https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65782
--- Comment #10 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-8 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:baef3efdc4992e4dcb7f4de62ff5bcb13bf05f60 commit r8-10016-gbaef3efdc4992e4dcb7f4de62ff5bcb13bf05f60 Author: Jakub Jelinek <ja...@redhat.com> Date: Fri Feb 14 15:47:55 2020 +0100 i386: Make xmm16-xmm31 call used even in ms ABI [PR65782] On Tue, Feb 04, 2020 at 11:16:06AM +0100, Uros Bizjak wrote: > I guess that Comment #9 patch form the PR should be trivially correct, > but althouhg it looks obvious, I don't want to propose the patch since > I have no means of testing it. I don't have means of testing it either. https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention?view=vs-2019 is quite explicit that [xyz]mm16-31 are call clobbered and only xmm6-15 (low 128-bits only) are call preserved. We are talking e.g. about /* { dg-options "-O2 -mabi=ms -mavx512vl" } */ typedef double V __attribute__((vector_size (16))); void foo (void); V bar (void); void baz (V); void qux (void) { V c; { register V a __asm ("xmm18"); V b = bar (); asm ("" : "=x" (a) : "0" (b)); c = a; } foo (); { register V d __asm ("xmm18"); V e; d = c; asm ("" : "=x" (e) : "0" (d)); baz (e); } } where according to the MSDN doc gcc incorrectly holds the c value in xmm18 register across the foo call; if foo is compiled by some Microsoft compiler (or LLVM), then it could clobber %xmm18. If all xmm18 occurrences are changed to say xmm15, then it is valid to hold the 128-bit value across the foo call (though, surprisingly, LLVM saves it into stack anyway). The other parts are I guess mainly about SEH. Consider e.g. void foo (void) { register double x __asm ("xmm14"); register double y __asm ("xmm18"); asm ("" : "=x" (x)); asm ("" : "=v" (y)); x += y; y += x; asm ("" : : "x" (x)); asm ("" : : "v" (y)); } looking at cross-compiler output, with -O2 -mavx512f this emits .file "abcdeq.c" .text .align 16 .globl foo .def foo; .scl 2; .type 32; .endef .seh_proc foo foo: subq $40, %rsp .seh_stackalloc 40 vmovaps %xmm14, (%rsp) .seh_savexmm %xmm14, 0 vmovaps %xmm18, 16(%rsp) .seh_savexmm %xmm18, 16 .seh_endprologue vaddsd %xmm18, %xmm14, %xmm14 vaddsd %xmm18, %xmm14, %xmm18 vmovaps (%rsp), %xmm14 vmovaps 16(%rsp), %xmm18 addq $40, %rsp ret .seh_endproc .ident "GCC: (GNU) 10.0.1 20200207 (experimental)" Does whatever assembler mingw64 uses even assemble this (I mean the .seh_savexmm %xmm16, 16 could be problematic)? I can find e.g. https://stackoverflow.com/questions/43152633/invalid-register-for-seh-savexmm-in-cygwin/43210527 which then links to https://gcc.gnu.org/PR65782 2020-02-08 Uroš Bizjak <ubiz...@gmail.com> Jakub Jelinek <ja...@redhat.com> PR target/65782 * config/i386/i386.h (CALL_USED_REGISTERS): Make xmm16-xmm31 call-used even in 64-bit ms-abi. * gcc.target/i386/pr65782.c: New test. Co-authored-by: Uroš Bizjak <ubiz...@gmail.com>
