llvm dev - Sep 2009 - [LLVMdev] disable insertion of unreachables

Hello all,

LLVM inserts unreachable instructions after every call to a terminating
function. Is there a way to disable this feature so that it treats
terminating function calls like any other function call, so the unreachable
instruction would not be inserted? Unfortunately, simply removing the
unreachable instructions after the fact would not suffice for my needs
because I need to preserve the original control flow of the program. That
is, I need to know the instruction that would have been executed if the call
to the terminating function didn't actually terminate the program.

Thanks!

Max
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What do you mean by "terminating function call"?  Is it one with the
"noreturn" attribute?  if so, the assembly language docs say that
program behavior is undefined if such a function ever returns.  If
your function could possibly return, it needs to not have that
attribute.

On Sun, Sep 6, 2009 at 4:49 PM, Max
Stonebraker<max.stonebraker at gmail.com> wrote:
> Hello all,
>
> LLVM inserts unreachable instructions after every call to a terminating
> function. Is there a way to disable this feature so that it treats
> terminating function calls like any other function call, so the unreachable
> instruction would not be inserted? Unfortunately, simply removing the
> unreachable instructions after the fact would not suffice for my needs
> because I need to preserve the original control flow of the program. That
> is, I need to know the instruction that would have been executed if the
call
> to the terminating function didn't actually terminate the program.
>
> Thanks!
>
> Max
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>

> if so, the assembly language docs say that
> program behavior is undefined if such a function
> ever returns.
Yes, that's true, but for some static analysis applications such as control
dependence analysis for programs that have arbitrary interprocedural control
flow, one needs these additional non-executable control flow edges from
noreturn functions to their immediate CFG successor.

Is there any way to avoid having the unreachables inserted in the first
place?

Max


On Sun, Sep 6, 2009 at 2:55 PM, Kenneth Uildriks <kennethuil at
gmail.com>wrote:
> What do you mean by "terminating function call"?  Is it one with
the
> "noreturn" attribute?  if so, the assembly language docs say that
> program behavior is undefined if such a function ever returns.  If
> your function could possibly return, it needs to not have that
> attribute.
>
> On Sun, Sep 6, 2009 at 4:49 PM, Max
> Stonebraker<max.stonebraker at gmail.com> wrote:
> > Hello all,
> >
> > LLVM inserts unreachable instructions after every call to a
terminating
> > function. Is there a way to disable this feature so that it treats
> > terminating function calls like any other function call, so the
> unreachable
> > instruction would not be inserted? Unfortunately, simply removing the
> > unreachable instructions after the fact would not suffice for my needs
> > because I need to preserve the original control flow of the program.
That
> > is, I need to know the instruction that would have been executed if
the
> call
> > to the terminating function didn't actually terminate the program.
> >
> > Thanks!
> >
> > Max
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
> >
> >
>
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