[PATCH] D18477: Drop debug info for DISubprograms that are not referenced by anything

[Adrian Prantl via llvm-commits]

> On Mar 25, 2016, at 12:41 PM, David Blaikie <dblaikie at gmail.com> wrote:
> 
> 
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> On Fri, Mar 25, 2016 at 12:33 PM, Adrian Prantl via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>> aprantl added a comment.
>> 
>> Digging further through the commit (and radar) history this feature has been added to support dtrace.
>> Instead of having everyone pay for this, I think it would be a more appropriate resolution for this to add something like a -gfull option to clang that retains every type in the compile unit.
> 
> Possibly - but is that what dtrace needs? It'll be a /lot/ of debug info... but yeah, having some filtering flags (with the default being what you are going for in this patch - if it's referenced by live code, we include it (types, subprograms, etc)).

Looking at the clang sources I noticed that the clang driver already accepts a -gfull option for gcc compatibility; it translates to -fno-eliminate-unused-debug-symbols and is ignored by cc1.

I think it would make sense to pass this option through to LLVM and move the collectDeadVariables logic from the DwarfUnit.cpp into GlobalDCE.cpp where dead functions are being deleted. When -fno-eliminate-unused-debug-symbols is present, GlobalDCE can insert the types of all local variables attached to the dead Function’s DISubprogram to the DICompileUnit’s set of retained types, thus preserving the spirit of r107027.

-- adrian