On Fri, Nov 22, 2019 at 5:39 PM Bernd Schmidt <[email protected]> wrote:
>
> On 11/22/19 3:04 PM, Uros Bizjak wrote:
> > On Fri, Nov 22, 2019 at 1:58 PM Bernd Schmidt <[email protected]>
> > wrote:
> >>
> >> A patch I posted recently fixes combine to take costs of JUMP_INSNs into
> >> account. That causes the pr30315 test to fail with -m32, since the cost
> >> of an add that sets the flags is estimated too high.
> >>
> >> The following seems to fix it. Bootstrapped and tested on x86_64-linux,
> >> ok?
> >
> > I think that the intention of the code below "The embedded comparison
> > operand is completely free." comment is to handle this case. It looks
> > that it should return the cost of the inside operation of COMPARE rtx.
>
> There seem to be two problems with that. We're dealing with patterns
> such as:
>
> (set (reg:CCC 17 flags)
> (compare:CCC (plus:SI (mem/c:SI (reg/f:SI 16 argp) [2 a+0 S4
> A32])
> (reg/v:SI 87 [ b ]))
> (mem/c:SI (reg/f:SI 16 argp) [2 a+0 S4 A32])))
Indeed, this is a different case, an overflow test that results in one
CMP insn. I think, we should check if the second operand is either 0
(then proceed as it is now), or if the second operand equals first
operand of PLUS insn, then we actually emit CMP insn (please see
PR30315).
Uros.
> If I remove the test for const0_rtx, it still doesn't work - I think
> setting *total to zero is ineffective, since we'll still count the MEM
> twice.
>
> So, how about the following?
>
>
> Bernd
>
> @@ -19502,9 +19502,12 @@
> }
>
> /* The embedded comparison operand is completely free. */
> - if (!general_operand (XEXP (x, 0), GET_MODE (XEXP (x, 0)))
> - && XEXP (x, 1) == const0_rtx)
> - *total = 0;
> + if (!general_operand (XEXP (x, 0), GET_MODE (XEXP (x, 0))))
> + {
> + *total = rtx_cost (XEXP (x, 0), GET_MODE (XEXP (x, 0)),
> + COMPARE, 0, speed);
> + return true;
> + }
>
> return false;
>
