Today we continue reading the WRL research report  on Swift Java compiler. We were discussing register allocations and solving it by means of graph coloring.  We will discuss the results of the study on Swift Java compiler next. The Swift java compiler was measured on a Alpha workstation which had one 667MHz processor and a 64KB on-chip data cache and a 4MB board cache.  The generated code was installed into a high performance JVM.  This was necessary so that the results be properly evaluated against the controlled conditions.  Only when the baseline is performant, can we find the results to be representative of the variables we control. A poor choice for baseline may hide gains from some of the variables or skew the results because of running time  variations.  In this case, the JVM chosen was already performing some form of CHA. This helps us evaluate the gains from the passes more appropriately. The heap size used was 100 MB.  Although the hardware seems less powerful as compared to recent processors, the configuration was decent at that time. Moreover, with the JVM baseline established, the trends could be expected to be the same on a different choice of system. The tests were performed on a number of applications from a variety of domains with varying lengths in program size. The initial set of results were taken with all optimizations.  Then they were taken without the class hierarchy analysis (CHA). This showed that the use of CHA greatly improves the overall performance. The overall speedup of the Swift generated code without CHA over the fast JVM is marginal because the JVM is already using some form of CHA to resolve method calls. The results were also compared for simple-CHA versus full CHA and it turned out that that the former was only somewhat less performant than the latter indicating it as a useful strategy when dynamic loading is present.
Swift Compilation could proceed at the rate of about 2000 lines of code per second with all optimizations except when escape analysis was on. Escape analysis may require slowed down the compilation by about 20-40%;