[dynamo] Add recompile reason for set_stance fail_on_recompile (#165445)

Fixes #163500

### Summary:
For `set_stance("fail_on_recompile")` failures will provide the reason why the recompilation occurred

### Impacts:
module: dynamo

Pull Request resolved: https://github.com/pytorch/pytorch/pull/165445
Approved by: https://github.com/williamwen42

test/dynamo/test_decorators.py

@@ -2,6 +2,7 @@
 import functools
 import operator
 import os
+import re
 import unittest.mock as mock
 from unittest.mock import patch
 
@@ -1472,6 +1473,30 @@ class DecoratorTests(torch._dynamo.test_case.TestCase):
         self.assertEqual(out1, inp + 2)
         self.assertEqual(out2, inp + 2)
 
+    def test_fail_on_recompile_shows_guard_details(self):
+        @torch.compile(backend="eager", dynamic=False)
+        def f(x):
+            return x + 1
+
+        f(torch.ones(4))
+        f(torch.ones(5))
+
+        def post_munge(s):
+            return re.sub(r"line number: \d+", "line number: N", s)
+
+        with torch.compiler.set_stance("fail_on_recompile"):
+            f(torch.ones(4))
+            self.assertExpectedInlineMunged(
+                RuntimeError,
+                lambda: f(torch.ones(7)),
+                """\
+Detected recompile when torch.compile stance is 'fail_on_recompile'. filename: 'test_decorators.py', function name: 'f', line number: N
+    triggered by the following guard failure(s):
+    - 0/0: tensor 'x' size mismatch at index 0. expected 4, actual 7
+    - 0/1: tensor 'x' size mismatch at index 0. expected 5, actual 7""",  # noqa: B950
+                post_munge=post_munge,
+            )
+
     def test_set_stance_fail_on_recompile_with_disable(self):
         @torch.compiler.disable
         def inner(x):

torch/_dynamo/eval_frame.py

@@ -235,7 +235,11 @@ def _callback_from_stance(callback: DynamoCallback) -> DynamoCallback:
             if not convert_frame.has_tensor_in_frame(frame):
                 return ConvertFrameReturn()
 
-            from torch._C._dynamo.eval_frame import _debug_get_precompile_entries
+            from torch._C._dynamo.eval_frame import (
+                _debug_get_cache_entry_list,
+                _debug_get_precompile_entries,
+            )
+            from torch._dynamo.guards import get_and_maybe_log_recompilation_reasons
 
             message = (
                 "Detected recompile when torch.compile stance is 'fail_on_recompile'. "
@@ -243,6 +247,17 @@ def _callback_from_stance(callback: DynamoCallback) -> DynamoCallback:
                 + f"function name: '{frame.f_code.co_name}', "
                 + f"line number: {frame.f_lineno}"
             )
+            cache_entries = _debug_get_cache_entry_list(frame.f_code)
+            if cache_entries:
+                reasons = get_and_maybe_log_recompilation_reasons(
+                    cache_entries[0], frame, skip_logging=True
+                )
+                if reasons:
+                    failures = textwrap.indent("\n".join(reasons), "- ")
+                    guard_failure_details = (
+                        f"triggered by the following guard failure(s):\n{failures}"
+                    )
+                    message += f"\n{textwrap.indent(guard_failure_details, '    ')}"
             precompile_entries = _debug_get_precompile_entries(frame.f_code)
             if len(precompile_entries) > 0:
                 message += "\nFailed on the following precompiled guards: "