Function try_broadcast_scalar_compare 

fn try_broadcast_scalar_compare(b: &BinaryExpr, ctx: &mut WalkCtx<'_>)

Inspect a comparison binop’s operands; if one is a known vector and the other is a known scalar f32, emit a constructor wrap around the scalar so the comparison evaluates as a vector-bool. Zero-length insertions only, so the wrap survives even when other passes have also edited the operands.