[LLVMdev] Disable the Module Verifier pass?

[Nick Lewycky]

John Criswell wrote:
> Zheng Wang wrote:
>> Hello,
>>
>> Is there anyway to disable the module verifier pass (in llvm-ld and llc)?
>>
>> I got an error as " Instruction does not dominate all uses!".
>> Obviously, there must be something wrong. The module verifier simply
>> aborts `llvm-ld` instead of generating bytecode. If somehow I can
>> disable the module verifier, then I can use llc to produce LLVM
>> assembly code for my program. This will help me to debug my pass.
>>
>
> llc assumes that its input passes verification, so disabling the
> verifier pass in the linker is probably not going to be as helpful as
> you think.
>
> You can, however, disable the verifier in opt.  So, you can do the
> following:
>
> 1) Run opt -std-link-opts -load<your pass.so>  -<your pass name>
> -disable-verify<input.bc>  -f -o<output.bc>
>
> The -std-link-opts option runs the optimization passes used by llvm-ld.
> You can now disassemble output.bc to see what your pass is doing wrong.
>
> If, for some reason, the bitcode writer cannot write your invalid
> bitcode to disk, then you will have to run the above command in the
> debugger.

Not necessarily. The -S option on opt will cause opt to run M->dump() 
for the whole module. This is great because unlike the bitcode writer, 
the module dumper is built to be resilient in the face of invalid IR. 
"opt [...] -disable-verify -S" is the way to debug a bad pass.

And indeed, trying to run the result through llc will simply not work. 
The parser will reject it as invalid.

Nick

   Remove the -disable-verify option so that opt crashes in the
> verifier.  Then use the debugger to examine what is wrong.  Remember
> that many LLVM classes (such as Module, Value, Instruction, BasicBlock,
> and Function) have a dump() method that will print their contents to the
> screen.  So, if using gdb, the verifier crashes because instruction I
> doesn't dominate all of its uses, then you can use:
>
> % call I->dump()
>
> ... to see what the instruction pointed to by I looks like.
>
> -- John T.
>
>> Cheers
>> Zheng
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