• Jonas Paulsson's avatar
    [LoopDataPrefetch + SystemZ] Let target decide on prefetching for each loop. · 36d4421f
    Jonas Paulsson authored
    This patch adds
    
    - New arguments to getMinPrefetchStride() to let the target decide on a
      per-loop basis if software prefetching should be done even with a stride
      within the limit of the hw prefetcher.
    
    - New TTI hook enableWritePrefetching() to let a target do write prefetching
      by default (defaults to false).
    
    - In LoopDataPrefetch:
    
      - A search through the whole loop to gather information before emitting any
        prefetches. This way the target can get information via new arguments to
        getMinPrefetchStride() and emit prefetches more selectively. Collected
        information includes: Does the loop have a call, how many memory
        accesses, how many of them are strided, how many prefetches will cover
        them. This is NFC to before as long as the target does not change its
        definition of getMinPrefetchStride().
    
      - If a previous access to the same exact address was 'read', and the
        current one is 'write', make it a 'write' prefetch.
    
      - If two accesses that are covered by the same prefetch do not dominate
        each other, put the prefetch in a block that dominates both of them.
    
      - If a ConstantMaxTripCount is less than ItersAhead, then skip the loop.
    
    - A SystemZ implementation of getMinPrefetchStride().
    
    Review: Ulrich Weigand, Michael Kruse
    
    Differential Revision: https://reviews.llvm.org/D70228
    36d4421f