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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//
5// This file was developed by the LLVM research group and is distributed under
6// the University of Illinois Open Source 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
Chris Lattner113f4f42002-06-25 16:13:24 +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"
Chris Lattner83d485b2002-02-12 22:39:50 +000018#include "llvm/Support/CFG.h"
Reid Spencer7c16caa2004-09-01 22:55:40 +000019#include "llvm/Support/LeakDetector.h"
Chris Lattner113f4f42002-06-25 16:13:24 +000020#include "SymbolTableListTraitsImpl.h"
21#include <algorithm>
Chris Lattnera2960002003-11-21 16:52:05 +000022using namespace llvm;
Chris Lattner2f7c9632001-06-06 20:29:01 +000023
Chris Lattnera2960002003-11-21 16:52:05 +000024namespace {
25 /// DummyInst - An instance of this class is used to mark the end of the
26 /// instruction list. This is not a real instruction.
27 struct DummyInst : public Instruction {
Chris Lattner5d1bc2c2005-01-29 00:35:33 +000028 DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd, 0, 0) {
Chris Lattnera2960002003-11-21 16:52:05 +000029 // This should not be garbage monitored.
30 LeakDetector::removeGarbageObject(this);
31 }
Brian Gaeke960707c2003-11-11 22:41:34 +000032
Chris Lattnera2960002003-11-21 16:52:05 +000033 virtual Instruction *clone() const {
34 assert(0 && "Cannot clone EOL");abort();
35 return 0;
36 }
37 virtual const char *getOpcodeName() const { return "*end-of-list-inst*"; }
Chris Lattner113f4f42002-06-25 16:13:24 +000038
Chris Lattnera2960002003-11-21 16:52:05 +000039 // Methods for support type inquiry through isa, cast, and dyn_cast...
40 static inline bool classof(const DummyInst *) { return true; }
41 static inline bool classof(const Instruction *I) {
42 return I->getOpcode() == OtherOpsEnd;
43 }
44 static inline bool classof(const Value *V) {
45 return isa<Instruction>(V) && classof(cast<Instruction>(V));
46 }
47 };
48}
Chris Lattner113f4f42002-06-25 16:13:24 +000049
Chris Lattnerf6c93e32005-01-30 00:09:23 +000050Instruction *ilist_traits<Instruction>::createSentinel() {
Chris Lattner113f4f42002-06-25 16:13:24 +000051 return new DummyInst();
52}
53iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) {
54 return BB->getInstList();
55}
56
57// Explicit instantiation of SymbolTableListTraits since some of the methods
58// are not in the public header file...
Chris Lattner41baa982003-11-05 05:15:42 +000059template class SymbolTableListTraits<Instruction, BasicBlock, Function>;
Chris Lattner113f4f42002-06-25 16:13:24 +000060
Chris Lattner2f7c9632001-06-06 20:29:01 +000061
Chris Lattnerbb5f0db2004-02-04 03:57:50 +000062BasicBlock::BasicBlock(const std::string &Name, Function *Parent,
63 BasicBlock *InsertBefore)
Chris Lattner4dfede82002-09-26 05:03:22 +000064 : Value(Type::LabelTy, Value::BasicBlockVal, Name) {
65 // Initialize the instlist...
66 InstList.setItemParent(this);
67
68 // Make sure that we get added to a function
69 LeakDetector::addGarbageObject(this);
70
71 if (InsertBefore) {
Chris Lattnerbb5f0db2004-02-04 03:57:50 +000072 assert(Parent &&
73 "Cannot insert block before another block with no function!");
74 Parent->getBasicBlockList().insert(InsertBefore, this);
75 } else if (Parent) {
76 Parent->getBasicBlockList().push_back(this);
Chris Lattner4dfede82002-09-26 05:03:22 +000077 }
78}
79
80
Chris Lattner2f7c9632001-06-06 20:29:01 +000081BasicBlock::~BasicBlock() {
Misha Brukmanede10c92004-04-16 17:37:12 +000082 assert(getParent() == 0 && "BasicBlock still linked into the program!");
Chris Lattner2f7c9632001-06-06 20:29:01 +000083 dropAllReferences();
Chris Lattner113f4f42002-06-25 16:13:24 +000084 InstList.clear();
Chris Lattner2f7c9632001-06-06 20:29:01 +000085}
86
Chris Lattner9ed7aef2002-09-06 21:33:15 +000087void BasicBlock::setParent(Function *parent) {
Chris Lattner184b2982002-09-08 18:59:35 +000088 if (getParent())
89 LeakDetector::addGarbageObject(this);
90
Chris Lattner9ed7aef2002-09-06 21:33:15 +000091 InstList.setParent(parent);
Chris Lattner184b2982002-09-08 18:59:35 +000092
93 if (getParent())
94 LeakDetector::removeGarbageObject(this);
Chris Lattner9ed7aef2002-09-06 21:33:15 +000095}
96
Chris Lattner02a71e72004-10-11 22:21:39 +000097void BasicBlock::removeFromParent() {
98 getParent()->getBasicBlockList().remove(this);
99}
100
101void BasicBlock::eraseFromParent() {
102 getParent()->getBasicBlockList().erase(this);
103}
104
Chris Lattnere09bbc82005-08-12 22:14:06 +0000105/// moveBefore - Unlink this instruction from its current function and
106/// insert it into the function that MovePos lives in, right before
107/// MovePos.
108void BasicBlock::moveBefore(BasicBlock *MovePos) {
109 MovePos->getParent()->getBasicBlockList().splice(MovePos,
110 getParent()->getBasicBlockList(), this);
111}
112
Chris Lattner02a71e72004-10-11 22:21:39 +0000113
Chris Lattner2f7c9632001-06-06 20:29:01 +0000114TerminatorInst *BasicBlock::getTerminator() {
115 if (InstList.empty()) return 0;
Chris Lattner113f4f42002-06-25 16:13:24 +0000116 return dyn_cast<TerminatorInst>(&InstList.back());
Chris Lattner2f7c9632001-06-06 20:29:01 +0000117}
118
119const TerminatorInst *const BasicBlock::getTerminator() const {
120 if (InstList.empty()) return 0;
Chris Lattner113f4f42002-06-25 16:13:24 +0000121 return dyn_cast<TerminatorInst>(&InstList.back());
Chris Lattner2f7c9632001-06-06 20:29:01 +0000122}
123
Vladimir Prusb5b6dc42006-06-08 15:46:18 +0000124Instruction* BasicBlock::getFirstNonPHI()
125{
126 BasicBlock::iterator i = begin(), e = end();
127 // All valid basic blocks should have a terminator,
128 // which is not a PHINode. If we have invalid basic
129 // block we'll get assert when dereferencing past-the-end
130 // iterator.
131 while (isa<PHINode>(i)) ++i;
132 return &*i;
133}
134
Chris Lattner2f7c9632001-06-06 20:29:01 +0000135void BasicBlock::dropAllReferences() {
Chris Lattner113f4f42002-06-25 16:13:24 +0000136 for(iterator I = begin(), E = end(); I != E; ++I)
137 I->dropAllReferences();
Chris Lattner2f7c9632001-06-06 20:29:01 +0000138}
139
Chris Lattnerce046ac2005-02-24 02:37:26 +0000140/// getSinglePredecessor - If this basic block has a single predecessor block,
141/// return the block, otherwise return a null pointer.
142BasicBlock *BasicBlock::getSinglePredecessor() {
143 pred_iterator PI = pred_begin(this), E = pred_end(this);
144 if (PI == E) return 0; // No preds.
145 BasicBlock *ThePred = *PI;
146 ++PI;
147 return (PI == E) ? ThePred : 0 /*multiple preds*/;
148}
149
Chris Lattner954c64d2005-04-21 16:06:03 +0000150/// removePredecessor - This method is used to notify a BasicBlock that the
151/// specified Predecessor of the block is no longer able to reach it. This is
Misha Brukmanb1c93172005-04-21 23:48:37 +0000152/// actually not used to update the Predecessor list, but is actually used to
Chris Lattner954c64d2005-04-21 16:06:03 +0000153/// update the PHI nodes that reside in the block. Note that this should be
154/// called while the predecessor still refers to this block.
155///
Chris Lattner9daef352005-04-12 18:52:14 +0000156void BasicBlock::removePredecessor(BasicBlock *Pred,
157 bool DontDeleteUselessPHIs) {
Chris Lattner25169ca2005-02-23 16:53:04 +0000158 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
Chris Lattnercf08c212005-02-23 07:09:08 +0000159 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
Jeff Cohen82639852005-04-23 21:38:35 +0000160 "removePredecessor: BB is not a predecessor!");
Chris Lattnercf08c212005-02-23 07:09:08 +0000161
Chris Lattner8d0b1b22004-12-11 22:10:29 +0000162 if (InstList.empty()) return;
Chris Lattnerbea72472004-07-06 17:44:17 +0000163 PHINode *APN = dyn_cast<PHINode>(&front());
164 if (!APN) return; // Quick exit.
Chris Lattner615d3cf2001-06-29 05:25:23 +0000165
166 // If there are exactly two predecessors, then we want to nuke the PHI nodes
Chris Lattnerbea72472004-07-06 17:44:17 +0000167 // altogether. However, we cannot do this, if this in this case:
Chris Lattnerf7373e42002-05-21 19:52:49 +0000168 //
169 // Loop:
170 // %x = phi [X, Loop]
171 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
172 // br Loop ;; %x2 does not dominate all uses
173 //
174 // This is because the PHI node input is actually taken from the predecessor
Misha Brukmanb1c93172005-04-21 23:48:37 +0000175 // basic block. The only case this can happen is with a self loop, so we
Chris Lattnerf7373e42002-05-21 19:52:49 +0000176 // check for this case explicitly now.
Misha Brukmanb1c93172005-04-21 23:48:37 +0000177 //
Chris Lattnerbea72472004-07-06 17:44:17 +0000178 unsigned max_idx = APN->getNumIncomingValues();
Chris Lattner615d3cf2001-06-29 05:25:23 +0000179 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
Chris Lattnerf7373e42002-05-21 19:52:49 +0000180 if (max_idx == 2) {
Chris Lattnerbea72472004-07-06 17:44:17 +0000181 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
Chris Lattnerf7373e42002-05-21 19:52:49 +0000182
183 // Disable PHI elimination!
184 if (this == Other) max_idx = 3;
185 }
186
Chris Lattner9daef352005-04-12 18:52:14 +0000187 // <= Two predecessors BEFORE I remove one?
188 if (max_idx <= 2 && !DontDeleteUselessPHIs) {
Chris Lattnerda558102001-10-02 03:41:24 +0000189 // Yup, loop through and nuke the PHI nodes
Chris Lattner113f4f42002-06-25 16:13:24 +0000190 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
Chris Lattner9daef352005-04-12 18:52:14 +0000191 // Remove the predecessor first.
192 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
Chris Lattner615d3cf2001-06-29 05:25:23 +0000193
194 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
Chris Lattnercaf5b502002-10-08 21:36:34 +0000195 if (max_idx == 2) {
Chris Lattneref8c8332003-04-25 23:14:19 +0000196 if (PN->getOperand(0) != PN)
197 PN->replaceAllUsesWith(PN->getOperand(0));
198 else
199 // We are left with an infinite loop with no entries: kill the PHI.
Chris Lattner9daef352005-04-12 18:52:14 +0000200 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
Chris Lattnercaf5b502002-10-08 21:36:34 +0000201 getInstList().pop_front(); // Remove the PHI node
202 }
203
204 // If the PHI node already only had one entry, it got deleted by
205 // removeIncomingValue.
Chris Lattner615d3cf2001-06-29 05:25:23 +0000206 }
207 } else {
208 // Okay, now we know that we need to remove predecessor #pred_idx from all
209 // PHI nodes. Iterate over each PHI node fixing them up
Chris Lattner708ee9d2004-06-05 00:11:27 +0000210 PHINode *PN;
Chris Lattner1749aaa2005-08-05 15:34:10 +0000211 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ) {
212 ++II;
Chris Lattner9daef352005-04-12 18:52:14 +0000213 PN->removeIncomingValue(Pred, false);
Nate Begemanb3923212005-08-04 23:24:19 +0000214 // If all incoming values to the Phi are the same, we can replace the Phi
215 // with that value.
Chris Lattner6f583502005-08-05 01:02:04 +0000216 if (Value *PNV = PN->hasConstantValue()) {
217 PN->replaceAllUsesWith(PNV);
218 PN->eraseFromParent();
219 }
Nate Begemanb3923212005-08-04 23:24:19 +0000220 }
Chris Lattner615d3cf2001-06-29 05:25:23 +0000221 }
222}
223
Chris Lattner2f7c9632001-06-06 20:29:01 +0000224
Chris Lattner7ceb0812005-04-21 16:04:49 +0000225/// splitBasicBlock - This splits a basic block into two at the specified
226/// instruction. Note that all instructions BEFORE the specified iterator stay
Misha Brukmanb1c93172005-04-21 23:48:37 +0000227/// as part of the original basic block, an unconditional branch is added to
Chris Lattner7ceb0812005-04-21 16:04:49 +0000228/// the new BB, and the rest of the instructions in the BB are moved to the new
229/// BB, including the old terminator. This invalidates the iterator.
230///
Misha Brukmanb1c93172005-04-21 23:48:37 +0000231/// Note that this only works on well formed basic blocks (must have a
Chris Lattner7ceb0812005-04-21 16:04:49 +0000232/// terminator), and 'I' must not be the end of instruction list (which would
233/// cause a degenerate basic block to be formed, having a terminator inside of
Misha Brukmanb1c93172005-04-21 23:48:37 +0000234/// the basic block).
Chris Lattner7ceb0812005-04-21 16:04:49 +0000235///
Chris Lattner6d569352003-08-24 03:41:39 +0000236BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) {
Chris Lattner2f7c9632001-06-06 20:29:01 +0000237 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
Misha Brukmanb1c93172005-04-21 23:48:37 +0000238 assert(I != InstList.end() &&
Jeff Cohen82639852005-04-23 21:38:35 +0000239 "Trying to get me to create degenerate basic block!");
Chris Lattner2f7c9632001-06-06 20:29:01 +0000240
Chris Lattnerbb5f0db2004-02-04 03:57:50 +0000241 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext());
Chris Lattner2f7c9632001-06-06 20:29:01 +0000242
Chris Lattnerc4c7ea52004-02-03 23:11:21 +0000243 // Move all of the specified instructions from the original basic block into
244 // the new basic block.
245 New->getInstList().splice(New->end(), this->getInstList(), I, end());
Chris Lattner2f7c9632001-06-06 20:29:01 +0000246
247 // Add a branch instruction to the newly formed basic block.
Chris Lattnera2960002003-11-21 16:52:05 +0000248 new BranchInst(New, this);
Chris Lattner4eed0b82002-02-25 00:35:07 +0000249
250 // Now we must loop through all of the successors of the New block (which
251 // _were_ the successors of the 'this' block), and update any PHI nodes in
252 // successors. If there were PHI nodes in the successors, then they need to
253 // know that incoming branches will be from New, not from Old.
254 //
Chris Lattner64d88bc2003-09-24 22:03:22 +0000255 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
Chris Lattner4eed0b82002-02-25 00:35:07 +0000256 // Loop over any phi nodes in the basic block, updating the BB field of
257 // incoming values...
258 BasicBlock *Successor = *I;
Chris Lattner708ee9d2004-06-05 00:11:27 +0000259 PHINode *PN;
Chris Lattner4eed0b82002-02-25 00:35:07 +0000260 for (BasicBlock::iterator II = Successor->begin();
Chris Lattner08d1b9d2004-06-05 17:43:52 +0000261 (PN = dyn_cast<PHINode>(II)); ++II) {
Chris Lattner4eed0b82002-02-25 00:35:07 +0000262 int IDX = PN->getBasicBlockIndex(this);
263 while (IDX != -1) {
264 PN->setIncomingBlock((unsigned)IDX, New);
265 IDX = PN->getBasicBlockIndex(this);
266 }
267 }
268 }
Chris Lattner2f7c9632001-06-06 20:29:01 +0000269 return New;
270}