llvm dev - Sep 2009 - [LLVMdev] LLVM SSA

Hi,

I am wondering if there are options that can be given to LLVM can be used to
generate code that is not in SSA, but in plain 3-address form ?  (for
example, if there is an existing pass that does the register allocation and
dead variable elimination)

For example, if I have:

int x = 0;

void main()
{
   x++;
   x++;
}

I guess, if that is not the case, then, one needs to write their own pass.

I have written a small pass on the existing IR, but my goal now is to get it
to use as few variables as possible.

thanks,
Martin.
-- 
View this message in context:
http://www.nabble.com/LLVM-SSA-tp25621668p25621668.html
Sent from the LLVM - Dev mailing list archive at Nabble.com.

ivtm <martinaide1 at yahoo.com> writes:
> I am wondering if there are options that can be given to LLVM can be used
to
> generate code that is not in SSA, but in plain 3-address form ?  (for
> example, if there is an existing pass that does the register allocation and
> dead variable elimination)
>
> For example, if I have:
>
> int x = 0;
>
> void main()
> {
>    x++;
>    x++;
> }
>
> I guess, if that is not the case, then, one needs to write their own pass.
Why do you want to avoid SSA?

SSA on LLVM is much simpler than it seems, the API makes generating SSA
natural, almost not noticing it. Your above example is trivial. Go to
http://www.llvm.org/demo and see how your C/C++ code is translated to
LLVM IR (pay attention to the options available on the web form).

And of course there are passes for register allocation, dead variable
elimination and more.

[snip]

-- 
Óscar

I am familiar with the LLVM IR a little bit and I am parsing much more
complex examples. I just gave this example, to show that I would like to
have only 1 variable, not 2, the way SSA would generate it.
I am actually using LLVM purely as a front end to translate to .bc files and
then I have my own parser from there.

At any rate, is there an option to the llvm-gcc --emit-llvm to tell it to
produce .bc files that are at least space optimized (or even better, not in
SSA form) ?

thanks


Óscar Fuentes wrote:
> 
> ivtm <martinaide1 at yahoo.com> writes:
> 
>> I am wondering if there are options that can be given to LLVM can be
used
>> to
>> generate code that is not in SSA, but in plain 3-address form ?  (for
>> example, if there is an existing pass that does the register allocation
>> and
>> dead variable elimination)
>>
>> For example, if I have:
>>
>> int x = 0;
>>
>> void main()
>> {
>>    x++;
>>    x++;
>> }
>>
>> I guess, if that is not the case, then, one needs to write their own
>> pass.
> 
> Why do you want to avoid SSA?
> 
> SSA on LLVM is much simpler than it seems, the API makes generating SSA
> natural, almost not noticing it. Your above example is trivial. Go to
> http://www.llvm.org/demo and see how your C/C++ code is translated to
> LLVM IR (pay attention to the options available on the web form).
> 
> And of course there are passes for register allocation, dead variable
> elimination and more.
> 
> [snip]
> 
> -- 
> Óscar
> 
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> 
> 
-- 
View this message in context:
http://www.nabble.com/LLVM-SSA-tp25621668p25625857.html
Sent from the LLVM - Dev mailing list archive at Nabble.com.