[all-commits] [llvm/llvm-project] f432cb: [mlir] Avoid rewriting unreachable blocks in the g...

[Vijay Kandiah via All-commits]

  Branch: refs/heads/users/mamini/greedy-rewrite-reachability
  Home:   https://github.com/llvm/llvm-project
  Commit: f432cbaeb17a9c01e373599fd5d0af1d0304a965
      https://github.com/llvm/llvm-project/commit/f432cbaeb17a9c01e373599fd5d0af1d0304a965
  Author: Vijay Kandiah <vkandiah at nvidia.com>
  Date:   2026-09-26 (Sat, 26 Sep 2026)

  Changed paths:
    M mlir/include/mlir/Transforms/GreedyPatternRewriteDriver.h
    M mlir/lib/Transforms/Utils/GreedyPatternRewriteDriver.cpp
    M mlir/test/Transforms/canonicalize-dce.mlir
    A mlir/test/Transforms/greedy-cfg-reachability.mlir
    M mlir/test/Transforms/test-strict-pattern-driver.mlir
    M mlir/test/lib/Dialect/Test/TestPatterns.cpp

  Log Message:
  -----------
  [mlir] Avoid rewriting unreachable blocks in the greedy driver

A rewrite can disconnect a block after the iteration's initial CFG sweep.
Track reachability through rewriter notifications and skip worklist
operations in unreachable blocks until the next iteration removes them.

Cache reachability per region and compare final successors after each
rewrite. Preserve the cache for successor-equivalent changes, added edges,
and block merges that keep surviving blocks reachable. Recompute for other
CFG changes, including entry changes and cross-region block moves.

Keep cache updates separate from reachability queries, returning failure
when a full traversal is required. Collect each successor set once for
validation and retain compact vector snapshots in the cache. Check
containing blocks when querying operations in nested regions, caching the
ancestor result until listener notifications invalidate it.

Cover inserted and redirected blocks, blocks connected before rewrite
completion, nested regions, block moves and merges, and explicit op lists.
Use observer diagnostics to check whether affected operations are processed
within a single greedy iteration. Document that skipped operations are not
automatically retried if a later rewrite makes their block reachable, and
test that behavior in each strictness mode.

Assisted-by: Codex



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