llvm dev - Jun 2010 - [LLVMdev] Warnings when using opt for read-only (preserving) passes

Hi,

I've written a FunctionPass that happens to be read-only (preserving):  
It doesn't modify the code in any way; it just does some analysis and  
dumps out the results for each function by overriding  
FunctionPass::print. I now need to make some changes to the pass, and  
these changes will mean that the results cannot be known until all  
functions have been visited. So there's no longer anything to do in  
FunctionPass::print. Instead I only need to call printf in  
FunctionPass::doFinalization to dump the final results.

This presents a minor problem. Taking out FunctionPass::print causes  
"opt -analyze ..." to give warnings: "Pass::print not implemented
for
pass!" Okay, makes sense, but when I take out the -analyze parameter,  
I get another warning: "WARNING: You're attempting to print out a  
bitcode file ..." This also makes sense, because opt assumes my pass  
has modified the code in some way, so it's trying to output the  
modifications.

But how can I get rid of these warnings? I can suppress the second one  
by adding "2> /dev/null" to the opt command, but that suppresses
the
entire error stream, which isn't good. I also tried converting my  
FunctionPass into a ModulePass, and iterating over the functions  
manually, but I ran into problems because I can't seem to require a  
function pass, such as UnifyFunctionExitNodes, to run on a function if  
I'm within a ModulePass.

Any other suggestions? Thanks,

Trevor

Trevor Harmon wrote:
> Hi,
>
> I've written a FunctionPass that happens to be read-only (preserving):
> It doesn't modify the code in any way; it just does some analysis and
> dumps out the results for each function by overriding
> FunctionPass::print. I now need to make some changes to the pass, and
> these changes will mean that the results cannot be known until all
> functions have been visited. So there's no longer anything to do in
> FunctionPass::print. Instead I only need to call printf in
> FunctionPass::doFinalization to dump the final results.
>
> This presents a minor problem. Taking out FunctionPass::print causes
> "opt -analyze ..." to give warnings: "Pass::print not
implemented for
> pass!" Okay, makes sense, but when I take out the -analyze parameter,
> I get another warning: "WARNING: You're attempting to print out a
> bitcode file ..." This also makes sense, because opt assumes my pass
> has modified the code in some way, so it's trying to output the
> modifications.
>
> But how can I get rid of these warnings?
opt -disable-output ...

  I can suppress the second one
> by adding "2>  /dev/null" to the opt command, but that
suppresses the
> entire error stream, which isn't good. I also tried converting my
> FunctionPass into a ModulePass, and iterating over the functions
> manually, but I ran into problems because I can't seem to require a
> function pass, such as UnifyFunctionExitNodes, to run on a function if
> I'm within a ModulePass.
>
> Any other suggestions? Thanks,
>
> Trevor
>
> _______________________________________________
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> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>

On Jun 30, 2010, at 9:10 PM, Nick Lewycky wrote:
> opt -disable-output ...
Thanks, that works nicely.

Any thoughts on why this parameter isn't mentioned in the docs
(http://llvm.org/cmds/opt.html
) or in the "opt --help" output? Was it just an oversight?

Trevor