[llvm] r243891 - [MCJIT] Fix a cast warning in the unit-test introduced in r243589.

[Aaron Ballman]

On Mon, Aug 3, 2015 at 2:25 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
>
> On Mon, Aug 3, 2015 at 11:03 AM, Lang Hames <lhames at gmail.com> wrote:
>>
>> Author: lhames
>> Date: Mon Aug  3 13:03:40 2015
>> New Revision: 243891
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=243891&view=rev
>> Log:
>> [MCJIT] Fix a cast warning in the unit-test introduced in r243589.
>>
>> Thanks to Aaron Ballman for spotting this.
>>
>> Modified:
>>     llvm/trunk/unittests/ExecutionEngine/MCJIT/MCJITCAPITest.cpp
>>
>> Modified: llvm/trunk/unittests/ExecutionEngine/MCJIT/MCJITCAPITest.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/ExecutionEngine/MCJIT/MCJITCAPITest.cpp?rev=243891&r1=243890&r2=243891&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/unittests/ExecutionEngine/MCJIT/MCJITCAPITest.cpp
>> (original)
>> +++ llvm/trunk/unittests/ExecutionEngine/MCJIT/MCJITCAPITest.cpp Mon Aug
>> 3 13:03:40 2015
>> @@ -514,7 +514,13 @@ TEST_F(MCJITCAPITest, addGlobalMapping)
>>    buildMCJITOptions();
>>    buildMCJITEngine();
>>
>> -  LLVMAddGlobalMapping(Engine, MappedFn,
>> reinterpret_cast<void*>(&localTestFunc));
>> +  union {
>> +    int (*raw)();
>> +    void *usable;
>> +  } functionPointer;
>> +  functionPointer.raw = &localTestFunc;
>
>
> This is actually UB, but I think it's somewhere in the UB subset that LLVM
> intentionally preserves the expected behavior of (& I'm not sure if we rely
> on this in other parts of LLVM/assume that all compilers used to build LLVM
> support this behavior).

I don't think we should rely on it when alternatives exist that aren't
UB, such as use of intptr_t and static_assert. I think the API for
LLVMAddGlobalMapping() is broken if it's requiring a function pointer
to be convertible to void * (note, I know nothing of
LLVMAddGlobalMappings, so I may also be off-base)...

~Aaron

>
>>
>> +
>> +  LLVMAddGlobalMapping(Engine, MappedFn, functionPointer.usable);
>>
>>    buildAndRunPasses();
>>
>>
>>
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