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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/64015] [5.0 Regression] AArch64 ICE due to conditional compare
Date: Mon, 24 Nov 2014 05:39:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64015

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Zhenqiang Chen from comment #2)
> 2) How to justify it is valueable (the overhead of ccmp is OK) when
> generating ccmp?

If we ignore the case for swapping.
Try this one:
int
test (int a, int b)
{
  return (a > 252) && b > 252;
}

With my patch to do the forcing:
test:
        cmp     w0, 252
        mov     w0, 252
        ccmp    w1, w0, 4, gt
        cset    w0, gt
        ret

Without:
test:
        cmp     w0, 252
        cset    w2, gt
        cmp     w1, 252
        cset    w0, gt
        and     w0, w2, w0
        ret

Or better yet take:
int
test (int a, int b)
{
  return (a > 321223) && b > 321224;
}
Without:
test:
        mov     w3, 59079
        mov     w2, 59080
        movk    w3, 0x4, lsl 16
        movk    w2, 0x4, lsl 16
        cmp     w0, w3
        cset    w3, gt
        cmp     w1, w2
        cset    w0, gt
        and     w0, w3, w0
        ret

With forcing:
test:
        mov     w3, 59079
        mov     w2, 59080
        movk    w3, 0x4, lsl 16
        movk    w2, 0x4, lsl 16
        cmp     w0, w3
        ccmp    w1, w2, 4, gt
        cset    w0, gt
        ret

--- CUT ---
Also take:
int
test (int a, int b)
{
  return (a > 33) && b > 33;
}
Without:
test:
        cmp     w0, 33
        cset    w2, gt
        cmp     w1, 33
        cset    w0, gt
        and     w0, w2, w0
        ret
With forcing:
test:
        cmp     w0, 33
        mov     w0, 33
        ccmp    w1, w0, 4, gt
        cset    w0, gt
        ret


See how with forcing is always the same size or smaller?