Today we continue to read the WRL research report on the Swift Java Compiler. We were discussing Global Common SubExpression elimination and global code motion. We were discussing how CSE is applied whenever there are two values that are equivalent and particularly even if neither of the two values are dominant. This is determined based on a work list. The values are all split into identical initial partitions based solely on their operation fields. For each of these partitions a set of values are build that takes one of the values in the partition. The partition is then split and the smaller of the two pis put into the worklist. This way each partition has all values equivalent.
Swift iterates through all the partitions and picks out the values from each partition. If a partition has more than one value, Swift picks out only the dominant value. It throws a way the other values.
CSE is very helpful in optimization. For example it removes the null checks against the parameters. In fact, CSE helps remove the same runtime check against the parameter from many places. In addition it removes the edges from the CFG.
#coding exercise
GetAlternateOddNumberRangeSumCubeRootSixthSquare (Double [] A)
{
if (A == null) return 0;
Return A.AlternateOddNumberRangeSumCubeRootSixthSquare();
}