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.orgTBR=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: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61522}
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