1 files changed, 36 insertions, 0 deletions
diff --git a/third_party/rust/cranelift-codegen/src/dce.rs b/third_party/rust/cranelift-codegen/src/dce.rs
new file mode 100644
index 0000000000..e3e855806d
--- /dev/null
+++ b/third_party/rust/cranelift-codegen/src/dce.rs
@@ -0,0 +1,36 @@
+//! A Dead-Code Elimination (DCE) pass.
+//!
+//! Dead code here means instructions that have no side effects and have no
+//! result values used by other instructions.
+
+use crate::cursor::{Cursor, FuncCursor};
+use crate::dominator_tree::DominatorTree;
+use crate::entity::EntityRef;
+use crate::inst_predicates::{any_inst_results_used, has_side_effect};
+use crate::ir::Function;
+use crate::timing;
+
+/// Perform DCE on `func`.
+pub fn do_dce(func: &mut Function, domtree: &mut DominatorTree) {
+    let _tt = timing::dce();
+    debug_assert!(domtree.is_valid());
+
+    let mut live = vec![false; func.dfg.num_values()];
+    for &block in domtree.cfg_postorder() {
+        let mut pos = FuncCursor::new(func).at_bottom(block);
+        while let Some(inst) = pos.prev_inst() {
+            {
+                if has_side_effect(pos.func, inst)
+                    || any_inst_results_used(inst, &live, &pos.func.dfg)
+                {
+                    for arg in pos.func.dfg.inst_args(inst) {
+                        let v = pos.func.dfg.resolve_aliases(*arg);
+                        live[v.index()] = true;
+                    }
+                    continue;
+                }
+            }
+            pos.remove_inst();
+        }
+    }
+}