OPTIMIZING THE JAVA VIRTUAL MACHINE INSTRUCTION SET BY ...

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Within this category, it was also observed that many of the benchmarks showed the
greatest change in performance when the final 14 despecializations were performed.
This result was expected since those specialized bytecodes that were executed with
least frequency were despecialized first. Figure 5.10 shows the proportion of the specialized
bytecodes represented by each of the specialized bytecodes considered in this
study. Figure 5.11 shows a cumulative distribution of the specialized bytecodes. This
reveals that the first 48 specialized bytecodes represent 16.9 percent of the specialized
bytecodes executed. The remaining 83.1 percent of the specialized bytecodes
executed were contributed by only the final 14 bytecodes listed in Table 5.1.
5.2.4 Category 3: Benchmarks with Irregular Performance
The final category contains all of the benchmarks that generated performance results
that did not fit into one of the first two categories. Only 16 benchmarks, or 10 percent
of the benchmark/virtual machine/architecture combinations considered in this study
were found to reside in this category. The results within this category were further
divided into four sub-categories:
• Benchmarks that closely approximated no difference in performance (3 benchmarks)
• Benchmarks that closely approximated a trend of slowing performance as the
number of despecializations performed increased (2 benchmarks)
• Benchmarks that showed, or closely approximated, a trend of improving performance
as the number of despecializations performed increased (6 benchmarks)
• Benchmarks that showed an irregular performance pattern that was not covered
by any of the preceding performance groups (5 benchmarks)
The first two groups within this category are not particularly interesting. They
include benchmarks that generated results that closely approximated either category
1 (no change in performance) or category 2 (decreased performance as the result of
performing despecialization). However, in each case, an interruption in the pattern of
behaviour was present. For example, all of the benchmarks in the first group would
have been included within category 1 if a tolerance value of three percent had been
selected instead of the two percent value used during this study. Similarly, the benchmarks
in the second group each showed exactly one despecialization condition that
interrupted the pattern of behaviour. Furthermore, the magnitude of the observed