Spatial Task Placement for Multi-CGRA

[guosran]

Summary

The MapCTOnCGRAArrayPass performs spatial mapping of taskflow.task operations onto a 2D CGRA grid. It optimizes task placement and SRAM assignment to minimize inter-tile communication and memory access latency.

Core Mechanism

• Graph-Based Modeling: Constructs a bipartite Task-Memory Graph to track SSA dependencies between tasks and shared memory access.

• Iterative Optimization: Employs a Coordinate Descent strategy that alternates between:

  1. Task Placement: Mapping tasks to grid tiles based on proximity to SSA producers and associated SRAMs.
  2. SRAM Assignment: Positioning SRAMs at the rounded centroid of all tasks accessing that specific memory.

• Heuristic Scoring: Uses a weighted scoring function considering SSA proximity, memory distance, and grid load balancing.

• The result for 'multi_nested_loop` is shown below:

[Copilot]

Pull request overview

This PR introduces a dependency-analysis pass and a spatial placement pass for Minimized Canonicalized Tasks (MCTs) onto a 2D multi-CGRA grid, plus tests that validate the new placement attributes on several kernels.

Changes:

• Add AnalyzeMCTDependencyPass to detect SSA and memory (RAW/WAR/WAW) dependencies between MCTs and to identify same-header fusion candidates.
• Add PlaceMCTOnCGRAPass implementing a critical-path–driven placement heuristic with adjacency-aware scoring and basic memory/SRAM assignment, and register both passes in the Taskflow pass pipeline and build system.
• Extend multi-CGRA Taskflow tests (parallel-nested, multi-nested, irregular-loop) with new RUN lines that invoke the placement pass and FileCheck the resulting taskflow.task placement attributes.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/multi-cgra/taskflow/parallel-nested/parallel-nested.mlir	Adds a placement pipeline invocation and PLACEMENT checks for 2 tasks’ CGRA coordinates and counts.
test/multi-cgra/taskflow/multi-nested/multi-nested.mlir	Adds placement pipeline and PLACEMENT checks for 5 tasks’ CGRA coordinates and counts in a more complex nested-loop scenario.
test/multi-cgra/taskflow/irregular-loop/irregular-loop.mlir	Extends the irregular-loop test with a placement pipeline and PLACEMENT checks for 3 tasks’ CGRA coordinates and counts.
lib/TaskflowDialect/Transforms/PlaceMCTOnCGRAPass.cpp	Implements the CGRA placer, including counter-chain extraction, dependency graph construction, ALAP-based task prioritization, heuristic scoring, placement annotation, and memory/SRAM mapping.
lib/TaskflowDialect/Transforms/CMakeLists.txt	Registers the new analysis and placement passes with the Taskflow transforms library build.
lib/TaskflowDialect/Transforms/AnalyzeMCTDependencyPass.cpp	Implements MCT dependency analysis, printing detailed per-task counter-chain and read/write sets plus a dependency summary.
include/TaskflowDialect/TaskflowPasses.td	Declares the analyze-mct-dependency and place-mct-on-cgra passes with documentation used by MLIR’s pass infrastructure.
include/TaskflowDialect/TaskflowPasses.h	Declares factory functions for constructing the new Taskflow passes.

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[Copilot]

@guosran I've opened a new pull request, #255, to work on those changes. Once the pull request is ready, I'll request review from you.

[ShangkunLi]

@guosran Before merging, plz sync with the main branch, and double-check whether I missed any format checking (e.g., comment ends with a period, comment starts with the description style).