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Why SSA Compilers?

(mcyoung.xyz)
160 points transpute | 1 comments | | HN request time: 0.223s | source
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zachixer ◴[] No.45675783[source]
Every time I see a clean SSA explainer like this, I’m reminded that the “simplicity” of SSA only exists because we’ve decided mutation is evil. It’s not that SSA is simpler — it’s that we’ve engineered our entire optimization pipeline around pretending state doesn’t exist.

It’s a brilliant illusion that works… until you hit aliasing, memory models, or concurrency, and suddenly the beautiful DAG collapses into a pile of phi nodes and load/store hell.

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1. vidarh ◴[] No.45675858[source]
SSA is appealing because you can defer the load/store hell until after a bunch of optimizations, though, and a lot of those optimizations becomes a lot easier to reason about when you get to pretend state doesn't exist.