Intra Escape Analysis in Jikes RVM

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Intra Escape Analysis in Jikes RVM

• Keerti Lakshminarayan
• Michael Suwandi

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Motivation

• Costs of Object Management
• Removal of the synchronization constructs
• Connection Graphs, Choi et al
• Very precise. Beneficial in a static compiler.
• But in Jikes ?
• Jikes RVM has a simple escape analysis
• Fast (single-pass) and conservative.

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Escape States Equi-Escape Sets

• Different escape categories
• No Escape
• Method Escape
• Thread Escape
• Simpler analysis in SSA, but more to analyze
  solution use Equi-Escape Sets

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Identifying Candidates (1/2)

• T q new T()
• T.field p or p T.field
• q.field p, or p q.field
• P q
• (T)p
• q.method(p)
• return p, or throw p

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Identifying Candidates (2/2)
class A public B b class B public int
x class Main public A test() A a
new A() a.b new B() for (int i 0 i
lt 2 i) B b a.b
println(b.x) a.b new B() a
new A() return a
new t1, A new t2, B putfield
t2, t1, (A.b) L0 phi t3, 0, t4 phi t5,
t2, t6 getfield t7, t5, (B.x) call
println, t7 new t6, B putfield t6,
t1, (A.b) addi t4, t3, 1 ifcmp t4, 2,
L0 new t8, A return t8
Global Escape
t8
t5
t1
t6
A.b
t2
No Escape
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Scalar Replacement (1/3)

• Scalar replace objects with No Escape state
  only!
• Replace the object with all of its instance
  fields
• Hunt down references using the reference maps and
  replace them too

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Scalar Replacement (2/3)
refmove t11, ltnullgt new t2, B
refmove t12, t2 L0 phi t3, 0, t4 phi t5,
t2, t6 phi t14, t12, t15 getfield t7,
t5, (B.x) call println, t7 new t6, B
refmove t15, t6 addi t4, t3, 1
ifcmp t4, 2, L0 new t8, A return t8
refmove t10, ltnullgt new t2, B
refmove t10, t2 L0 phi t3, 0, t4 phi t5,
t2, t6 getfield t7, t5, (B.x) call
println, t7 new t6, B refmove t10,
t6 addi t4, t3, 1 ifcmp t4, 2, L0
new t8, A return t8
new t1, A new t2, B putfield
t2, t1, (A.b) L0 phi t3, 0, t4 phi t5,
t2, t6 getfield t7, t5, (B.x) call
println, t7 new t6, B putfield t6,
t1, (A.b) addi t4, t3, 1 ifcmp t4, 2,
L0 new t8, A return t8
Scalar replacement
Enter SSA
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Scalar Replacement (3/3)
refmove t11, ltnullgt new t2, B
refmove t12, t2 L0 phi t3, 0, t4 phi t5,
t2, t6 phi t14, t12, t15 getfield t7,
t5, (B.x) call println, t7 new t6, B
refmove t15, t6 addi t4, t3, 1
ifcmp t4, 2, L0 new t8, A return t8
refmove t11, ltnullgt move t16, 0
move t17, t16 L0 phi t3, 0, t4 phi t18,
t16, t19 phi t20, t17, t21 move t7,
t18 call println, t7 move t19, 0
move t21, t19 addi t4, t3, 1 ifcmp
t4, 2, L0 new t8, A return t8
Global Escape
Global Escape
2nd iteration
No Escape
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Evaluation and Future Work

• We are sorry we cannot thrill you with our graphs
  and tables as yet!
• First synthetic benchmarks. Later JavaG, JLex
• Measuring against Jikes RVM on how many
  candidates found/replaced and how long it takes
  to perform the analysis/transformation
• Our goal is to show the usefulness (hopefully) of
  the equi-escape sets in escape analysis for
  dynamic compilers over the more precise (but more
  time consuming) connection graph.
• Interprocedual analysis remove synchronization
  for thread local objects

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Learning from the ProjectAcknowledgements and
References

• Escape Analysis thankfully in Java
• Actual implementation requires tweaks
• Continued learning of the structure of the Jikes
  RVM
• Escape Analysis Thomas Kotzmann
• Connection Graphs Choi et al.
• Escape Analysis in the Jikes RVM Magill and
  Spoonhower
• Jungwoo, BK, and Prof. Mckinley