llvm dev - Sep 2018 - [DWARF] .debug_loc tracking of variable location

Hello all, could someone point me in the right direction? I am not 
completely sure I understand the process of tracking variable location 
(I mean in LLVM code). When we are transforming IR to machine-specific 
code and assembly how do we exactly track the location of a variable (in 
terms of .debug_loc section). At which classes/functions should I look?

To be more specific: I am trying to debug 
https://bugs.llvm.org/show_bug.cgi?id=38714 but currently I am kind of 
stuck.

-- 
Best Regards,

Victor Leschuk | Software Engineer | Access Softek

Hi Victor,
> On Sep 25, 2018, at 10:29 AM, Victor Leschuk via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hello all, could someone point me in the right direction? I am not
completely sure I understand the process of tracking variable location (I mean
in LLVM code). When we are transforming IR to machine-specific code and assembly
how do we exactly track the location of a variable (in terms of .debug_loc
section). At which classes/functions should I look?
I’m not very familiar with the backend, but hopefully you’ll find these notes
useful (& perhaps others can chime in with corrections).

There’s an analysis called LiveDebugVariables which plays an important role in
tracking locations for debug values. It’s invoked both before and after register
allocation (see VirtRegRewriter). Before RA, it builds a location list (a map
from PC ranges to registers or stack slots) for every debug variable. During RA,
these location lists are updated: vregs are mapped to physical
ones/killed/copied etc. After RA, LiveDebugVariables inserts DBG_VALUE
instructions into the program in a way that (should) accurately & completely
convey the information in its location lists.

> To be more specific: I am trying to debug
https://bugs.llvm.org/show_bug.cgi?id=38714 but currently I am kind of stuck.
I haven’t looked at this too closely, but I think it’d be worth looking at the
output from `-debug-only=livedebugvars`. Why isn’t the location list of `argc`
split when it’s moved to w22? Where is that copy introduced, and is that code
updating the LDV analysis correctly?

vedant

> 
> -- 
> Best Regards,
> 
> Victor Leschuk | Software Engineer | Access Softek
> 
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