rustc: Exemplary use of FxHashSet/BitSet/IntervalSet throughout;
no linear membership tests on hot paths.
swift-0001: LoadableByAddress.cpp StructLoweringState uses SmallVector
with std::find for largeLoadableArgs/applies membership — O(I×A)
per function, 322x overhead at A=500. Fix: SmallPtrSet shadow.
swift-0001: QualifiedLookupRequest::evaluate (NameLookup.cpp:2860) pushes
protocol superclassDecl onto BFS stack unconditionally — visited.insert()
return not checked. Nearby ClassDecl arm (line 2833) is correctly guarded.
Diamond protocol hierarchies sharing a class superclass trigger O(2^D)
re-traversal on every qualified member lookup. Fix: check .second.
llvm, gcc, webkit: CLEAN in available sparse-clone code.
