i386: Fix wrong-code x86 issue with avx512{f,vl} fma PR93009

i386: Fix wrong-code x86 issue with avx512{f,vl} fma PR93009

As mentioned in the PR, the following testcase is miscompiled with avx512vl.
The reason is that the fma *_bcst_1 define_insns have two alternatives:
"=v,v" "0,v" "v,0" "m,m" and use the same
vfmadd213* %3<avx512bcst>, %2, %0<sd_mask_op4>
pattern.  If the first alternative is chosen, everything is ok, but if the
second alternative is chosen, %2 and %0 are the same register, so instead
of doing dest=dest*another+membcst we do dest=dest*dest+membcst.
Now, to fix this, either we'd need separate:
  "vfmadd213<ssemodesuffix>\t{%3<avx512bcst>, %2, %0<sd_mask_op4>|%0<sd_mask_op4>, %2, %3<avx512bcst>}
   vfmadd213<ssemodesuffix>\t{%3<avx512bcst>, %1, %0<sd_mask_op4>|%0<sd_mask_op4>, %1, %3<avx512bcst>}"
where for the second alternative, we'd just use %1 instead of %2, but
what I think is actually cleaner is just use a single alternative and
make the two multiplication operands commutative, which they really are.

2020-01-15  Jakub Jelinek  <jakub@redhat.com>

	PR target/93009
	* config/i386/sse.md
	(*<sd_mask_codefor>fma_fmadd_<mode><sd_maskz_name>_bcst_1,
	*<sd_mask_codefor>fma_fmsub_<mode><sd_maskz_name>_bcst_1,
	*<sd_mask_codefor>fma_fnmadd_<mode><sd_maskz_name>_bcst_1,
	*<sd_mask_codefor>fma_fnmsub_<mode><sd_maskz_name>_bcst_1): Use
	just a single alternative instead of two, make operands 1 and 2
	commutative.

	* gcc.target/i386/avx512vl-pr93009.c: New test.