From 542bc80f5947ff8458d88a8231dde6877ca31921 Mon Sep 17 00:00:00 2001
From: Will Feng <yfeng.us@gmail.com>
Date: Sat, 25 Oct 2025 01:20:48 -0700
Subject: [PATCH] Disallow both interpret modes active

---
 helion/exc.py              |  4 ++++
 helion/runtime/settings.py | 10 ++++++++--
 test/test_breakpoint.py    | 22 ++++++++++++++++++++++
 3 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/helion/exc.py b/helion/exc.py
index 6f5c02358..de002c026 100644
--- a/helion/exc.py
+++ b/helion/exc.py
@@ -269,6 +269,10 @@ class BreakpointInDeviceLoopRequiresInterpret(BaseError):
     message = "breakpoint() inside an `hl.tile` or `hl.grid` loop requires TRITON_INTERPRET=1 or HELION_INTERPRET=1."
 
 
+class BothInterpretModesActive(BaseError):
+    message = "Cannot have both TRITON_INTERPRET=1 and HELION_INTERPRET=1 active simultaneously. Please use only one interpret mode."
+
+
 class UndefinedVariable(BaseError):
     message = "{} is not defined."
 
diff --git a/helion/runtime/settings.py b/helion/runtime/settings.py
index 48aa1e97c..583f4de3e 100644
--- a/helion/runtime/settings.py
+++ b/helion/runtime/settings.py
@@ -232,8 +232,14 @@ def _get_autotune_random_seed() -> int:
 
 
 def _get_ref_mode() -> RefMode:
-    interpret = _env_get_bool("HELION_INTERPRET", False)
-    return RefMode.EAGER if interpret else RefMode.OFF
+    triton_interpret = os.environ.get("TRITON_INTERPRET") == "1"
+    helion_interpret = _env_get_bool("HELION_INTERPRET", False)
+
+    # Ban having both interpret modes active
+    if triton_interpret and helion_interpret:
+        raise exc.BothInterpretModesActive
+
+    return RefMode.EAGER if helion_interpret else RefMode.OFF
 
 
 @dataclasses.dataclass
diff --git a/test/test_breakpoint.py b/test/test_breakpoint.py
index c0e4e5a65..8dc5a527c 100644
--- a/test/test_breakpoint.py
+++ b/test/test_breakpoint.py
@@ -89,6 +89,9 @@ def _run_breakpoint_in_subprocess(
         )
 
         env = os.environ.copy()
+        # Set the env vars in the subprocess environment (needed for the ban check)
+        env["TRITON_INTERPRET"] = str(triton_interpret)
+        env["HELION_INTERPRET"] = str(helion_interpret)
         result = subprocess.run(
             [sys.executable, "-c", script],
             env=env,
@@ -128,6 +131,16 @@ def _run_device_breakpoint_test(
                     out = bound(x)
                 torch.testing.assert_close(out, x)
 
+    def _run_device_breakpoint_both_interpret_test(
+        self, triton_interpret: int, helion_interpret: int
+    ) -> None:
+        """Test that having both interpret modes active is banned."""
+        # Environment variables are already set by subprocess, just verify they're both 1
+        assert triton_interpret == 1 and helion_interpret == 1
+        # When both are set to 1, creating a kernel should raise an error
+        with self.assertRaises(exc.BothInterpretModesActive):
+            self._make_device_breakpoint_kernel()
+
     def test_device_breakpoint_no_interpret(self) -> None:
         self._run_breakpoint_in_subprocess(
             test_name=self._testMethodName,
@@ -152,6 +165,15 @@ def test_device_breakpoint_helion_interpret(self) -> None:
             helion_interpret=1,
         )
 
+    def test_device_breakpoint_both_interpret_banned(self) -> None:
+        """Test that having both TRITON_INTERPRET and HELION_INTERPRET active is banned."""
+        self._run_breakpoint_in_subprocess(
+            test_name=self._testMethodName,
+            runner_method="_run_device_breakpoint_both_interpret_test",
+            triton_interpret=1,
+            helion_interpret=1,
+        )
+
     def _run_host_breakpoint_test(
         self, triton_interpret: int, helion_interpret: int
     ) -> None: