instruction {
Gabor Greife9ecc682008-04-06 20:25:17 +000039 // allocate space for exactly zero operands
40 void *operator new(size_t s) {
41 return User::operator new(s, 0);
42 }
Gordon Henriksen14a55692007-12-10 02:14:30 +000043 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd, 0, 0) {
44 // This should not be garbage monitored.
45 LeakDetector::removeGarbageObject(this);
46 }
47
48 Instruction *clone() const {
49 assert(0 && "Cannot clone EOL");abort();
50 return 0;
51 }
52 const char *getOpcodeName() const { return "*end-of-list-inst*"; }
53
54 // Methods for support type inquiry through isa, cast, and dyn_cast...
55 static inline bool classof(const DummyInst *) { return true; }
56 static inline bool classof(const Instruction *I) {
57 return I->getOpcode() == OtherOpsEnd;
58 }
59 static inline bool classof(const Value *V) {
60 return isa<Instruction>(V) && classof(cast<Instruction>(V));
61 }
62 };
Chris Lattnera2960002003-11-21 16:52:05 +000063}
Chris Lattner113f4f42002-06-25 16:13:24 +000064
Chris Lattnerf6c93e32005-01-30 00:09:23 +000065Instruction *ilist_traits<Instruction>::createSentinel() {
Chris Lattner113f4f42002-06-25 16:13:24 +000066 return new DummyInst();
67}
68iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) {
69 return BB->getInstList();
70}
71
72// Explicit instantiation of SymbolTableListTraits since some of the methods
73// are not in the public header file...
Chris Lattnerb47aa542007-04-17 03:26:42 +000074template class SymbolTableListTraits<Instruction, BasicBlock>;
Chris Lattner113f4f42002-06-25 16:13:24 +000075
Chris Lattner2f7c9632001-06-06 20:29:01 +000076
Chris Lattnerb47aa542007-04-17 03:26:42 +000077BasicBlock::BasicBlock(const std::string &Name, Function *NewParent,
Nick Lewycky4d43d3c2008-04-25 16:53:59 +000078 BasicBlock *InsertBefore)
79 : Value(Type::LabelTy, Value::BasicBlockVal), Parent(0) {
Chris Lattner4dfede82002-09-26 05:03:22 +000080
81 // Make sure that we get added to a function
82 LeakDetector::addGarbageObject(this);
83
84 if (InsertBefore) {
Chris Lattnerb47aa542007-04-17 03:26:42 +000085 assert(NewParent &&
Chris Lattnerbb5f0db2004-02-04 03:57:50 +000086 "Cannot insert block before another block with no function!");
Chris Lattnerb47aa542007-04-17 03:26:42 +000087 NewParent->getBasicBlockList().insert(InsertBefore, this);
88 } else if (NewParent) {
89 NewParent->getBasicBlockList().push_back(this);
Chris Lattner4dfede82002-09-26 05:03:22 +000090 }
Chris Lattner32ab6432007-02-12 05:18:08 +000091
92 setName(Name);
Chris Lattner4dfede82002-09-26 05:03:22 +000093}
94
95
Gordon Henriksen14a55692007-12-10 02:14:30 +000096BasicBlock::~BasicBlock() {
97 assert(getParent() == 0 && "BasicBlock still linked into the program!");
98 dropAllReferences();
99 InstList.clear();
Chris Lattner2f7c9632001-06-06 20:29:01 +0000100}
101
Chris Lattner9ed7aef2002-09-06 21:33:15 +0000102void BasicBlock::setParent(Function *parent) {
Chris Lattner184b2982002-09-08 18:59:35 +0000103 if (getParent())
104 LeakDetector::addGarbageObject(this);
105
Chris Lattnerb47aa542007-04-17 03:26:42 +0000106 // Set Parent=parent, updating instruction symtab entries as appropriate.
107 InstList.setSymTabObject(&Parent, parent);
Chris Lattner184b2982002-09-08 18:59:35 +0000108
109 if (getParent())
110 LeakDetector::removeGarbageObject(this);
Chris Lattner9ed7aef2002-09-06 21:33:15 +0000111}
112
Chris Lattner02a71e72004-10-11 22:21:39 +0000113void BasicBlock::removeFromParent() {
114 getParent()->getBasicBlockList().remove(this);
115}
116
117void BasicBlock::eraseFromParent() {
118 getParent()->getBasicBlockList().erase(this);
119}
120
Chris Lattner4091f462006-09-23 04:03:45 +0000121/// moveBefore - Unlink this basic block from its current function and
122/// insert it into the function that MovePos lives in, right before MovePos.
Chris Lattnere09bbc82005-08-12 22:14:06 +0000123void BasicBlock::moveBefore(BasicBlock *MovePos) {
124 MovePos->getParent()->getBasicBlockList().splice(MovePos,
125 getParent()->getBasicBlockList(), this);
126}
127
Chris Lattner4091f462006-09-23 04:03:45 +0000128/// moveAfter - Unlink this basic block from its current function and
129/// insert it into the function that MovePos lives in, right after MovePos.
130void BasicBlock::moveAfter(BasicBlock *MovePos) {
131 Function::iterator I = MovePos;
132 MovePos->getParent()->getBasicBlockList().splice(++I,
133 getParent()->getBasicBlockList(), this);
134}
135
Chris Lattner02a71e72004-10-11 22:21:39 +0000136
Chris Lattner2f7c9632001-06-06 20:29:01 +0000137TerminatorInst *BasicBlock::getTerminator() {
138 if (InstList.empty()) return 0;
Chris Lattner113f4f42002-06-25 16:13:24 +0000139 return dyn_cast<TerminatorInst>(&InstList.back());
Chris Lattner2f7c9632001-06-06 20:29:01 +0000140}
141
Dan Gohmanaad83c82007-11-19 20:46:23 +0000142const TerminatorInst *BasicBlock::getTerminator() const {
Chris Lattner2f7c9632001-06-06 20:29:01 +0000143 if (InstList.empty()) return 0;
Chris Lattner113f4f42002-06-25 16:13:24 +0000144 return dyn_cast<TerminatorInst>(&InstList.back());
Chris Lattner2f7c9632001-06-06 20:29:01 +0000145}
146
Dan Gohmanf96e1372008-05-23 21:05:58 +0000147Instruction* BasicBlock::getFirstNonPHI() {
148 BasicBlock::iterator i = begin();
149 // All valid basic blocks should have a terminator,
150 // which is not a PHINode. If we have an invalid basic
151 // block we'll get an assertion failure when dereferencing
152 // a past-the-end iterator.
153 while (isa<PHINode>(i)) ++i;
154 return &*i;
Vladimir Prusb5b6dc42006-06-08 15:46:18 +0000155}
156
Chris Lattner2f7c9632001-06-06 20:29:01 +0000157void BasicBlock::dropAllReferences() {
Chris Lattner113f4f42002-06-25 16:13:24 +0000158 for(iterator I = begin(), E = end(); I != E; ++I)
159 I->dropAllReferences();
Chris Lattner2f7c9632001-06-06 20:29:01 +0000160}
161
Chris Lattnerce046ac2005-02-24 02:37:26 +0000162/// getSinglePredecessor - If this basic block has a single predecessor block,
163/// return the block, otherwise return a null pointer.
164BasicBlock *BasicBlock::getSinglePredecessor() {
165 pred_iterator PI = pred_begin(this), E = pred_end(this);
166 if (PI == E) return 0; // No preds.
167 BasicBlock *ThePred = *PI;
168 ++PI;
169 return (PI == E) ? ThePred : 0 /*multiple preds*/;
170}
171
Torok Edwinc8080122008-12-11 10:36:07 +0000172/// getUniquePredecessor - If this basic block has a unique predecessor block,
173/// return the block, otherwise return a null pointer.
174/// Note that unique predecessor doesn't mean single edge, there can be
Torok Edwin32bfb5d2008-12-11 11:44:49 +0000175/// multiple edges from the unique predecessor to this block (for example
176/// a switch statement with multiple cases having the same destination).
Torok Edwinc8080122008-12-11 10:36:07 +0000177BasicBlock *BasicBlock::getUniquePredecessor() {
178 pred_iterator PI = pred_begin(this), E = pred_end(this);
179 if (PI == E) return 0; // No preds.
180 BasicBlock *PredBB = *PI;
181 ++PI;
182 for (;PI != E; ++PI) {
183 if (*PI != PredBB)
184 return 0;
Torok Edwin32bfb5d2008-12-11 11:44:49 +0000185 // The same predecessor appears multiple times in the predecessor list.
186 // This is OK.
Torok Edwinc8080122008-12-11 10:36:07 +0000187 }
188 return PredBB;
189}
190
Chris Lattner954c64d2005-04-21 16:06:03 +0000191/// removePredecessor - This method is used to notify a BasicBlock that the
192/// specified Predecessor of the block is no longer able to reach it. This is
Misha Brukmanb1c93172005-04-21 23:48:37 +0000193/// actually not used to update the Predecessor list, but is actually used to
Chris Lattner954c64d2005-04-21 16:06:03 +0000194/// update the PHI nodes that reside in the block. Note that this should be
195/// called while the predecessor still refers to this block.
196///
Chris Lattner9daef352005-04-12 18:52:14 +0000197void BasicBlock::removePredecessor(BasicBlock *Pred,
Nick Lewycky4d43d3c2008-04-25 16:53:59 +0000198 bool DontDeleteUselessPHIs) {
Chris Lattner25169ca2005-02-23 16:53:04 +0000199 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
Chris Lattnercf08c212005-02-23 07:09:08 +0000200 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
Jeff Cohen82639852005-04-23 21:38:35 +0000201 "removePredecessor: BB is not a predecessor!");
Chris Lattnercf08c212005-02-23 07:09:08 +0000202
Chris Lattner8d0b1b22004-12-11 22:10:29 +0000203 if (InstList.empty()) return;
Chris Lattnerbea72472004-07-06 17:44:17 +0000204 PHINode *APN = dyn_cast<PHINode>(&front());
205 if (!APN) return; // Quick exit.
Chris Lattner615d3cf2001-06-29 05:25:23 +0000206
207 // If there are exactly two predecessors, then we want to nuke the PHI nodes
Chris Lattnerbea72472004-07-06 17:44:17 +0000208 // altogether. However, we cannot do this, if this in this case:
Chris Lattnerf7373e42002-05-21 19:52:49 +0000209 //
210 // Loop:
211 // %x = phi [X, Loop]
212 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
213 // br Loop ;; %x2 does not dominate all uses
214 //
215 // This is because the PHI node input is actually taken from the predecessor
Misha Brukmanb1c93172005-04-21 23:48:37 +0000216 // basic block. The only case this can happen is with a self loop, so we
Chris Lattnerf7373e42002-05-21 19:52:49 +0000217 // check for this case explicitly now.
Misha Brukmanb1c93172005-04-21 23:48:37 +0000218 //
Chris Lattnerbea72472004-07-06 17:44:17 +0000219 unsigned max_idx = APN->getNumIncomingValues();
Chris Lattner615d3cf2001-06-29 05:25:23 +0000220 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
Chris Lattnerf7373e42002-05-21 19:52:49 +0000221 if (max_idx == 2) {
Chris Lattnerbea72472004-07-06 17:44:17 +0000222 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
Chris Lattnerf7373e42002-05-21 19:52:49 +0000223
224 // Disable PHI elimination!
225 if (this == Other) max_idx = 3;
226 }
227
Chris Lattner9daef352005-04-12 18:52:14 +0000228 // <= Two predecessors BEFORE I remove one?
229 if (max_idx <= 2 && !DontDeleteUselessPHIs) {
Chris Lattnerda558102001-10-02 03:41:24 +0000230 // Yup, loop through and nuke the PHI nodes
Chris Lattner113f4f42002-06-25 16:13:24 +0000231 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
Chris Lattner9daef352005-04-12 18:52:14 +0000232 // Remove the predecessor first.
Nick Lewycky4d43d3c2008-04-25 16:53:59 +0000233 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
Chris Lattner615d3cf2001-06-29 05:25:23 +0000234
235 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
Chris Lattnercaf5b502002-10-08 21:36:34 +0000236 if (max_idx == 2) {
Chris Lattneref8c8332003-04-25 23:14:19 +0000237 if (PN->getOperand(0) != PN)
238 PN->replaceAllUsesWith(PN->getOperand(0));
239 else
240 // We are left with an infinite loop with no entries: kill the PHI.
Chris Lattner9daef352005-04-12 18:52:14 +0000241 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
Chris Lattnercaf5b502002-10-08 21:36:34 +0000242 getInstList().pop_front(); // Remove the PHI node
243 }
244
245 // If the PHI node already only had one entry, it got deleted by
246 // removeIncomingValue.
Chris Lattner615d3cf2001-06-29 05:25:23 +0000247 }
248 } else {
249 // Okay, now we know that we need to remove predecessor #pred_idx from all
250 // PHI nodes. Iterate over each PHI node fixing them up
Chris Lattner708ee9d2004-06-05 00:11:27 +0000251 PHINode *PN;
Chris Lattner1749aaa2005-08-05 15:34:10 +0000252 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
253 ++II;
Nick Lewycky4d43d3c2008-04-25 16:53:59 +0000254 PN->removeIncomingValue(Pred, false);
Nate Begemanb3923212005-08-04 23:24:19 +0000255 // If all incoming values to the Phi are the same, we can replace the Phi
256 // with that value.
Owen Anderson4e744af2006-06-14 04:43:14 +0000257 Value* PNV = 0;
258 if (!DontDeleteUselessPHIs && (PNV = PN->hasConstantValue())) {
Chris Lattner6f583502005-08-05 01:02:04 +0000259 PN->replaceAllUsesWith(PNV);
260 PN->eraseFromParent();
261 }
Nate Begemanb3923212005-08-04 23:24:19 +0000262 }
Chris Lattner615d3cf2001-06-29 05:25:23 +0000263 }
264}
265
Chris Lattner2f7c9632001-06-06 20:29:01 +0000266
Chris Lattner7ceb0812005-04-21 16:04:49 +0000267/// splitBasicBlock - This splits a basic block into two at the specified
268/// instruction. Note that all instructions BEFORE the specified iterator stay
Misha Brukmanb1c93172005-04-21 23:48:37 +0000269/// as part of the original basic block, an unconditional branch is added to
Chris Lattner7ceb0812005-04-21 16:04:49 +0000270/// the new BB, and the rest of the instructions in the BB are moved to the new
271/// BB, including the old terminator. This invalidates the iterator.
272///
Misha Brukmanb1c93172005-04-21 23:48:37 +0000273/// Note that this only works on well formed basic blocks (must have a
Chris Lattner7ceb0812005-04-21 16:04:49 +0000274/// terminator), and 'I' must not be the end of instruction list (which would
275/// cause a degenerate basic block to be formed, having a terminator inside of
Misha Brukmanb1c93172005-04-21 23:48:37 +0000276/// the basic block).
Chris Lattner7ceb0812005-04-21 16:04:49 +0000277///
Chris Lattner6d569352003-08-24 03:41:39 +0000278BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) {
Chris Lattner2f7c9632001-06-06 20:29:01 +0000279 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
Misha Brukmanb1c93172005-04-21 23:48:37 +0000280 assert(I != InstList.end() &&
Jeff Cohen82639852005-04-23 21:38:35 +0000281 "Trying to get me to create degenerate basic block!");
Chris Lattner2f7c9632001-06-06 20:29:01 +0000282
Dan Gohman804c95d2008-07-28 21:51:04 +0000283 BasicBlock *InsertBefore = next(Function::iterator(this))
284 .getNodePtrUnchecked();
285 BasicBlock *New = BasicBlock::Create(BBName, getParent(), InsertBefore);
Chris Lattner2f7c9632001-06-06 20:29:01 +0000286
Chris Lattnerc4c7ea52004-02-03 23:11:21 +0000287 // Move all of the specified instructions from the original basic block into
288 // the new basic block.
289 New->getInstList().splice(New->end(), this->getInstList(), I, end());
Chris Lattner2f7c9632001-06-06 20:29:01 +0000290
291 // Add a branch instruction to the newly formed basic block.
Gabor Greife9ecc682008-04-06 20:25:17 +0000292 BranchInst::Create(New, this);
Chris Lattner4eed0b82002-02-25 00:35:07 +0000293
294 // Now we must loop through all of the successors of the New block (which
295 // _were_ the successors of the 'this' block), and update any PHI nodes in
296 // successors. If there were PHI nodes in the successors, then they need to
297 // know that incoming branches will be from New, not from Old.
298 //
Chris Lattner64d88bc2003-09-24 22:03:22 +0000299 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
Chris Lattner4eed0b82002-02-25 00:35:07 +0000300 // Loop over any phi nodes in the basic block, updating the BB field of
301 // incoming values...
302 BasicBlock *Successor = *I;
Chris Lattner708ee9d2004-06-05 00:11:27 +0000303 PHINode *PN;
Chris Lattner4eed0b82002-02-25 00:35:07 +0000304 for (BasicBlock::iterator II = Successor->begin();
Chris Lattner08d1b9d2004-06-05 17:43:52 +0000305 (PN = dyn_cast<PHINode>(II)); ++II) {
Chris Lattner4eed0b82002-02-25 00:35:07 +0000306 int IDX = PN->getBasicBlockIndex(this);
307 while (IDX != -1) {
308 PN->setIncomingBlock((unsigned)IDX, New);
309 IDX = PN->getBasicBlockIndex(this);
310 }
311 }
312 }
Chris Lattner2f7c9632001-06-06 20:29:01 +0000313 return New;
314}