Software engineering research often requires analyzing multiple revisions of several software projects, be it to make and test predictions or to observe and identify patterns in how software evolves. However, code analysis tools are almost exclusively designed for the analysis of one specific version of the code, and the time and resources requirements grow linearly with each additional revision to be analyzed. Thus, code studies often observe a relatively small number of revisions and projects. Furthermore, each programming ecosystem provides dedicated tools, hence researchers typically only analyze code of one language, even when researching topics that should generalize to other ecosystems. To alleviate these issues, frameworks and models have been developed to combine analysis tools or automate the analysis of multiple revisions, but little research has gone into actually removing redundancies in multi-revision, multi-language code analysis. We present a novel end-to-end approach that systematically avoids redundancies every step of the way: when reading sources from version control, during parsing, in the internal code representation, and during the actual analysis. We evaluate our open-source implementation, LISA, on the full history of 300 projects, written in 3 different programming languages, computing basic code metrics for over 1.1 million program revisions. When analyzing many revisions, LISA requires less than a second on average to compute basic code metrics for all files in a single revision, even for projects consisting of millions of lines of code.

1. Carol V. Alexandru, Sebastiano Panichella, Harald C. Gall
Software Evolution and Architecture Lab
University of Zurich, Switzerland
{alexandru,panichella,gall}@ifi.uzh.ch
22.02.2017
SANER’17
Klagenfurt, Austria

2. The Problem Domain
• Static analysis (e.g. #Attr., McCabe, coupling...)
1

3. The Problem Domain
v0.7.0 v1.0.0 v1.3.0 v2.0.0 v3.0.0 v3.3.0 v3.5.0
2
• Static analysis (e.g. #Attr., McCabe, coupling...)

4. The Problem Domain
v0.7.0 v1.0.0 v1.3.0 v2.0.0 v3.0.0 v3.3.0 v3.5.0
2
• Static analysis (e.g. #Attr., McCabe, coupling...)
• Many revisions, fine-grained historical data

5. A Typical Analysis Process
3
www
clone
select project

6. A Typical Analysis Process
www
clone
checkout
select project
select revision
3

7. A Typical Analysis Process
www
clone
checkout analysis tool
Res
select project
select revision
apply
tool
store
analysis
results
3

8. A Typical Analysis Process
www
clone
checkout analysis tool
Res
select project
select revision
apply
tool
store
analysis
results
more revisions?
3

9. A Typical Analysis Process
www
clone
checkout analysis tool
Res
select project
select revision
apply
tool
store
analysis
results
more revisions?
more projects?
3

10. Redundancies all over...
4
Redundancies in
historical code analysis
Impact on Code
Study Tools

11. Redundancies all over...
Redundancies in
historical code analysis
Few files change
Only small parts of
a file change
Across Revisions
Impact on Code
Study Tools
4

12. Redundancies all over...
Redundancies in
historical code analysis
Few files change
Only small parts of
a file change
Across Revisions
Impact on Code
Study Tools
Repeated analysis
of "known" code
4

13. Redundancies all over...
Redundancies in
historical code analysis
Few files change
Only small parts of
a file change
Changes may not
even affect results
Across Revisions
Impact on Code
Study Tools
Repeated analysis
of "known" code
Storing redundant
results
4

14. Redundancies all over...
4
Redundancies in
historical code analysis
Few files change
Across Languages
Only small parts of
a file change
Changes may not
even affect results
Each language has
their own toolchain
Yet they share
many metrics
Across Revisions
Impact on Code
Study Tools
Repeated analysis
of "known" code
Storing redundant
results

15. Redundancies all over...
Redundancies in
historical code analysis
Few files change
Across Languages
Only small parts of
a file change
Changes may not
even affect results
Each language has
their own toolchain
Yet they share
many metrics
Across Revisions
Impact on Code
Study Tools
Repeated analysis
of "known" code
Storing redundant
results
Re-implementing
identical analyses
Generalizability is
expensive
4

16. Redundancies all over...
Redundancies in
historical code analysis
Few files change
Across Languages
Only small parts of
a file change
Changes may not
even affect results
Each language has
their own toolchain
Yet they share
many metrics
Across Revisions
Impact on Code
Study Tools
Repeated analysis
of "known" code
Storing redundant
results
Re-implementing
identical analyses
Generalizability is
expensive
5

17. Important!
6
Techniques
implemented
in LISA
Your
favourite
analysis
features
Pick what you like!

18. #1: Avoid Checkouts

19. Avoid checkouts
7
clone

20. Avoid checkouts
7
clone
checkout
read write

21. Avoid checkouts
7
clone
checkout
read
read write
analyze

22. Avoid checkouts
7
clone
checkout
read
For every file: 2 read ops + 1 write op
Checkout includes irrelevant files
Need 1 CWD for every revision to be analyzed in parallel
read write
analyze

23. Avoid checkouts
8
clone analyze
read

24. Avoid checkouts
8
clone analyze
Only read relevant files in a single read op
No write ops
No overhead for parallization
read

25. Avoid checkouts
8
clone analyze
Only read relevant files in a single read op
No write ops
No overhead for parallization
Git
Analysis Tool
File Abstraction Layer
read

26. Avoid checkouts
8
clone analyze
Only read relevant files in a single read op
No write ops
No overhead for parallization
Git
Analysis Tool
File Abstraction Layer
E.g. for the JDK Compiler:
class JavaSourceFromCharrArray(name: String, val code: CharBuffer)
extends SimpleJavaFileObject(URI.create("string:///" + name), Kind.SOURCE) {
override def getCharContent(): CharSequence = code
}
read

27. Avoid checkouts
clone analyze
Only read relevant files in a single read op
No write ops
No overhead for parallization
Git
Analysis Tool
File Abstraction Layer
E.g. for the JDK Compiler:
class JavaSourceFromCharrArray(name: String, val code: CharBuffer)
extends SimpleJavaFileObject(URI.create("string:///" + name), Kind.SOURCE) {
override def getCharContent(): CharSequence = code
}
read
9

28. #2: Use a multi-revision representation
of your sources

29. Merge ASTs
rev. 1
rev. 2
rev. 3
rev. 4
10

30. rev. 1
rev. 2
rev. 3
rev. 4
11
rev. 1
Merge ASTs

31. rev. 1
rev. 2
rev. 3
rev. 4
12
rev. 2
Merge ASTs

32. Merge ASTs
rev. 1
rev. 2
rev. 3
rev. 4
13
rev. 3

33. Merge ASTs
rev. 1
rev. 2
rev. 3
rev. 4
14
rev. 4

34. Merge ASTs
rev. 1
rev. 2
rev. 3
rev. 4
15

35. Merge ASTs
rev. 1
rev. 2
rev. 3
rev. 4
16
rev. range [1-4]
rev. range [1-2]

36. Merge ASTs
rev. 1
rev. 2
rev. 3
rev. 4
AspectJ (~440k LOC):
1 commit: 2.2M nodes
All >7000 commits: 6.5M nodes
17

37. Merge ASTs
rev. 1
rev. 2
rev. 3
rev. 4
AspectJ (~440k LOC):
1 commit: 2.2M nodes
All >7000 commits: 6.5M nodes
18

38. Merge ASTs
rev. 1
rev. 2
rev. 3
rev. 4
AspectJ (~440k LOC):
1 commit: 2.2M nodes
All >7000 commits: 6.5M nodes
19

39. #3: Store AST nodes only if
they're needed for analysis

40. public class Demo {
public void run() {
for (int i = 1; i< 100; i++) {
if (i % 3 == 0 || i % 5 == 0) {
System.out.println(i)
}
}
}
What's the complexity (1+#forks)
and name for each method and
class?
20

41. public class Demo {
public void run() {
for (int i = 1; i< 100; i++) {
if (i % 3 == 0 || i % 5 == 0) {
System.out.println(i)
}
}
}
140 AST nodes
(using ANTLR)
parse
What's the complexity (1+#forks)
and name for each method and
class?
20

42. public class Demo {
public void run() {
for (int i = 1; i< 100; i++) {
if (i % 3 == 0 || i % 5 == 0) {
System.out.println(i)
}
}
}
140 AST nodes
(using ANTLR)
parse
CompilationUnit
TypeDeclaration
Modifiers
public
Members
Method
Modifiers
public
Name
run
Name
Demo
Parameters ReturnType
PrimitiveType
VOID
Body
Statements
...
...
What's the complexity (1+#forks)
and name for each method and
class?
20

43. public class Demo {
public void run() {
for (int i = 1; i< 100; i++) {
if (i % 3 == 0 || i % 5 == 0) {
System.out.println(i)
}
}
}
What's the complexity (1+#forks)
and name for each method and
class?
140 AST nodes
(using ANTLR)
parse filtered parse
TypeDeclaration
Method
Name
run
Name
DemoForStatement
IfStatement
ConditionalExpression
7 AST nodes
(using ANTLR)
21

44. public class Demo {
public void run() {
for (int i = 1; i< 100; i++) {
if (i % 3 == 0 || i % 5 == 0) {
System.out.println(i)
}
}
}
What's the complexity (1+#forks)
and name for eachmethod and
class?
140 AST nodes
(using ANTLR)
parse filtered parse
TypeDeclaration
Method
Name
run
Name
DemoForStatement
IfStatement
ConditionalExpression
7 AST nodes
(using ANTLR)
22

45. public class Demo {
public void run() {
for (int i = 1; i< 100; i++) {
if (i % 3 == 0 || i % 5 == 0) {
System.out.println(i)
}
}
}
What's the complexity (1+#forks)
and name for eachmethod and
class?
140 AST nodes
(using ANTLR)
parse filtered parse
TypeDeclaration
Method
Name
run
Name
DemoForStatement
IfStatement
ConditionalExpression
7 AST nodes
(using ANTLR)
23

46. #4: Use non-duplicative data structures
to store your results

47. rev. 1
rev. 2
rev. 3
rev. 4
24

48. rev. 1
rev. 2
rev. 3
rev. 4
24

49. rev. 1
rev. 2
rev. 3
rev. 4
24
[1-1]
label
#attr
mcc
[4-4]
label
#attr
mcc
InnerClass
0 4
1 2 4
[2-3]
label
#attr
mcc

50. rev. 1
rev. 2
rev. 3
rev. 4 [1-1]
label
#attr
mcc
[4-4]
label
#attr
mcc
InnerClass
0 4
1 2 4
[2-3]
label
#attr
mcc
25

51. LISA also does:
#5: Parallel Parsing
#6: Asynchronous graph computation
#7: Generic graph computations
applying to ASTs from compatible
languages
26

52. To Summarize...

53. The LISA Analysis Process
27
www
clone
select project

54. The LISA Analysis Process
27
www
clone
parallel parse
into merged
graph
select project
Language Mappings
(Grammar to Analysis)
determines which AST
nodes are loaded
ANTLRv4
Grammar used by
Generates Parser

55. The LISA Analysis Process
27
www
clone
parallel parse
into merged
graph
Res
select project
store
analysis
results
Analysis formulated as
Graph Computation
Language Mappings
(Grammar to Analysis) used by
Async. compute
determines which AST
nodes are loaded
determines which
data is persisted
ANTLRv4
Grammar used by
Generates Parser
runs
on graph

56. The LISA Analysis Process
27
www
clone
parallel parse
into merged
graph
Res
select project
store
analysis
results
more projects?
Analysis formulated as
Graph Computation
Language Mappings
(Grammar to Analysis) used by
Async. compute
determines which AST
nodes are loaded
determines which
data is persisted
ANTLRv4
Grammar used by
Generates Parser
runs
on graph

57. How well does it work, then?

58. Marginal cost for +1 revision
41.670
4.633
0.525 0.109 0.082 0.071 0.052 0.041 0.032 0.033
0
5
10
15
20
25
30
35
40
45
50
1 10 100 1000 2000 3000 4000 5000 6000 7000
Average Parsing+Computation time per Revision when
analyzing n revisions of AspectJ (10 common metrics)
Seconds
# of revisions
28

59. Overall Performance Stats
29
Language Java C# JavScript
#Projects 100 100 100
#Revisions 646'261 489'764 204'301
#Files (parsed!) 3'235'852 3'234'178 507'612
#Lines (parsed!) 1'370'998'072 961'974'773 194'758'719
Total Runtime (RT)¹ 18:43h 52:12h 29:09h
Median RT¹ 2:15min 4:54min 3:43min
Tot. Avg. RT per Rev.² 84ms 401ms 531ms
Med. Avg. RT per Rev.² 30ms 116ms 166ms
¹ Including cloning and persisting results
² Excluding cloning and persisting results

60. What's the catch?
(There are a few...)

61. The (not so) minor stuff
• Must implement analyses from scratch
• No help from a compiler
• Non-file-local analyses need some effort
30

62. The (not so) minor stuff
• Must implement analyses from scratch
• No help from a compiler
• Non-file-local analyses need some effort
• Moved files/methods etc. add overhead
• Uniquely identifying files/entities is hard
• (No impact on results, though)
30

63. Language matters
31
Javascript C# Java
E.g.: Javascript takes longer because:
• Larger files, less modularization
• Slower parser (automatic semicolon-insertion)

64. LISA is EXTREME
32
complex
feature-rich
heavyweight
simple
generic
lightweight

65. Thank you for your attention
SANER ‘17, Klagenfurt, 22.02.2017
Read the paper: http://t.uzh.ch/Fj
Try the tool: http://t.uzh.ch/Fk
Get the slides: http://t.uzh.ch/Fm
Contact me: alexandru@ifi.uzh.ch