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Volume 1, Part 1: Introduction to the Intel
®
Itanium
®
Architecture
filled. The Itanium architecture enables procedures to communicate register usage to
the processor. This allows the processor to schedule procedure register operations even
when there is a low degree of ILP. See
2.5
Compiler to Processor Communication
The Itanium architecture provides mechanisms, such as instruction templates, branch
hints, and cache hints to enable the compiler to communicate compile-time information
to the processor. In addition, it allows compiled code to manage the processor
hardware using runtime information. These communication mechanisms are vital in
minimizing the performance penalties associated with branches and cache misses.
The cost of branches is minimized by permitting code to communicate branch
information to the hardware in advance of the actual branch.
Every memory load and store in the Itanium architecture has a 2-bit cache hint field in
which the compiler encodes its prediction of the spatial and/or temporal locality of the
memory area being accessed. A processor based on the Itanium architecture can use
this information to determine the placement of cache lines in the cache hierarchy to
improve utilization. This is particularly important as the cost of cache misses is
expected to increase.
2.6
Speculation
There are two types of speculation: control and data. In both control and data
speculation, the compiler exposes ILP by issuing an operation early and removing the
latency of this operation from critical path. The compiler will issue an operation
speculatively if it is reasonably sure that the speculation will be beneficial. To be
beneficial two conditions should hold: (1) it must be statistically frequent enough that
the probability it will require recovery is small, and (2) issuing the operation early
should expose further ILP-enhancing optimization. Speculation is one of the primary
mechanisms for the compiler to exploit statistical ILP by overlapping, and therefore
tolerating, the latencies of operations.
2.6.1
Control Speculation
Control speculation is the execution of an operation before the branch which guards it.
Consider the code sequence below:
if (a>b) load(ld_addr1,target1)
else load(ld_addr2, target2)
If the operation
load(ld_addr1,target1)
were to be performed prior to the
determination of
(a>b)
, then the operation would be control speculative with respect to
the controlling condition
(a>b)
. Under normal execution, the operation
load(ld_addr1,target1)
may or may not execute. If the new control speculative load
causes an exception, then the exception should only be serviced if
(a>b)
is true. When
Содержание ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3
Страница 1: ......
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 ...
Страница 13: ...1 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 33: ...1 22 Volume 1 Part 1 Introduction to the Intel Itanium Architecture ...
Страница 57: ...1 46 Volume 1 Part 1 Execution Environment ...
Страница 147: ...1 136 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
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 248: ...236 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 249: ...2 1 Intel Itanium Architecture Software Developer s Manual Rev 2 3 Part I System Architecture Guide ...
Страница 250: ...2 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
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 ...
Страница 750: ...2 502 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
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 ...
Страница 862: ...2 614 Volume 2 Part 2 External Interrupt Architecture ...
Страница 870: ...2 622 Volume 2 Part 2 Performance Monitoring Support ...
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Страница 941: ...3 42 Volume 3 Instruction Reference cmp illegal_operation_fault PR p1 0 PR p2 0 Interruptions Illegal Operation fault ...
Страница 1099: ...3 200 Volume 3 Instruction Reference padd Interruptions Illegal Operation fault ...
Страница 1191: ...3 292 Volume 3 Pseudo Code Functions Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 1295: ...3 396 Volume 3 Resource and Dependency Semantics ...
Страница 1296: ......
Страница 1302: ...402 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
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 ...