1:148
Volume 1, Part 2: Memory Reference
3.2.3
Data Prefetch Hint
The
lfetch
instruction requests that lines be moved between different levels of the
memory hierarchy. Like all hint instructions defined in the Itanium architecture,
lfetch
has no effect on program correctness, and any microarchitecture implementation may
choose to ignore it.
3.3
Instruction Dependencies
Data and control dependencies are fundamental factors in optimization and instruction
scheduling. Such dependencies can prevent a compiler from scheduling instructions in
an order that would yield shorter critical paths and better resource usage since they
restrict the placement of instructions relative to other instructions on which they are
dependent.
In general, memory references are the major source of control and data dependencies
that cannot be broken due to getting a wrong answer (if a data dependency is broken)
or raising a fault that should not be raised (if a control dependency is broken). This
section describes:
• Background material on memory reference dependencies.
• Descriptions of how dependencies constrain code scheduling on traditional
architectures.
describes memory reference features defined in the Itanium architecture
that increase the number of dependencies that can be removed by a compiler.
3.3.1
Control Dependencies
An instruction is
control dependent
on a branch if the direction taken by the branch
affects whether the instruction is executed. In the code below, the load instruction is
control dependent on the branch:
(p1)br.cond some_label
ld8 r4=[r5]
The following sections provide overviews of control dependencies and their effects on
optimization.
3.3.1.1
Instruction Scheduling and Control Dependencies
The code below contains a control dependency at the branch instruction:
add
r7=r6,1
// Cycle 0
add r13=r25,r27
cmp.eq
p1,p2=r12,r23
(p1)
br.cond
some_label
;;
ld4
r2=[r3]
;;
// Cycle 1
sub
r4=r2,r11
// Cycle 3
Содержание ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3
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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 941: ...3 42 Volume 3 Instruction Reference cmp illegal_operation_fault PR p1 0 PR p2 0 Interruptions Illegal Operation fault ...
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Страница 1191: ...3 292 Volume 3 Pseudo Code Functions Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
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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 ...