diff --git a/src/interp.rs b/src/interp.rs
index 2133386..b04f056 100644
--- a/src/interp.rs
+++ b/src/interp.rs
@@ -14,7 +14,6 @@ pub struct InterpContext {
     memories: PerEntity<Memory, InterpMemory>,
     tables: PerEntity<Table, InterpTable>,
     globals: PerEntity<Global, ConstVal>,
-    trace_log: Vec<(usize, Vec<ConstVal>)>,
 }
 
 type MultiVal = SmallVec<[ConstVal; 2]>;
@@ -73,7 +72,6 @@ impl InterpContext {
             memories,
             tables,
             globals,
-            trace_log: vec![],
         }
     }
 
@@ -191,7 +189,7 @@ impl InterpContext {
                                 multivalue[0]
                             })
                             .collect::<Vec<_>>();
-                        self.trace_log.push((id, args));
+                        eprintln!("TRACE: {}: {:?}", id, &args[..]);
                         smallvec![]
                     }
                     &ValueDef::None | &ValueDef::Placeholder(..) | &ValueDef::BlockParam(..) => {
diff --git a/src/passes.rs b/src/passes.rs
index c001335..93de4ad 100644
--- a/src/passes.rs
+++ b/src/passes.rs
@@ -5,3 +5,4 @@ pub mod dom_pass;
 pub mod empty_blocks;
 pub mod maxssa;
 pub mod resolve_aliases;
+pub mod trace;
diff --git a/src/passes/trace.rs b/src/passes/trace.rs
new file mode 100644
index 0000000..8c5f9d0
--- /dev/null
+++ b/src/passes/trace.rs
@@ -0,0 +1,18 @@
+//! Trace-insertion pass.
+
+use crate::entity::EntityRef;
+use crate::ir::*;
+
+pub fn run(body: &mut FunctionBody) {
+    for (block, data) in body.blocks.entries_mut() {
+        let value = ValueDef::Trace(
+            block.index(),
+            data.params
+                .iter()
+                .map(|&(_, param)| param)
+                .collect::<Vec<_>>(),
+        );
+        let value = body.values.push(value);
+        data.insts.insert(0, value);
+    }
+}