The document discusses the concepts of speculation and predication within the context of Intel's Itanium (IA-64) architecture and its explicit parallel instruction computing. It explains how these techniques are employed to enhance instruction-level parallelism (ILP) by managing control and data dependencies to improve performance. The document concludes with insights on the benefits and challenges of utilizing predication and speculation in processor design.

1. Beatriz Aguilar Gallo
SPECULATION
AND
PREDICATION

2. 1. Introduction
2. Introduction to Predication
3. Introduction to Speculation
4. Intel Itanium (IA-64), EPIC Architecture
5. Conclusions
OUTLINE

3. ! ILP measured the number of instructions that can be
performed during a single clock cycle
1. INTRODUCTION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

4. ! ILP measured the number of instructions that can be
performed during a single clock cycle
! Limited by: - Dependences
- Branches
1. INTRODUCTION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

5. ! ILP measured the number of instructions that can be
performed during a single clock cycle
! Limited by: - Dependences
- Branches
! Two techniques to exploit ILP
! Predication
! Speculation
1. INTRODUCTION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

6. ! ILP measured the number of instructions that can be
performed during a single clock cycle
! Limited by: - Dependences
- Branches
! Two techniques to exploit ILP
! Predication
! Speculation
! EPIC (Explicitly Parallel Instruction Computing)
! Intel Itanium processor
1. INTRODUCTION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

7. 2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

8. ! Control dependences limit the amount of parallelism that can
be exploited
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

9. ! Control dependences limit the amount of parallelism that can
be exploited
! Predication " An instruction refers to a condition, which is
evaluated as part of the instruction execution.
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

10. ! Control dependences limit the amount of parallelism that can
be exploited
! Predication " An instruction refers to a condition, which is
evaluated as part of the instruction execution.
! If the condition is true, the instruction is executed normally
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

11. ! Control dependences limit the amount of parallelism that can
be exploited
! Predication " An instruction refers to a condition, which is
evaluated as part of the instruction execution.
! If the condition is true, the instruction is executed normally
! if the condition is false, the execution continues as if the instruction
were a no-op
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

12. ! Control dependences limit the amount of parallelism that can
be exploited
! Predication " An instruction refers to a condition, which is
evaluated as part of the instruction execution.
! If the condition is true, the instruction is executed normally
! if the condition is false, the execution continues as if the instruction
were a no-op
! Effects of predication
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

13. ! Control dependences limit the amount of parallelism that can
be exploited
! Predication " An instruction refers to a condition, which is
evaluated as part of the instruction execution.
! If the condition is true, the instruction is executed normally
! if the condition is false, the execution continues as if the instruction
were a no-op
! Effects of predication
! Eliminate branches " execute both path of the flow
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

14. ! Control dependences limit the amount of parallelism that can
be exploited
! Predication " An instruction refers to a condition, which is
evaluated as part of the instruction execution.
! If the condition is true, the instruction is executed normally
! if the condition is false, the execution continues as if the instruction
were a no-op
! Effects of predication
! Eliminate branches " execute both path of the flow
! Converts control dependences into data dependences " If-conversion
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

15. ! Control dependences limit the amount of parallelism that can
be exploited
! Predication " An instruction refers to a condition, which is
evaluated as part of the instruction execution.
! If the condition is true, the instruction is executed normally
! if the condition is false, the execution continues as if the instruction
were a no-op
! Effects of predication
! Eliminate branches " execute both path of the flow
! Converts control dependences into data dependences " If-conversion
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

16. ! If-conversion " Transforms conditional branches into
! Operations that defines predicates
! Operations guarded by predicates, corresponding to
alternative control paths
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

17. ! Control dependences limit the amount of parallelism that can be
exploited
! Predication " An instruction refers to a condition, which is
evaluated as part of the instruction execution.
! If the condition is true, the instruction is executed normally
! if the condition is false, the execution continues as if the instruction was
a no-op
! Effects of predication
! Eliminate branches " execute both path of the flow
! Converts control dependences into data dependences " If-conversion
! Necessary include predicated instructions to the ISA
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

18. ! Predication example
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

19. ! Predication complications
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

20. ! Predication complications
! Increase the fetch utilization
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

21. ! Predication complications
! Increase the fetch utilization
! When Annul an operation?
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

22. ! Predication complications
! Increase the fetch utilization
! When Annul an operation?
! Early in the pipeline during instruction issue " the value of
controlling condition must be known early
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

23. ! Predication complications
! Increase the fetch utilization
! When Annul an operation?
! Early in the pipeline during instruction issue " the value of
controlling condition must be known early
! Later in the pipeline before
commit any result or raise an exception " annulled instruction
will consume FU and
will have negative
impact in performance
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

24. Predication is useful for
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

25. Predication in useful for
! Implementing short alternative control flows
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

26. Predication is useful for
! Implementing short alternative control flows
! Eliminating some unpredictable branches
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

27. Predication is useful for
! Implementing short alternative control flows
! Eliminating some unpredictable branches
! Reducing the overhead of global code scheduling
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

28. Predication is useful for
! Implementing short alternative control flows
! Eliminating some unpredictable branches
! Reducing the overhead of global code scheduling
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS
Predication usefulness limited by

29. Predication is useful for
! Implementing short alternative control flows
! Eliminating some unpredictable branches
! Reducing the overhead of global code scheduling
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS
Predication usefulness limited by
! Predicated instructions annulled take processor
resources

30. Predication is useful for
! Implementing short alternative control flows
! Eliminating some unpredictable branches
! Reducing the overhead of global code scheduling
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS
Predication usefulness limited by
! Predicated instructions annulled take processor resources
! Most useful when the predicate can be evaluated early

31. Predication is useful for
! Implementing short alternative control flows
! Eliminating some unpredictable branches
! Reducing the overhead of global code scheduling
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS
Predication usefulness limited by
! Predicated instructions annulled take processor resources
! Most useful when the predicate can be evaluated early
! Conditional instructions can be limited with complex
alternative sequences

32. Predication is useful for
! Implementing short alternative control flows
! Eliminating some unpredictable branches
! Reducing the overhead of global code scheduling
2. INTRODUCTION TO PREDICATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS
Predication usefulness limited by
! Predicated instructions annulled take processor resources
! Most useful when the predicate can be evaluated early
! Conditional instructions can be limited with complex
alternative sequences
! Speed penalty compared with unconditional instructions

33. 3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

34. ! Idea of speculation " refers to the early execution of memory
operations in order to hide their latency
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

35. ! Idea of speculation " refers to the early execution of memory
operations in order to hide their latency
! Two techniques to apply
! Hardware Speculation
! Software Speculation
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

36. ! Idea of speculation " refers to the early execution of memory
operations in order to hide their latency
! Two techniques to apply
! Hardware Speculation
! Software Speculation
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

37. ! Two techniques to apply
! Hardware Speculation " hardware tables
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

38. ! Two techniques to apply
! Hardware Speculation " hardware tables
! Advantages 1.) It is responsive to changes in program behavior
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

39. ! Two techniques to apply
! Hardware Speculation " hardware tables
! Advantages 1.) It is responsive to changes in program behavior
2.) Can apply the optimization to selective instances
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

40. ! Two techniques to apply
! Hardware Speculation " hardware tables
! Advantages 1.) It is responsive to changes in program behavior
2.) Can apply the optimization to selective instances
! Disadvantage " requires that the optimization can be applied
as the instructions travel down the pipeline
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

41. ! Idea of speculation " refers to the early execution of memory
operations in order to hide their latency
! Two techniques to apply
! Hardware Speculation
! Software Speculation
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

42. ! Two techniques to apply
! Software Speculation " directly into instructions
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

43. ! Two techniques to apply
! Software Speculation " directly into instructions
! Advantages 1.) The program can be transformed assuming
the speculations are correct
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

44. ! Two techniques to apply
! Software Speculation " directly into instructions
! Advantages 1.) The program can be transformed assuming
the speculations are correct
2.) The optimizations need not be applied on each
dynamic instance as it travels down the pipeline
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

45. ! Two techniques to apply
! Software Speculation " directly into instructions
! Advantages 1.) The program can be transformed assuming
the speculations are correct
2.) The optimizations need not be applied on each
dynamic instance as it travels down the pipeline
! Disadvantage 1.) Latency associated
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

46. ! Two techniques to apply
! Software Speculation " directly into instructions
! Advantages 1.) The program can be transformed assuming
the speculations are correct
2.) The optimizations need not be applied on each
dynamic instance as it travels down the pipeline
! Disadvantage 1.) Latency associated
2.) Necessary a recompilation
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

47. ! Two types of speculation
! Control Speculation
! Data Speculation
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

48. ! Two types of speculation
! Control Speculation
! Data Speculation
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

49. ! Two types of speculation
! Control Speculation
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

50. ! Two types of speculation
! Control Speculation
! Break control dependences
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

51. ! Two types of speculation
! Control Speculation
! Break control dependences
! How to break a control dependence?
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

52. ! Two types of speculation
! Control Speculation
! Break control dependences
! How to break a control dependence?
Making an operation’s execution independent of the branch
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

53. ! Two types of speculation
! Control Speculation
! Break control dependences
! How to break a control dependence?
Making an operation’s execution independent of the branch
! Problem "
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

54. ! Two types of speculation
! Control Speculation
! Break control dependences
! How to break a control dependence?
Making an operation’s execution independent of the branch
! Problem " correct handling of exceptions
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

55. ! Control Speculation Example:
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

56. ! Two types of speculation
! Control Speculation
! Data Speculation
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

57. ! Two types of speculation
! Data Speculation
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

58. ! Two types of speculation
! Data Speculation
! Breaks data flow dependences between memory operations
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

59. ! Two types of speculation
! Data Speculation
! Breaks data flow dependences between memory operations
! How to break a data dependence?
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

60. ! Two types of speculation
! Data Speculation
! Breaks data flow dependences between memory operations
! How to break a data dependence?
Guessing that the two memory operations will access different
locations.
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

61. ! Data Speculation Example:
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

62. ! Control + Data Speculation Example:
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

63. ! How to deal with exceptions ?
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

64. ! How to deal with exceptions ?
! Ignore exceptions for speculative instructions. “Fast mode” in
several processors.
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

65. ! How to deal with exceptions ?
! Ignore exceptions for speculative instructions. “Fast mode” in
several processors.
! Checks are introduced to determine when an exception should
occur.
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

66. ! How to deal with exceptions ?
! Ignore exceptions for speculative instructions. “Fast mode” in
several processors.
! Checks are introduced to determine when an exception should
occur.
! Poison bits " attached to the result registers written by
speculated instructions when the instructions cause
exceptions.
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

67. ! How to deal with exceptions ?
! Ignore exceptions for speculative instructions. “Fast mode” in
several processors.
! Checks are introduced to determine when an exception should
occur.
! Poison bits " attached to the result registers written by
speculated instructions when the instructions cause
exceptions.
! Hardware buffers the instruction result until it is certain that
the instruction is no longer speculative.
3. INTRODUCTION TO SPECULATION
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

68. ! Explictily Parallel Instruction Computing" indicated
parallelism of programs explicitly in the instruction sequence
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

69. ! Explictily Parallel Instruction Computing" indicated
parallelism of programs explicitly in the instruction sequence
! Designed for high performance scientific and enterprise
computing
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

70. ! Explictily Parallel Instruction Computing" indicated
parallelism of programs explicitly in the instruction sequence
! Designed for high performance scientific and enterprise
computing
! Itanium support predication and speculation
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

71. ! Explictily Parallel Instruction Computing" indicated
parallelism of programs explicitly in the instruction sequence
! Designed for high performance scientific and enterprise
computing
! Itanium support predication and speculation " is able to:
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

72. ! Explictily Parallel Instruction Computing" indicated
parallelism of programs explicitly in the instruction sequence
! Designed for high performance scientific and enterprise
computing
! Itanium support predication and speculation " is able to:
! Increase throughput
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

73. ! Explictily Parallel Instruction Computing" indicated
parallelism of programs explicitly in the instruction sequence
! Designed for high performance scientific and enterprise
computing
! Itanium support predication and speculation " is able to:
! Increase throughput
! Reduce the need for explicit transfers and associated pipeline stalls
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

74. ! Explictily Parallel Instruction Computing" indicated
parallelism of programs explicitly in the instruction sequence
! Designed for high performance scientific and enterprise
computing
! Itanium support predication and speculation " is able to:
! Increase throughput
! Reduce the need for explicit transfers and associated pipeline stalls
PREDICATION
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

75. ! Explictily Parallel Instruction Computing" indicated
parallelism of programs explicitly in the instruction sequence
! Designed for high performance scientific and enterprise
computing
! Itanium support predication and speculation " is able to:
! Increase throughput
! Reduce the need for explicit transfers and associated pipeline stalls
PREDICATION
! Reduce the latency associated with loads from memory,
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

76. ! Explictily Parallel Instruction Computing" indicated
parallelism of programs explicitly in the instruction sequence
! Designed for high performance scientific and enterprise
computing
! Itanium support predication and speculation " is able to:
! Increase throughput
! Reduce the need for explicit transfers and associated pipeline stalls
PREDICATION
! Reduce the latency associated with loads from memory
SPECULATION
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

77. ! Predication in IA-64
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

78. ! Predication in IA-64
! Every instruction in the IA-64 architecture can be predicated
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

79. ! Predication in IA-64
! Every instruction in the IA-64 architecture can be predicated
! An instruction is predicated by specifying a predicate register
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

80. ! Predication in IA-64
! Every instruction in the IA-64 architecture can be predicated
! An instruction is predicated by specifying a predicate register
! Lower overhead in if-conversion
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

81. ! Predication in IA-64
! Every instruction in the IA-64 architecture can be predicated
! An instruction is predicated by specifying a predicate register
! Lower overhead in if-conversion
! Speculation in IA-64
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

82. ! Predication in IA-64
! Every instruction in the IA-64 architecture can be predicated
! An instruction is predicated by specifying a predicate register
! Lower overhead in if-conversion
! Speculation in IA-64
! Separate support for control speculation " deferring with exceptions
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

83. ! It is possible use predication + speculation in IA-64?
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

84. ! It is possible use predication + speculation in IA-64?
YES, IMPACT project
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

85. ! It is possible use predication + speculation in IA-64?
YES, IMPACT project
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

86. ! Performance: Predication, Control Speculation, Data
Speculation, Predication + Speculation
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

87. ! Itanium Nowadays
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

88. ! Itanium Nowadays
! Intel Itanium 9560 serie, Poulson (2012)
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

89. ! Itanium Nowadays
! Intel Itanium 9560 serie, Poulson (2012)
! Next " Kittson 32 nm instead of 22 nm
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

90. ! Itanium Nowadays
! Intel Itanium 9560 serie, Poulson (2012)
! Next " Kittson 32 nm instead of 22 nm
! Will it be the last Itanium?
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

91. ! Itanium Nowadays
! Intel Itanium 9560 serie, Poulson (2012)
! Next " Kittson 32 nm instead of 22 nm
! Will it be the last Itanium?
! Maybe…
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

92. ! Itanium Nowadays
! Intel Itanium 9560 serie, Poulson (2012)
! Next " Kittson 32 nm instead of 22 nm
! Will it be the last Itanium?
! Maybe…
! Why?
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

93. ! Itanium Nowadays
! Intel Itanium 9560 serie, Poulson (2012)
! Next " Kittson 32 nm instead of 22 nm
! Will it be the last Itanium?
! Maybe…
! Why?
! High performance chip 15-core Xeon E7 v2 chip
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

94. ! Itanium Nowadays
! Intel Itanium 9560 serie, Poulson (2012)
! Next " Kittson 32 nm instead of 22 nm
! Will it be the last Itanium?
! Maybe…
! Why?
! High performance chip 15-core Xeon E7 v2 chip
! No compatibility problems
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

95. ! Itanium Nowadays
! Intel Itanium 9560 serie, Poulson (2012)
! Next " Kittson 32 nm instead of 22 nm
! Will it be the last Itanium?
! Maybe…
! Why?
! High performance chip 15-core Xeon E7 v2 chip
! No compatibility problems
! Out of order processors
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

96. ! Itanium Nowadays
! Intel Itanium 9560 serie, Poulson (2012)
! Next " Kittson 32 nm instead of 22 nm
! Will it be the last Itanium?
! Maybe…
! Why?
! High performance chip 15-core Xeon E7 v2 chip
! No compatibility problems
! Out of order processors
! Advantages:
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

97. ! Itanium Nowadays
! Intel Itanium 9560 serie, Poulson (2012)
! Next " Kittson 32 nm instead of 22 nm
! Will it be the last Itanium?
! Maybe…
! Why?
! High performance chip 15-core Xeon E7 v2 chip
! No compatibility problems
! Out of order processors
! Advantages:
! Instructions from different basic blocks to execute at the same time
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

98. ! Itanium Nowadays
! Intel Itanium 9560 serie, Poulson (2012)
! Next " Kittson 32 nm instead of 22 nm
! Will it be the last Itanium?
! Maybe…
! Why?
! High performance chip 15-core Xeon E7 v2 chip
! No compatibility problems
! Out of order processors
! Advantages:
! Instructions from different basic blocks to execute at the same time
! Dynamic scheduled
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

99. ! Itanium Nowadays
! Intel Itanium 9560 serie, Poulson (2012)
! Next " Kittson 32 nm instead of 22 nm
! Will it be the last Itanium?
! Maybe…
! Why?
! High performance chip 15-core Xeon E7 v2 chip
! No compatibility problems
! Out of order processors
! Advantages:
! Instructions from different basic blocks to execute at the same time
! Dynamic scheduled
! No changes in the ISA
4. INTEL ITANIUM (IA 64), EPIC ARCHITECTURE
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

100. ! Predication and speculation good techniques to ILP
5. CONCLUSIONS
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

101. ! Predication and speculation good techniques to ILP
! Itanium was good to include these features in the past but
nowadays the appearance of new processors that support out
of order execution and are more compatibles with the
applications is causing that the used of Itanium decrease.
5. CONCLUSIONS
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

102. ! Predication and speculation good techniques to ILP
! Itanium was good to include these features in the past but
nowadays the appearance of new processors that support out
of order execution and are more compatibles with the
applications is causing that the used of Itanium decrease.
! Not always it is possible predict how the market will evolve
5. CONCLUSIONS
INTRODUCTION | INTRODUCTION TO PREDICATION | INTRODUCTION TO SPECULATION | INTEL ITANIUM (IA-64), EPIC ARCHITECTURE | CONCLUSIONS

103. Beatriz Aguilar Gallo
SPECULATION
AND
PREDICATION