NiccoloN
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Parallelism and Runtime Invariant
Compile-time optimization must not trade away execution parallelism or worsen theoretical runtime behavior. The absence of a precise runtime measurement does not make such a trade acceptable.
In particular, a compile-time optimization must not:
- serialize work that can execute independently;
- coarsen lane, core, batch, or scheduling granularity in a way that reduces available execution parallelism;
- increase the theoretical runtime critical path, instruction count, memory traffic, synchronization, or required copies merely to reduce compiler work;
- merge independently scheduled work when doing so may reduce concurrency.
Compiler representations may share analysis, planning, or code-generation work only when the emitted execution retains the same independent work, schedule semantics, and available parallelism. If runtime impact cannot be measured precisely, it must be established from the transformation's semantics; uncertainty is not permission to accept a possible runtime regression.