llvm dev - Jun 2007 - [LLVMdev] Address of label

Hello,

 

I search information in order to access address (i.e. value) of label directly
in llvm assembler file.

This can be useful to realize jump table from address, etc.

 

I generate the file branch.ll from a C file.

In this file, we saw that branches are realized by affecting virtually an id to
each label and use a switch in order to find the right target.

I want to know if there is another way to do this, for instance, by accessing
the address of label and to branch directly to it?

 

In order to optimize the program (to decrease the cost of branch dispatch), I
use the following command line:

llvmc -O5 -o branch_opt branch.bc

llc -march=arm -mcpu=arm1136j-s -mattr=+v6 -f -o branch_opt.s branch_opt.bc

 

In the optimized program (branch_opt.arm),  I saw that all branches are not
suppressed.

I want to know, if it is possible to suppress the remaining useless branches? if
yes, how ?

 

Thanks in advance.

 

Mikaël.

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This question needs an FAQ. This is the fourth time I've seen this 
question asked on llvm-dev. Could someone in-the-know write a succinct 
FAQ on this topic and add it to the documentation (similarly to the one 
I did for GEP)? I think that would help answer these kinds of questions 
in the future.

Mikael: sorry, I don't have the answer, but I'm sure someone will 
(again!) answer this question :)

Reid.

Peltier, Mikael wrote:
> Hello,
>
> I search information in order to access address (i.e. value) of label 
> directly in llvm assembler file.
>
> This can be useful to realize jump table from address, etc.
>
> I generate the file /branch.ll/ from a C file.
>
> In this file, we saw that branches are realized by affecting virtually 
> an id to each label and use a switch in order to find the right target.
>
> I want to know if there is another way to do this, for instance, by 
> accessing the address of label and to branch directly to it?
>
> In order to optimize the program (to decrease the cost of branch 
> dispatch), I use the following command line:
>
> /llvmc –O5 –o branch_opt branch.bc/
>
> /llc –march=arm –mcpu=arm1136j-s –mattr=+v6 –f –o branch_opt.s 
> branch_opt.bc/
>
> In the optimized program (/branch_opt.arm/), I saw that all branches 
> are not suppressed.
>
> I want to know, if it is possible to suppress the remaining useless 
> branches? if yes, how ?
>
> Thanks in advance.
>
> Mikaël.
>
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