Summary:
**TL;DR**: make DCE faster by replacing a Set<Value*> with a MemoryLocations sparse bitset (representing all the memory locations stored by the collection of all values in the set).
**Details**
The goal of this PR is to optimize this function from AliasDb:
```
bool AliasDb::writesToAlias(Node* n, const ValueSet& vs) const {
const auto writtenTo = getWrites(n);
if (writtenTo.empty()) {
return false;
}
MemoryLocations locs;
for (const auto v : vs) {
auto it = elementMap_.find(v);
if (it != elementMap_.end()) {
const auto& vlocs = memoryDAG_->getMemoryLocations(it->second);
if (writtenTo.intersects(vlocs)) {
return true;
}
}
}
return false;
}
```
In the DCE use case, we have a ValueSet of live values, into which we insert `Value*`s; and sometimes need to check whether a node mutates any of the live values using `writesToAlias`.
Looping through all the values in the ValueSet and indexing into the elementMap_ is slow; so if we can pre-compute the MemoryLocations set, this speeds up the function. In some large model examples, I see ~15-25x speedups from this change.
**Implementation**: To avoid exposing too many details of AliasDb, I introduce a friend class `ValueAndMemoryLocationSet`, which is an insert-only set of Values, which also maintains the corresponding MemoryLocations.
Then in AliasDb, I use `ValueAndMemoryLocationSet` if we're using AliasDb for analysis, and otherwise use a `Set<Value*>` if we don't have AliasDb.
Test Plan: Rely on unit tests.
Differential Revision: D74827086
Pull Request resolved: https://github.com/pytorch/pytorch/pull/153645
Approved by: https://github.com/eellison
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68311
prim::SetAttr is listed as an op with side effects, but in AliasDb, `analyzeSetAttr` already accounts for its behavior. By removing it from the list of ops with side effects, dead code elimination will work in a few other scenarios.
Test Plan: Imported from OSS
Reviewed By: mrshenli
Differential Revision: D32409510
fbshipit-source-id: 52ed9e19f92afb95c669ad3c2440f72f9515ba4c
