moved crates in lib/ to src/, renamed crates, modified some files' text (#660)

moved crates in lib/ to src/, renamed crates, modified some files' text (#660)

cranelift/codegen/src/unreachable_code.rs

@@ -0,0 +1,46 @@
+//! Unreachable code elimination.
+
+use crate::cursor::{Cursor, FuncCursor};
+use crate::dominator_tree::DominatorTree;
+use crate::flowgraph::ControlFlowGraph;
+use crate::ir;
+use crate::timing;
+use log::debug;
+
+/// Eliminate unreachable code.
+///
+/// This pass deletes whole EBBs that can't be reached from the entry block. It does not delete
+/// individual instructions whose results are unused.
+///
+/// The reachability analysis is performed by the dominator tree analysis.
+pub fn eliminate_unreachable_code(
+    func: &mut ir::Function,
+    cfg: &mut ControlFlowGraph,
+    domtree: &DominatorTree,
+) {
+    let _tt = timing::unreachable_code();
+    let mut pos = FuncCursor::new(func);
+    while let Some(ebb) = pos.next_ebb() {
+        if domtree.is_reachable(ebb) {
+            continue;
+        }
+
+        debug!("Eliminating unreachable {}", ebb);
+        // Move the cursor out of the way and make sure the next lop iteration goes to the right
+        // EBB.
+        pos.prev_ebb();
+
+        // Remove all instructions from `ebb`.
+        while let Some(inst) = pos.func.layout.first_inst(ebb) {
+            debug!(" - {}", pos.func.dfg.display_inst(inst, None));
+            pos.func.layout.remove_inst(inst);
+        }
+
+        // Once the EBB is completely empty, we can update the CFG which removes it from any
+        // predecessor lists.
+        cfg.recompute_ebb(pos.func, ebb);
+
+        // Finally, remove the EBB from the layout.
+        pos.func.layout.remove_ebb(ebb);
+    }
+}