[LLVMdev] Transforming SwitchInst to BranchInst (original) (raw)

Chen Li meloli87 at gmail.com
Fri Jul 24 11:15:26 PDT 2015

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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