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add description how the ilist_traits<Instruction> works

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llvm-svn: 65732
This commit is contained in:
Gabor Greif 2009-02-28 22:46:37 +00:00
parent 34181d9bcc
commit 2def3e8ae7
1 changed files with 13 additions and 2 deletions
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15
include/llvm/BasicBlock.h
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@ -25,11 +25,22 @@ class TerminatorInst;
template<> struct ilist_traits<Instruction>
: public SymbolTableListTraits<Instruction, BasicBlock> {
// createSentinel is used to create a node that marks the end of the list...
// createSentinel is used to get hold of a node that marks the end of
// the list...
// The sentinel is relative to this instance, so we use a non-static
// method.
Instruction *createSentinel() const {
// since i(p)lists always publicly derive from the corresponding
// traits, placing a data member in this class will augment i(p)list.
// But since the NodeTy is expected to publicly derive from
// ilist_node<NodeTy>, there is a legal viable downcast from it
// to NodeTy. We use this trick to superpose i(p)list with a "ghostly"
// NodeTy, which becomes the sentinel. Dereferencing the sentinel is
// forbidden (save the ilist_node<NodeTy>) so noone will ever notice
// the superposition.
return const_cast<Instruction*>(static_cast<const Instruction*>(&Sentinel));
}
static void destroySentinel(Instruction *I) { I = I; }
static void destroySentinel(Instruction*) {}
static iplist<Instruction> &getList(BasicBlock *BB);
static ValueSymbolTable *getSymTab(BasicBlock *ItemParent);
static int getListOffset();