interpreter jit is for debugging

Author: iritkatriel

InternalDocs/jit.md

@@ -59,18 +59,24 @@ and an instance of `_PyUOpExecutor_Type` is created to contain it.
 After a `JUMP_BACKWARD` instruction invokes the uop optimizer to create a uop
 executor, it transfers control to this executor via the `GOTO_TIER_TWO` macro.
 
-When the JIT is configured to run on its interpreter (i.e., python is
-configured with
-[`--enable-experimental-jit=interpreter`](https://docs.python.org/dev/using/configure.html#cmdoption-enable-experimental-jit)),
-the executor jumps to `tier2_dispatch:` in
+CPython implements two executors. Here we describe the JIT interpreter,
+which is the simpler of them and is therefore useful for debugging and analyzing
+the uops generation and optimization stages. To run it, we configure the
+JIT to run on its interpreter (i.e., python is configured with
+[`--enable-experimental-jit=interpreter`](https://docs.python.org/dev/using/configure.html#cmdoption-enable-experimental-jit)).
+
+When invoked, the executor jumps to the `tier2_dispatch:` label in
 [`Python/ceval.c`](../Python/ceval.c), where there is a loop that
-executes the micro-ops. The micro-ops are are defined in
-[`Python/executor_cases.c.h`](../Python/executor_cases.c.h),
+executes the micro-ops. The body of this loop is a switch statement over
+the uops IDs, reselmbling the one used in the adaptive interpreter.
+
+The swtich implementing the uops is in [`Python/executor_cases.c.h`](../Python/executor_cases.c.h),
 which is generated by the build script
 [`Tools/cases_generator/tier2_generator.py`](../Tools/cases_generator/tier2_generator.py)
 from the bytecode definitions in
 [`Python/bytecodes.c`](../Python/bytecodes.c).
-This loop exits when an `_EXIT_TRACE` or `_DEOPT` uop is reached,
+
+When an `_EXIT_TRACE` or `_DEOPT` uop is reached, the uop interpreter exits
 and execution returns to the adaptive interpreter.
 
 ## Invalidating Executors