swift234

Improvement of the inlining heuristic.

Main changes:
*) Instruction costs are not counted for blocks which are dead after inlining
*) Terminator instructions which get constant after inlining increase the threshold
*) Calls inside loops increase the threshold

In theory this should be a step towards making the performance not so dependent on the inlining heuristic.
But I must admit that I still did some fine tuning of all the parameters to get the best results.

Improvements in the benchmarks:
-O:
Chars: +11%
CommonMarkRender: +11%
DollarReduce: +22%
ForLoops: +22%
Forest: +10%
HeapSort: +36%
ImageProc: +14%
StrCat: +14%
StrComplexWalk: +70%
StrToInt: +11%
StringWalk: +99%

-Ounchecked:
Ary: +40%
Ary2: +30%
EditDistance: +22%
Forest: +18%
HeapSort: +50%
Histogram: +11%
StrCat: +12%
StrComplexWalk: +63%
StrSplitter: +11%
StrToInt: +17%
StringWalk: +75%

Regressions (I will file radars for them):
-Ounchecked:
PolymorphicCalls: -21%
QuickSort: -22%
Rectangles: -12%

Code size of the PerfTests_O decreased by 8% 
Code size of the PerfTests_Ounchecked increased by 1%



Swift SVN r24801