Mercurial > hg > CbC > CbC_llvm
diff docs/HistoricalNotes/2001-02-13-Reference-MemoryResponse.txt @ 0:95c75e76d11b LLVM3.4
LLVM 3.4
author | Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> |
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date | Thu, 12 Dec 2013 13:56:28 +0900 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/docs/HistoricalNotes/2001-02-13-Reference-MemoryResponse.txt Thu Dec 12 13:56:28 2013 +0900 @@ -0,0 +1,47 @@ +Date: Tue, 13 Feb 2001 18:25:42 -0600 +From: Vikram S. Adve <vadve@cs.uiuc.edu> +To: Chris Lattner <sabre@nondot.org> +Subject: RE: LLVM Concerns... + +> 1. Reference types +> Right now, I've spec'd out the language to have a pointer type, which +> works fine for lots of stuff... except that Java really has +> references: constrained pointers that cannot be manipulated: added and +> subtracted, moved, etc... Do we want to have a type like this? It +> could be very nice for analysis (pointer always points to the start of +> an object, etc...) and more closely matches Java semantics. The +> pointer type would be kept for C++ like semantics. Through analysis, +> C++ pointers could be promoted to references in the LLVM +> representation. + + +You're right, having references would be useful. Even for C++ the *static* +compiler could generate references instead of pointers with fairly +straightforward analysis. Let's include a reference type for now. But I'm +also really concerned that LLVM is becoming big and complex and (perhaps) +too high-level. After we get some initial performance results, we may have +a clearer idea of what our goals should be and we should revisit this +question then. + +> 2. Our "implicit" memory references in assembly language: +> After thinking about it, this model has two problems: +> A. If you do pointer analysis and realize that two stores are +> independent and can share the same memory source object, + +not sure what you meant by "share the same memory source object" + +> there is +> no way to represent this in either the bytecode or assembly. +> B. When parsing assembly/bytecode, we effectively have to do a full +> SSA generation/PHI node insertion pass to build the dependencies +> when we don't want the "pinned" representation. This is not +> cool. + +I understand the concern. But again, let's focus on the performance first +and then look at the language design issues. E.g., it would be good to know +how big the bytecode files are before expanding them further. I am pretty +keen to explore the implications of LLVM for mobile devices. Both bytecode +size and power consumption are important to consider there. + +--Vikram +