pub fn add_block(&mut self) -> BasicBlockId {
        let block = BasicBlock {
            id: self.blocks.len(),
            statements: vec![],
            terminator: Terminator::Crash,
        };
        self.blocks.push(block);
        self.blocks.len() - 1
    }
Add a new basic block and return its block ID.
weld/src/sir/mod.rs