Volume 1, Part 2: Software Pipelining and Loop Support
1:187
and a decision is made to exit the loop. The special case in which a software-pipelined
loop branch is executed with
EC
equal to 0 can occur in unrolled software-pipelined
loops if the target of the
cexit
branch is set to the next sequential bundle.
There are two types of software-pipelined loop branches for counted loops.
br.ctop
is
taken when a decision to continue kernel loop execution is made, and is not taken
otherwise. It is used when the loop execution decision is located at the bottom of the
loop.
br.cexit
is not taken when a decision to continue kernel loop execution is made,
and is taken otherwise. It is used when the loop execution decision is located
somewhere other than the bottom of the loop.
5.4.3.2
Counted Loop Example
A conceptual view of a pipelined iteration of the example counted loop on
with II equal to one is shown below:
stage 1:(p16)
ld4 r4 = [r5],4
stage 2:(p17)
---
// empty stage
stage 3:(p18)
add r7 = r4,r9
stage 4:(p19)
st4 [r6] = r7,4
To generate an efficient pipeline, the compiler must take into account the latencies of
instructions and the available functional units. For this example, the load latency is two
and the load and add are scheduled two cycles apart. The pipeline below is coded
assuming there are two memory ports and the loop count is 200.
Figure 5-1.
ctop and cexit Execution Flow
000915
EC?
LC?
LC - -
LC = LC
LC = LC
LC = LC
EC = EC
EC - -
EC - -
EC = EC
PR[63] = 0
PR[63] = 0
PR[63] = 0
PR[63] = 1
RRB - -
RRB - -
RRB - -
RRB = RRB
ctop, cexit
== 0 (epilog)
! = 0
> 1
== 0
==1
(prolog / kernel)
(special unrolled loops)
ctop: branch
cexit: fall-thru
ctop: fall-thru
cexit: branch
Содержание ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3
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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 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 ...
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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 ...