[Inductor] Clarify mutation related comments (#112466)

oulgen · pytorchmergebot · commit 7f77ec37be80 · 2023-11-01T18:39:58.000Z
Pull Request resolved: #112466 Approved by: https://github.com/Chillee
diff --git a/torch/_inductor/scheduler.py b/torch/_inductor/scheduler.py
@@ -1169,12 +1169,21 @@ def __init__(self, nodes):
             str, BaseSchedulerNode
         ] = dict()  # set in fuse_nods()
 
-        # we handle mutation by renaming modified versions of the same
+        # mutation_real_name: Maps back to the original name for codegen
+        # Example:
+        # If you mutate buf0 inside of buf1's kernel, then:
+        # mutation_real_name = {"buf0" : "buf1"}
+        # all subsequent uses of buf0 become buf1's usage in dependency graph
+        self.mutation_real_name = {}
+
+        # We handle mutation by renaming modified versions of the same
         # buffer in the dependency graph to prevent cycles.
         # mutation_renames: tracks the current name for a given buffer
         #                   (changed once per mutation)
-        self.mutation_real_name = {}
-        # mutation_real_name: maps back to the original name for codegen
+        # Example:
+        # If you mutate buf0 inside of buf1's kernel, then:
+        # mutation_renames = {"buf1" : "buf0"}
+        # in codegen we only use buf0, never buf1
         self.mutation_renames = {}
 
         self.compute_dependencies()
