Function recognize_causal_conv 

pub fn recognize_causal_conv(stmts: &[Stmt<'_>]) -> Option<CausalConvSpec>

Recognize Let Y be causal conv of X with weight WC state CS over T taps — the three loops: the ring shift CS[(t−1)·chan+c] ← CS[t·chan+c], the append of X, and the tap reduce against WC.