diff --git a/src/mir/builder/control_flow/joinir/routing.rs b/src/mir/builder/control_flow/joinir/routing.rs
index e9ca6b5d..f0bfa28b 100644
--- a/src/mir/builder/control_flow/joinir/routing.rs
+++ b/src/mir/builder/control_flow/joinir/routing.rs
@@ -35,53 +35,65 @@ impl MirBuilder {
         // Phase 195: Use unified trace
         trace::trace().routing("router", &func_name, "try_cf_loop_joinir called");
 
-        // Phase 49-4 + Phase 80: Multi-target routing
-        // - Core ON なら代表2本（print_tokens / ArrayExt.filter）は JoinIR を優先し、失敗したら LoopBuilder へフォールバック
-        // - Core OFF では従来通り dev フラグで opt-in
-        // Note: Arity does NOT include implicit `me` receiver
-        // Phase 188: Add "main" routing for loop pattern expansion
-        // Phase 170: Add JsonParserBox methods for selfhost validation
-        let core_on = crate::config::env::joinir_core_enabled();
-        let is_target = match func_name.as_str() {
-            "main" => true,  // Phase 188-Impl-1: Enable JoinIR for main function (Pattern 1)
-            "JoinIrMin.main/0" => true,  // Phase 188-Impl-2: Enable JoinIR for JoinIrMin.main/0 (Pattern 2)
-            "JsonTokenizer.print_tokens/0" => {
-                if core_on {
-                    true
-                } else {
-                    std::env::var("HAKO_JOINIR_PRINT_TOKENS_MAIN")
-                        .ok()
-                        .as_deref()
-                        == Some("1")
-                }
-            }
-            "ArrayExtBox.filter/2" => {
-                if core_on {
-                    true
-                } else {
-                    std::env::var("HAKO_JOINIR_ARRAY_FILTER_MAIN")
-                        .ok()
-                        .as_deref()
-                        == Some("1")
-                }
-            }
-            // Phase 170-A-1: Enable JsonParserBox methods for JoinIR routing
-            "JsonParserBox._trim/1" => true,
-            "JsonParserBox._skip_whitespace/2" => true,
-            "JsonParserBox._match_literal/2" => true,
-            "JsonParserBox._parse_string/2" => true,
-            "JsonParserBox._parse_array/2" => true,
-            "JsonParserBox._parse_object/2" => true,
-            // Phase 170-A-1: Test methods (simplified versions)
-            "TrimTest.trim/1" => true,
-            "Main.trim/1" => true,  // Phase 171-fix: Main box variant
-            "Main.trim_string_simple/1" => true,  // Phase 33-13: Simple trim variant
-            "TrimTest.main/0" => true,  // Phase 170: TrimTest.main for loop pattern test
-            _ => false,
-        };
+        // Phase 170-4: Structure-based routing option
+        // When NYASH_JOINIR_STRUCTURE_ONLY=1, skip function name whitelist
+        // and route purely based on loop structure analysis
+        let structure_only = std::env::var("NYASH_JOINIR_STRUCTURE_ONLY")
+            .ok()
+            .as_deref()
+            == Some("1");
 
-        if !is_target {
-            return Ok(None);
+        if structure_only {
+            trace::trace().routing("router", &func_name, "Structure-only mode enabled, skipping whitelist");
+        } else {
+            // Phase 49-4 + Phase 80: Multi-target routing (legacy whitelist)
+            // - Core ON なら代表2本（print_tokens / ArrayExt.filter）は JoinIR を優先し、失敗したら LoopBuilder へフォールバック
+            // - Core OFF では従来通り dev フラグで opt-in
+            // Note: Arity does NOT include implicit `me` receiver
+            // Phase 188: Add "main" routing for loop pattern expansion
+            // Phase 170: Add JsonParserBox methods for selfhost validation
+            let core_on = crate::config::env::joinir_core_enabled();
+            let is_target = match func_name.as_str() {
+                "main" => true,  // Phase 188-Impl-1: Enable JoinIR for main function (Pattern 1)
+                "JoinIrMin.main/0" => true,  // Phase 188-Impl-2: Enable JoinIR for JoinIrMin.main/0 (Pattern 2)
+                "JsonTokenizer.print_tokens/0" => {
+                    if core_on {
+                        true
+                    } else {
+                        std::env::var("HAKO_JOINIR_PRINT_TOKENS_MAIN")
+                            .ok()
+                            .as_deref()
+                            == Some("1")
+                    }
+                }
+                "ArrayExtBox.filter/2" => {
+                    if core_on {
+                        true
+                    } else {
+                        std::env::var("HAKO_JOINIR_ARRAY_FILTER_MAIN")
+                            .ok()
+                            .as_deref()
+                            == Some("1")
+                    }
+                }
+                // Phase 170-A-1: Enable JsonParserBox methods for JoinIR routing
+                "JsonParserBox._trim/1" => true,
+                "JsonParserBox._skip_whitespace/2" => true,
+                "JsonParserBox._match_literal/2" => true,
+                "JsonParserBox._parse_string/2" => true,
+                "JsonParserBox._parse_array/2" => true,
+                "JsonParserBox._parse_object/2" => true,
+                // Phase 170-A-1: Test methods (simplified versions)
+                "TrimTest.trim/1" => true,
+                "Main.trim/1" => true,  // Phase 171-fix: Main box variant
+                "Main.trim_string_simple/1" => true,  // Phase 33-13: Simple trim variant
+                "TrimTest.main/0" => true,  // Phase 170: TrimTest.main for loop pattern test
+                _ => false,
+            };
+
+            if !is_target {
+                return Ok(None);
+            }
         }
 
         // Debug log when routing through JoinIR Frontend