Sun Microelectronics
298
UltraSPARC User’s Manual
Floating-point stores other than
ST{X}FSR
can store the result of a floating-point or
graphics instruction other than
FDIV
or
FSQRT
and be in the same group. For ex-
ample:
Floating-point stores of the result of an
FDIV
or
FSQRT
are treated the same as a
dependent floating-point instruction.
ST(X)FSR
cannot be dispatched in the two groups following a floating-point or
graphics instruction that references the floating-point registers. For example:
To simplify critical timing paths, floating-point operations are usually stalled in
the G Stage until earlier floating-point operations with a different precision com-
plete, regardless of data dependency. This behavior is described more precisely in
the following two rules. Floating-point loads and stores are independent of these
mixed precision rules.
1.
A floating-point or graphics instruction that follows an
FMOV
,
FABS
,
FNEG
of different precision break the group, even if there is no data dependency.
For example:
2.
A floating-point or graphics instruction following an operation other than
FMOV
,
FABS
,
FNEG
,
FDIV
,
FSQRT
of different precision is stalled until the
N
2
Stage of the earlier operation, even if there is no data dependency. For
example:
As an exception to the previous rule,
FDIV
or
FSQRT
can be grouped with an old-
er operation of different precision, but are stalled until the N
2
Stage of the earlier
operation otherwise.
FADDs
f2, f5,
f6
G
E
C
N
1
N
2
N
3
W
STF
f6, [address]
G
E
C
N
1
N
2
N
3
W
FMULd
G
E
C
N
1
N
2
N
3
W
STFSR
G
E
C
N
1
N
2
N
3
FMOVs
G
E
C
N
1
N
2
N
3
W
FMULd
G
E
C
N
1
N
2
N
3
W
FADDs
f2, f5,
f0
G
E
C
N
1
N
2
N
3
W
FMULd f2, f2, f2
G
E
C
N
1
N
2
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com