llvm-project/llvm/lib/VMCore/BasicBlock.cpp

260 lines
9.3 KiB
C++

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