JIT: Delete old DFS and dominator implementations #96927
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- Remove `BasicBlock::bbIDom`. Move it into `DomTreeNode` instead so that multiple dominator trees aren't sharing a field in the basic block. - Introduce `FlowGraphDominatorTree::BuildFromRegularFlow`. It builds a dominator tree over the regular flow, ignoring exceptional flow. Switch the block weighting logic to be based on this tree. - Remove the old DFS - Remove the old dominator computation - Remove the old `DomTreeVisitor` and rename `NewDomTreeVisitor` -> `DomTreeVisitor` - Rename `BasicBlock::bbNewPostorderNum` -> `BasicBlock::bbPostorderNum`
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch Issue Details
Minor diffs expected due to differences in treatment of unreachable blocks when computing the new regular flow dominators.
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jakobbotsch
commented
Jan 13, 2024
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| if (!dfsTree->Contains(predBlock)) | ||
| { | ||
| DBG_SSA_JITDUMP(" Unreachable node\n"); |
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This was a preexisting bug. The below loop would read the bbIDom set by the old dominator computation in this case.
This was referenced Jan 13, 2024
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cc @dotnet/jit-contrib PTAL @BruceForstall Diffs. Some minor code diffs, due to the more precise exceptional flow handling. Some larger TP improvements. |
This was referenced Jan 16, 2024
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BruceForstall
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Jan 16, 2024
tmds
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Jan 23, 2024
- Switch the block weighting logic to be based on the new dominator tree - Remove the old DFS - Remove the old dominator computation - Remove the old `DomTreeVisitor` and rename `NewDomTreeVisitor` -> `DomTreeVisitor` - Rename `BasicBlock::bbNewPostorderNum` -> `BasicBlock::bbPostorderNum`
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DomTreeVisitorand renameNewDomTreeVisitor->DomTreeVisitorBasicBlock::bbNewPostorderNum->BasicBlock::bbPostorderNumSome diffs expected due to the more precise handling of exceptional flow. Some TP improvements expected from removing some unnecessary DFS/dominator computations. More improvements should come with follow-ups to avoid some unnecessary recomputations.