[Bug target/92821] Miscompilation when passing 8-bit enum to extern function

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92821

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hjl.tools at gmail dot com,
                   |                            |hubicka at gcc dot gnu.org,
                   |                            |matz at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I believe it is a LLVM bug.
At least, reading
https://github.com/hjl-tools/x86-psABI/wiki/x86-64-psABI-1.0.pdf, I can't find
in the Parameter Passing section anything that would say that arguments smaller
than 64-bit are passed sign or zero extended to 64-bit like some other psABIs
require.  The only related thing is
"When a value of type _Bool is returned or passed in a register or on the
stack,
bit 0 contains the truth value and bits 1 to 7 shall be zero."
with a footnote:
"Other bits are left unspecified, hence the consumer side of those values can
rely on it being 0 or 1 when truncated to 8 bit."
which says that _Bool has only significant low 8 bits and the rest is
unspecified.