1 Date: Tue, 13 Feb 2001 13:29:52 -0600 (CST) 2 From: Chris Lattner <sabre (a] nondot.org> 3 To: Vikram S. Adve <vadve (a] cs.uiuc.edu> 4 Subject: LLVM Concerns... 5 6 7 I've updated the documentation to include load store and allocation 8 instructions (please take a look and let me know if I'm on the right 9 track): 10 11 file:/home/vadve/lattner/llvm/docs/LangRef.html#memoryops 12 13 I have a couple of concerns I would like to bring up: 14 15 1. Reference types 16 Right now, I've spec'd out the language to have a pointer type, which 17 works fine for lots of stuff... except that Java really has 18 references: constrained pointers that cannot be manipulated: added and 19 subtracted, moved, etc... Do we want to have a type like this? It 20 could be very nice for analysis (pointer always points to the start of 21 an object, etc...) and more closely matches Java semantics. The 22 pointer type would be kept for C++ like semantics. Through analysis, 23 C++ pointers could be promoted to references in the LLVM 24 representation. 25 26 2. Our "implicit" memory references in assembly language: 27 After thinking about it, this model has two problems: 28 A. If you do pointer analysis and realize that two stores are 29 independent and can share the same memory source object, there is 30 no way to represent this in either the bytecode or assembly. 31 B. When parsing assembly/bytecode, we effectively have to do a full 32 SSA generation/PHI node insertion pass to build the dependencies 33 when we don't want the "pinned" representation. This is not 34 cool. 35 I'm tempted to make memory references explicit in both the assembly and 36 bytecode to get around this... what do you think? 37 38 -Chris 39 40
