1. 15 May, 2019 1 commit
    • Tobias Tebbi's avatar
      Reland: [csa] verify skipped write-barriers in MemoryOptimizer · a19c3ffb
      Tobias Tebbi authored
      With very few exceptions, this verifies all skipped write-barriers in
      CSA and Torque, showing that the MemoryOptimizer together with some
      type information on the stored value are enough to avoid unsafe skipped
      write-barriers.
      
      Changes to CSA:
      SKIP_WRITE_BARRIER and Store*NoWriteBarrier are verified by the
      MemoryOptimizer by default.
      Type information about the stored values (TNode<Smi>) is exploited to
      safely skip write barriers for stored Smi values.
      In some cases, the code is re-structured to make it easier to consume
      for the MemoryOptimizer (manual branch and load elimination).
      
      Changes to the MemoryOptimizer:
      Improve the MemoryOptimizer to remove write barriers:
      - When the store happens to a CSA-generated InnerAllocate, by ignoring
        Bitcasts and additions.
      - When the stored value is the HeapConstant of an immortal immovable root.
      - When the stored value is a SmiConstant (recognized by BitcastToTaggedSigned).
      - Fast C-calls are treated as non-allocating.
      - Runtime calls can be white-listed as non-allocating.
      
      Remaining missing cases:
      - C++-style iterator loops with inner pointers.
      - Inner allocates that are reloaded from a field where they were just stored
        (for example an elements backing store). Load elimination would fix that.
      - Safe stored value types that cannot be expressed in CSA (e.g., Smi|Hole).
        We could handle that in Torque.
      - Double-aligned allocations, which are not lowered in the MemoryOptimizer
        but in CSA.
      
      Drive-by change: Avoid Smi suffix for StoreFixedArrayElement since this
      can be handled by overload resolution (in Torque and C++).
      
      Reland Change: Support pointer compression operands.
      
      R=jarin@chromium.org
      TBR=mvstanton@chromium.org
      
      Bug: v8:7793
      Change-Id: I84e1831eb6bf9be14f36db3f8b485ee4fab6b22e
      Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1612904
      Auto-Submit: Tobias Tebbi <tebbi@chromium.org>
      Reviewed-by: 's avatarMichael Stanton <mvstanton@chromium.org>
      Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
      Cr-Commit-Position: refs/heads/master@{#61522}
      a19c3ffb
  2. 07 May, 2019 1 commit