On Thu, 14 Jan 2021, Jakub Jelinek wrote: > On Thu, Jan 14, 2021 at 09:28:31AM +0100, Jakub Jelinek via Gcc-patches wrote: > > I'm afraid yes, because it is not a toplevel routine, but something called > > from the c-family pretty-printers, so it can be in the middle of arbitrary > > C/C++ expressions. And printing > > (3 * (access to a memory object of type 'int' at offset 12 bytes from 't') > > + 31) * 42 > > would be just weird. > > > > > We could print, instead of *((int *)t + 3), "access to a memory > > > object of type 'int' at offset 12 bytes from 't'", thus explain > > > in plain english. > > > > > > That said, *((int *)t + 3) is exactly what the access is, > > > > *((int *)&t + 3) actually, the code I haven't touched has multiple bugs. > > > > The user generally doesn't know the exact layout of the structures, > > and especially with C++ templates it is extremely hard to figure that out, > > so even when we could print verbose text it would be helpful to give a hint > > (in your text something like (which falls into 't.u.b')). > > I don't see how we can print both the MEM_REF type and TBAA type in a way > > that would be understandable to the user. > > > > Could we print > > t.u.b > > if the TBAA type is compatible with the type of the reference and perhaps > > *(int*)&t.u.b > > if it is incompatible? > > >From the aliasing perspective that is still different, but we don't print > > the TBAA type anyway.
True. As said we could simply add a GCC extension to write a MEM_REF in source and print that syntax ... then it would be valid (GCC) C/C++. > There is another option I forgot about, but perhaps it is too verbose. > Print > *(int*)((char*)&t + offsetof (struct T, u.b)) or rather offsetof (struct T, u) to not single out a specific union member? Richard. > so like > *(int*)((char*)&t + 12) > but print the offset in a more user-friendly way.
