Question

I’m holding a Type* in my hand. How do I find out its size (the size objects of this type will occupy in memory) in bits / bytes? I see all kinds of methods allowing me to get “primitive” or “scalar” size, but that won’t help me with aggregate types…

Answer 1

The size depends on the target (for several reasons, alignment being one of them).

In LLVM versions 3.2 and above, you need to use DataLayout, in particular its getTypeAllocSize method. This returns the size in bytes, there’s also a bit version named getTypeAllocSizeInBits. A DataLayout instance can be obtained by creating it from the current module: DataLayout* TD = new DataLayout(M).

With LLVM up to version 3.1 (including), use TargetData instead of DataLayout. It exposes the same getTypeAllocSize methods, though.