Up until now the generation of vector instructions was taking place
during the top-down post-order traversal of vectorizeRec(). The issue
with this approach is that the vector instructions emitted during the
traversal can be reordered by the scheduler, making it challenging to
place them without breaking the def-before-uses rule.
With this patch we separate the vectorization decisions (done in
`vectorizeRec()`) from the code generation phase (`emitVectors()`). The
vectorization decisions are stored in the `Actions` vector and are used
by `emitVectors()` to drive code generation.
SelectInsts need special treatment because they are not always
straightforward to vectorize. This patch disables vectorization unless
they are trivially vectorizable.
InstrMaps is a helper data structure that maps scalars to vectors and
the reverse. This is used by the vectorizer to figure out which vectors
it can extract scalar values from.
This patch registers the "createInstr" callback that notifies the
scheduler about newly created instructions. This guarantees that all
newly created instructions have a corresponding DAG node associated with
them. Without this the pass crashes when the scheduler encounters the
newly created vector instructions.
This patch also changes the lifetime of the sandboxir Ctx variable in
the SandboxVectorizer pass. It needs to be destroyed after the passes
get destroyed. Without this change when components like the Scheduler
get destroyed Ctx will have already been freed, which is not legal.
This patch adds the basic API for the Legality component of the
vectorizer. It also adds some very basic code in the bottom-up
vectorizer that uses the API.
