1:60
Volume 1, Part 1: Application Programming Model
Three types of atomic semaphore operations are defined: exchange (
xchg
); compare
and exchange (
cmpxchg
); and fetch and add (
fetchadd
).
The
xchg
target is loaded with the zero-extended contents of the memory location
addressed by the first source and then the second source is stored into the same
memory location.
The
cmpxchg
target is loaded with the zero-extended contents of the memory location
addressed by the first source; if the zero-extended value is equal to the contents of the
Compare and Exchange Compare Value application register (CCV), then the second
source is stored into the same memory location. The
cmp8xchg16
instruction loads the
target with 8 bytes from the memory location addressed by the first source; if this
value is equal to the contents of the CCV register, then the second source and the CSD
register are both stored into memory at the 16-byte-aligned address which contains the
memory location loaded.
The
fetchadd
instruction specifies one general register source, one general register
target, and an immediate. The
fetchadd
target is loaded with the zero-extended
contents of the memory location addressed by the source and then the immediate is
added to the loaded value and the result is stored into the same memory location.
4.4.4
Control Speculation
Special mechanisms are provided to allow for compiler-directed speculation. This
speculation takes two forms, control speculation and data speculation, with a separate
mechanism to support each. See also
“Data Speculation” on page 1:63
4.4.4.1
Control Speculation Concepts
Control speculation describes the compiler optimization where an instruction or a
sequence of instructions is executed before it is known that the dynamic control flow of
the program will actually reach the point in the program where the sequence of
instructions is needed. This is done with instruction sequences that have long execution
latencies. Starting the execution early allows the compiler to overlap the execution with
other work, increasing the parallelism and decreasing overall execution time. The
compiler performs this optimization when it determines that it is very likely that the
dynamic control flow of the program will eventually require this calculation. In cases
where the control flow is such that the calculation turns out not to be needed, its results
are simply discarded (the results in processor registers are simply not used).
Since the speculative instruction sequence may not be required by the program, no
exceptions encountered that would be visible to the program can be signalled until it is
determined that the program’s control flow does require the execution of this
instruction sequence. For this reason, a mechanism is provided for recording the
occurrence of an exception so that it can be signalled later if and when it is necessary.
In such a situation, the exception is said to be deferred. When an exception is deferred
by an instruction, a special token is written into the target register to indicate the
existence of a deferred exception in the program.
Deferred exception tokens are represented differently in the general and floating-point
register files. In general registers, an additional bit is defined for each register called
the NaT bit (Not a Thing). Thus general registers are 65 bits wide. A NaT bit equal to 1
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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 ...
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 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 ...
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 ...
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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 ...
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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 ...