RE: Bogus REG_EQUIV note generation [was RE: Deep CSE bug!]

[Jeffrey A Law <law at redhat dot com>]

On Wed, 2004-06-23 at 08:31, Dave Korn wrote:
>   Right, gotcha.  What I've done so far is part 1) of the above - passing
> down the constant equivalent cst_y from emit_move_insn to emit_move_insn_1 -
> and then using operand_subword on it in just the same way as the loop that
> breaks up the move operation:
> 
> ---------->snip!<----------
> @@ -3467,6 +3473,7 @@ emit_move_insn_1 (x, y)
>  	{
>  	  rtx xpart = operand_subword (x, i, 1, mode);
>  	  rtx ypart = operand_subword (y, i, 1, mode);
> +        rtx y_cstpart = 0;
>  
>  	  /* If we can't get a part of Y, put Y into memory if it is a
>  	     constant.  Otherwise, force it into a register.  If we still
> @@ -3485,6 +3492,14 @@ emit_move_insn_1 (x, y)
>  	  need_clobber |= (GET_CODE (xpart) == SUBREG);
>  
>  	  last_insn = emit_move_insn (xpart, ypart);
> +
> +        /* Will we attach a REG_EQUAL note? */
> +        if (y_cst && GET_CODE (xpart) == SUBREG && GET_CODE (XEXP (xpart,
> 0)) == REG)
> +        {
> +            y_cstpart = operand_subword (y_cst, i, 1, mode);
> +            if (y_cstpart)
> +                set_unique_reg_note (last_insn, REG_EQUAL, y_cstpart);
> +        }
>  	}
>  
>        seq = get_insns ();
> ---------->snip!<----------
> 
>   And that fixes the failing testcase all by itself, since the REG_EQUAL
> notes now contain only the value in the subreg - 0 or -1, according to which
> subword it was - and that gives us the correct value for src_eqv in CSE, and
> the equivalence chains don't get mixed up.
> 
>   I'm not 100% sure how to emit the nop move, though.  I can't recursively
> call emit_move_insn{_1} (x, y) or we'll just recurse and start re-emitting
> the move-by-words infinitely.  I presume I have to do something like
> 
>         rtx nop_move = gen_rtx_SET (mode, x, y);
>         last_insn = emit_insn (nop_move);
> 
> yes?  I'll be giving that a go after I hit send on this post, anyway.
Looks like the right idea.  You might have a peek at
emit_no_conflict_block.  In fact, I'm not sure why we're not using
emit_no_conflict_block since it's whole purpose is to do a series
of operations on a multi-word object one word at a time, add the
necessary notes, etc etc.

jeff