[LLVMdev] Transforming SwitchInst to BranchInst

[Chen Li]

> 
> On Jul 24, 2015, at 10:46 AM, Zhoulai <zell08v at gmail.com> wrote:
> 
> Hi, 
> 
> Are there some built-in LLVM transformation pass, or written library code that transforms LLVM::SwitchInst into if-condition statements (LLVM:: BranchInst)?

There is a -lowerswitch pass that rewrites switch instructions with a sequence of branches. 
http://llvm.org/docs/Passes.html#lowerswitch-lower-switchinsts-to-branches <http://llvm.org/docs/Passes.html#lowerswitch-lower-switchinsts-to-branches>

thanks,
chen



> 
> The purpose of the transformation is that we have a legacy program analyzer that includes an LLVM pass manipulating if-condition statements. Statements of LLVM::SwithchInst should have been handled in the same manner but was not done. Thus to transform these SwitchInst to if-condition looks a viable alternative for us.  
> 
> To illustrate, I give a simple C snippet with 'switch' and the expected transformation.
> ---------------------------------------- 
> Original program: 
> 
>  char grade;
>  ...
>   switch(grade)
>     {
>     case 'A' :
>       printf("Excellent!\n" );
>       break;
>     case 'B' :
>       printf("Well done\n" );
>       break;
>   
>     default :
>       printf("Invalid grade\n" );
>     }
> 
> may be transformed to something like
> 
> if (grad=='A') 
>           printf("Excellent!\n" );
> else if (grad=='B')
>       printf("Well done\n" );
> else 
>        printf("Invalid grade\n" );
> -------------------------------------------------
>  
> Are you aware of such a transformation pass ? Thanks.
> Zhoulai
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