[LLVMdev] alloc_size metadata

[Nuno Lopes]

Hi,

I'm implementing the alloc_size function attribute in clang. This  
attribute exists in gcc since version 4.3.
The attribute specifies that a function returns a buffer with the size  
given by the multiplication of the specified arguments.  I would like  
to add new metadata to pass this information to LLVM IR.

For example, take the following C code:

void* my_calloc(size_t, size_t) __attribute__((alloc_size(1,2)));

void* fn() {
   return my_calloc(1, 3);
}


which would get translated to:


define i8* @fn() {
entry:
   %call = call i8* @my_calloc(i32 1, i32 3), !alloc_size !0
   ret i8* %call
}

declare i8* @my_calloc(i32, i32)

!0 = metadata !{i32 0, i32 1}


The downsize is that the metadata is added to all call sites, since  
it's not possible to attach metadata to function declarations.

Any comment, suggestion, etc?

Thanks,
Nuno