05-Superblocks

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Lecture 5:Lecture 5: SuperblocksSuperblocks

COS 598CCOS 598C – – Advanced CompilersAdvanced Compilers

Prof. David AugustCOS 598C - Advanced Compilers

RegionsRegions

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Regions (2)Regions (2)

+ ,!

--

.

/!0

. 1

.0"&


Region Type 1Region Type 1 – – TraceTrace

2 $ 30

435

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. 6

. 6

*((7

89"::;&

BB2

BB4

BB6

BB5

BB1

BB3

80 20

10

90

10

90

10

80 20

10




LinearizingLinearizing a Tracea Trace

BB2

BB4

BB6

BB5

BB1

BB3

80 20 (side exit)

10 (side exit)

90

10 (entry count)

90 (entry/

exit count)

10 (exit count)

8020 (side entrance)

10 (side entrance)


Intelligent Trace Layout for IIntelligent Trace Layout for I--Cache PerformanceCache Performance

BB2

BB4

BB6

BB5

BB1

BB3

trace1

trace 2

trace 3

The rest

Intraprocedural code placement

Procedure positioning

Procedure splitting

Procedure viewTrace view


Issues With Selecting TracesIssues With Selecting Traces

2

3<=

>- /$)$

8!$

8!$

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$

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3 3

BB2

BB4

BB6

BB5

BB1

BB3

80 20

10

90

10

90

10

80 20

10


Trace Selection AlgorithmTrace Selection Algorithm

i = 0;

mark all BBs unvisited

while (there are unvisited nodes) do

seed = unvisited BB with largest execution freq

trace[i] += seed

mark seed visited

current = seed

/* Grow trace forward */

while (1) do

next = best_successor_of(current)

if (next == 0) then break

trace[i] += next

mark next visited

current = next

endwhile

/* Grow trace backward analogously */ i++

endwhile



!Prof. David AugustCOS 598C - Advanced Compilers

Best Successor/PredecessorBest Successor/Predecessor

>9:

2./31

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>

*

9

8" *((&

best_successor_of(BB)

e = control flow edge with highest

probability leaving BB

if (e is a backedge) then

return 0endif

if (probability(e) <= THRESHOLD) then

return 0

endif

d = destination of e

if (d is visited) then

return 0

endif

return d

endprocedure

"Prof. David AugustCOS 598C - Advanced Compilers

Class Problem 1Class Problem 1

BB2

BB4

BB6

BB5

BB1

BB3

20 80

100

450

20 80

BB3

BB6

BB6

51 49

49

10

41

10

41

Find the traces. Assume

a threshold probability

of 60%.

#Prof. David AugustCOS 598C - Advanced Compilers


BB1

100

BB2 BB3

BB5 BB6BB4

BB7

BB8

40

135 100

35

75

25

25

50 10 5

60

15

100

Find the traces. Assume

a threshold probability of 60%.


Traces are Nice, But …Traces are Nice, But …

2

2)

,

A

.

.

.

2

BB2

BB4

BB6

BB5

BB1

BB3

80 20

10

90

10

90

10

80 20

10




Region Type 2Region Type 2 – – SuperblockSuperblock

. $ 30

435

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2

.

.

*:2

B:

BB2

BB4

BB6

BB5

BB1

BB3

80 20

10

90

10

90

10

80 20

10


Tail DuplicationTail Duplication

245

,

8<B$*

C

BB2

BB4

BB6

BB5

BB1

BB3

80 20

10

90

10

90

10

80 20

10


Superblock FormationSuperblock Formation

BB2

BB4

BB6

BB5

BB1

BB3

80 20

10

90

10

90

10

80 20

10

BB2

BB4

BB6

BB5’

BB1

BB3

80 20

8

72

10

64.8

7.2

80 20

26

BB6’

BB4’

18

2.8 25.2

2


Issues withIssues with SuperblocksSuperblocks

.

9

!

809.

.

*:(6 *:*(.

BB2

BB4

BB6

BB5’

BB1

BB3

80 20

8

72

10

64.8

7.2

80 20

26

BB6’

BB4’

18

2.8 25.2

2





BB2

BB4

BB7

BB5

BB1

BB3

20 80

100

450

20 80

BB6

BB8

BB9

51 49

49

10

41

10

41

Create the superblocks, trace

threshold is 60%

05-Superblocks

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