Re: [rvm-research] How to fix buggy SSA

Hi,

  I need to modify the code in SSA form and get problems. So I poked around and here I made my issue more specific with the hope someone could guess where the problem might be:

Observation 1: in opt compiler, if I create a phase where I insert a call to an empty function before every getfield (or putfield, getstatic, putstatic) in SSA form, like the following, I get a crash on some benchmarks.

ir.options.SSA = true;
new SSATuneUp().perform(ir);
// insert "call dummy()" before every getfield in the IR, where dummy() does nothing
new LeaveSSA().perform(ir);
ir.options.SSA = false;

Observation 2: if I insert a fence instead of a function call, everything works fine.

Observation 3: if I still insert function calls but in non-SSA form, everything works fine.

I used the default SSATuneUp configuration, aka, scalars only.

Any idea would be appreciated. Thanks.

- Lei

On Apr 26, 2013, at 11:02 AM, Erik Brangs wrote:

> Hi,
> 
> On 24.04.2013 17:03, Lei Zhao wrote:
>> It seems SSA is buggy in the opt compiler.
> 
> Yes, that's why it's disabled by default.
> 
>> I need to have a working
>> SSA for my project but unfortunately have no clue where to start fixing
>> it. 
> 
> I assume that you only need scalar SSA. IIRC the heap-array SSA form is
> considered so broken that it would be easier to rewrite it.
> 
>> Could someone familiar with this give me some advice? Thanks.
> 
> If you haven't done so already, you could search the researchers mailing
> list archive for information about SSA. There were various threads about
> it in the past few months. IIRC David Grove and Ian Rogers answered the
> bulk of the questions.
> 
> 
> Kind regards,
> 
> Erik Brangs
> 
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