llvm dev - Apr 2009 - [LLVMdev] debug stoppoint nodes with -fast option

I need to generate line number debug information for PIC16 target. 
PIC16 does not support dwarf format. It supports coff format. So I need 
to custom handle the STOPPOINT nodes. Without -fast option the STOPPOINT 
nodes are not created in dag because of the below check in 
SelectionDAGBuild.cpp
     if (Fast)
        DAG.setRoot(DAG.getDbgStopPoint(getRoot(),
 If I give -fast option then the Fast flag is true, but the dag doesn't 
contain STOPPOINT nodes. If  I have simple loads and stores in source 
code, the dag doesn't contain them too. Why are these nodes not being 
created?

Thanks
Vasudev

On Apr 5, 2009, at 11:54 PMPDT, vasudev wrote:
> I need to generate line number debug information for PIC16 target.
> PIC16 does not support dwarf format. It supports coff format. So I  
> need
> to custom handle the STOPPOINT nodes. Without -fast option the  
> STOPPOINT
> nodes are not created in dag because of the below check in
> SelectionDAGBuild.cpp
>     if (Fast)
>        DAG.setRoot(DAG.getDbgStopPoint(getRoot(),
> If I give -fast option then the Fast flag is true, but the dag doesn't
> contain STOPPOINT nodes.
Right.  Currently, the way we tell whether optimization was requested  
at the command line level is to look at -fast; -O0 == -fast.
The stoppoint nodes enforce an ordering of loads and stores  
corresponding to the original source, which means that putting them in  
without -fast would lead to codegen (scheduling) differences between - 
O and -O -g.  We don't want that.

Instead, the debug info is transferred at this point from stoppoint  
nodes to the DebugLoc field in each MachineInstr node.  You should  
probably use that.

(The current state of debug info with -O is that we think -g never  
affects codegen; violations of that should be reported as bugs.  The  
quality of the debug info has not been worked on much and is  
problematic.)
> If  I have simple loads and stores in source
> code, the dag doesn't contain them too. Why are these nodes not being
> created?

I don't know.  Something to do with your target, they appear for me.

Thanks for the info regarding DebugLoc field.  Another related question 
that I have is  regarding debug info for local variables.  With -fast 
option, ISD::DECLARE nodes are created in DAG for debug info of local 
variables. I am planning to custom handle these nodes, get the required 
info from llvm.dbg.variable global address and emit it in ISel.  But 
without -fast option ISD::DECLARE nodes are not created. How can i 
access the debug info for local variables in that case? Is it available 
directly somewhere in AsmPrinter  like the debug info for  global variables?


Dale Johannesen wrote:
> On Apr 5, 2009, at 11:54 PMPDT, vasudev wrote:
>
>   
>> I need to generate line number debug information for PIC16 target.
>> PIC16 does not support dwarf format. It supports coff format. So I  
>> need
>> to custom handle the STOPPOINT nodes. Without -fast option the  
>> STOPPOINT
>> nodes are not created in dag because of the below check in
>> SelectionDAGBuild.cpp
>>     if (Fast)
>>        DAG.setRoot(DAG.getDbgStopPoint(getRoot(),
>> If I give -fast option then the Fast flag is true, but the dag
doesn't
>> contain STOPPOINT nodes.
>>     
>
> Right.  Currently, the way we tell whether optimization was requested  
> at the command line level is to look at -fast; -O0 == -fast.
> The stoppoint nodes enforce an ordering of loads and stores  
> corresponding to the original source, which means that putting them in  
> without -fast would lead to codegen (scheduling) differences between - 
> O and -O -g.  We don't want that.
>
> Instead, the debug info is transferred at this point from stoppoint  
> nodes to the DebugLoc field in each MachineInstr node.  You should  
> probably use that.
>
> (The current state of debug info with -O is that we think -g never  
> affects codegen; violations of that should be reported as bugs.  The  
> quality of the debug info has not been worked on much and is  
> problematic.)
>
>   
>> If  I have simple loads and stores in source
>> code, the dag doesn't contain them too. Why are these nodes not
being
>> created?
>>     
>
>
> I don't know.  Something to do with your target, they appear for me.
>
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