Function rewrite_phi_sources

crates/rustc_codegen_spirv/src/linker/inline.rs:1069–1098

Helper for adjusting `OpPhi` source label IDs, when the terminator of the `original_label_id`-labeled block got moved to `blocks[original_block_idx]`.

(original_label_id: Word, blocks: &mut [Block], new_block_idx: usize)

/// Helper for adjusting `OpPhi` source label IDs, when the terminator of the
/// `original_label_id`-labeled block got moved to `blocks[original_block_idx]`.
fn rewrite_phi_sources(original_label_id: Word, blocks: &mut [Block], new_block_idx: usize) {
    let new_label_id = blocks[new_block_idx].label_id().unwrap();

    // HACK(eddyb) can't keep `blocks` borrowed, the loop needs mutable access.
    let target_ids: SmallVec<[_; 4]> = outgoing_edges(&blocks[new_block_idx]).collect();

    for target_id in target_ids {
        let target_block = blocks
            .iter_mut()
            .find(|b| b.label_id().unwrap() == target_id)
            .unwrap();
        let phis = target_block
            .instructions
            .iter_mut()
            .filter(|inst| {
                // These are the only instructions that are allowed before `OpPhi`.
                !matches!(inst.class.opcode, Op::Line | Op::NoLine)
            })
            .take_while(|inst| inst.class.opcode == Op::Phi);
        for phi in phis {
            for value_and_source_id in phi.operands.chunks_mut(2) {
                let source_id = value_and_source_id[1].id_ref_any_mut().unwrap();
                if *source_id == original_label_id {
                    *source_id = new_label_id;
                    break;
                }
            }
        }
    }
}