https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88717
Bug ID: 88717 Summary: Unnecessary vzeroupper Product: gcc Version: 9.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: hjl.tools at gmail dot com CC: ubizjak at gmail dot com, wei3.xiao at intel dot com, xuepeng.guo at intel dot com Target Milestone: --- Target: i386,x86_64 [hjl@gnu-cfl-1 tmp]$ cat x.i typedef float __v16sf __attribute__ ((__vector_size__ (64))); typedef float __m512 __attribute__ ((__vector_size__ (64), __may_alias__)); void foo (float *p, __m512 x) { *p = ((__v16sf)x)[0]; } [hjl@gnu-cfl-1 tmp]$ gcc -mavx512f -S x.i -O2 [hjl@gnu-cfl-1 tmp]$ cat x.s .file "x.i" .text .p2align 4,,15 .globl foo .type foo, @function foo: .LFB0: .cfi_startproc vmovss %xmm0, (%rdi) vzeroupper ret .cfi_endproc .LFE0: .size foo, .-foo .ident "GCC: (GNU) 8.2.1 20181215 (Red Hat 8.2.1-6)" .section .note.GNU-stack,"",@progbits [hjl@gnu-cfl-1 tmp]$ Since __m512 is passed to foo, vzeroupper isn't needed.