[Bug target/88592] New: Passing of packed structures on sparc64 different than in clang

[gcc-bugzilla at mkarcher dot dialup.fu-berlin.de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88592

            Bug ID: 88592
           Summary: Passing of packed structures on sparc64 different than
                    in clang
           Product: gcc
           Version: 8.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gcc-bugzilla at mkarcher dot dialup.fu-berlin.de
  Target Milestone: ---

As noted while filing a bug on rustc because rustc does not correctly implement
the Sparc64 ABI regarding floating point fields of "small" structures, I
stumbled across a difference between gcc an clang, as shown in
https://github.com/rust-lang/rust/issues/57103 (the important piece is quoted
below):

struct str3 {
  float f;  // passed in most-significant half of %o0 (gcc) or in %f0 (clang)
  int i;    // passed in least-significant half of %o0
} __attribute__((packed));

Without __attribute__((packed)), clang, gcc and the ABI standard agree to pass
f in %f0. The ABI standard doesn't contain anything about packed structures, so
I don't see a way to decide whether gcc or clang is right. I report a bug on
both products to raise awareness.