[PATCH] Change representation of instruction ranges where variable is accessible.

[Alexey Samsonov]

Thanks for the review!

================
Comment at: lib/CodeGen/AsmPrinter/DwarfDebug.cpp:1385
@@ -1384,3 @@
-        assert(MI.getNumOperands() > 1 && "Invalid machine instruction!");
-        // Keep track of user variables in order of appearance. Create the
-        // empty history for each variable so that the order of keys in
----------------
David Blaikie wrote:
> Alexey Samsonov wrote:
> > David Blaikie wrote:
> > > Did the need for this ahead-of-time initialization of the MapVector go away in your change? How?
> > Yes, it went away. Need for ahead-of-time initialization is somewhat ugly, this really should be responsibility of calculateDbgValueHistory().
> > 
> > calculateDbgValueHistory() traverses all machine instructions in function, and the first time we see a DBG_VALUE for a new variable, it will
> > be added to map by the call to "startInstrRange()".
> > 
> Was there a reason this wasn't possible previously? (I seem to recall this was kept around in the previous commit to provide stability to the output? - why is the "on first use" order stable now?)
> 
> It might've been helpful to pull this out as a separate commit if it's an isolated piece of cleanup (if it's not isolated I wouldn't mind unedrstanding what is it about the rest of your change that changed things here so that this was no longer needed)
Good point, looks like it's possible with current code as well (apparently, it became possible as code evolved during the review).
I will put this into a separate commit.

http://reviews.llvm.org/D3861