https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91994
--- Comment #10 from Uroš Bizjak <ubizjak at gmail dot com> --- Richard, since vzeroupper clobbers only xmm0-xmm15 (xmm0-xmm7 on 32it targets), shouldn't we use SSE_REGS instead of ALL_SSE_REGS here: Index: i386.c =================================================================== --- i386.c (revision 276660) +++ i386.c (working copy) @@ -13530,7 +13530,7 @@ ix86_avx_u128_mode_needed (rtx_insn *insn) modes wider than 256 bits. It's only safe to issue a vzeroupper if all SSE registers are clobbered. */ const function_abi &abi = insn_callee_abi (insn); - if (!hard_reg_set_subset_p (reg_class_contents[ALL_SSE_REGS], + if (!hard_reg_set_subset_p (reg_class_contents[SSE_REGS], abi.mode_clobbers (V4DImode))) return AVX_U128_ANY;