Volume 1, Part 2: Software Pipelining and Loop Support
1:189
There are a few differences in the operation of the while loop branch compared to the
counted loop branch. The while loop branch does not access
LC
— a branch predicate
determines the behavior of this branch instead. During the kernel and epilog phases,
the branch predicate is one and zero respectively. During the prolog phase, the branch
predicate may be either zero or one depending on the scheme used to program the
while loop. Also,
p16
is always set to zero after rotation. The reasons for these
differences are related to the nature of while loops and will be explained in more depth
with an example in a later section.
5.4.4
Terminology Review
The terms below were introduced in the preceding sections:
Initiation Interval (II)
The number of cycles between the start of successive source iterations in
a software pipelined loop. Each stage of the pipeline is II cycles long.
Prolog
The first phase of a software-pipelined loop, in which the pipeline is filled.
Kernel
The second phase of a software-pipelined loop, in which the pipeline is full.
Epilog
The third phase of a software-pipelined loop, in which the pipeline is
drained.
Source Iteration
An iteration of the original source code loop.
Kernel Iteration
An iteration of the loop that implements the software pipeline.
Register Rotation
A form of register renaming that is visible to software. Registers are
renamed with respect to a register rename base that is decremented.
Figure 5-2.
wtop and wexit Execution Flow
000916
EC?
PR[qp]?
EC = EC
EC - -
EC - -
EC = EC
PR[63] = 0
PR[63] = 0
PR[63] = 0
PR[63] = 0
RRB - -
RRB - -
RRB - -
RRB = RRB
wtop, wexit
== 0 (prolog / epilog)
== 1
> 1
== 0
==1
(prolog /
kernel)
(special unrolled loops)
wtop: branch
wexit: fall-thru
wtop: fall-thru
wexit: branch
(prolog /
epilog)
( epilog)
Summary of Contents for ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3
Page 1: ......
Page 11: ...x Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 13: ...1 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 33: ...1 22 Volume 1 Part 1 Introduction to the Intel Itanium Architecture ...
Page 57: ...1 46 Volume 1 Part 1 Execution Environment ...
Page 147: ...1 136 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 149: ...1 138 Volume 1 Part 2 About the Optimization Guide ...
Page 191: ...1 180 Volume 1 Part 2 Predication Control Flow and Instruction Stream ...
Page 230: ......
Page 248: ...236 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 250: ...2 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 264: ...2 16 Volume 2 Part 1 Intel Itanium System Environment ...
Page 380: ...2 132 Volume 2 Part 1 Interruptions ...
Page 398: ...2 150 Volume 2 Part 1 Register Stack Engine ...
Page 486: ...2 238 Volume 2 Part 1 IA 32 Interruption Vector Descriptions ...
Page 750: ...2 502 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 754: ...2 506 Volume 2 Part 2 About the System Programmer s Guide ...
Page 796: ...2 548 Volume 2 Part 2 Interruptions and Serialization ...
Page 808: ...2 560 Volume 2 Part 2 Context Management ...
Page 842: ...2 594 Volume 2 Part 2 Floating point System Software ...
Page 850: ...2 602 Volume 2 Part 2 IA 32 Application Support ...
Page 862: ...2 614 Volume 2 Part 2 External Interrupt Architecture ...
Page 870: ...2 622 Volume 2 Part 2 Performance Monitoring Support ...
Page 891: ......
Page 1099: ...3 200 Volume 3 Instruction Reference padd Interruptions Illegal Operation fault ...
Page 1295: ...3 396 Volume 3 Resource and Dependency Semantics ...
Page 1296: ......
Page 1302: ...402 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 1494: ...4 192 Volume 4 Base IA 32 Instruction Reference FWAIT Wait See entry for WAIT ...
Page 1647: ...Volume 4 Base IA 32 Instruction Reference 4 345 ROL ROR Rotate See entry for RCL RCR ROL ROR ...
Page 1884: ...4 582 Volume 4 IA 32 SSE Instruction Reference ...
Page 1885: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 Index ...
Page 1886: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 1898: ...INDEX Index 12 Index for Volumes 1 2 3 and 4 ...