[llvm] r238447 - AsmPrinter: Suppress warnings on GCC from r238362, NFC

[Aaron Ballman]

On Thu, May 28, 2015 at 2:28 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
>
> On Thu, May 28, 2015 at 11:09 AM, Duncan P. N. Exon Smith
> <dexonsmith at apple.com> wrote:
>>
>> Author: dexonsmith
>> Date: Thu May 28 13:09:13 2015
>> New Revision: 238447
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=238447&view=rev
>> Log:
>> AsmPrinter: Suppress warnings on GCC from r238362, NFC
>>
>> GCC seems to have some overzealous warnings about strict aliasing.
>
>
> If the warning is wrong, can we just disable it rather than contorting the
> code to suppress it? (especially with the risk that warnings like this in
> GCC tend to be powered by their optimizer & thus might see through this &
> start warning again)

There were questions as to whether the warning was or was not a false
positive which should be answered before turning off the warning over
it. That being said, I don't see a whole lot of strict aliasing
warnings happening in general. If GCC's optimizer changes and starts
warning on this again, we should probably take more time to understand
why.

~Aaron

>
>>
>> Rafael reports that this patch suppresses them on GCC 4.9, and I'm
>> hoping this will work for GCC 4.7 as well.  I'll watch [1] and iterate
>> if necessary.
>>
>> [1]: http://bb.pgr.jp/builders/clang-3stage-x86_64-linux/builds/8597
>>
>> Modified:
>>     llvm/trunk/include/llvm/CodeGen/DIE.h
>>
>> Modified: llvm/trunk/include/llvm/CodeGen/DIE.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/DIE.h?rev=238447&r1=238446&r2=238447&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/include/llvm/CodeGen/DIE.h (original)
>> +++ llvm/trunk/include/llvm/CodeGen/DIE.h Thu May 28 13:09:13 2015
>> @@ -340,11 +340,11 @@ private:
>>      new (reinterpret_cast<void *>(Val.buffer)) T(V);
>>    }
>>
>> -  template <class T> T &get() { return *reinterpret_cast<T
>> *>(Val.buffer); }
>> -  template <class T> const T &get() const {
>> -    return *reinterpret_cast<const T *>(Val.buffer);
>> +  template <class T> T *get() { return reinterpret_cast<T *>(Val.buffer);
>> }
>> +  template <class T> const T *get() const {
>> +    return reinterpret_cast<const T *>(Val.buffer);
>>    }
>> -  template <class T> void destruct() { get<T>().~T(); }
>> +  template <class T> void destruct() { get<T>()->~T(); }
>>
>>    /// Destroy the underlying value.
>>    ///
>> @@ -378,11 +378,11 @@ private:
>>        return;
>>  #define HANDLE_DIEVALUE_SMALL(T)
>> \
>>    case is##T:
>> \
>> -    construct<DIE##T>(X.get<DIE##T>());
>> \
>> +    construct<DIE##T>(*X.get<DIE##T>());
>> \
>>      return;
>>  #define HANDLE_DIEVALUE_LARGE(T)
>> \
>>    case is##T:
>> \
>> -    construct<const DIE##T *>(X.get<const DIE##T *>());
>> \
>> +    construct<const DIE##T *>(*X.get<const DIE##T *>());
>> \
>>      return;
>>  #include "llvm/CodeGen/DIEValue.def"
>>      }
>> @@ -425,12 +425,12 @@ public:
>>  #define HANDLE_DIEVALUE_SMALL(T)
>> \
>>    const DIE##T &getDIE##T() const {
>> \
>>      assert(getType() == is##T && "Expected " #T);
>> \
>> -    return get<DIE##T>();
>> \
>> +    return *get<DIE##T>();
>> \
>>    }
>>  #define HANDLE_DIEVALUE_LARGE(T)
>> \
>>    const DIE##T &getDIE##T() const {
>> \
>>      assert(getType() == is##T && "Expected " #T);
>> \
>> -    return *get<const DIE##T *>();
>> \
>> +    return **get<const DIE##T *>();
>> \
>>    }
>>  #include "llvm/CodeGen/DIEValue.def"
>>
>>
>>
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