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annotate docs/HistoricalNotes/2001-07-06-LoweringIRForCodeGen.txt @ 112:4b203247047d

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ignore TailCall failure in SelectionDAGBuilder (not Unreachable instruction)
author MitsukiMiyagi
date Mon, 07 Mar 2016 22:07:35 +0900
parents 95c75e76d11b
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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1 Date: Fri, 6 Jul 2001 16:56:56 -0500
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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 <lattner@cs.uiuc.edu>
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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4 Subject: lowering the IR
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5
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6 BTW, I do think that we should consider lowering the IR as you said. I
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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7 didn't get time to raise it today, but it comes up with the SPARC
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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8 move-conditional instruction. I don't think we want to put that in the core
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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9 VM -- it is a little too specialized. But without a corresponding
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10 conditional move instruction in the VM, it is pretty difficult to maintain a
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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11 close mapping between VM and machine code. Other architectures may have
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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12 other such instructions.
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13
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14 What I was going to suggest was that for a particular processor, we define
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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15 additional VM instructions that match some of the unusual opcodes on the
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16 processor but have VM semantics otherwise, i.e., all operands are in SSA
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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17 form and typed. This means that we can re-generate core VM code from the
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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18 more specialized code any time we want (so that portability is not lost).
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19
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20 Typically, a static compiler like gcc would generate just the core VM, which
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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21 is relatively portable. Anyone (an offline tool, the linker, etc., or even
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22 the static compiler itself if it chooses) can transform that into more
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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23 specialized target-specific VM code for a particular architecture. If the
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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24 linker does it, it can do it after all machine-independent optimizations.
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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25 This would be the most convenient, but not necessary.
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26
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27 The main benefit of lowering will be that we will be able to retain a close
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Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
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28 mapping between VM and machine code.
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29
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30 --Vikram
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31