Re: [Lightning] sse instructions and gcc warnings

[Paulo César Pereira de Andrade]

Paolo Bonzini wrote:

  Hi,

  I just updated the lightning code I wrote during the weekend to
work on x86_64.

>>    This started happening when I added calls to jit_str_c, jit_str_uc,
>> etc, and apparently doesn't happen if there are only calls to
>> jit_stxi_s, jit_stxi_us, etc, but I am not 100% sure now.
>
> Yes, jit_str_c and jit_str_uc are indeed responsible.

  It does not happen in x86_64.

>>>>     Also about @subject, I needed to add a global function to check
>>>> if a double is zero, because apparently the i387 goes nonsense if
>>>> a function using vector instructions was called.

  Also does not happen in x86_64.

>>> Argument passing in i387 was buggy, it is kind of impossible to get it
>>> right due to the stack-like registers. :(


  Now the bad news :-)

  Load/store of float32 simply does not work, examples:
    jit_ldr_f(JIT_FPR0, JIT_R1);
    jit_stxi_d(..., JIT_V1, JIT_FPR0);
and
    jit_ldxi_d(JIT_FPR0, JIT_V1, ....);
    [...]
    jit_str_f(JIT_R1, JIT_FPR0);

  Another problem is that:
    jit_ldr_c or jit_ldr_s   (JIT_R0, JIT_R1)
    [...]
    jit_stxi_l(JIT_R0, JIT_V1, ...);
does not sign extend the top 32 bits, but jit_stxi_ul paired with
jit_ldr_uc or jit_ldr_us sign extends (zeros out top 32 bits). From
the test cases I currently use, it appears to sign extend int32, but
I just added all small ints to the same fallback for now...

  About the x86_64 warnings, I simply cannot get rid of this pattern:

elightning.c:1125: warning: cast from pointer to integer of different size

that is generated for every jit_patch and jit_patch_at, but is not
generated for jit_patch_movi. Probably not a big problem, unless it
has problem with jit_set_ip(<above-2-or-4-GB>), should be just some
noise in build output.

Thanks,
Paulo