Substantially revamp the local spiller, causing it to actually improve the

Substantially revamp the local spiller, causing it to actually improve the
generated code over the simple spiller.  The new local spiller generates
substantially better code than the simple one in some cases, by reusing
values that are loaded out of stack slots and kept available in registers.

This primarily helps programs that are spilling a lot, and there is still
stuff that can be done to improve it.  This patch makes the local spiller
the default, as it's only a tiny bit slower than the simple spiller (it
increases the runtime of llc by < 1%).

Here are some numbers with speedups.

Program    #reuse  old(s)    new(s)  Speedup

Povray:     3452,  16.87 ->  15.93   (5.5%)
177.mesa:   2176,   2.77 ->   2.76   (0%)
179.art:      35,  28.43 ->  28.01   (1.5%)
183.equake:   55,  61.44 ->  61.41   (0%)
188.ammp:    869, 174    -> 149      (15%)

164.gzip:     43,  40.73 ->  40.71   (0%)
175.vpr:     351,  18.54 ->  17.34   (6.5%)
176.gcc:    2471,   5.01 ->   4.92   (1.8%)
181.mcf       42,  79.30 ->  75.20   (5.2%)
186.crafty:  484,  29.73 ->  30.04   (-1%)
197.parser:  251,  10.47 ->  10.67   (-1%)
252.eon:    1501,   1.98 ->   1.75   (12%)
253.perlbm: 1183,  14.83 ->  14.42   (2.8%)
254.gap:     825,   7.46 ->   7.29   (2.3%)
255.vortex:  285,  10.51 ->  10.27   (2.3%)
256.bzip2:    63,  55.70 ->  55.20   (0.9%)
300.twolf:   830,  21.63 ->  22.00   (-1%)

PtrDist/ks    14,  32.75 -> 17.53    (46.5%)
Olden/tsp     46,   8.71 ->  8.24    (5.4%)
Free/distray  70,   1.09 ->  0.99    (9.2%)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16629 91177308-0d34-0410-b5e6-96231b3b80d8