3:24
Volume 3: Instruction Reference
br
The loop-type branches (
br.cloop
,
br.ctop
,
br.cexit
,
br.wtop
, and
br.wexit
) are
only allowed in instruction slot 2 within a bundle. Executing such an instruction in either
slot 0 or 1 will cause an Illegal Operation fault, whether the branch would have been
taken or not.
Read after Write (RAW) and Write after Read (WAR) dependency requirements are
slightly different for branch instructions. Changes to BRs, PRs, and PFS by non-branch
instructions are visible to a subsequent branch instruction in the same instruction group
(i.e., a limited RAW is allowed for these resources). This allows for a low-latency
compare-branch sequence, for example. The normal RAW requirements apply to the LC
and EC application registers, and the RRBs.
Within an instruction group, a WAR dependency on PR 63 is not allowed if both the
reading and writing instructions are branches. For example, a
br.wtop
or
br.wexit
may not use PR[63] as its qualifying predicate and PR[63] cannot be the qualifying
predicate for any branch preceding a
br.wtop
or
br.wexit
in the same instruction
group.
For dependency purposes, the loop-type branches effectively always write their
associated resources, whether they are taken or not. The cloop type effectively always
writes LC. When LC is 0, a cloop branch leaves it unchanged, but hardware may
implement this as a re-write of LC with the same value. Similarly,
br.ctop
and
br.cexit
effectively always write LC, EC, the RRBs, and PR[63].
br.wtop
and
br.wexit
effectively always write EC, the RRBs, and PR[63].
Values for various branch hint completers are shown in the following tables. Whether
Prediction Strategy hints are shown in
. Sequential Prefetch hints are shown in
. Branch Cache Deallocation hints are shown in
. See
“Branch Prediction Hints” on page 1:78
Figure 2-4.
Operation of br.wtop and br.wexit
PR[qp]?
wtop, wexit
wtop: Branch
wexit: Fall-thru
wtop: Fall-thru
wexit: Branch
EC?
EC--
PR[63] = 0
RRB--
EC--
PR[63] = 0
RRB--
> 1
== 1
== 0
EC = EC
PR[63] = 0
RRB--
EC = EC
PR[63] = 0
RRB = RRB
(Prolog /
Epilog)
(Epilog)
==0 (Prolog / Epilog)
(Special
Unrolled
Loops)
== 1
Kernel)
(Prolog /
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 ...