Function estimate_branch_sensitive_backedges 

fn estimate_branch_sensitive_backedges(
    graph: &PathGraph<'_>,
    component: &LoopComponent,
    dependencies: &LocalDependencyIndex,
    root_closure: &FxHashSet<Local>,
    local_summary: &LoopLocalSummary,
) -> Option<usize>

Estimate extra budget needed when a loop-carried sink is controlled by internal SCC branches.

This is still a dataflow hint: the sink depends on a local that is assigned inside the SCC. The extra budget accounts for a separate limitation of the path extractor, where the unsafe source may live on a branch combination that is not reached by the shortest value-dependency chain alone.