[LDV][RAGreedy] Inform LiveDebugVariables about new VRegs added by InlineSpiller

Summary:
Make sure RAGreedy informs LiveDebugVariables about new VRegs
that is introduced at spill by InlineSpiller.

Consider this example

 LDV: !"var"	 [48r;128r):0 Loc0=%2

 48B   %2 = ...
 ...
 128B  %7 = ADD %2, ...

If %2 is spilled the InlineSpiller will insert spill/reload
instructions and introduces some new vregs. So we get

 48B   %4 = ...
 56B   spill %4
 ...
 120B  reload %5
 128B  %3 = ADD %5, ...

In the past we did not inform LDV about this, and when reintroducing
DBG_VALUE instruction LDV still got information that "var" had the
location of the spilled register %2 for the interval [48r;128r).
The result was bad, since we mapped "var" to the spill slot even
before the spill happened:

 %4 = ...
 DBG_VALUE %spill.0, !"var"
 spill %4 to %spill.0
 ...
 reload %5
 %3 = ADD %5, ...

This patch will inform LDV about the interval split introduced
due to spilling. So the location map in LDV will become

 !"var"	[48r;56r):1 [56r;120r):0 [120r;128r):2 Loc0=%2 Loc1=%4 Loc2=%5

And when inserting DBG_VALUE instructions we get

 %4 = ...
 DBG_VALUE %4, !"var"
 spill %4 to %spill.0
 DBG_VALUE %spill.0, !"var"
 ...
 reload %5
 DBG_VALUE %5, !"var"
 %3 = ADD %5, ...

Fixes: https://bugs.llvm.org/show_bug.cgi?id=38899

Reviewers: jmorse, vsk, aprantl

Reviewed By: jmorse

Subscribers: dstenb, wuzish, MatzeB, qcolombet, nemanjai, hiraditya, jsji, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69584