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From Egor Pasko <egor.pa...@gmail.com>
Subject Re: [general] GSoC 2008 Refactor Java Bytecode Translator
Date Mon, 31 Mar 2008 12:20:35 GMT
On the 0x417 day of Apache Harmony Okonechnikov Konstantin wrote:
> On 29 Mar 2008 15:11:14 +0300, Egor Pasko <egor.pasko@gmail.com> wrote:
> 
> 
> > Another idea: if you prefer not to start from the IRBuilder
> > refactoring, there is an alternative way. The task is to separate
> > JavaLabelPrepass into two passes:
> > 1. marking basic blocks
> > 2. data flow analysis
> 
> 
> Well, I have decided to start with IRBuilder.

nice! I love that.

> I suppose that developing the translator will require much more
> time,

truly

> and it will be better not to interrupt this process.

pretty logical :)

> But if it is essentially to divide JavaLabelPrepass
> at first, I could start with it.

obviously, not essential, I would rather recomment to start from IRBuilder.

> And I have some more questions:
> 1) What for do we need LabelInst,

there is a convention that LabelInst stands as the first instruction
in each basic block, stores the block name, type and reference-to.

You can find it in printed HIR like "I44:L13: bcmap:5"

For example, you can write:
(LabelInst*)node->getFirstInst())->isCatchLabel() to know if the block
is a catch block.

Catch blocks correspond to exception handlers. CatchLabelInst (which
is a LabelInst in catch block) keeps information about the exact type
of the exception handler)

> what is IRBuilder::currentLabel? Is it some kind of node index?

yes! IRBuilder is stateful, it appends instructions to the current
node denoted by currentLabel.

> ( IrBuilder::AppenInst uses it to get the node for appending
> instructions) 2) As I understood CSE is a part of optimization. Do
> we need to remove it? 
>
> If yes, IrBuilder::CSEHashTable serves only this purpose, doesn't
> it?

yes, it is private. CSE is done locally in IRBuilder, cseHashTable is
cleared on each new basic block.

>  3) What for does Simplifier need to propgate source operands
> copies?

well, to always propagate is just a cheap optimization. Reduces
expression sizes and makes successful cseHashTable searches more
often.

>  Didn't find out yet how the translator interacts with IrBuilder, continue
> working on this subject.

-- 
Egor Pasko


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