llvm dev - Apr 2014 - [LLVMdev] Emit code for 'unreachable'

Hi,
Is it somehow possible to have LLVM emit machine code for the
'unreachable'
IR instruction, which would assert that it indeed never gets reached?

Vadim
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Hello

x86 backend emits ud2 instruction in this case

On Mon, Apr 14, 2014 at 1:46 PM, Vadim Chugunov <vadimcn at gmail.com>
wrote:
> Hi,
> Is it somehow possible to have LLVM emit machine code for the
'unreachable'
> IR instruction, which would assert that it indeed never gets reached?
>
> Vadim
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>


-- 
With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University

On Mon, Apr 14, 2014 at 2:46 AM, Vadim Chugunov <vadimcn at gmail.com>
wrote:
> Hi,
> Is it somehow possible to have LLVM emit machine code for the
'unreachable'
> IR instruction, which would assert that it indeed never gets reached?
Take a look at LLVM's implementation of an "llvm_unreachable"
macro to
see how the LLVM project does this.

Essentially lllvm's unreachable IR instruction is /not/ an assert or
check, it's a compiler hint. So at -O0, LLVM's llvm_unreachable
compiles to a check/assert, at higher optimization levels it compiles
to an intrinsic that is lowered to an unreachable IR instruction and
is used to assist optimization.

- David

I am not seeing this happening, at least not for unreachables that
follow calls to 'noreturn' functions.

On Apr 14, 2014, at 3:48 AM, Anton Korobeynikov <anton at
korobeynikov.info> wrote:
> Hello
>
> x86 backend emits ud2 instruction in this case
>
> On Mon, Apr 14, 2014 at 1:46 PM, Vadim Chugunov <vadimcn at
gmail.com> wrote:
>> Hi,
>> Is it somehow possible to have LLVM emit machine code for the
'unreachable'
>> IR instruction, which would assert that it indeed never gets reached?
>>
>> Vadim
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
>
> --
> With best regards, Anton Korobeynikov
> Faculty of Mathematics and Mechanics, Saint Petersburg State University