Volume 1, Part 1: Application Programming Model
1:75
The counted loop type (
br.cloop
) uses the Loop Count (LC) application register. If LC is
non-zero then it is decremented and the branch is taken. If LC is zero, the branch falls
through. The modulo-scheduled loop type branches (
br.ctop
,
br.cexit
,
br.wtop
,
br.wexit
) are described in
“Modulo-scheduled Loop Support” on page 1:75
type branches (
br.cloop
,
br.ctop
,
br.cexit
,
br.wtop
,
br.wexit
) are allowed only in
slot 2 of a bundle. A loop type branch executed in slot 0 or 1 will cause an Illegal
Operation fault.
Instructions are provided to move data between branch registers and general registers
(
mov =br
,
mov br=
).
and
summarize state and instructions
relating to branching.
4.5.1
Modulo-scheduled Loop Support
Support for software-pipelined loops is provided through rotating registers and loop
branch types. Software pipelining of a loop is analogous to hardware pipelining of a
functional unit. The loop body is partitioned into multiple “stages” with zero or more
instructions in each stage. Modulo-scheduled loops have three phases: prolog, kernel,
and epilog. During the prolog phase, new loop iterations are started each time around
(filling the software pipeline). During the kernel phase, the pipeline is full. A new loop
br.ia
Invoke the IA-32 instruction set
Unconditional
Indirect
br.cloop
Counted loop branch
Loop count
IP-rel
br.ctop, br.cexit
Modulo-scheduled counted loop
Loop count and Epilog
count
IP-rel
br.wtop, br.wexit
Modulo-scheduled while loop
Qualifying predicate
and Epilog count
IP-rel
brl.cond or brl
Long conditional branch
Qualifying predicate
IP-rel
brl.call
Long conditional procedure call
Qualifying predicate
IP-rel
Table 4-23.
State Relating to Branching
Register
Function
BRs
Branch registers
PRs
Predicate registers
CFM
Current Frame Marker
PFS
Previous Function State application register
LC
Loop Count application register
EC
Epilog Count application register
Table 4-24.
Instructions Relating to Branching
Mnemonic
Operation
br
Branch
brl
Long branch
brp
Provide early hint information about a future branch
mov =br
Move from BR to GR
mov br=
Move from GR to BR
Table 4-22.
Branch Types (Continued)
Mnemonic
Function
Branch Condition
Target Address
Содержание ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 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 ...
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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 ...
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