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Volume 1, Part 1: Execution Environment
The ordering rules and the dependency restrictions allow the processor to dynamically
re-order instructions, execute instructions with non-unit latency, or even concurrently
execute instructions on opposing sides of a stop or taken branch, provided that correct
sequencing is enforced and the appearance of sequential execution is presented to the
programmer.
IP is a special resource in that reads and writes of IP behave as though the instruction
stream was being executed serially, rather than in parallel. RAW dependencies on IP are
allowed, and the reader gets the IP of the bundle in which it is contained. So, each
bundle being executed in parallel logically reads IP, increments it and writes it back.
WAW is also allowed.
Ignored ARs are not exceptional for dependency checking purposes. RAW and WAW
dependencies to ignored ARs are not allowed.
For more details on resource dependencies, see
Chapter 5, “Resource and Dependency
3.4.1
RAW Dependency Special Cases
There are four special cases in which RAW register dependencies within an instruction
group are permitted. These special cases are the
alloc
instruction, check load
instructions, instructions that affect branching, and the
ld8.fill
and
st8.spill
instructions.
The
alloc
instruction implicitly writes the Current Frame Marker (CFM) which is
implicitly read by all instructions accessing the stacked subset of the general register
file. Instructions that access the stacked subset of the general register file may appear
in the same instruction group as alloc and will see the stack frame specified by the
alloc
.
Note:
Some instructions have RAW or WAW dependencies on resources other than
CFM affected by
alloc
and are thus not allowed in the same instruction group
after an
alloc
:
flushrs
,
loadrs
, move from AR[BSPSTORE], move from
AR[RNAT],
br.cexit
,
br.ctop
,
br.wexit
,
br.wtop
,
br.call
,
brl.call
,
br.ia
,
br.ret
,
clrrrb
,
cover
, and
rfi
. See
Chapter 5, “Resource and Depen-
for details. Also note that
alloc
is required to be
the first instruction in an instruction group.
A check load instruction may or may not perform a load since it is dependent upon its
corresponding advanced load. If the check load misses the ALAT it will execute a load
from memory. A check load and a subsequent instruction that reads the target of the
check load may exist in the same instruction group. The dependent instruction will get
the new value loaded by the check load.
A branch may read branch registers and may implicitly read predicate registers, the LC,
EC, and PFS application registers, as well as CFM. Except for LC, EC and predicate
registers, writes to any of these registers by a non-branch instruction will be visible to a
subsequent branch in the same instruction group. Writes to predicate registers by any
non-floating-point instruction will be visible to a subsequent branch in the same
instruction group. RAW register dependencies within the same instruction group are not
allowed for LC and EC. Dynamic RAW dependencies where the predicate writer is a
floating-point instruction and the reader is a branch are also not allowed within the
same instruction group. Branches
br.cond
,
br.call
,
brl.cond
,
brl.call
,
br.ret
and
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 ...