[llvm-dev] Alignment of GVMemoryBlocks

[Alex Horn via llvm-dev]

Hello,

Is anyone familiar with the ExecutionEngine, particularly the handling of GVMemoryBlocks?

Line 114 in Create(GV,TD) is suspicious [1]:

  static char *Create(const GlobalVariable *GV, const DataLayout& TD) {
    Type *ElTy = GV->getValueType();
    size_t GVSize = (size_t)TD.getTypeAllocSize(ElTy);
    void *RawMemory = ::operator new(
        alignTo(sizeof(GVMemoryBlock), TD.getPreferredAlignment(GV)) + GVSize);
    new(RawMemory) GVMemoryBlock(GV);
    return static_cast<char*>(RawMemory) + sizeof(GVMemoryBlock); // <— [1]
  }

Example:

	Suppose sizeof(GVMemoryBlock) == 3 bytes. Further, assume the preferred TD-alignment is on 4-byte boundaries. Finally, for sake of argument, assume RawMemory points to address 4. Then Create(GV, TD) returns 7, a non-aligned address with respect to the preferred TD-alignment.

Is this expected?

Many thanks for your time!

- Alex

[1] https://github.com/llvm-mirror/llvm/blob/91b6092209489b4790826efc66fce178a6ec7f46/lib/ExecutionEngine/ExecutionEngine.cpp#L114

PS

	Also, if anyone happens to know, why is the empty ~GVMemoryBlock() destructor explicitly called in the deleted() callback? The last comment left there seems to indicate someone else before me was also puzzled by this :)
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