[LLVMdev] warning from -instcombine

[Chris Lattner]

On Feb 27, 2009, at 1:47 AM, Jay Foad wrote:

> Hi,
>
> I noticed this code in lib/Transforms/Scalar/InstructionCombining.cpp:
>
>      cerr << "WARNING: While resolving call to function '"
>           << Callee->getName() << "' arguments were dropped!\n";
>
> If you're using LLVM as a static compiler, this warning is a bit
> incongruous, because it's not formatted in the same way as warnings
> from the front end, and it isn't suppressed by -w.

I agree that this sucks.  :(

Unfortunately, there is no really good solution for this right now.   
We do not have great location information in the LLVM IR unless debug  
info is around, so it is hard to produce decent diagnostics.

OTOH, this specific warning is very useful, it can identify some  
serious issues that can only be detected at link-time.

Edwin says:
> How about setting an error flag, and error message in the Module, then
> let the caller know the Module is broken?
> Sort of like what should happen on invalid inline assembly  instead of
> abort(), as we already talked about.


I agree. Giving optimizer/codegen a real diagnostics subsystem as  
Edwin proposes does sound like the right first step, even if it  
doesn't fix the "not having location info" problem. This would also  
handle the issues where the code generator will abort when presented  
with invalid inline asm, etc.  If you were using a JIT you could  
recover from this instead of displaying it to the user.

-Chris