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 GECN
1
N
2
N
3
W
STF f6, [address] GECN
1
N
2
N
3
W
FMULd GECN
1
N
2
N
3
W
STFSR GECN
1
N
2
N
3
FMOVs GECN
1
N
2
N
3
W
FMULd GECN
1
N
2
N
3
W
FADDs f2, f5, f0 GECN
1
N
2
N
3
W
FMULd f2, f2, f2 GECN
1
N
2
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