Add RemoveSubsequentEquivalentCtrl Canonicalization Pattern

[MatthiasReumann]

Description

This pull request add a RemoveSubsequentEquivalentCtrl pattern to the canonicalization of the CtrlOp, which is currently not implemented.

This pattern will probably also be used in the "Writing Your First Optimization Pass" section in the Getting Started guide. (#1555)

Checklist

• The pull request only contains commits that are focused and relevant to this change.
• I have added appropriate tests that cover the new/changed functionality.
• I have updated the documentation to reflect these changes.
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• I have reviewed my own code changes.

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[codecov]

Codecov Report

❌ Patch coverage is 96.42857% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
mlir/lib/Dialect/QCO/IR/Modifiers/CtrlOp.cpp	96.4%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[burgholzer]

Just a brief comment here: We should really consider lifting the constraint that Ctrl modifiers (and modifiers in general) must only contain a single unitary operation. If we would allow multiple operations in a modifier, then we would get this optimization basically for free based on the current canonicalization and a canonicalization that pulls together separate CtrlOp with shared controls.
Something to think about a little.

[MatthiasReumann]

Just a brief comment here: We should really consider lifting the constraint that Ctrl modifiers (and modifiers in general) must only contain a single unitary operation. If we would allow multiple operations in a modifier, then we would get this optimization basically for free based on the current canonicalization and a canonicalization that pulls together separate CtrlOp with shared controls. Something to think about a little.

I haven't thought it through thoroughly, but this sounds very reasonable - at least for the optimization introduced in this pull request.