Re: [Qemu-devel] [PATCH 04/14] target/ppc: introduce GEN_VSX_HELPER_X3 macro to fpu_helper.c

[Richard Henderson <richard.henderson@linaro.org>]

On 5/5/19 2:52 AM, Mark Cave-Ayland wrote:
> Right, it looks like VSX_CMP is the culprit here. Am I right in thinking that it's
> best to remove the opc parameter from GEN_VSX_HELPER_X3 above, and then have a
> separate gen and helper function for just the VSX_CMP instructions? Presumably this
> reduces of the overhead at both translation and execution time for the instructions
> that don't require it.

Yep.

I think the best fix for VSX_CMP is to return the value that is to be assigned
to cr[6], and let it assign like so:

  gen_helper_foo(cpu_crf[6], other, arguments);

(Or if the opcode bit is unset,

  TCGv_i32 ignored = tcg_temp_new_i32();
  gen_helper_foo(ignored, other arguments);
  tcg_temp_free_i32(ignored);
)

at which point these functions do not modify tcg globals, so the decl
can be improved to

  DEF_HELPER_FLAGS_2(xvcmpeqdp, TCG_CALL_NO_RWG, i32, ptr, ptr, ptr)

To keep the assignment vs exception order, you remove the direct call to
do_float_check_status and use gen_helper_float_check_status.


r~