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annotate docs/HistoricalNotes/2001-02-13-Reference-MemoryResponse.txt @ 0:95c75e76d11b LLVM3.4

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LLVM 3.4
author Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
date Thu, 12 Dec 2013 13:56:28 +0900
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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1 Date: Tue, 13 Feb 2001 18:25:42 -0600
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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2 From: Vikram S. Adve <vadve@cs.uiuc.edu>
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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3 To: Chris Lattner <sabre@nondot.org>
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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4 Subject: RE: LLVM Concerns...
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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5
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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6 > 1. Reference types
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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7 > Right now, I've spec'd out the language to have a pointer type, which
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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8 > works fine for lots of stuff... except that Java really has
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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9 > references: constrained pointers that cannot be manipulated: added and
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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10 > subtracted, moved, etc... Do we want to have a type like this? It
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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11 > could be very nice for analysis (pointer always points to the start of
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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12 > an object, etc...) and more closely matches Java semantics. The
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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13 > pointer type would be kept for C++ like semantics. Through analysis,
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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14 > C++ pointers could be promoted to references in the LLVM
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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15 > representation.
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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16
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17
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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18 You're right, having references would be useful. Even for C++ the *static*
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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19 compiler could generate references instead of pointers with fairly
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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20 straightforward analysis. Let's include a reference type for now. But I'm
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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21 also really concerned that LLVM is becoming big and complex and (perhaps)
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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22 too high-level. After we get some initial performance results, we may have
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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23 a clearer idea of what our goals should be and we should revisit this
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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24 question then.
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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25
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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26 > 2. Our "implicit" memory references in assembly language:
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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27 > After thinking about it, this model has two problems:
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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28 > A. If you do pointer analysis and realize that two stores are
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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29 > independent and can share the same memory source object,
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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30
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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31 not sure what you meant by "share the same memory source object"
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32
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33 > there is
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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34 > no way to represent this in either the bytecode or assembly.
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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35 > B. When parsing assembly/bytecode, we effectively have to do a full
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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36 > SSA generation/PHI node insertion pass to build the dependencies
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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37 > when we don't want the "pinned" representation. This is not
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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38 > cool.
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39
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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40 I understand the concern. But again, let's focus on the performance first
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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41 and then look at the language design issues. E.g., it would be good to know
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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42 how big the bytecode files are before expanding them further. I am pretty
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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43 keen to explore the implications of LLVM for mobile devices. Both bytecode
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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44 size and power consumption are important to consider there.
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45
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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46 --Vikram
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47