RE: Question regarding preventing optimizing out of register in expansion

["Peryt, Sebastian" <sebastian.peryt@intel.com>]

> Subject: Re: Question regarding preventing optimizing out of register in
> expansion
> 
> On 6/26/18 4:05 AM, Peryt, Sebastian wrote:
> > With some changes simplified implementation of my expansion is as follows:
> > tmp_op0 = gen_reg_rtx (mode);
> > emit_move_insn (tmp_op0, op0);
> 
> You set tmp_op0 here, and then....
> 
> 
> > emit_insn (gen_rtx_SET (tmp_op0, reg));
> 
> You set it again here without ever using it above, so it's dead code, which
> explains why it's removed.

Oh.... My bad - I oversimplified my code. Now I can see it.

This should be more appropriate:
tmp_op0 = gen_reg_rtx (mode);
emit_move_insn (tmp_op0, op0);
tmp_op1 = gen_reg_rtx (mode);
emit_move_insn (tmp_op1, op1);

// This is important part
reg = gen_rtx_REG(wide_mode, XMM2_REG);
op3 = gen_rtx_PLUS (mode, tmp_op1, GEN_INT (128));
emit_insn (gen_rtx_SET (reg, op3));

emit_insn (gen_myinsn(op2, reg));

op3 = gen_rtx_PLUS (mode, tmp_op0, GEN_INT (128));
emit_insn (gen_rtx_SET (op3, reg));
////

Also I'd like to one more time point out that without additional -mavx or -mavx2 
I'm getting expected register moves before and after my instr. With those options
only *after*. This is the part that I don't get especially - why.

> 
> Peter
>