This document proposes a two-level just-in-time compilation approach using one interpreter and one engine. It finds that by providing different interpreter definitions to the RPython meta-tracing compiler, different kinds of compilers and compilations can be derived, such as tracing, method, and threaded code compilers. The key idea is an adaptive RPython system that performs multitier compilation by generating different interpreters from a generic interpreter and driving the RPython engine accordingly. This challenges the assumption in the JIT community that a meta-tracing compiler can only perform tracing compilation.

1. Two-level Just-in-Time Compilation with One
Interpreter and One Engine
Yusuke Izawa 1
Hidehiko Masuhara 1
Carl Friedrich Bolz-Tereick 2
1Tokyo Institute of Technology
2Heinrich-Heine-Universität Düsseldorf
PEPM 2022
January 18, 2022
Two-level JIT Compilation with .. PEPM 2022 1 / 15

2. Outline
1. Introduction: the folklore in a JIT community and our findings
2. Proposal: Adaptive RPython that performs multitier compilation with “one
interpreter” and “one engine”
3. Observation: to confirm that Adaptive RPython “actually” works
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3. Folklore: A Meta-JIT Compiler Performs a Fixed Kind of
JIT Compilation
• Build an interpreter from scratch for realizing different kinds of JIT
compilers
Interptracing Interpmethod Interpthreaded
Meta-JIT
compiler
Meta-JIT
compiler
Meta-JIT
compiler
Tracing JIT Method JIT
Threaded Code
Gen.[ICOOOLPS 2021]
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4. Folklore: A Meta-JIT Compiler Performs a Fixed Kind of
JIT Compilation
• Build an interpreter from scratch for realizing different kinds of JIT
compilers
Interptracing Interpmethod Interpthreaded
Meta-JIT
compiler
Meta-JIT
compiler
Meta-JIT
compiler
Tracing JIT Method JIT
Threaded Code
Gen.[ICOOOLPS 2021]
consisting CALL insts in bytecode:
removing indirect-branching
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5. Folklore: A Meta-JIT Compiler Performs a Fixed Kind of
JIT Compilation
• Build an interpreter from scratch for realizing different kinds of JIT
compilers
Interptracing Interpmethod Interpthreaded
RPython Truffle/Graal
Meta-JIT
compiler
PyPy TruffleRuby Threaded Code
Gen.[ICOOOLPS 2021]
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6. Our Findings Will Affect JIT Community’s Assumption
JIT community assumes that ..
• Meta-tracing JIT compiler can
only do tracing compilation
RPython[interp, source] = ptracing
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7. Our Findings Will Affect JIT Community’s Assumption
JIT community assumes that ..
• Meta-tracing JIT compiler can
only do tracing compilation
But, with our findings ..
• Let meta-tracing JIT do several
compilations, like
− method compilation
− threaded code compilation
− etc.
RPython[interp, source] = ptracing RPython[interp, source] = pα
RPython[interp, source] = pβ
RPython[interp, source] = pγ
· · ·
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8. Our Findings
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9. Our Findings
By providing different interp definitions to RPython, can derive different kinds
of outputs
E.g. when passes ..
Two-level JIT Compilation with .. PEPM 2022 5 / 15

10. Our Findings
By providing different interp definitions to RPython, can derive different kinds
of outputs
E.g. when passes ..
• interptracing to RPython → tracing compilation
RPython[interptracing, source] = ptracing
Two-level JIT Compilation with .. PEPM 2022 5 / 15

11. Our Findings
By providing different interp definitions to RPython, can derive different kinds
of outputs
E.g. when passes ..
• interptracing to RPython → tracing compilation
• interpmethod to RPython → method compilation
RPython[interptracing, source] = ptracing
RPython[interpmethod, source] = pmethod
Two-level JIT Compilation with .. PEPM 2022 5 / 15

12. Our Findings
By providing different interp definitions to RPython, can derive different kinds
of outputs
E.g. when passes ..
• interptracing to RPython → tracing compilation
• interpmethod to RPython → method compilation
• interpthreaded to RPython → threaded compilation
RPython[interptracing, source] = ptracing
RPython[interpmethod, source] = pmethod
RPython[interpthreaded, source] = pthreaded
Two-level JIT Compilation with .. PEPM 2022 5 / 15

13. Our Findings
By providing different interp definitions to RPython, can derive different kinds
of outputs
E.g. when passes ..
• interptracing to RPython → tracing compilation
• interpmethod to RPython → method compilation
• interpthreaded to RPython → threaded compilation
RPython[interptracing, source] = ptracing
RPython[interpmethod, source] = pmethod
RPython[interpthreaded, source] = pthreaded
 In other words ..
By changing an interpreter, we can get different kinds of compilers
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14. Proposal: Multitier Compilation on Adaptive RPython
Adaptive RPython performs multitier compilation with “one interpreter” and
“one engine”
optimization level
threaded code baseline 2 · · ·
tracing
method
tracing + method
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15. Proposal: Multitier Compilation on Adaptive RPython
Adaptive RPython performs multitier compilation with “one interpreter” and
“one engine”
optimization level
threaded code baseline 2 · · ·
tracing
method
tracing + method
With Adaptive RPython ..
one generic interp. → common interp + a bit different definitions
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16. Proposal: Multitier Compilation on Adaptive RPython
Adaptive RPython performs multitier compilation with “one interpreter” and
“one engine”
optimization level
threaded code baseline 2 · · ·
tracing
method
tracing + method
With Adaptive RPython ..
one generic interp. → common interp + a bit different definitions
perform on one engine = RPython
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17. Overview: Adaptive RPython Performs Multitier
Compilation
(1) A developer writes a generic
interp
Generic interp
Adaptive RPython
Pre-processor
Adaptive RPython
P.E. System
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18. Overview: Adaptive RPython Performs Multitier
Compilation
(2) Pass information to the
pre-processor
Generic interp
Adaptive RPython
Pre-processor
Which instruc-
tions will be
transformed?
Adaptive RPython
P.E. System
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19. Overview: Adaptive RPython Performs Multitier
Compilation
(3) Generate interps from generic
interp
Generic interp
Adaptive RPython
Pre-processor
Which instruc-
tions will be
transformed?
Icommon
Itracing Ithreaded Imethod
Adaptive RPython
P.E. System
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20. Overview: Adaptive RPython Performs Multitier
Compilation
(4) Pass information to the offline
P.E.
Generic interp
Adaptive RPython
Pre-processor
Which instruc-
tions will be
transformed?
Icommon
Itracing Ithreaded Imethod
Adaptive RPython
P.E. System
Source program
and info about
static and dy-
namic inputs
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21. Overview: Adaptive RPython Performs Multitier
Compilation
(5) Tracing compilation:
choose Icommon and Itracing
RPython[Icommon + Itracing,
P, V] = P′
tracing
Generic interp
Adaptive RPython
Pre-processor
Which instruc-
tions will be
transformed?
Icommon
Itracing Ithreaded Imethod
Adaptive RPython
P.E. System
Source program
and info about
static and dy-
namic inputs
Ptracing
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22. Overview: Adaptive RPython Performs Multitier
Compilation
(6) Threaded code gen. [Izawa et al., 2021]
:
choose Icommon and Ithreaded
RPython[Icommon + Ithreaded,
P, V] = P′
threaded
Generic interp
Adaptive RPython
Pre-processor
Which instruc-
tions will be
transformed?
Icommon
Itracing Ithreaded Imethod
Adaptive RPython
P.E. System
Source program
and info about
static and dy-
namic inputs
Ptracing Pthreaded
Two-level JIT Compilation with .. PEPM 2022 7 / 15

23. Overview: Adaptive RPython Performs Multitier
Compilation
(7) Method compilation:
choose Icommon and Imethod
RPython[Icommon + Imethod,
P, V] = P′
method
Generic interp
Adaptive RPython
Pre-processor
Which instruc-
tions will be
transformed?
Icommon
Itracing Ithreaded Imethod
Adaptive RPython
P.E. System
Source program
and info about
static and dy-
namic inputs
Ptracing Pthreaded Pmethod
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24. Overview: How to Drive the RPython Engine [ICOOOLPS 2021]
Meta-tracing JIT
• Trace the execution of an interp.
Threaded code generation
A
B
C
D
JUMP
E
F
RET
c
a
l
l
[p0]
i1 = load(..)
i1 = int_add(..)
i2 = int_lt(..)
guard_true(i2) [p0]
..
..
jump(p0)
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25. Overview: How to Drive the RPython Engine [ICOOOLPS 2021]
Meta-tracing JIT
• Trace the execution of an interp
Threaded code generation
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26. Overview: How to Drive the RPython Engine [ICOOOLPS 2021]
Meta-tracing JIT
• Trace the execution of an interp
Threaded code generation
• Traverse the entire method body
• Not trace inside the handlers
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27. Overview: How to Drive the RPython Engine [ICOOOLPS 2021]
Meta-tracing JIT
• Trace the execution of an interp
Threaded code generation
• Traverse the entire method body
• Not trace inside the handlers
A
B
C
D
JUMP
E
F
RET
c
a
l
l
c
a
l
l
Traverse the en-
tire method body Not trace the
inside but
leave CALL to
the handler
Cut/stitch the
temporal trace
[p0]
i7 = call_i(ConstClass(DUP, ..))
i12 = call_i(ConstClass(CONST_I ..))
i16 = call_i(ConstClass(LT, ..))
guard_true(i16) [p0]
...
jump(p0)
[p0]
...
i28 = call_i(ConstClass(CALL, ..))
...
i32 = call_i(ConstClass(RET, ..2))
leave_portal_frame(0)
finish(i32)
bridge
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28. Overview: How to Drive the RPython Engine [ICOOOLPS 2021]
Meta-tracing JIT
• Trace the execution of an interp
Threaded code generation
• Traverse the entire method body
• Not trace inside the handlers
tweaking an interp
A
B
C
D
JUMP
E
F
RET
c
a
l
l
c
a
l
l
Traverse the en-
tire method body Not trace the
inside but
leave CALL to
the handler
Cut/stitch the
temporal trace
[p0]
i7 = call_i(ConstClass(DUP, ..))
i12 = call_i(ConstClass(CONST_I ..))
i16 = call_i(ConstClass(LT, ..))
guard_true(i16) [p0]
...
jump(p0)
[p0]
...
i28 = call_i(ConstClass(CALL, ..))
...
i32 = call_i(ConstClass(RET, ..2))
leave_portal_frame(0)
finish(i32)
bridge
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29. Method-traversal Interpreter: How to Drive the
RPython Engine [ICOOOLPS 2021]
 traverse depth-firstly the entire method body w/ traverse_stack
@dont_look_insdie
def ADD():
..
while True:
if opcde == JUMP_IF:
top = pop()
target = bytecode[pc++]
if top.is_true():
traverse_stack.push(pc++)
pc = target
else:
traverse_stack.push(target)
pc++
elif opcode == JUMP:
target = bytecode[pc++]
if not traverse_stack.is_empty():
pc = traverse_stack.pop()
else:
finish()
elif opcode == RET:
if not traverse_stack.is_empty():
pc = traverse_stack.pop()
else:
return pop()

30. Method-traversal Interpreter: How to Drive the
RPython Engine [ICOOOLPS 2021]
 traverse depth-firstly the entire method body w/ traverse_stack
@dont_look_insdie
def ADD():
..
while True:
if opcde == JUMP_IF:
top = pop()
target = bytecode[pc++]
if top.is_true():
traverse_stack.push(pc++)
pc = target
else:
traverse_stack.push(target)
pc++
elif opcode == JUMP:
target = bytecode[pc++]
if not traverse_stack.is_empty():
pc = traverse_stack.pop()
else:
finish()
elif opcode == RET:
if not traverse_stack.is_empty():
pc = traverse_stack.pop()
else:
return pop()
Suppress inlining

31. Method-traversal Interpreter: How to Drive the
RPython Engine [ICOOOLPS 2021]
 traverse depth-firstly the entire method body w/ traverse_stack
@dont_look_insdie
def ADD():
..
while True:
if opcde == JUMP_IF:
top = pop()
target = bytecode[pc++]
if top.is_true():
traverse_stack.push(pc++)
pc = target
else:
traverse_stack.push(target)
pc++
elif opcode == JUMP:
target = bytecode[pc++]
if not traverse_stack.is_empty():
pc = traverse_stack.pop()
else:
finish()
elif opcode == RET:
if not traverse_stack.is_empty():
pc = traverse_stack.pop()
else:
return pop()
Suppress inlining
Save another side
to traverse later

32. Method-traversal Interpreter: How to Drive the
RPython Engine [ICOOOLPS 2021]
 traverse depth-firstly the entire method body w/ traverse_stack
@dont_look_insdie
def ADD():
..
while True:
if opcde == JUMP_IF:
top = pop()
target = bytecode[pc++]
if top.is_true():
traverse_stack.push(pc++)
pc = target
else:
traverse_stack.push(target)
pc++
elif opcode == JUMP:
target = bytecode[pc++]
if not traverse_stack.is_empty():
pc = traverse_stack.pop()
else:
finish()
elif opcode == RET:
if not traverse_stack.is_empty():
pc = traverse_stack.pop()
else:
return pop()
Suppress inlining
Save another side
to traverse later
Jump to another side
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33. The Design of Generic Interpreter
• From a generic interp, Adaptive RPython generates interps including MTI
 Embed tier-specific definitions in a meta-tracing-based interpreter
1. Declare JitTierDriver jittierdriver = JitTierDriver(pc='pc')
def interp(self);
..
if opcode == JUMP_IF:
target = bytecode[pc]
elif opcode == JUMP:
target = bytecode[pc]
elif opcode == RET:
w_x = self.pop()
elif ..
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34. The Design of Generic Interpreter
• From a generic interp, Adaptive RPython generates interps including MTI
 Embed tier-specific definitions in a meta-tracing-based interpreter
1. Declare JitTierDriver
2. Define can_enter_tier1_XX at
JUMP_IF, JUMP, RET for threaded
code gen. and method comp.
jittierdriver = JitTierDriver(pc='pc')
def interp(self);
..
if opcode == JUMP_IF:
target = bytecode[pc]
jittierdriver.can_enter_tier1_branch(
true_path=target,false_path=pc+1,
cond=self.is_true)
if we_are_in_tier2():
elif opcode == JUMP:
target = bytecode[pc]
jittierdriver.can_enter_tier1_jump(target=target)
elif opcode == RET:
w_x = self.pop()
jittierdriver.can_enter_tier1_ret(ret_value=w_x)
elif ..
Two-level JIT Compilation with .. PEPM 2022 11 / 15

35. The Design of Generic Interpreter
• From a generic interp, Adaptive RPython generates interps including MTI
 Embed tier-specific definitions in a meta-tracing-based interpreter
1. Declare JitTierDriver
2. Define can_enter_tier1_XX at
JUMP_IF, JUMP, RET for threaded
code gen. and method comp.
3. Define interp. for tracing JIT inside
we_are_in_tier2
jittierdriver = JitTierDriver(pc='pc')
def interp(self);
..
if opcode == JUMP_IF:
target = bytecode[pc]
jittierdriver.can_enter_tier1_branch(
true_path=target,false_path=pc+1,
cond=self.is_true)
if we_are_in_tier2():
do stuff for tracing JIT
elif opcode == JUMP:
target = bytecode[pc]
jittierdriver.can_enter_tier1_jump(target=target)
if we_are_in_tier2():
do stuff for tracing JIT
elif opcode == RET:
w_x = self.pop()
jittierdriver.can_enter_tier1_ret(ret_value=w_x)
if we_are_in_tier2():
do stuff for tracing JIT
elif ..
Two-level JIT Compilation with .. PEPM 2022 11 / 15

36. The Design of Generic Interpreter
• From a generic interp, Adaptive RPython generates interps including MTI
 Embed tier-specific definitions in a meta-tracing-based interpreter
1. Declare JitTierDriver
2. Define can_enter_tier1_XX at
JUMP_IF, JUMP, RET for threaded
code gen. and method comp.
3. Define interp. for tracing JIT inside
we_are_in_tier2
4. The pre-processor generates
method-traversal interp and tracing
interp from this
jittierdriver = JitTierDriver(pc='pc')
def interp(self);
..
if opcode == JUMP_IF:
target = bytecode[pc]
jittierdriver.can_enter_tier1_branch(
true_path=target,false_path=pc+1,
cond=self.is_true)
if we_are_in_tier2():
do stuff for tracing JIT
elif opcode == JUMP:
target = bytecode[pc]
jittierdriver.can_enter_tier1_jump(target=target)
if we_are_in_tier2():
do stuff for tracing JIT
elif opcode == RET:
w_x = self.pop()
jittierdriver.can_enter_tier1_ret(ret_value=w_x)
if we_are_in_tier2():
do stuff for tracing JIT
elif ..
Two-level JIT Compilation with .. PEPM 2022 11 / 15

37. Observation: Can Adaptive RPython “Actually” Work? (1)
Setup
• Write TLA lang. interpreter in Adaptive RPython
• Run TLA interpreter on small examples
− loopabit: nested loop
− callabit: two functions – one is suitable for tracing, the other is for
thraeded code gen. (method)
NOTE
• Current multitier is the combination of threaded code gen. and tracing
(two-level)
Two-level JIT Compilation with .. PEPM 2022 12 / 15

38. Observation: Can Adaptive RPython “Actually” Work? (2)
Situation in callabit: increasing an optimization level
program JIT applied to f JIT applied to g
callabit_baseline_interp threaded (interpreted)
function f
(for threaded
code gen.)
function g
(for trac-
ing comp.)
call
ret
threaded code
generation
interpreted
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39. Observation: Can Adaptive RPython “Actually” Work? (2)
Situation in callabit: increasing an optimization level
program JIT applied to f JIT applied to g
callabit_baseline_interp threaded (interpreted)
callabit_baseline_only threaded threaded
function f
(for threaded
code gen.)
function g
(for trac-
ing comp.)
call
ret
threaded code
generation
threaded code
generation
Two-level JIT Compilation with .. PEPM 2022 13 / 15

40. Observation: Can Adaptive RPython “Actually” Work? (2)
Situation in callabit: increasing an optimization level
program JIT applied to f JIT applied to g
callabit_baseline_interp threaded (interpreted)
callabit_baseline_only threaded threaded
callabit_tracing_baseline tracing baseline
function f
(for threaded
code gen.)
function g
(for trac-
ing comp.)
call
ret
tracing compi-
lation
threaded code
generation
Two-level JIT Compilation with .. PEPM 2022 13 / 15

41. Observation: Can Adaptive RPython “Actually” Work? (2)
Situation in callabit: increasing an optimization level
program JIT applied to f JIT applied to g
callabit_baseline_interp threaded (interpreted)
callabit_baseline_only threaded threaded
callabit_tracing_baseline tracing baseline
callabit_baseline_tracing threaded tracing
function f
(for threaded
code gen.)
function g
(for trac-
ing comp.)
call
ret
threaded code
generation
tracing compi-
lation
Two-level JIT Compilation with .. PEPM 2022 13 / 15

42. Observation: Can Adaptive RPython “Actually” Work? (2)
Situation in callabit: increasing an optimization level
program JIT applied to f JIT applied to g
callabit_baseline_interp threaded (interpreted)
callabit_baseline_only threaded threaded
callabit_tracing_baseline tracing baseline
callabit_baseline_tracing threaded tracing
callabit_tracing_only tracing tracing
function f
(for threaded
code gen.)
function g
(for trac-
ing comp.)
call
ret
tracing compi-
lation
tracing compi-
lation
Two-level JIT Compilation with .. PEPM 2022 13 / 15

43. Observation: Running Speeds and Trace Sizes
• Actually worked: compilation speed is reaching to tracing compilation
c
a
l
l
a
b
i
t
_
b
a
s
e
l
i
n
e
_
i
n
t
e
r
p
c
a
l
l
a
b
i
t
_
b
a
s
e
l
i
n
e
_
o
n
l
y
c
a
l
l
a
b
i
t
_
b
a
s
e
l
i
n
e
_
t
r
a
c
i
n
g
c
a
l
l
a
b
i
t
_
t
r
a
c
i
n
g
_
b
a
s
e
l
i
n
e
c
a
l
l
a
b
i
t
_
t
r
a
c
i
n
g
_
o
n
l
y
0.0
0.5
1.0
1.5
2.0
2.5
3.0
The
speed
up
ratio
(interp
=
1)
TLA w/ Adaptive RPython (Stable speed)
# Traces
0
50
100
150
200
250
300
350
400
callabit_baseline_interp
callabit_baseline_only
callabit_baseline_tracing
callabit_tracing_baseline
callabit_tracing_only
Increasing
better
smaller
Two-level JIT Compilation with .. PEPM 2022 14 / 15

44. Observation: Running Speeds and Trace Sizes
• Actually worked: compilation speed is reaching to tracing compilation
• Promising signs: multitier is same speed but smaller code size compared
to single tier → might get good performance in the future
c
a
l
l
a
b
i
t
_
b
a
s
e
l
i
n
e
_
i
n
t
e
r
p
c
a
l
l
a
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i
t
_
b
a
s
e
l
i
n
e
_
o
n
l
y
c
a
l
l
a
b
i
t
_
b
a
s
e
l
i
n
e
_
t
r
a
c
i
n
g
c
a
l
l
a
b
i
t
_
t
r
a
c
i
n
g
_
b
a
s
e
l
i
n
e
c
a
l
l
a
b
i
t
_
t
r
a
c
i
n
g
_
o
n
l
y
0.0
0.5
1.0
1.5
2.0
2.5
3.0
The
speed
up
ratio
(interp
=
1)
TLA w/ Adaptive RPython (Stable speed)
# Traces
0
50
100
150
200
250
300
350
400
callabit_baseline_interp
callabit_baseline_only
callabit_baseline_tracing
callabit_tracing_baseline
callabit_tracing_only
better
smaller
Two-level JIT Compilation with .. PEPM 2022 14 / 15

45. Conclusion and Future Work
Conclusion
• Adaptive RPython actually worked on a small
lang.
RPython [I, P, V] = P′
RPython [ Icommon + Itracing, P, V ] = P′
tracing
RPython [ Icommon + Ithreaded, P, V ] = P′
threaded
RPython [ Icommon + Imethod, P, V ] = P′
method
One
Engine
One Interpreter
Multitier
Outputs
Derive from
Generic Interp.
Common
Interp.
Tweaked
Defs.
Future Work
Two-level JIT Compilation with .. PEPM 2022 15 / 15

46. Conclusion and Future Work
Conclusion
• Adaptive RPython actually worked on a small
lang.
RPython [I, P, V] = P′
RPython [ Icommon + Itracing, P, V ] = P′
tracing
RPython [ Icommon + Ithreaded, P, V ] = P′
threaded
RPython [ Icommon + Imethod, P, V ] = P′
method
One
Engine
One Interpreter
Multitier
Outputs
Derive from
Generic Interp.
Common
Interp.
Tweaked
Defs.
Future Work
• Decide multitier compilation
strategy
− How to shift between
levels?
− How to decide an
appropriate level?
• Implement our ideas on PyPy
Two-level JIT Compilation with .. PEPM 2022 15 / 15

47. Conclusion and Future Work
Conclusion
• Adaptive RPython actually worked on a small
lang.
RPython [I, P, V] = P′
RPython [ Icommon + Itracing, P, V ] = P′
tracing
RPython [ Icommon + Ithreaded, P, V ] = P′
threaded
RPython [ Icommon + Imethod, P, V ] = P′
method
One
Engine
One Interpreter
Multitier
Outputs
Derive from
Generic Interp.
Common
Interp.
Tweaked
Defs.
Future Work
• Decide multitier compilation
strategy
− How to shift between
levels?
− How to decide an
appropriate level?
• Implement our ideas on PyPy
Two-level JIT Compilation with .. PEPM 2022 15 / 15

48. References I
Izawa, Y., Masuhara, H., Bolz-Tereick, C. F., and Cong, Y. (2021).
Threaded code generation with a meta-tracing JIT compiler.
The Journal of Object Technology Special Issue for ICOOOLPS 2021, pages 1–11.
Accepted.
Two-level JIT Compilation with .. PEPM 2022 1 / 1