[llvm-commits] [llvm] r59011 - in /llvm/trunk: include/llvm/Transforms/Utils/DbgInfoUtils.h lib/Transforms/Utils/DbgInfoUtils.cpp

[Chris Lattner]

On Nov 17, 2008, at 9:58 AM, Devang Patel wrote:

>
> On Nov 15, 2008, at 10:41 PM, Chris Lattner wrote:
>
>>
>> On Nov 10, 2008, at 4:53 PM, Devang Patel wrote:
>>
>>> Author: dpatel
>>> Date: Mon Nov 10 18:53:02 2008
>>> New Revision: 59011
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=59011&view=rev
>>> Log:
>>> Add utility routines to remove dead debug info.
>>
>> Hi Devang,
>>
>> Instead of making this a "minipass" which is called by other  
>> passes, why not just make instcombine (and only instcombine) do  
>> this?  Instcombine runs many times in a typical compilation, and it  
>> can do this very cheaply (cost proportional to the number of debug  
>> intrinsics, instead of scanning entire functions even when there  
>> are none).
>
> However we want
> 	$ opt -adce foo.bc -o foo.optimzed.bc
> to preserve valid debug info.

How wouldn't it?


>>> +    // If a llvm.dbg.stoppoint is placed just before an  
>>> unconditional
>>> +    // branch then remove the llvm.dbg.stoppoint intrinsic.
>>> +    else if (BranchInst *UC = dyn_cast<BranchInst>(Next)) {
>>> +      if (UC->isUnconditional()
>>
>> Why?  This doesn't seem right.
>
> If it is a unconditional branch then sooner or later the cfg will be  
> simplified and this may get in a way for a pass doing simple clean.

I don't understand.  You're saying that the intrinsic will prevent  
simplifycfg from doing a transformation?  That seems like a problem  
that should be fixed in the simplifycfg pass.

-Chris