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Volume 1, Part 2: Floating-point Applications
1:213
6.3.5
Multiple Status Fields
The FPSR is divided into one main (architectural) status field and three additional
identical status fields. These additional status fields could be used to performance
advantage.
First, divide and square-root sequences (described in
) contain operations
that might cause intermediate results to overflow/underflow or be inexact even if the
final result may not. In order to maintain correct IEEE flag status the status flags of
these computations need to be discarded. One of these additional status fields
(typically status field 1) can be used to discard these flags.
Second, speculating floating-point operations requires maintaining the status flags of
the speculated operations distinct from the architectural status flags until the
speculated operations are committed to architectural state (if they ever are). One of
these additional status fields (typically status fields 2 or 3) can be used for this
purpose.
Consider the Livermore FORTRAN kernel 16 – Monte Carlo Search
DO 470 k= 1,n
k2= k2+1
j4= j2+k+k
j5= ZONE(j4)
IF( j5-n ) 420,475,450
415 IF( j5-n+II ) 430,425,425
420 IF( j5-n+LB ) 435,415,415
425 IF( PLAN(j5)-R) 445,480,440
430 IF( PLAN(j5)-S) 445,480,440
435 IF( PLAN(j5)-T) 445,480,440
440 IF( ZONE(j4-1)) 455,485,470
445 IF( ZONE(j4-1)) 470,485,455
450 k3= k3+1
IF( D(j5)-(D(j5-1)*(T-D(j5-2))**2
,
+(S-D(j5-3))**2
,
+(R-D(j5-4))**2)) 445,480,440
455 m= m+1
IF( m-ZONE(1) ) 465,465,460
460 m= 1
465 IF( i1-m) 410,480,410
470 CONTINUE
475 CONTINUE
480 CONTINUE
485 CONTINUE
Profiling indicates that the conditional after statement 450 is most frequently executed.
It is therefore advantageous to speculatively execute the computation in the conditional
while the conditionals in 415...445 are being evaluated. In the event that any of the
conditionals in 415...445 cause the control to be moved on beyond 450 the results (and
flags) of the speculatively computed operations (of the conditional after statement 450)
can be discarded.
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 ...