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Chris Lattner184b2982002-09-08 18:59:35 +00001//===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===//
John Criswell482202a2003-10-20 19:43:21 +00002//
3// 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.
7//
8//===----------------------------------------------------------------------===//
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
105
Chris Lattner2f7c9632001-06-06 20:29:01 +0000106TerminatorInst *BasicBlock::getTerminator() {
107 if (InstList.empty()) return 0;
Chris Lattner113f4f42002-06-25 16:13:24 +0000108 return dyn_cast<TerminatorInst>(&InstList.back());
Chris Lattner2f7c9632001-06-06 20:29:01 +0000109}
110
111const TerminatorInst *const BasicBlock::getTerminator() const {
112 if (InstList.empty()) return 0;
Chris Lattner113f4f42002-06-25 16:13:24 +0000113 return dyn_cast<TerminatorInst>(&InstList.back());
Chris Lattner2f7c9632001-06-06 20:29:01 +0000114}
115
116void BasicBlock::dropAllReferences() {
Chris Lattner113f4f42002-06-25 16:13:24 +0000117 for(iterator I = begin(), E = end(); I != E; ++I)
118 I->dropAllReferences();
Chris Lattner2f7c9632001-06-06 20:29:01 +0000119}
120
Chris Lattnerce046ac2005-02-24 02:37:26 +0000121/// getSinglePredecessor - If this basic block has a single predecessor block,
122/// return the block, otherwise return a null pointer.
123BasicBlock *BasicBlock::getSinglePredecessor() {
124 pred_iterator PI = pred_begin(this), E = pred_end(this);
125 if (PI == E) return 0; // No preds.
126 BasicBlock *ThePred = *PI;
127 ++PI;
128 return (PI == E) ? ThePred : 0 /*multiple preds*/;
129}
130
Chris Lattner615d3cf2001-06-29 05:25:23 +0000131// removePredecessor - This method is used to notify a BasicBlock that the
132// specified Predecessor of the block is no longer able to reach it. This is
133// actually not used to update the Predecessor list, but is actually used to
134// update the PHI nodes that reside in the block. Note that this should be
135// called while the predecessor still refers to this block.
136//
Chris Lattner9daef352005-04-12 18:52:14 +0000137void BasicBlock::removePredecessor(BasicBlock *Pred,
138 bool DontDeleteUselessPHIs) {
Chris Lattner25169ca2005-02-23 16:53:04 +0000139 assert((hasNUsesOrMore(16)||// Reduce cost of this assertion for complex CFGs.
Chris Lattnercf08c212005-02-23 07:09:08 +0000140 find(pred_begin(this), pred_end(this), Pred) != pred_end(this)) &&
Chris Lattner615d3cf2001-06-29 05:25:23 +0000141 "removePredecessor: BB is not a predecessor!");
Chris Lattnercf08c212005-02-23 07:09:08 +0000142
Chris Lattner8d0b1b22004-12-11 22:10:29 +0000143 if (InstList.empty()) return;
Chris Lattnerbea72472004-07-06 17:44:17 +0000144 PHINode *APN = dyn_cast<PHINode>(&front());
145 if (!APN) return; // Quick exit.
Chris Lattner615d3cf2001-06-29 05:25:23 +0000146
147 // If there are exactly two predecessors, then we want to nuke the PHI nodes
Chris Lattnerbea72472004-07-06 17:44:17 +0000148 // altogether. However, we cannot do this, if this in this case:
Chris Lattnerf7373e42002-05-21 19:52:49 +0000149 //
150 // Loop:
151 // %x = phi [X, Loop]
152 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
153 // br Loop ;; %x2 does not dominate all uses
154 //
155 // This is because the PHI node input is actually taken from the predecessor
156 // basic block. The only case this can happen is with a self loop, so we
157 // check for this case explicitly now.
158 //
Chris Lattnerbea72472004-07-06 17:44:17 +0000159 unsigned max_idx = APN->getNumIncomingValues();
Chris Lattner615d3cf2001-06-29 05:25:23 +0000160 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
Chris Lattnerf7373e42002-05-21 19:52:49 +0000161 if (max_idx == 2) {
Chris Lattnerbea72472004-07-06 17:44:17 +0000162 BasicBlock *Other = APN->getIncomingBlock(APN->getIncomingBlock(0) == Pred);
Chris Lattnerf7373e42002-05-21 19:52:49 +0000163
164 // Disable PHI elimination!
165 if (this == Other) max_idx = 3;
166 }
167
Chris Lattner9daef352005-04-12 18:52:14 +0000168 // <= Two predecessors BEFORE I remove one?
169 if (max_idx <= 2 && !DontDeleteUselessPHIs) {
Chris Lattnerda558102001-10-02 03:41:24 +0000170 // Yup, loop through and nuke the PHI nodes
Chris Lattner113f4f42002-06-25 16:13:24 +0000171 while (PHINode *PN = dyn_cast<PHINode>(&front())) {
Chris Lattner9daef352005-04-12 18:52:14 +0000172 // Remove the predecessor first.
173 PN->removeIncomingValue(Pred, !DontDeleteUselessPHIs);
Chris Lattner615d3cf2001-06-29 05:25:23 +0000174
175 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
Chris Lattnercaf5b502002-10-08 21:36:34 +0000176 if (max_idx == 2) {
Chris Lattneref8c8332003-04-25 23:14:19 +0000177 if (PN->getOperand(0) != PN)
178 PN->replaceAllUsesWith(PN->getOperand(0));
179 else
180 // We are left with an infinite loop with no entries: kill the PHI.
Chris Lattner9daef352005-04-12 18:52:14 +0000181 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
Chris Lattnercaf5b502002-10-08 21:36:34 +0000182 getInstList().pop_front(); // Remove the PHI node
183 }
184
185 // If the PHI node already only had one entry, it got deleted by
186 // removeIncomingValue.
Chris Lattner615d3cf2001-06-29 05:25:23 +0000187 }
188 } else {
189 // Okay, now we know that we need to remove predecessor #pred_idx from all
190 // PHI nodes. Iterate over each PHI node fixing them up
Chris Lattner708ee9d2004-06-05 00:11:27 +0000191 PHINode *PN;
Chris Lattner08d1b9d2004-06-05 17:43:52 +0000192 for (iterator II = begin(); (PN = dyn_cast<PHINode>(II)); ++II)
Chris Lattner9daef352005-04-12 18:52:14 +0000193 PN->removeIncomingValue(Pred, false);
Chris Lattner615d3cf2001-06-29 05:25:23 +0000194 }
195}
196
Chris Lattner2f7c9632001-06-06 20:29:01 +0000197
198// splitBasicBlock - This splits a basic block into two at the specified
199// instruction. Note that all instructions BEFORE the specified iterator stay
200// as part of the original basic block, an unconditional branch is added to
201// the new BB, and the rest of the instructions in the BB are moved to the new
202// BB, including the old terminator. This invalidates the iterator.
203//
204// Note that this only works on well formed basic blocks (must have a
205// terminator), and 'I' must not be the end of instruction list (which would
206// cause a degenerate basic block to be formed, having a terminator inside of
207// the basic block).
208//
Chris Lattner6d569352003-08-24 03:41:39 +0000209BasicBlock *BasicBlock::splitBasicBlock(iterator I, const std::string &BBName) {
Chris Lattner2f7c9632001-06-06 20:29:01 +0000210 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
211 assert(I != InstList.end() &&
212 "Trying to get me to create degenerate basic block!");
213
Chris Lattnerbb5f0db2004-02-04 03:57:50 +0000214 BasicBlock *New = new BasicBlock(BBName, getParent(), getNext());
Chris Lattner2f7c9632001-06-06 20:29:01 +0000215
Chris Lattnerc4c7ea52004-02-03 23:11:21 +0000216 // Move all of the specified instructions from the original basic block into
217 // the new basic block.
218 New->getInstList().splice(New->end(), this->getInstList(), I, end());
Chris Lattner2f7c9632001-06-06 20:29:01 +0000219
220 // Add a branch instruction to the newly formed basic block.
Chris Lattnera2960002003-11-21 16:52:05 +0000221 new BranchInst(New, this);
Chris Lattner4eed0b82002-02-25 00:35:07 +0000222
223 // Now we must loop through all of the successors of the New block (which
224 // _were_ the successors of the 'this' block), and update any PHI nodes in
225 // successors. If there were PHI nodes in the successors, then they need to
226 // know that incoming branches will be from New, not from Old.
227 //
Chris Lattner64d88bc2003-09-24 22:03:22 +0000228 for (succ_iterator I = succ_begin(New), E = succ_end(New); I != E; ++I) {
Chris Lattner4eed0b82002-02-25 00:35:07 +0000229 // Loop over any phi nodes in the basic block, updating the BB field of
230 // incoming values...
231 BasicBlock *Successor = *I;
Chris Lattner708ee9d2004-06-05 00:11:27 +0000232 PHINode *PN;
Chris Lattner4eed0b82002-02-25 00:35:07 +0000233 for (BasicBlock::iterator II = Successor->begin();
Chris Lattner08d1b9d2004-06-05 17:43:52 +0000234 (PN = dyn_cast<PHINode>(II)); ++II) {
Chris Lattner4eed0b82002-02-25 00:35:07 +0000235 int IDX = PN->getBasicBlockIndex(this);
236 while (IDX != -1) {
237 PN->setIncomingBlock((unsigned)IDX, New);
238 IDX = PN->getBasicBlockIndex(this);
239 }
240 }
241 }
Chris Lattner2f7c9632001-06-06 20:29:01 +0000242 return New;
243}