[Mlir-commits] [mlir] [mlir] Improve `GreedyPatternRewriteDriver` and pass documentation (PR #77614)

[Matthias Springer]

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@@ -23,16 +23,21 @@ further below. All passes in MLIR derive from `OperationPass` and adhere to the
 following restrictions; any noncompliance will lead to problematic behavior in
 multithreaded and other advanced scenarios:
 
-*   Must not modify any state referenced or relied upon outside the current
-    operation being operated on. This includes adding or removing operations
-    from the parent block, changing the attributes(depending on the contract
-    of the current operation)/operands/results/successors of the current operation.
-*   Must not modify the state of another operation not nested within the current
-    operation being operated on.
-    *   Other threads may be operating on these operations simultaneously.
-*   Must not inspect the state of sibling operations.
+*   Must not inspect the state of operations that are siblings of the operation
+    that the pass operates on. Must neither access operations nested under those
+    siblings.
     *   Other threads may be modifying these operations in parallel.
     *   Inspecting the state of ancestor/parent operations is permitted.
+*   Must not modify the state of operations other than the operation that the
+    pass operates on ("current operation") and its nested operations. This
+    includes adding, modifying or removing other operations from an ancestor
+    block.
+    *   Other threads may be operating on these operations simultaneously.
+    *   The attributes of the current operation may be modified freely.
+    *   The operands of the current operation may be modified, as long as no
----------------
matthias-springer wrote:

This is a bit sus. Example:

- Pass instance 1: `currentOp->setOperand(0, currentOp->getBlock()->getArgument(0)`
- Pass instance 2: `print(currentOp->getBlock()->getArgument(0).getUses().size()`

Instance 1 modifies the current op. That is allowed. (Or is it? The use list of a parent block argument changes. Does this count as "modifying per parent op"?).

Instance 2 reads the number of uses of a parent block argument. That is allowed. But there's a race condition if both instances run in parallel.

Maybe the only modifications that we should allow are "modifying attributes"?


https://github.com/llvm/llvm-project/pull/77614