[Bug default/30363] Location of return type not tracked in ABI model.

["woodard at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30363

--- Comment #1 from Ben Woodard <woodard at redhat dot com> ---
I know one of the founding principles of libabigail is that it assumes the
compiler implements the calling convention correctly. I do not think that this
is entirely sufficient. I think that there are several cases where we should
also verify parameter and return type locations.

1) Compiler bugs such as this one
2) Compilation options, for example if the same library with the same defined
types were compiled without SSE support then the compiler may choose a
different version of the calling convention which passed the vector array type
by pointer reference rather than as a value in a vector register. This one is
really subtle and may be the source of several problems that we have here in
HPC.
3) Inter compiler variation, there are subtle cases where differences in the
interpretation of the calling convention could lead to differences in the
allocation of registers and stack. In theory, this should not happen but it
actually does and this has been a problem that has led to the entire HPC
community creating vertical software stacks with every compiler.

Therefore, I believe that we need to include the location of the parameters and
the return value in our ABI model to catch these problems.

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