Abstract * Foil Index for this file
Addon
Given by Zoran Budimlic at Java for CSE Meeting on Dec 16 1996. Foils prepared Jan 12 1997
Abstract * Foil Index for this file
Addon
| Based on Summer work by Zoran Budimlic at JavaSoft and Collaboration with Ken Kennedy |
| Java bytecodes are at a higher level than ordinary assembly code |
| Exceptions greatly reduce code movement opportunities |
| OOP style (lots of method calls) reduces the data flow information available |
| No knowledge about the whole program at compile time |
| Standard trilema: functionality vs. portability vs. performance |
| Adopt the current javac strategy: one class at a time, no changes to VM, lowest performance |
| Or sacrifice some portability and functionality for better optimization |
| Or sacrifice a lot of portability and functionality for best performance |
This table of Contents
Abstract
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| Zoran Budimlic |
| Rice University |
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| Java bytecodes are at a higher level than ordinary assembly code |
| exceptions greatly reduce code movement opportunities |
| OOP style (lots of method calls) reduces the data flow information available |
| no knowledge about the whole program at compile time |
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| standard trilema: functionality vs. portability vs. performance |
| adopt the current javac strategy: one class at a time, no changes to VM, lowest performance |
| sacrifice some portability and functionality for better optimization |
| sacrifice a lot of portability and functionality for best performance |
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| based on summer work in JavaSoft |
| standalone, cross-bytecode, one class at a time |
local and peephole optimizations
|
| SSA construction |
simple SSA optimizations
|
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| requires no changes to VM |
| insensitive to the choice of source compiler and interpreter/JIT compiler |
| no interprocedural optimizations |
| low performance gain |
| space for some additional, though limited improvements |
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| Java doesn't have registers |
local variables are not the same:
|
operand stack should be used to shorten the bytecode sequence
|
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| interprocedural optimizations of the part of the program that is available |
| make some assumptions about the code at a compile time, pass the information about it to the run-time |
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OOP Style
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inheritance
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limited analysis
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| inlining has to preserve field privacy |
| simple idea: inline both methods and data |
we can only inline objects that we instantiated
|
| preliminary experiments (Linpack by hand) give ~2 times speed increase, with 20-30% code size increase |
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| compile and optimize classes assuming static intraclass calls |
| have two versions of each class, one for instantiation, one for inheritance |
| requires the run-time environment to know about this and have appropriate behavior |
| duplicates the code size |
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| wait until the whole program is available at the client's side |
| perform the full range of heavy-duty optimizations, generate native code |
| high performance, loss of portability |
| ongoing research ("classical" optimizations, Jeff Dean's thesis) |
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| many Java instructions can cause an exception |
| exact exception model |
| no appropriate model for methods with exception handlers yet |
| greatly reduces code movement opportunities |
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determine instructions that will not cause exceptions
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enclose the whole method code in a try
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| some portability and functionality has to be sacrificed for high performance |
| within factor 2 of native C expected for Web based programs |
| with native-code, whole program optimizing Java compiler, very limited use of exceptions in user programs, we should expect getting very close to native C performance |
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| Java is becoming the language of choice in many applications, from WWW to scientific code |
| it has many appealing features |
| unfortunately, it is very hard to optimize |
| fortunately, it is very hard to optimize, so I can get my thesis out of it |