forked from OSchip/llvm-project
260 lines
9.3 KiB
C++
260 lines
9.3 KiB
C++
//===-- BasicBlock.cpp - Implement BasicBlock related methods -------------===//
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//
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// This file implements the BasicBlock class for the VMCore library.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/BasicBlock.h"
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#include "llvm/iTerminators.h"
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#include "llvm/Type.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Constant.h"
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#include "llvm/iPHINode.h"
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#include "llvm/SymbolTable.h"
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#include "Support/LeakDetector.h"
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#include "SymbolTableListTraitsImpl.h"
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#include <algorithm>
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// DummyInst - An instance of this class is used to mark the end of the
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// instruction list. This is not a real instruction.
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//
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struct DummyInst : public Instruction {
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DummyInst() : Instruction(Type::VoidTy, OtherOpsEnd) {
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// This should not be garbage monitored.
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LeakDetector::removeGarbageObject(this);
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}
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virtual Instruction *clone() const {
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assert(0 && "Cannot clone EOL");abort();
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return 0;
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}
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virtual const char *getOpcodeName() const { return "*end-of-list-inst*"; }
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// Methods for support type inquiry through isa, cast, and dyn_cast...
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static inline bool classof(const DummyInst *) { return true; }
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static inline bool classof(const Instruction *I) {
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return I->getOpcode() == OtherOpsEnd;
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}
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static inline bool classof(const Value *V) {
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return isa<Instruction>(V) && classof(cast<Instruction>(V));
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}
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};
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Instruction *ilist_traits<Instruction>::createNode() {
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return new DummyInst();
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}
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iplist<Instruction> &ilist_traits<Instruction>::getList(BasicBlock *BB) {
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return BB->getInstList();
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}
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// Explicit instantiation of SymbolTableListTraits since some of the methods
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// are not in the public header file...
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template SymbolTableListTraits<Instruction, BasicBlock, Function>;
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// BasicBlock ctor - If the function parameter is specified, the basic block is
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// automatically inserted at the end of the function.
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//
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BasicBlock::BasicBlock(const std::string &name, Function *Parent)
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: Value(Type::LabelTy, Value::BasicBlockVal, name) {
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// Initialize the instlist...
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InstList.setItemParent(this);
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// Make sure that we get added to a function
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LeakDetector::addGarbageObject(this);
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if (Parent)
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Parent->getBasicBlockList().push_back(this);
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}
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/// BasicBlock ctor - If the InsertBefore parameter is specified, the basic
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/// block is automatically inserted right before the specified block.
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///
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BasicBlock::BasicBlock(const std::string &Name, BasicBlock *InsertBefore)
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: Value(Type::LabelTy, Value::BasicBlockVal, Name) {
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// Initialize the instlist...
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InstList.setItemParent(this);
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// Make sure that we get added to a function
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LeakDetector::addGarbageObject(this);
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if (InsertBefore) {
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assert(InsertBefore->getParent() &&
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"Cannot insert block before another block that is not embedded into"
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" a function yet!");
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InsertBefore->getParent()->getBasicBlockList().insert(InsertBefore, this);
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}
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}
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BasicBlock::~BasicBlock() {
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dropAllReferences();
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InstList.clear();
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}
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void BasicBlock::setParent(Function *parent) {
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if (getParent())
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LeakDetector::addGarbageObject(this);
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InstList.setParent(parent);
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if (getParent())
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LeakDetector::removeGarbageObject(this);
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}
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// Specialize setName to take care of symbol table majik
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void BasicBlock::setName(const std::string &name, SymbolTable *ST) {
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Function *P;
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assert((ST == 0 || (!getParent() || ST == &getParent()->getSymbolTable())) &&
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"Invalid symtab argument!");
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if ((P = getParent()) && hasName()) P->getSymbolTable().remove(this);
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Value::setName(name);
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if (P && hasName()) P->getSymbolTable().insert(this);
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}
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TerminatorInst *BasicBlock::getTerminator() {
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if (InstList.empty()) return 0;
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return dyn_cast<TerminatorInst>(&InstList.back());
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}
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const TerminatorInst *const BasicBlock::getTerminator() const {
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if (InstList.empty()) return 0;
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return dyn_cast<TerminatorInst>(&InstList.back());
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}
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void BasicBlock::dropAllReferences() {
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for(iterator I = begin(), E = end(); I != E; ++I)
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I->dropAllReferences();
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}
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// hasConstantReferences() - This predicate is true if there is a
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// reference to this basic block in the constant pool for this method. For
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// example, if a block is reached through a switch table, that table resides
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// in the constant pool, and the basic block is reference from it.
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//
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bool BasicBlock::hasConstantReferences() const {
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for (use_const_iterator I = use_begin(), E = use_end(); I != E; ++I)
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if (::isa<Constant>((Value*)*I))
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return true;
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return false;
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}
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// removePredecessor - This method is used to notify a BasicBlock that the
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// specified Predecessor of the block is no longer able to reach it. This is
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// actually not used to update the Predecessor list, but is actually used to
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// update the PHI nodes that reside in the block. Note that this should be
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// called while the predecessor still refers to this block.
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//
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void BasicBlock::removePredecessor(BasicBlock *Pred) {
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assert(find(pred_begin(this), pred_end(this), Pred) != pred_end(this) &&
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"removePredecessor: BB is not a predecessor!");
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if (!isa<PHINode>(front())) return; // Quick exit.
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pred_iterator PI(pred_begin(this)), EI(pred_end(this));
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unsigned max_idx;
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// Loop over the rest of the predecessors until we run out, or until we find
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// out that there are more than 2 predecessors.
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for (max_idx = 0; PI != EI && max_idx < 3; ++PI, ++max_idx) /*empty*/;
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// If there are exactly two predecessors, then we want to nuke the PHI nodes
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// altogether. We cannot do this, however if this in this case however:
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//
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// Loop:
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// %x = phi [X, Loop]
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// %x2 = add %x, 1 ;; This would become %x2 = add %x2, 1
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// br Loop ;; %x2 does not dominate all uses
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//
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// This is because the PHI node input is actually taken from the predecessor
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// basic block. The only case this can happen is with a self loop, so we
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// check for this case explicitly now.
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//
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assert(max_idx != 0 && "PHI Node in block with 0 predecessors!?!?!");
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if (max_idx == 2) {
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PI = pred_begin(this);
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BasicBlock *Other = *PI == Pred ? *++PI : *PI;
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// Disable PHI elimination!
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if (this == Other) max_idx = 3;
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}
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if (max_idx <= 2) { // <= Two predecessors BEFORE I remove one?
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// Yup, loop through and nuke the PHI nodes
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while (PHINode *PN = dyn_cast<PHINode>(&front())) {
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PN->removeIncomingValue(Pred); // Remove the predecessor first...
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// If the PHI _HAD_ two uses, replace PHI node with its now *single* value
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if (max_idx == 2) {
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if (PN->getOperand(0) != PN)
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PN->replaceAllUsesWith(PN->getOperand(0));
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else
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// We are left with an infinite loop with no entries: kill the PHI.
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PN->replaceAllUsesWith(Constant::getNullValue(PN->getType()));
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getInstList().pop_front(); // Remove the PHI node
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}
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// If the PHI node already only had one entry, it got deleted by
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// removeIncomingValue.
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}
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} else {
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// Okay, now we know that we need to remove predecessor #pred_idx from all
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// PHI nodes. Iterate over each PHI node fixing them up
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for (iterator II = begin(); PHINode *PN = dyn_cast<PHINode>(II); ++II)
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PN->removeIncomingValue(Pred);
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}
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}
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// splitBasicBlock - This splits a basic block into two at the specified
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// instruction. Note that all instructions BEFORE the specified iterator stay
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// as part of the original basic block, an unconditional branch is added to
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// the new BB, and the rest of the instructions in the BB are moved to the new
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// BB, including the old terminator. This invalidates the iterator.
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//
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// Note that this only works on well formed basic blocks (must have a
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// terminator), and 'I' must not be the end of instruction list (which would
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// cause a degenerate basic block to be formed, having a terminator inside of
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// the basic block).
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//
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BasicBlock *BasicBlock::splitBasicBlock(iterator I) {
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assert(getTerminator() && "Can't use splitBasicBlock on degenerate BB!");
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assert(I != InstList.end() &&
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"Trying to get me to create degenerate basic block!");
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BasicBlock *New = new BasicBlock("", getParent());
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// Go from the end of the basic block through to the iterator pointer, moving
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// to the new basic block...
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Instruction *Inst = 0;
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do {
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iterator EndIt = end();
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Inst = InstList.remove(--EndIt); // Remove from end
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New->InstList.push_front(Inst); // Add to front
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} while (Inst != &*I); // Loop until we move the specified instruction.
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// Add a branch instruction to the newly formed basic block.
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InstList.push_back(new BranchInst(New));
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// Now we must loop through all of the successors of the New block (which
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// _were_ the successors of the 'this' block), and update any PHI nodes in
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// successors. If there were PHI nodes in the successors, then they need to
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// know that incoming branches will be from New, not from Old.
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//
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for (BasicBlock::succ_iterator I = succ_begin(New), E = succ_end(New);
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I != E; ++I) {
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// Loop over any phi nodes in the basic block, updating the BB field of
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// incoming values...
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BasicBlock *Successor = *I;
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for (BasicBlock::iterator II = Successor->begin();
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PHINode *PN = dyn_cast<PHINode>(II); ++II) {
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int IDX = PN->getBasicBlockIndex(this);
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while (IDX != -1) {
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PN->setIncomingBlock((unsigned)IDX, New);
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IDX = PN->getBasicBlockIndex(this);
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}
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}
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}
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return New;
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}
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