[LLVMdev] [PATCH] Support asm comment output

David Greene dag at cray.com
Mon Jul 13 13:34:53 PDT 2009

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)?
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.

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.

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.

Of course, our requirements aren't the same as everyone else's requirements
so I understand that there may be tighter tolerances in some use cases.  
Examples of where the MachineInstr comments might be a problem would be 


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