The same three shapes written in C and as first-class IR aggregates,
compiled by the same clang. { i8, i64 } agrees. { i8, float } does not: C
packs both halves into rax, the IR form answers in al and xmm0. And a
24-byte struct does not agree at all -- C spills through an sret pointer,
the IR form returns it in rax, rdx and rcx, and rcx is a register SysV never
uses for a return value.
That resolves the ret-big anomaly the first pass noted and moved past, and
it makes the finding stronger than it was written: the internal convention
is not the C ABI, not only undocumented in the emitted IR.
spike_call0 deleted with it -- declared, never bound, and the two unused
probes were removed for the same reason.
Joseph Ferano
6bd353bb8c