https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99234
--- Comment #17 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Liu Hao from comment #15)
> Thanks. The 'Final fix' looks good to me.
>
> I applied it locally and built GCC. With a debugger, I verified that after
> the try-catch statement, all non-volatile XMM registers (6-15) had been
> restored properly.
>
>
>
> ```
> // x86_64-w64-mingw32-g++ -O2 -fno-omit-frame-pointer test.cc
>
> __attribute__((__noinline__)) void clobber_xmm6()
> {
> __asm__ volatile ("xorpd %%xmm6, %%xmm6" ::: "xmm6");
> throw 42; // remove this to get expected result
> }
>
> int main()
> {
> static const double xmm5 = 5.123456;
> static const double xmm6 = 6.123456;
> static const double xmm7 = 7.123456;
> static const double xmm8 = 8.123456;
> static const double xmm9 = 9.123456;
> static const double xmm10 = 10.123456;
> static const double xmm11 = 11.123456;
> static const double xmm12 = 12.123456;
> static const double xmm13 = 13.123456;
> static const double xmm14 = 14.123456;
> static const double xmm15 = 15.123456;
> __asm__ volatile ("movsd %0, %%xmm5 " :: "m"(xmm5 ));
That would certainly need : "xmm5" in clobbers (etc.).
And isn't really portable anyway, the compiler can choose to put
anything into %xmm6 in between that and the asm before printf.
But, loading the value from memory into some double temporary (with "=x" for
many of them)
in an asm and then e.g. just "+x" them in empty asms and then comparing values
will likely reproduce it too.
> __asm__ volatile ("movsd %0, %%xmm6 " :: "m"(xmm6 ));
> __asm__ volatile ("movsd %0, %%xmm7 " :: "m"(xmm7 ));
> __asm__ volatile ("movsd %0, %%xmm8 " :: "m"(xmm8 ));
> __asm__ volatile ("movsd %0, %%xmm9 " :: "m"(xmm9 ));
> __asm__ volatile ("movsd %0, %%xmm10" :: "m"(xmm10));
> __asm__ volatile ("movsd %0, %%xmm11" :: "m"(xmm11));
> __asm__ volatile ("movsd %0, %%xmm12" :: "m"(xmm12));
> __asm__ volatile ("movsd %0, %%xmm13" :: "m"(xmm13));
> __asm__ volatile ("movsd %0, %%xmm14" :: "m"(xmm14));
> __asm__ volatile ("movsd %0, %%xmm15" :: "m"(xmm15));
>
> try {
> clobber_xmm6();
> }
> catch(...) { }
>
> double value;
> __asm__ volatile ("movsd %%xmm6, %0" : "=x"(value));
> __builtin_printf("value = %g\n", value); // expect `123.456`
You mean 6.123456 ? And in any case, I'd suggest whatever.625 or other
constants which won't suffer from rounding etc.
