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[Lightning] Re: Some questions about minor changes

From: Paolo Bonzini
Subject: [Lightning] Re: Some questions about minor changes
Date: Fri, 24 Sep 2010 10:54:03 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100907 Fedora/3.1.3-1.fc13 Lightning/1.0b3pre Mnenhy/0.8.3 Thunderbird/3.1.3

On 09/24/2010 10:16 AM, Paulo César Pereira de Andrade wrote:
   About the questions:
o Is it a problem to use byte or word opcodes, i.e. will it cause some kind
   of register stall, or something, like setting %al or testing %ax, when only
   that is used, e.g. setting %al as "hidden" counter of xmm registers used
   when calling a varargs function, or test %ax after fnstw?

I think it's good as long as you read the small register after possibly writing the large one. Writing the small register and reading the large one later has performance penalties, instead.

o Would it be a good idea to either add new interfaces, or change the
   existing one? e.g. jit_prepare and jit_prolog would be better with 3
   arguments,to properly calculate the stack offsets, when keeping the stack 
aligned at
   16 bytes, otherwise, it requires a not so clear logic, to "intercept" the
   first call to jit_pusharg_t, jit_arg_t and/or jit_allocai.

Can you explain exactly why?

   I understand that, to some extent, I am adding significant extra
complexity to lightning, by adding support to any number of arguments
for example.

No, your work is much appreciated, even though I'm wondering myself if you wouldn't have made your life easier by using LLVM...


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