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rmacnak-google opened this issue Feb 26, 2020 · 0 comments
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Incorrect write barrier elimination #40780

rmacnak-google opened this issue Feb 26, 2020 · 0 comments
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area-vm Use area-vm for VM related issues, including code coverage, and the AOT and JIT backends.

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@rmacnak-google
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Using verification code added in https://dart-review.googlesource.com/c/sdk/+/137240, I see that https://dart-review.googlesource.com/c/sdk/+/136221 causes incorrect write barrier elimination in Splay.

$ ./out/ReleaseX64/dart --verify-store-buffer ~/benchmarks/Splay/dart/Splay.dart
./../runtime/vm/heap/scavenger.cc: 512: error: Old object 0x7feaf6403091 references new object 0x7feaf8c79cb9, but it is not in any store buffer. Consider using rr to watch the slot 0x7feaf64030b0 to reverse-continue to find the store with a missing barrier.

rr reveals that last write to 0x7feaf64030b0 was
StoreInstanceField(v213 . right = v245, NoStoreBarrier)

StoreInstanceField(v213 . right = v245, NoStoreBarrier)
v209 <- AllocateObject(Node) T{Node}

v213 <- phi(v209, v255) alive T{Node}
v217 <- phi(v316 T{Node}, v259) alive T{Node?}
v245 <- phi(v237 T{Node}, v217 T{Node}) alive T{Node}
v255 <- phi(v213, v245) alive T{Node}
v255 <- phi(v213, v245) alive T{Node}
v259 <- phi(v271, v247) alive T{Node?}

v237 <- LoadField(v217 T{Node} . right) T{Node?}
v247 <- LoadField(v245 . right) T{Node?}
v271 <- LoadField(v269 . left) T{Node?}
v316 <- LoadField(v8 T{SplayTree} . root) T{Node?}

v213 can come from a field load, so it is not safe to remove the barrier.
@rmacnak-google rmacnak-google added the area-vm Use area-vm for VM related issues, including code coverage, and the AOT and JIT backends. label Feb 26, 2020
dart-bot pushed a commit that referenced this issue Feb 26, 2020
@rmacnak-google
Revert "[vm] Re-land aggressive write-barrier elimination."
7fd8ad5 
This reverts commit c7d7552.

Reason for revert: #40780

Original change's description:
> [vm] Re-land aggressive write-barrier elimination.
> 
> It incorrectly assumed that all stores in Dart code write to Instances.
> There is actually one exception, Contexts, which do not inherit from Instance.
> 
> I've added asserts to ensure this kind of bug cannot resurface.
> 
> The original change is in patchset 4.
> 
> Change-Id: Ic2d8d05e70a4de738eb9fb5980487b4f27111b8c
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/136221
> Commit-Queue: Samir Jindel <[email protected]>
> Reviewed-by: Martin Kustermann <[email protected]>
> Reviewed-by: Ryan Macnak <[email protected]>

[email protected],[email protected],[email protected]

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I1891677b21560c7fc5a54a8eb800ef5850654402
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/137290
Reviewed-by: Ryan Macnak <[email protected]>
Commit-Queue: Ryan Macnak <[email protected]>
dart-bot pushed a commit that referenced this issue Feb 27, 2020
@rmacnak-google
[vm, gc] Verify the store buffer contains all old-space objects that …
2a5d058 
…reference new-space objects.

Speed-up ObjectSets.

Fix pointer verification before and after scavenging to set the correct mark expectation being on concurrent marking state.

Bug: #40780
Change-Id: Ic7ce6d5a829e41634083b0c274b9764da3f4b619
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/137240
Commit-Queue: Ryan Macnak <[email protected]>
Reviewed-by: Alexander Markov <[email protected]>
Reviewed-by: Siva Annamalai <[email protected]>
dart-bot pushed a commit that referenced this issue Feb 27, 2020
@rmacnak-google
[vm, gc] Add Splay as a test of various GC modes and verification tools.
275bc63 
Bug: #40780
Change-Id: I2b760c4e2884f400e1dcfbd77f21fa9c4d96f25c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/137645
Reviewed-by: Alexander Markov <[email protected]>
Commit-Queue: Ryan Macnak <[email protected]>
dart-bot pushed a commit that referenced this issue Mar 10, 2020
@mkustermann
Revert "Re-land "[vm] Aggressive write-barrier elimination.""
30a12a3 
This reverts commit eff1a9f.

Reason for revert:
  Causes flaky hits of RELEASE_ASSERT in marker.cc, see b/151131634.

Original change's description:
> Re-land "[vm] Aggressive write-barrier elimination."
> 
> The original revision is in Patchset 3.
> 
> Four bugs were fixed:
> 
> 1. JoinEntryInstr::SuccessorCount() is not the correct way to get the
>    number of successor blocks from the Join block;
>    JoinEntryInstr::last_instruction()->SuccessorCount() must be used
>    instead.
> 
> 2. BitVector::Equals() was non-deterministically returning 'false'
>    for equal vectors.
> 
> 3. All blocks need to be processed at least once during the Analysis
>    phase (not only in the SaveResults phase).
> 
> 4. We were not removing write barriers from StoreIndexed instructions,
>    even though we had support for it.
> 
> This reverts commit 7fd8ad5.
> 
> Fixes #40780
> 
> Change-Id: I9650ec2c547ec49cf88ca0524e14f6c245621f6a
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/138086
> Commit-Queue: Samir Jindel <[email protected]>
> Reviewed-by: Martin Kustermann <[email protected]>
> Reviewed-by: Ryan Macnak <[email protected]>

[email protected],[email protected],[email protected]

Change-Id: If9afd84465175fad2431405a97e9293c8bd5e476
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/138808
Reviewed-by: Martin Kustermann <[email protected]>
Commit-Queue: Martin Kustermann <[email protected]>
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