https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102811
--- Comment #16 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Uroš Bizjak from comment #15)
> (In reply to Hongtao.liu from comment #14)
> > (In reply to Uroš Bizjak from comment #13)
> > > (In reply to Hongtao.liu from comment #12)
> > > > >
> > > > > Just noticed that for some reason two VPXORs are emitted. One should
> > > > > be
> > > > > enough for both VPINSRW insns.
> > > >
> > > > With new alternative in your attached match(vpblenw one), RA could reuse
> > > > zero register, w/o that, xmm0/xmm1 need to be explictly clear for the
> > > > upper
> > > > bits.
> > > > vpblendw $1, %xmm1, %xmm2, %xmm1 # 14 [c=4 l=6]
> > > > *vec_setv8hf_0/8
> > >
> > > True, but I'd expect some post-reload(?) pass to propagate zeros and
> > > remove
> > > redundant initializations.
> >
> > On the other hand, if not use expand_vector_set (which treats zero register
> > as both input and output), but emit_insn(gen_sse4_1_pinsrph(...)) with a new
> > pseudo register as dest. the redudant initialization could be optimized off
> > by fwprop1.
> >
> > pextrw $0, %xmm1, %eax
> > pextrw $0, %xmm0, %edx
> > vpxor %xmm1, %xmm1, %xmm1
> > vpinsrw $0, %edx, %xmm1, %xmm0
> > vpinsrw $0, %eax, %xmm1, %xmm1
> > vcvtph2ps %xmm1, %xmm1
> > vcvtph2ps %xmm0, %xmm0
> > vaddss %xmm1, %xmm0, %xmm0
> > vinsertps $0xe, %xmm0, %xmm0, %xmm0
> > vcvtps2ph $4, %xmm0, %xmm0
>
> Then we will lose optimization in expand vector set:
>
> case E_V8HFmode:
> if (TARGET_AVX2)
> {
> mmode = SImode;
> gen_blendm = gen_sse4_1_pblendph;
> blendm_const = true;
> }
> else
> use_vec_merge = true;
> break;
>
> Maybe we should simply copy "target" to a new pseudo here:
>
> do_vec_merge:
> tmp = gen_rtx_VEC_DUPLICATE (mode, val);
> tmp = gen_rtx_VEC_MERGE (mode, tmp, target,
> GEN_INT (HOST_WIDE_INT_1U << elt));
> emit_insn (gen_rtx_SET (target, tmp));
>
> OTOH, if recycling "target" inhibits FWprop, we should perhaps copy "target"
> to a new pseudo at the beginning of the expand_vector_set?
ix86_expand_vector_set is mainly used by vec_set_optab which exactly takes
target as both input and output, it seems we can't create a new target for
that.
