r224835 - Initialize CodeGeneratorImpl::Ctx in constructor.

[David Blaikie]

On Thu, Dec 25, 2014 at 9:49 AM, Yaron Keren <yaron.keren at gmail.com> wrote:

> msan uninitialized use diagnostic may be more useful to value variables,
> as nullptr pointer access will core dump without msan. Initializing
> pointers to nullptr is done everywhere in llvm and clang (search for
> '(nullptr)')
>

There are certainly places where initializing to nullptr is necessary
(because the null value is used/tested before any write occurs). And I
don't doubt there are many places where it's unnecessary & done out of
habit/consistency/forward-aovidance of problems (either due to the code
being written before we had MSan, etc - or because the author wasn't aware
of the tradeoffs).


> such as
>
> DIBuilder::DIBuilder(Module &m, bool AllowUnresolvedNodes)
>     : M(m), VMContext(M.getContext()), TempEnumTypes(nullptr),
>       TempRetainTypes(nullptr), TempSubprograms(nullptr), TempGVs(nullptr),
>       DeclareFn(nullptr), ValueFn(nullptr),
>       AllowUnresolvedNodes(AllowUnresolvedNodes) {}
>
> isn't init to nullptr the "right" thing to do?
>

Not necessarily. This isn't a hard-and-fast rule, but we've certainly
pushed back on initializing variables that don't need initialization when
it was motivated by silencing a tool that wasn't smart enough to know that
these initializations weren't needed (such as GCC's warnings).


>
>
> 2014-12-25 18:46 GMT+02:00 David Blaikie <dblaikie at gmail.com>:
>
>> Any particular reason? It's sometimes handy to leave things uninitialized
>> if they stents intended to be read until after some other write - in that
>> way, msan can catch bugs when that constraint is violated.
>> On Dec 25, 2014 3:41 AM, "Yaron Keren" <yaron.keren at gmail.com> wrote:
>>
>>> Author: yrnkrn
>>> Date: Thu Dec 25 05:38:15 2014
>>> New Revision: 224835
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=224835&view=rev
>>> Log:
>>> Initialize CodeGeneratorImpl::Ctx in constructor.
>>>
>>>
>>> Modified:
>>>     cfe/trunk/lib/CodeGen/ModuleBuilder.cpp
>>>
>>> Modified: cfe/trunk/lib/CodeGen/ModuleBuilder.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/ModuleBuilder.cpp?rev=224835&r1=224834&r2=224835&view=diff
>>>
>>> ==============================================================================
>>> --- cfe/trunk/lib/CodeGen/ModuleBuilder.cpp (original)
>>> +++ cfe/trunk/lib/CodeGen/ModuleBuilder.cpp Thu Dec 25 05:38:15 2014
>>> @@ -59,7 +59,7 @@ namespace {
>>>      CodeGeneratorImpl(DiagnosticsEngine &diags, const std::string&
>>> ModuleName,
>>>                        const CodeGenOptions &CGO, llvm::LLVMContext& C,
>>>                        CoverageSourceInfo *CoverageInfo = nullptr)
>>> -      : Diags(diags), CodeGenOpts(CGO), HandlingTopLevelDecls(0),
>>> +      : Diags(diags), Ctx(nullptr), CodeGenOpts(CGO),
>>> HandlingTopLevelDecls(0),
>>>          CoverageInfo(CoverageInfo),
>>>          M(new llvm::Module(ModuleName, C)) {}
>>>
>>>
>>>
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>>>
>>
>
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