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From: "amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107114] [13 Regression] Failure to discover
 range results in bogus warning
Date: Mon, 03 Oct 2022 15:46:05 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107114

--- Comment #1 from Andrew Macleod <amacleod at redhat dot com> ---
Looks like something in the change is causing the loop analysis to not be a=
ble
to count the iterations.


> Analyzing # of iterations of loop 1
>   exit condition [1, + , 1] !=3D 0
>   bounds on difference of bases: -1 ... -1
>   result:
>     # of iterations 65535, bounded by 65535
109,110d68
<    Loops range found for a_lsm.14_26: [irange] short int [1, 9] NONZERO 0=
xf
and calculated range :[irange] short int VARYING
< Global Exported: a_lsm.14_26 =3D [irange] short int [1, 9] NONZERO 0xf
112,114c70,72
<    Loops range found for c_lsm.16_29: [irange] int [1, 2115902953] NONZERO
0x7fffffff and calculated range :[irange] int [-1618507910, +INF]
< Global Exported: c_lsm.16_29 =3D [irange] int [1, 2115902953] NONZERO
0x7fffffff
< Folding PHI node: a_lsm.14_26 =3D PHI <1(2), _11(12)>

before this change, loop analysis decided the range of _26 as
a_lsm.14_26: [irange] short int [1, 9] NONZERO 0xf a

afterwards, it doesn't even seem to see the loop.  IN fact, before LCSSA
creates a whole bunch of new blocks too.

< ;; Created LCSSA PHI: a_lsm.14_15 =3D PHI <a_lsm.14_26(8)>
< ;; Created LCSSA PHI: a_lsm_flag.15_16 =3D PHI <a_lsm_flag.15_28(8)>
< ;; Created LCSSA PHI: d_47 =3D PHI <d_13(7)>
<=20
< Updating SSA:
< Registering new PHI nodes in block #13
< Updating SSA information for statement if (a_lsm.14_26 !=3D 0)
< Registering new PHI nodes in block #6
< Registering new PHI nodes in block #12
< Updating SSA information for statement a.9_9 =3D (unsigned short) a_lsm.1=
4_26;
< Registering new PHI nodes in block #16
< Registering new PHI nodes in block #7
< Registering new PHI nodes in block #8
< Updating SSA information for statement if (d_13 !=3D 0B)
< Registering new PHI nodes in block #9
< Updating SSA information for statement if (a_lsm_flag.15_28 !=3D 0)
< Registering new PHI nodes in block #10
< Updating SSA information for statement a =3D a_lsm.14_26;
< Registering new PHI nodes in block #11
< Registering new PHI nodes in block #19
< Registering new PHI nodes in block #15=