[LLVMdev] [PATCH] Support asm comment output

Chris Lattner clattner at apple.com
Mon Jul 13 13:49:23 PDT 2009

On Jul 13, 2009, at 1:34 PM, David Greene wrote:

> On Monday 13 July 2009 13:29, David Greene wrote:
>> I forgot about the LLVM instruction information.  That's something  
>> that
>> can't be synthesized by the asmprinter.  Again, we only emit some  
>> of this
>> with special debug flags so we don't carry the original IR around in
>> comments all the time.  :)
> If the FI question can be answered (how do we know it's a spill slot)?

I just responded separately.

> Then the above is the only use I think we don't have a long-term  
> answer for.
> I don't see how asmprinter can synthesize this information.

I agree, but our isel currently doesn't propagate this in any other  
way either.  Lets just defer this issue for now.

> Line numbers are still a problem because we need to propagate the  
> information
> from LLVM IR to MachineInstrs and there's currently no DebugLoc  
> information
> in LLVM IR Instructions.  I'll take a look at the existing DebugLoc  
> and see if
> we can put our LLVM IR line number info there instead of printing it  
> to
> comments early.

Just generate stoppoints like llvm-gcc.

> If it's any comfort, we've been running with this MachineInstr for a
> very long time and done multiple public releases.  We always go  
> through
> asm to do our x86 compiles and no one has ever complained about  
> compile
> time or memory usage in this area (legalize is actually our biggest  
> problem).
> And we compile HUGE source files containing very large functions.

We care most about -O0 compile times, which generally don't use  
legalize or selection dags at all, and use the local register allocator.


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