https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82735
--- Comment #11 from Uroš Bizjak <ubizjak at gmail dot com> --- (In reply to Uroš Bizjak from comment #9) > (In reply to Richard Biener from comment #4) > > Indeed as far as I understand an unspec volatile isn't sth clobbering > > registers (not even memory?!). The insn is missing inputs/outputs > > (we might be able to model that lowparts are preserved). > > Since the instruction operates on the whole pack (8 or 16 SSE registers), > this approach will introduce uninitialized uses, and will clobber the whole > register pack. Since SSE registers are callee-saved this means all registers > will be saved in function prologue and restored in the epilogue. I was typing a bit too fast here: SSE registers are NOT preserved across function calls for SYSV ABI, and lower 128bit are preserved for MS ABI.
