• Ross McIlroy's avatar
    Revert "[csa] verify skipped write-barriers in MemoryOptimizer" · dd6c9536
    Ross McIlroy authored
    This reverts commit da7322c0.
    
    Reason for revert: Breaking the pointer compression bots, e.g.:
    https://ci.chromium.org/p/v8/builders/ci/V8%20Linux64%20-%20pointer%20compression/3047
    
    Original change's description:
    > [csa] verify skipped write-barriers in MemoryOptimizer
    > 
    > 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++).
    > 
    > R=​jarin@chromium.org
    > TBR=mvstanton@chromium.org
    > 
    > Change-Id: I0af9b710673f350e0fe81c2e59f37da93c024b7c
    > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1571414
    > Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
    > Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
    > Cr-Commit-Position: refs/heads/master@{#61016}
    
    TBR=mvstanton@chromium.org,jarin@chromium.org,tebbi@chromium.org
    
    Change-Id: I36877cd6d08761726ef8dce8a3e3f2ce3eebe6cf
    No-Presubmit: true
    No-Tree-Checks: true
    No-Try: true
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1585732Reviewed-by: 's avatarRoss McIlroy <rmcilroy@chromium.org>
    Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#61038}
    dd6c9536
memory-optimizer.h 5.45 KB