[LLVMdev] LLVM SSA

[ivtm]

I tried using the mem2reg pass with  opt,

e.g. opt -reg2mem x.bc > x2.bc

where x.bc was produced with:

llvm-gcc -O2 -emit-llvm -c x.c -o x.bc

This did not reduce the # of variables in x2.bc

I use -O2 because it produces the least # of instructions and hence the
least # of new SSA virtual registers.

Do you have a set of options to give to llvm-gcc or opt in mind ?

My goal is to take a .c file and obtain a .bc file with the smallest # 
(or as small as possible) of variables.

Thanks




Reid Kleckner wrote:
> 
> LLVM IR is always in SSA form.  If you *really* don't want it to be,
> use allocas for everything and then don't run the mem2reg optimization
> pass.  This will represent all of your variables as stack locations
> instead of registers, and it will not be SSA.
> 
> Reid
> 
> On Sat, Sep 26, 2009 at 3:55 PM, ivtm <martinaide1 at yahoo.com> wrote:
>>
>> I tried the -O0 option and I am still getting output in SSA form:
>>
>> I do:
>> llvm-gcc -O0 -emit-llvm -c x.c -o x.bc,
>>
>> and then:
>>
>> llvm-dis x.bc
>>
>>
>>
>>
>> Anton Korobeynikov-2 wrote:
>>>
>>>> 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) ?
>>> Yes, -O0
>>>
>>> --
>>> With best regards, Anton Korobeynikov
>>> Faculty of Mathematics and Mechanics, Saint Petersburg State University
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>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
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>>>
>>>
>>
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