On Fri, Jan 14, 2022 at 2:44 PM Hongyu Wang <wwwhhhyyy...@gmail.com> wrote:
>
> > Are there any technical obstacles to introduce subst to
> > define_{,insn_and_}split?
>
> gccint says: define_subst can be used only in define_insn and
> define_expand, it cannot be used in other expressions (e.g. in
> define_insn_and_split).
Hm, hm ... annoying ...
> I have no idea how to implement it in current infrastructure.
>
> > In the proposed patch, if the output register is also mentioned in the
> > input, then clearing before insn will clear the value in the input
> > register. The solution in the i386.md also takes care of this issue.
> >
>
> For this, I think we can add REGNO checks for operands in condition
> (which means there is true dependency).
Let's go in your direction, considering the limitations of current
infrastructure.
+{
+ if (TARGET_DEST_FALSE_DEPENDENCY
+ && get_attr_dest_false_dep (insn) ==
+ DEST_FALSE_DEP_TRUE)
+ output_asm_insn ("vxorps\t{%x0, %x0, %x0}", operands);
+ return "vgetmant<ssemodesuffix>\t{%2, <round_saeonly_mask_op3>%1,
%0<mask_operand3>|%0<mask_operand3>, %1<round_saeonly_mask_op3>, %2}";
+}
There is no need to pass the information via attributes. IMO, you
shoud use subst attribute directly in the condition:
{
if (TARGET_DEST_FALSE_DEPENDENCY
&& <mask3_dest_false_dep_attr>
&& !reg_mentioned_p (operands[0], operands[1]))
output_asm_insn ("vxorps\t{%x0, %x0, %x0}", operands);
return ".....";
}
Assume the above works, so please:
- rename TARGET_DEST_FALSE_DEPENDENCY to something less generic, maybe
following existing BMI example with TARGET_AVOID_FALSE_DEP_FOR_AVX512F
- rename "mask3_dest_false_dep_attr" to "mask3_false_dep_for_avx512f_cond"
Please note reg_mentioned_p in the above condition. This function
returns nonzero if register op0 appears somewhere within op1 and is
critical for the correct operation of your patch.
Uros.
