OPTIMIZING THE JAVA VIRTUAL MACHINE INSTRUCTION SET BY ...

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212 Chapter 10 Future Work The previous chapters in this thesis have described explorations performed into despecialization and multicode substitution. While these studies have covered many topics within those areas, additional questions remain to be answered which are outside of the scope of this thesis. Possible areas of closely related future work are described in the following sections. 10.1 Despecialization The primary areas of future research within despecialization include considering the impact of additional despecializations which have not yet been tested and considering the impact of despecialization in additional computing environments. Each of these areas is discussed in further detail in the following subsections. 10.1.1 Evaluating the Impact of 76 Despecializations The despecialization research conducted during this thesis identified a total of 76 specialized bytecodes that can be expressed in terms of one, or a short sequence of other general purpose Java bytecodes. However, performance testing has only been considered for 67 of these bytecodes. Additional work must be conducted in order to determine if performing the remaining despecializations will have any negative impact on the correctness or verifiability of Java class files. The three typecast bytecodes i2b, i2c and i2s must be given special consideration with respect to verifiability. The modifications performed by i2b, i2c and i2s to values on the stack can easily be expressed in terms of a logical operations and constant values. Furthermore, these bytecodes do not throw
213 exceptions if the value being cast is too large to express in the destination data type. As a result, it appears that these bytecodes can be despecialized to a sequence of logical operations. However, it remains to be seen if there are requirements stipulated by the verifier that will not be met once such a substitution is performed. Despecializing the tableswitch bytecode must also be considered carefully. While there are no concerns with the verifiability of a functionally equivalent lookupswitch bytecode, making this substitution has the potential to increase the number of bytes in the code attribute considerably. Such an increase could violate the maximum code attribute size of 65536 bytes imposed by the Java Virtual Machine Specification. Additional work needs to be performed in order to determine if this is a problem in practice. Performance testing should also be performed in order to determine if there is a large negative impact on application performance which makes performing this despecialization impractical. 10.1.2 Further Load / Store Despecializations The despecializations presented previously reduced the total number of load and store bytecodes from 50 to 10. However, further reductions may be possible. The work performed by aload, fload and iload is identical. Each of these bytecodes copies a four byte block of memory from a local variable to the operand stack. Similarly, dload and lload perform the same task, copying an 8 byte block of memory. As a result, it may be possible to reduce the number of load instructions from 5 to 2. One instruction could be named cat1load. It would be responsible for copying the four bytes that represent a category one value. Similarly, a new cat2load bytecode would be responsible for copying the eight bytes that represent a category two value. It is clear that such a transformation would still provide correct application behaviour, but it remains to be seen if making this change would negatively impact the ability of the virtual machine to perform verification. Corresponding arguments can also be made about the 5 store bytecodes that were not despecialized previously. As a result, performing this transformation in addition to the load and store despecializations described previously would reduce the total number of load and store bytecodes required from 50 to 4.
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OPTIMIZING THE JAVA VIRTUAL MACHINE
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Abstract Since its public introduct
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Acknowledgments While my name is th
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2.4.4 Direct Threading . . . . . .
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7.2 An Overview of Multicodes . . .
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List of Figures 2.1 Core Virtual Ma
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7.11 201 compress Performance by Mu
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B.1 The Steps Followed to Evaluate
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6.1 Most Frequently Occurring Const
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1 Chapter 1 Introduction When Moore
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3 Studies were conducted that consi
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5 Chapter 2 An Overview of Java Thi
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7 Addressing this need led to the d
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9 performs garbage collection, a cl
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11 also has the ability to contain
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13 ... i − 1 iload 0x04 dstore 0x
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15 ... aload 3 iconst 2 faload ...
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17 Condition Equal Unequal Greater
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19 transfered to the start of a new
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21 piled into machine language inst
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23 Figure 2.6: Interpreter Engine C
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25 Figure 2.8: Interpreter Engine C
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27 The following section examines t
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29 execute (JMethod * method, Slot
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31 codelets shown in this example a
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33 3.1 Instruction Set Design The a
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35 is replaced with a new opcode if
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37 method. However, the Java Virtua
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39 3.2.5 Bytecode Optimization Tool
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41 each bytecode executed as was ac
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43 executing the application. The a
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45 Chapter 4 Despecialization The J
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47 ... i − 1 iload 3 iload 0x04 i
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49 purpose bytecodes. The notation,
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51 is present in the constant pool
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53 ... iload 3 iflt ... i − 1 i i
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55 the stack challenging in some ca
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Figure 4.7: Despecialization of Bra
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59 Specialized Bytecode load store
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61 tual machine (RVM). Version 2.3.
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63 Test Total Weighted Condition Pe
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69 4.2.6 Performance Summary Compar
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71 Category Original Desp. Percent
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73 the maximum value encountered af
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75 • Efficient support of new lan
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77 difference in the performance of
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79 JGF RayTracer: A 150 by 150 pixe
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81 # Average % of Specialized Despe
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83 provided by only two vendors. IB
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Figure 5.1: Average Performance Res
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87 Figure 5.4: Performance Results
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89 Figure 5.8: Performance Results
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91 ences in background processes, m
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93 difference in performance due to
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95 when a pure interpreter virtual
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97 It is observed that many of the
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99 Within this category, it was als
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101 machine code for the idioms. As
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103 were performed was less than 0.
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105 these despecializations in a me
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107 Chapter 6 Operand Profiling Cha
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109 the applications. In addition,
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111 The aload 0 bytecode was the mo
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113 function being integrated. Beca
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115 Implementing alignment rules un
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117 these data types in the list of
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Figure 6.3: Distribution of Local V
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121 are never executed by any of th
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123 load and store bytecodes. It is
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125 the time because the index bein
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127 6.2.5 Fields Only four bytecode
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129 Figure 6.8: Data types Accessed
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131 lar, the new set of specialized
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133 multicode block is defined to b
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135 Figure 7.1: Two Bytecodes and t
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137 because of the presence of the
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139 cache performance. As a result,
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141 Block 1: Block 2: aload 0 → g
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143 Sequence Count Score getfield a
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Figure 7.3: Iterative Multicode Ide
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147 number of bytecodes that will b
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149 BlockList: A list of the byteco
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151 Both the Total Bytecodes Score
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153 ... i − 1 ❄ ifeq 0x00 0x15
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155 Figure 7.7: Number of Unique Ca
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Figure 7.9: Cumulative Multicode Bl
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159 However, while considering long
Page 179 and 180: 161 Figure 7.10: 201 compress Perfo
Page 181 and 182: 163 Figure 7.14: Length 209 db Perf
Page 183 and 184: 165 Figure 7.18: 222 mpegaudio Perf
Page 185 and 186: 167 7.6.2 Overall Performance Acros
Page 187 and 188: 169 a larger portion of the instruc
Page 189 and 190: 171 // iload_1: stack[sp+1] = local
Page 191 and 192: 173 // iload_1: // iconst_1: // iad
Page 193 and 194: 175 Such bytecodes have a variable
Page 195 and 196: 177 ∆ x1 /x 2 /x 3 /.../x n→ an
Page 197 and 198: 179 Popping any values left on the
Page 199 and 200: 181 7.9 Conclusion This chapter has
Page 201 and 202: 183 ated will differ from that occu
Page 203 and 204: 185 Figure 8.1: A Comparison of the
Page 205 and 206: 187 performed impacts the sequences
Page 207 and 208: 189 Figure 8.2: 201 compress Perfor
Page 209 and 210: 191 Figure 8.5: 213 javac Performan
Page 211 and 212: 193 Compared to the complete despec
Page 213 and 214: 195 Figure 8.10: 209 db Performance
Page 215 and 216: 197 performing multicode substituti
Page 217 and 218: 199 Chapter 9 An Efficient Multicod
Page 219 and 220: 201 alphabet employed by each of th
Page 221 and 222: 9.4 An Algorithm for the Most Contr
Page 223 and 224: Figure 9.3: The Impact of Algorithm
Page 225 and 226: 207 Algorithm NonOverlappingScore(n
Page 227 and 228: 209 Algorithm CountUniqueOccurrence
Page 229: 211 this algorithm did not consider
Page 233 and 234: 215 Figure 10.1: Multicode Blocks u
Page 235 and 236: 217 approximately 30 percent of the
Page 237 and 238: 219 a strategy other than direct th
Page 239 and 240: 221 10.2.6 Combining Multicodes and
Page 241 and 242: 223 10.2.9 Expanding the Class File
Page 243 and 244: 225 revealed that none of the const
Page 245 and 246: 227 based on these profile results
Page 247 and 248: 229 stitution were performed. It co
Page 249 and 250: 231 [13] B. Alpern, C. R. Attanasio
Page 251 and 252: 233 [33] K. Casey, D. Gregg, M. A.
Page 253 and 254: 235 [55] D. Gregg and J. Waldron. P
Page 255 and 256: 237 [78] E. M. McCreight. A space-e
Page 257 and 258: 239 [100] L. A. Smith, J. M. Bull,
Page 259 and 260: 241 [120] T. A. Welch. A technique
Page 261 and 262: 243 # Len Score Multicode % 1 30 10
Page 271 and 272: 253 Table A.5 continued: # Len Scor
Page 277 and 278: 259 the level of entropy within the
Page 279 and 280: 261 there are no pointers to these
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263 information for each method so
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265 to emit four files that were su
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Figure B.1: The Steps Followed to E
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269 B.7 Summary This Chapter has de
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271 Selected Honors and Awards Cont
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273 Departmental and University Pre
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