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JIT: Validate DFS tree in post-phase checks #95652

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jakobbotsch opened this issue Dec 5, 2023 · 1 comment · Fixed by #95682
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JIT: Validate DFS tree in post-phase checks #95652

jakobbotsch opened this issue Dec 5, 2023 · 1 comment · Fixed by #95682
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area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI
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9.0.0

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@jakobbotsch
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Recomputing the DFS will cause m_dfs and m_loops to return nonsensical results (i.e. the results aren't just outdated). We should validate in post-phase checks that the DFS tree we're storing matches the flow graph, and explicitly null out the relevant information when we invalidate it.
@jakobbotsch jakobbotsch added this to the 9.0.0 milestone Dec 5, 2023
@jakobbotsch jakobbotsch self-assigned this Dec 5, 2023
@dotnet-issue-labeler dotnet-issue-labeler bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Dec 5, 2023
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ghost commented Dec 5, 2023

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Issue Details

Recomputing the DFS will cause m_dfs and m_loops to return nonsensical results (i.e. the results aren't just outdated). We should validate in post-phase checks that the DFS tree we're storing matches the flow graph, and explicitly null out the relevant information when we invalidate it.

Author: jakobbotsch
Assignees: jakobbotsch
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area-CodeGen-coreclr
Milestone: 9.0.0

@jakobbotsch jakobbotsch mentioned this issue Dec 5, 2023
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jakobbotsch added a commit to jakobbotsch/runtime that referenced this issue Dec 6, 2023
@jakobbotsch
JIT: Add post-phase validation of DFS tree
d27e91b 
Add a post-phase check that validates that the DFS tree matches the
current flow graph when it is non-null.

Add a `fgInvalidateDfsTree()` that invalidates the DFS tree and derived
annotations on it (dominators and loops). We invalidate after RBO, which
is the last point we expect to make use of the flow graph information.

Compute new DFS and loops as part of loop unrolling to make the DFS tree
correct after this point too. Some TP regressions are expected due to
this.

To sum up we now keep this information valid from loop finding until
RBO.

Fix dotnet#95652
@jakobbotsch jakobbotsch mentioned this issue Dec 6, 2023
Merged
@ghost ghost added the in-pr There is an active PR which will close this issue when it is merged label Dec 6, 2023
jakobbotsch added a commit that referenced this issue Dec 8, 2023
@jakobbotsch
JIT: Add post-phase validation of DFS tree (#95682)
ba1d799 
Add a post-phase check that validates that the DFS tree matches the
current flow graph when it is non-null.

Add a `fgInvalidateDfsTree()` that invalidates the DFS tree and derived
annotations on it (dominators and loops). We invalidate after RBO, which
is the last point we expect to make use of the flow graph information.

Fix #95652
@ghost ghost removed the in-pr There is an active PR which will close this issue when it is merged label Dec 8, 2023
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JIT: Add post-phase validation of DFS tree jakobbotsch/runtime
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