blazingly fasterer

2026-07-21 15:43:35 +02:00
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+# Compiler Performance Optimization Invariant
+
+## Scope
+
+This invariant applies to:
+
+- ONNX-to-Spatial lowering;
+- graph and trivial merge;
+- PEFT scheduling;
+- scheduled materialization;
+- deferred communication;
+- Spatial-to-PIM lowering;
+- bufferization;
+- memory coalescing;
+- liveness planning;
+- PIM code generation.
+
+## Invariant
+
+A compiler compile-time or memory optimization must not reduce available
+hardware parallelism or worsen theoretical execution time. In the absence of a
+precise runtime model, it is forbidden to serialize independent work, reduce
+the number of simultaneously schedulable compute instances, replace parallel
+graph or core batches with sequential loops, introduce recomputation, add
+runtime copies, increase communication or instruction count, or lengthen the
+schedule critical path merely to reduce compiler time or memory usage.
+
+An optimization is acceptable only when its static runtime proxies are equal or
+better.
+
+## Forbidden optimization trades
+
+Do not:
+
+- use fewer parallel lanes or cores to simplify IR;
+- scalarize a valid graph or core batch;
+- replace independent operations with one sequential loop;
+- recompute values to reduce storage;
+- add device/device or host/device copies to reduce peak memory;
+- change hardware parameters to make a benchmark easier;
+- reduce communication concurrency by imposing a global serial order;
+- increase emitted instruction count to reduce compiler analysis;
+- move PIM work to the host.
+
+## Required proof
+
+Every performance change must report before and after:
+
+- compiler wall time;
+- compiler peak RSS;
+- IR operation and value counts at the changed stage;
+- logical compute-instance count;
+- graph compute batch and scheduled batch lane counts;
+- PEFT class and core assignment;
+- maximum scheduled critical-path or step count;
+- MVM/VMM and vector instruction counts;
+- send and receive counts and bytes;
+- total emitted instruction count;
+- maximum instructions assigned to one core;
+- number and size of runtime memory copies;
+- final host, weights, logical-core, physical-core, and maximum-core memory;
+- numerical validation.
+
+## Stop rule
+
+If compile time or memory improves but a runtime proxy worsens, stop and reject
+the change.