Wenbin Zhang
2010-Aug-27 21:28 UTC
[LLVMdev] how to check whether from basicblock A we can go to basicblock B within the same function?
----- Original Message ----- From: "John Criswell" <criswell at illinois.edu> To: "Wenbin Zhang" <zhangwen at cse.ohio-state.edu> Cc: <llvmdev at cs.uiuc.edu> Sent: Friday, August 27, 2010 5:09 PM Subject: Re: [LLVMdev] how to check whether from basicblock A we can go to basicblock B within the same function?> Wenbin Zhang wrote: >> Dear all, >> Is there a way to check whether we can go from A to B within a >> function when I'm writing a pass? > > I assume you are asking whether control flow can pass from BasicBlock A > to BasicBlock B. In that case, yes: all you need to do is look at the > terminator instruction of BasicBlock A and see if it can branch to > BasicBlock B.Yes, also switch and invoke instruction have the similar effects. So does it mean that I need to recursively traverse all the possible destinations from A (following the terminator instructions) to see whether I can reach B? Thanks.> > There's a new indirect branch instruction; I don't believe it is used > very often. You might have to handle those specially, but I'll let > others comment on that. > > -- John T. > >> Thanks. >> Best, >> --Wenbin >Best, --Wenbin
John Criswell
2010-Aug-27 21:57 UTC
[LLVMdev] how to check whether from basicblock A we can go to basicblock B within the same function?
Wenbin Zhang wrote:> ----- Original Message ----- > From: "John Criswell" <criswell at illinois.edu> > To: "Wenbin Zhang" <zhangwen at cse.ohio-state.edu> > Cc: <llvmdev at cs.uiuc.edu> > Sent: Friday, August 27, 2010 5:09 PM > Subject: Re: [LLVMdev] how to check whether from basicblock A we can go to > basicblock B within the same function? > > > >> Wenbin Zhang wrote: >> >>> Dear all, >>> Is there a way to check whether we can go from A to B within a >>> function when I'm writing a pass? >>> >> I assume you are asking whether control flow can pass from BasicBlock A >> to BasicBlock B. In that case, yes: all you need to do is look at the >> terminator instruction of BasicBlock A and see if it can branch to >> BasicBlock B. >> > > Yes, also switch and invoke instruction have the similar effects. >Every basic block ends with a terminator instruction that indicates which basic block or basic blocks it should branch to next. Switch, invoke, and branch are all terminator instructions. There may be more that I don't remember.> So does it mean that I need to recursively traverse all the possible > destinations from A (following the terminator instructions) to see whether I > can reach B? >Are you wanting to know if B is a successor of A in the control flow graph, or are you wanting to know if there is a path from A to B in the control flow graph? The first question only requires that you look at the terminator instruction of basic block A. The second question requires that you traverse the control-flow graph, starting at A, and see if there is a path from A to B. -- John T.> Thanks. > > >> There's a new indirect branch instruction; I don't believe it is used >> very often. You might have to handle those specially, but I'll let >> others comment on that. >> >> -- John T. >> >> >>> Thanks. >>> Best, >>> --Wenbin >>> > > Best, > --Wenbin > >
Guoliang Jin
2010-Aug-27 22:05 UTC
[LLVMdev] how to check whether from basicblock A we can go to basicblock B within the same function?
> Every basic block ends with a terminator instruction that indicates > which basic block or basic blocks it should branch to next. Switch, > invoke, and branch are all terminator instructions. There may be more > that I don't remember. >Why not just use the predecessor and successor iterator? http://llvm.org/docs/ProgrammersManual.html#iterate_preds
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