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Chris Lattner2f7c9632001-06-06 20:29:01 +00001//===-- BasicBlock.cpp - Implement BasicBlock related functions --*- C++ -*--=//
2//
Chris Lattnerf739fa82002-04-08 22:03:57 +00003// This file implements the BasicBlock class for the VMCore library.
Chris Lattner2f7c9632001-06-06 20:29:01 +00004//
5//===----------------------------------------------------------------------===//
6
Chris Lattner6e6f5be2002-04-08 00:15:29 +00007#include "ValueHolderImpl.h"
Chris Lattner2f7c9632001-06-06 20:29:01 +00008#include "llvm/iTerminators.h"
Chris Lattner2f7c9632001-06-06 20:29:01 +00009#include "llvm/Type.h"
Chris Lattner83d485b2002-02-12 22:39:50 +000010#include "llvm/Support/CFG.h"
Chris Lattnerfb5ae022001-12-03 18:02:31 +000011#include "llvm/iPHINode.h"
Vikram S. Adve32b5d842001-07-30 18:47:24 +000012#include "llvm/CodeGen/MachineInstr.h"
Chris Lattner2f7c9632001-06-06 20:29:01 +000013
14// Instantiate Templates - This ugliness is the price we have to pay
15// for having a ValueHolderImpl.h file seperate from ValueHolder.h! :(
16//
Chris Lattnerf739fa82002-04-08 22:03:57 +000017template class ValueHolder<Instruction, BasicBlock, Function>;
Chris Lattner2f7c9632001-06-06 20:29:01 +000018
Chris Lattnerf739fa82002-04-08 22:03:57 +000019BasicBlock::BasicBlock(const std::string &name, Function *Parent)
Chris Lattner2d189a52001-09-07 16:44:17 +000020 : Value(Type::LabelTy, Value::BasicBlockVal, name), InstList(this, 0),
21 machineInstrVec(new MachineCodeForBasicBlock) {
Chris Lattnerf2a738c2001-07-14 06:13:19 +000022 if (Parent)
23 Parent->getBasicBlocks().push_back(this);
Chris Lattner2f7c9632001-06-06 20:29:01 +000024}
25
26BasicBlock::~BasicBlock() {
27 dropAllReferences();
28 InstList.delete_all();
Vikram S. Adve32b5d842001-07-30 18:47:24 +000029 delete machineInstrVec;
Chris Lattner2f7c9632001-06-06 20:29:01 +000030}
31
32// Specialize setName to take care of symbol table majik
Chris Lattner7f74a562002-01-20 22:54:45 +000033void BasicBlock::setName(const std::string &name, SymbolTable *ST) {
Chris Lattnerf739fa82002-04-08 22:03:57 +000034 Function *P;
Chris Lattner2d189a52001-09-07 16:44:17 +000035 assert((ST == 0 || (!getParent() || ST == getParent()->getSymbolTable())) &&
36 "Invalid symtab argument!");
Chris Lattner2f7c9632001-06-06 20:29:01 +000037 if ((P = getParent()) && hasName()) P->getSymbolTable()->remove(this);
38 Value::setName(name);
39 if (P && hasName()) P->getSymbolTable()->insert(this);
40}
41
Chris Lattnerf739fa82002-04-08 22:03:57 +000042void BasicBlock::setParent(Function *parent) {
Chris Lattner2f7c9632001-06-06 20:29:01 +000043 if (getParent() && hasName())
44 getParent()->getSymbolTable()->remove(this);
45
46 InstList.setParent(parent);
47
48 if (getParent() && hasName())
49 getParent()->getSymbolTableSure()->insert(this);
50}
51
52TerminatorInst *BasicBlock::getTerminator() {
53 if (InstList.empty()) return 0;
54 Instruction *T = InstList.back();
Chris Lattnerda558102001-10-02 03:41:24 +000055 if (isa<TerminatorInst>(T)) return cast<TerminatorInst>(T);
Chris Lattner2f7c9632001-06-06 20:29:01 +000056 return 0;
57}
58
59const TerminatorInst *const BasicBlock::getTerminator() const {
60 if (InstList.empty()) return 0;
Chris Lattnerda558102001-10-02 03:41:24 +000061 if (const TerminatorInst *TI = dyn_cast<TerminatorInst>(InstList.back()))
62 return TI;
Chris Lattner2f7c9632001-06-06 20:29:01 +000063 return 0;
64}
65
66void BasicBlock::dropAllReferences() {
67 for_each(InstList.begin(), InstList.end(),
68 std::mem_fun(&Instruction::dropAllReferences));
69}
70
Chris Lattner3462ae32001-12-03 22:26:30 +000071// hasConstantReferences() - This predicate is true if there is a
Chris Lattner2f7c9632001-06-06 20:29:01 +000072// reference to this basic block in the constant pool for this method. For
73// example, if a block is reached through a switch table, that table resides
74// in the constant pool, and the basic block is reference from it.
75//
Chris Lattner3462ae32001-12-03 22:26:30 +000076bool BasicBlock::hasConstantReferences() const {
Chris Lattner2f7c9632001-06-06 20:29:01 +000077 for (use_const_iterator I = use_begin(), E = use_end(); I != E; ++I)
Chris Lattnerca142372002-04-28 19:55:58 +000078 if (::isa<Constant>((Value*)*I))
Chris Lattner2f7c9632001-06-06 20:29:01 +000079 return true;
80
81 return false;
82}
83
Chris Lattner615d3cf2001-06-29 05:25:23 +000084// removePredecessor - This method is used to notify a BasicBlock that the
85// specified Predecessor of the block is no longer able to reach it. This is
86// actually not used to update the Predecessor list, but is actually used to
87// update the PHI nodes that reside in the block. Note that this should be
88// called while the predecessor still refers to this block.
89//
90void BasicBlock::removePredecessor(BasicBlock *Pred) {
Chris Lattner83d485b2002-02-12 22:39:50 +000091 assert(find(pred_begin(this), pred_end(this), Pred) != pred_end(this) &&
Chris Lattner615d3cf2001-06-29 05:25:23 +000092 "removePredecessor: BB is not a predecessor!");
Chris Lattnerda558102001-10-02 03:41:24 +000093 if (!isa<PHINode>(front())) return; // Quick exit.
Chris Lattner615d3cf2001-06-29 05:25:23 +000094
Chris Lattner83d485b2002-02-12 22:39:50 +000095 pred_iterator PI(pred_begin(this)), EI(pred_end(this));
Chris Lattner615d3cf2001-06-29 05:25:23 +000096 unsigned max_idx;
97
98 // Loop over the rest of the predecessors until we run out, or until we find
99 // out that there are more than 2 predecessors.
100 for (max_idx = 0; PI != EI && max_idx < 3; ++PI, ++max_idx) /*empty*/;
101
102 // If there are exactly two predecessors, then we want to nuke the PHI nodes
Chris Lattnerf7373e42002-05-21 19:52:49 +0000103 // altogether. We cannot do this, however if this in this case however:
104 //
105 // Loop:
106 // %x = phi [X, Loop]
107 // %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
108 // br Loop ;; %x2 does not dominate all uses
109 //
110 // This is because the PHI node input is actually taken from the predecessor
111 // basic block. The only case this can happen is with a self loop, so we
112 // check for this case explicitly now.
113 //
Chris Lattner615d3cf2001-06-29 05:25:23 +0000114 assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
Chris Lattnerf7373e42002-05-21 19:52:49 +0000115 if (max_idx == 2) {
116 PI = pred_begin(this);
117 BasicBlock *Other = *PI == Pred ? *++PI : *PI;
118
119 // Disable PHI elimination!
120 if (this == Other) max_idx = 3;
121 }
122
Chris Lattner615d3cf2001-06-29 05:25:23 +0000123 if (max_idx <= 2) { // <= Two predecessors BEFORE I remove one?
Chris Lattnerda558102001-10-02 03:41:24 +0000124 // Yup, loop through and nuke the PHI nodes
125 while (PHINode *PN = dyn_cast<PHINode>(front())) {
Chris Lattner615d3cf2001-06-29 05:25:23 +0000126 PN->removeIncomingValue(Pred); // Remove the predecessor first...
127
128 assert(PN->getNumIncomingValues() == max_idx-1 &&
129 "PHI node shouldn't have this many values!!!");
130
131 // If the PHI _HAD_ two uses, replace PHI node with its now *single* value
132 if (max_idx == 2)
133 PN->replaceAllUsesWith(PN->getOperand(0));
134 delete getInstList().remove(begin()); // Remove the PHI node
135 }
136 } else {
137 // Okay, now we know that we need to remove predecessor #pred_idx from all
138 // PHI nodes. Iterate over each PHI node fixing them up
Chris Lattnerf7373e42002-05-21 19:52:49 +0000139 for (iterator II = begin(); PHINode *PN = dyn_cast<PHINode>(*II); ++II)
140 PN->removeIncomingValue(Pred);
Chris Lattner615d3cf2001-06-29 05:25:23 +0000141 }
142}
143
Chris Lattner2f7c9632001-06-06 20:29:01 +0000144
145// splitBasicBlock - This splits a basic block into two at the specified
146// instruction. Note that all instructions BEFORE the specified iterator stay
147// as part of the original basic block, an unconditional branch is added to
148// the new BB, and the rest of the instructions in the BB are moved to the new
149// BB, including the old terminator. This invalidates the iterator.
150//
151// Note that this only works on well formed basic blocks (must have a
152// terminator), and 'I' must not be the end of instruction list (which would
153// cause a degenerate basic block to be formed, having a terminator inside of
154// the basic block).
155//
Chris Lattner4cee8d82001-06-27 23:41:11 +0000156BasicBlock *BasicBlock::splitBasicBlock(iterator I) {
Chris Lattner2f7c9632001-06-06 20:29:01 +0000157 assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
158 assert(I != InstList.end() &&
159 "Trying to get me to create degenerate basic block!");
160
161 BasicBlock *New = new BasicBlock("", getParent());
162
163 // Go from the end of the basic block through to the iterator pointer, moving
164 // to the new basic block...
165 Instruction *Inst = 0;
166 do {
Chris Lattner4cee8d82001-06-27 23:41:11 +0000167 iterator EndIt = end();
Chris Lattner2f7c9632001-06-06 20:29:01 +0000168 Inst = InstList.remove(--EndIt); // Remove from end
169 New->InstList.push_front(Inst); // Add to front
170 } while (Inst != *I); // Loop until we move the specified instruction.
171
172 // Add a branch instruction to the newly formed basic block.
173 InstList.push_back(new BranchInst(New));
Chris Lattner4eed0b82002-02-25 00:35:07 +0000174
175 // Now we must loop through all of the successors of the New block (which
176 // _were_ the successors of the 'this' block), and update any PHI nodes in
177 // successors. If there were PHI nodes in the successors, then they need to
178 // know that incoming branches will be from New, not from Old.
179 //
180 for (BasicBlock::succ_iterator I = succ_begin(New), E = succ_end(New);
181 I != E; ++I) {
182 // Loop over any phi nodes in the basic block, updating the BB field of
183 // incoming values...
184 BasicBlock *Successor = *I;
185 for (BasicBlock::iterator II = Successor->begin();
186 PHINode *PN = dyn_cast<PHINode>(*II); ++II) {
187 int IDX = PN->getBasicBlockIndex(this);
188 while (IDX != -1) {
189 PN->setIncomingBlock((unsigned)IDX, New);
190 IDX = PN->getBasicBlockIndex(this);
191 }
192 }
193 }
Chris Lattner2f7c9632001-06-06 20:29:01 +0000194 return New;
195}