[LLVMdev] Valid debug information being deleted by DAGCombiner

John Criswell criswell at illinois.edu
Thu Apr 14 19:07:23 PDT 2011

On 4/14/11 8:22 PM, Villmow, Micah wrote:
> Found another bitcode file where a debug symbol is being dropped.
> In the attached bitcode file, the variable gid is not in the debug output.

Dumb question: Have you looked to see if mem2reg is destroying (or not 
maintaining) the debug information of interest (or put another way, was 
the variable gid promoted to an LLVM register and therefore had its 
debug information destroyed)?

I haven't used LLVM's new debug facilities, so my knowledge is out of 
date, but I think optimizations are still permitted to remove debug info.

-- John T.

> *From:*llvmdev-bounces at cs.uiuc.edu 
> [mailto:llvmdev-bounces at cs.uiuc.edu] *On Behalf Of *Villmow, Micah
> *Sent:* Thursday, April 14, 2011 5:31 PM
> *To:* llvmdev at cs.uiuc.edu
> *Subject:* [LLVMdev] Valid debug information being deleted by DAGCombiner
> I am working on some debug problems that we are seeing with the x86 
> backend and OpenCL.
> The input is linked.bc. There are three debug values, ip, tid and gid.
> llc -march=x86 linked.bc -o linked-x86.s <-- assembly file has all 
> three values in the debug info section
> However, if I attempt to optimize the bitcode with the following command:
> opt -disable-opt -inline-all -mem2reg linked.bc -o optimized.bc
> llc -march=x86 optimized.bc -o optimized-x86.s <-- Assembly file only 
> has ip and gid in the debug info section.
> Any idea on how to get this to work? I've attached the output, which 
> is missing the 'tid' debug variable.
> Thanks,
> Micah
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