soft-fp64/fadd: Move common code out of both branches of an if-statement

The previous two commits were just setting the scene for this change.

The mix(..., __propagateFloat64NaN(a, b), propagate) statements are not
identical in the two halves, but they are equivalent.  The first clause
of the mix in the else-branch is trivally ±Inf.  The first clause in the
then-branch __packFloat64(aSign, aExp, aFracHi, aFracLo).  The
preceeding conditions prove that aExp=0x7ff, aFracHi=0, and aFracLo=0.

Results on the 308 shaders extracted from the fp64 portion of the OpenGL
CTS:

Tiger Lake and Ice Lake had similar results. (Tiger Lake shown)
total instructions in shared programs: 819560 -> 787258 (-3.94%)
instructions in affected programs: 757737 -> 725435 (-4.26%)
helped: 74
HURT: 0
helped stats (abs) min: 43 max: 3545 x̄: 436.51 x̃: 296
helped stats (rel) min: 3.54% max: 6.16% x̄: 4.52% x̃: 4.36%
95% mean confidence interval for instructions value: -548.42 -324.61
95% mean confidence interval for instructions %-change: -4.68% -4.37%
Instructions are helped.

total cycles in shared programs: 6817254 -> 6483227 (-4.90%)
cycles in affected programs: 6385272 -> 6051245 (-5.23%)
helped: 74
HURT: 0
helped stats (abs) min: 430 max: 33271 x̄: 4513.88 x̃: 3047
helped stats (rel) min: 4.28% max: 7.45% x̄: 5.48% x̃: 5.31%
95% mean confidence interval for cycles value: -5610.46 -3417.30
95% mean confidence interval for cycles %-change: -5.65% -5.32%
Cycles are helped.

total spills in shared programs: 591 -> 553 (-6.43%)
spills in affected programs: 591 -> 553 (-6.43%)
helped: 1
HURT: 0

total fills in shared programs: 1353 -> 1307 (-3.40%)
fills in affected programs: 1353 -> 1307 (-3.40%)
helped: 1
HURT: 0

Reviewed-by: Matt Turner <[email protected]>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4142>

0 files changed, 0 insertions, 0 deletions