[PATCH] D11958: Add a -gmodules option to the clang driver.

Adrian Prantl via cfe-commits cfe-commits at lists.llvm.org
Wed Aug 19 13:22:09 PDT 2015


> On Aug 19, 2015, at 1:12 PM, David Blaikie <dblaikie at gmail.com> wrote:
> 
> 
> 
> On Tue, Aug 11, 2015 at 1:49 PM, Adrian Prantl <aprantl at apple.com <mailto:aprantl at apple.com>> wrote:
> aprantl created this revision.
> aprantl added reviewers: dblaikie, echristo.
> aprantl added a subscriber: cfe-commits.
> aprantl set the repository for this revision to rL LLVM.
> 
> This patch adds a -gmodules option to the driver and a -dwarf-ext-refs to cc1 to enable the use of external type references in the debug info (a.k.a. module debugging).
> 
> The driver expands -gmodules to "-g -fmodule-format=obj -dwarf-ext-refs" and passes that to cc1.
> Most options that start with -g (e.g., -gdwarf-2) also turn on -g, and module requires object-container-wrapped modules, "-dwarf-ext-refs" been the actual low-level option for turning on external type references.
> 
> Rationale for the choice of names (and this is really all there is to review in this patch):
> "-gmodules": is meant to pair nicely with "-fmodules"
> "-dwarf-ext-refs": Fits into the naming scheme of similar options like "-dwarf-column-info" and "-dwarf-debug-flags". Spelling out the option "-dwarf-external-type-references" seemed to be overkill.
> 
> Sounds reasonable - and the flag will be for more than just types eventually anyway (specifically references to members (functions, etc) of types too).
>  
> All this does at the moment is set a flag codegenopts. Having this flag in place is a prerequisite for emitting debug info into modules: The debug info for a module needs to use external type references for types defined in (other) modules or we would violate the minimal deserialization requirements (cf. test/PCH/check-deserializations.cpp).
> 
> Could you explain what you mean by "violate the minimal deserialization requirements”

There are tests in the testsuite to ensure that when deserializing a type from a module, only the bare minimum is actually deserialized. For example:

a.h
class A {};

b.h
class B { A a; };

When emitting debug info for B we need to emit an external reference for A instead of recursively emitting A (and thus “illegally” deserializing A from a.pcm).

> 
> Mechanically, the patch looks fine/exactly what you'd expect. Feel free to commit whenever you're ready.

thanks,
adrian

>  
> 
> Repository:
>   rL LLVM
> 
> http://reviews.llvm.org/D11958 <https://urldefense.proofpoint.com/v2/url?u=http-3A__reviews.llvm.org_D11958&d=BQMFaQ&c=eEvniauFctOgLOKGJOplqw&r=cTx6f1tAfqPeajYunFWp7_8ot79RnHyNteqzig4fXmA&m=OYlTn71sx_aJ_kkl6dcJDmmGe2SZ2AOMtPSiptwqe3M&s=9Oww56T9mtLMfzpO0B3gFzdboCnRX1kVMs8QUq18Tpw&e=>
> 
> Files:
>   docs/CommandGuide/clang.rst
>   include/clang/Driver/CC1Options.td
>   include/clang/Driver/Options.td
>   include/clang/Frontend/CodeGenOptions.def
>   lib/CodeGen/CGDebugInfo.cpp
>   lib/CodeGen/CGDebugInfo.h
>   lib/CodeGen/ObjectFilePCHContainerOperations.cpp
>   lib/Driver/Tools.cpp
>   lib/Frontend/CompilerInvocation.cpp
>   test/Driver/debug-options.c

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