1:152
Volume 1, Part 2: Memory Reference
3.4.1
Speculation Model in the Intel
®
Itanium
®
Architecture
The limitations imposed by dependencies on instruction scheduling can be solved by
separating the loading of data from the exception handling or the acknowledgment of
data conflicts. The Itanium architecture supports special speculative versions of
instructions to accomplish this:
• Control speculative load instructions defer exceptions.
• Data speculative load instructions save address information.
• Special check instructions check for exceptions or data conflicts.
An Itanium speculative load can be moved above a dependency barrier (shown as a
dashed line) as shown in
The check detects a deferred exception or a conflict with an intervening store and
provides a mechanism to recover from failed speculation. With this support, speculative
loads and their uses can be scheduled earlier than non-speculative instructions. As a
result, the memory latencies of these loads can be hidden more easily than for
non-speculative loads.
3.4.2
Using Data Speculation in the Intel
®
Itanium
®
Architecture
Data speculation in the Itanium architecture uses a special load instruction (
ld.a
)
called an
advanced load
instruction and an associated check instruction (
chk.a
or
ld.c
)
to validate data-speculated results.
When the
ld.a
instruction is executed, an entry is allocated in a hardware structure
called the Advanced Load Address Table (ALAT). The ALAT is indexed by physical
register number and records the load address, the type of the load, and the size of the
load.
A check instruction must be executed before the result of an advanced load can be used
by any non-speculative instruction. The check instruction must specify the same
register number as the corresponding advanced load.
When a check instruction is executed, the ALAT is searched for an entry with the same
target physical register number and type. If an entry is found, execution continues
normally with the next instruction.
Figure 3-2.
Speculation Model in the Intel
®
Itanium
®
Architecture
Control or
Data Dependency
Original Load
Uses of Load
Speculative Load
Control or
Data Dependency
Check for Exception or
Uses of Load
Memory Conflict
Before Speculation
After Speculation
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Страница 11: ...x Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 12: ...1 1 Intel Itanium Architecture Software Developer s Manual Rev 2 3 Part I Application Architecture Guide ...
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Страница 33: ...1 22 Volume 1 Part 1 Introduction to the Intel Itanium Architecture ...
Страница 57: ...1 46 Volume 1 Part 1 Execution Environment ...
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Страница 149: ...1 138 Volume 1 Part 2 About the Optimization Guide ...
Страница 191: ...1 180 Volume 1 Part 2 Predication Control Flow and Instruction Stream ...
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Страница 249: ...2 1 Intel Itanium Architecture Software Developer s Manual Rev 2 3 Part I System Architecture Guide ...
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Страница 264: ...2 16 Volume 2 Part 1 Intel Itanium System Environment ...
Страница 380: ...2 132 Volume 2 Part 1 Interruptions ...
Страница 398: ...2 150 Volume 2 Part 1 Register Stack Engine ...
Страница 486: ...2 238 Volume 2 Part 1 IA 32 Interruption Vector Descriptions ...
Страница 749: ...2 501 Intel Itanium Architecture Software Developer s Manual Rev 2 3 Part II System Programmer s Guide ...
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Страница 754: ...2 506 Volume 2 Part 2 About the System Programmer s Guide ...
Страница 796: ...2 548 Volume 2 Part 2 Interruptions and Serialization ...
Страница 808: ...2 560 Volume 2 Part 2 Context Management ...
Страница 842: ...2 594 Volume 2 Part 2 Floating point System Software ...
Страница 850: ...2 602 Volume 2 Part 2 IA 32 Application Support ...
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Страница 1494: ...4 192 Volume 4 Base IA 32 Instruction Reference FWAIT Wait See entry for WAIT ...
Страница 1564: ...4 262 Volume 4 Base IA 32 Instruction Reference LES Load Full Pointer See entry for LDS LES LFS LGS LSS ...
Страница 1565: ...Volume 4 Base IA 32 Instruction Reference 4 263 LFS Load Full Pointer See entry for LDS LES LFS LGS LSS ...
Страница 1568: ...4 266 Volume 4 Base IA 32 Instruction Reference LGS Load Full Pointer See entry for LDS LES LFS LGS LSS ...
Страница 1583: ...Volume 4 Base IA 32 Instruction Reference 4 281 LSS Load Full Pointer See entry for LDS LES LFS LGS LSS ...
Страница 1647: ...Volume 4 Base IA 32 Instruction Reference 4 345 ROL ROR Rotate See entry for RCL RCR ROL ROR ...
Страница 1663: ...Volume 4 Base IA 32 Instruction Reference 4 361 SHL SHR Shift Instructions See entry for SAL SAR SHL SHR ...
Страница 1668: ...4 366 Volume 4 Base IA 32 Instruction Reference SIDT Store Interrupt Descriptor Table Register See entry for SGDT SIDT ...
Страница 1884: ...4 582 Volume 4 IA 32 SSE Instruction Reference ...
Страница 1885: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 Index ...
Страница 1886: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 1898: ...INDEX Index 12 Index for Volumes 1 2 3 and 4 ...