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Document the new GVN number table structure.

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llvm-svn: 119865
This commit is contained in:
Owen Anderson 2010-11-19 22:48:40 +00:00
parent 7445ae1145
commit 0d05099294
1 changed files with 12 additions and 0 deletions
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12
lib/Transforms/Scalar/GVN.cpp
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@ -677,8 +677,13 @@ namespace {
ValueTable VN;
/// NumberTable - A mapping from value numers to lists of Value*'s that
/// have that value number. Use lookupNumber to query it.
DenseMap<uint32_t, std::pair<Value*, void*> > NumberTable;
BumpPtrAllocator TableAllocator;
/// insert_table - Push a new Value to the NumberTable onto the list for
/// its value number.
void insert_table(uint32_t N, Value *V) {
std::pair<Value*, void*>& Curr = NumberTable[N];
if (!Curr.first) {
@ -693,6 +698,8 @@ namespace {
Curr.second = Node;
}
/// erase_table - Scan the list of values corresponding to a given value
/// number, and remove the given value if encountered.
void erase_table(uint32_t N, Value *V) {
std::pair<Value*, void*>* Prev = 0;
std::pair<Value*, void*>* Curr = &NumberTable[N];
@ -1886,6 +1893,11 @@ bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
return false;
}
// lookupNumber - In order to find a leader for a given value number at a
// specific basic block, we first obtain the list of all Values for that number,
// and then scan the list to find one whose block dominates the block in
// question. This is fast because dominator tree queries consist of only
// a few comparisons of DFS numbers.
Value *GVN::lookupNumber(BasicBlock *BB, uint32_t num) {
std::pair<Value*, void*> Vals = NumberTable[num];
if (!Vals.first) return 0;