To reduce conditional judges in the loop in `findIndependencePairs()`, I
have tried a couple of tweaks.
* Isolate the final result in `TestVectors`
`using TestVectors = llvm::SmallVector<std::pair<TestVector,
CondState>>;`
The final result was just piggybacked on `TestVector`, so it has been
isolated.
* Filter out and sort `ExecVectors` by the final result
It will cost more in constructing `ExecVectors`, but it can reduce at
least one conditional judgement in the loop.
0ed61db6fd