[PATCH] ADCE: Remove debug info intrinsics in dead scopes

[Duncan P. N. Exon Smith via llvm-commits]

> On 2016-Mar-29, at 12:58, Adrian Prantl <aprantl at apple.com> wrote:
> 
>> 
>> On Mar 29, 2016, at 12:48 PM, Adrian Prantl via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>> 
>> 
>>> On Mar 29, 2016, at 12:34 PM, Duncan P. N. Exon Smith <dexonsmith at apple.com> wrote:
>>> 
>>> During ADCE, track which debug info scopes still have live references
>>> from the code, and delete debug info intrinsics for the dead ones.
>>> 
>>> These intrinsics describe the locations of variables (in registers or
>>> stack slots).  If there's no code left corresponding to a variable's
>>> scope, then there's no way to reference the variable in the debugger and
>>> it doesn't matter what its value is.
>>> 
>>> I add a DEBUG printout when the described location in an SSA register,
>>> in case it helps some trying to track down why locations get lost.
>>> However, we still delete these; the root problem is that the scope
>>> itself isn't attached to any real code.
>> 
>> Thanks!
>> 
>>> 
>>> <0001-ADCE-Remove-debug-info-intrinsics-in-dead-scopes.patch>
>> 
>> One review comment: There should also be a testcase where the scope is in an inlined function.
> 
> Thinking of to, there should also be a negative test where the dbg intrinsic is the last remaining instruction in its scope but there is another instruction in a child-scope of the intrinsic’s scope, thus preventing the optimization from happening.
> 
> -- adrian

Added both cases.  Please have another look!

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