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From: "amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/101254] [12 Regression] gcc head does not
 comply fully to -fwrapv since r12-1723
Date: Tue, 29 Jun 2021 15:09:58 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101254

--- Comment #2 from Andrew Macleod <amacleod at redhat dot com> ---
Created attachment 51082
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D51082&action=3Dedit
patch

I *think* this is correct.   but wrapv and signed stuff sometimes confuses =
me
:-)
when -fwrapv is on,  +INf - -INF is -1 ?  is this correct?
in which case, the relations that were being added for minus were not quite
correct in this case.

given    lhs =3D op1 - op2
if op1 > op2, we were producing a range of [1, +INF].  which is fine for
unsigned.   but for signed, that edge condition for -INF means the range sh=
ould
be [0, +INF].
likewise, if op1 >=3D op2, then result range would be [0, +INF]

Is this is correct?   I hope that  -INF - -INF still equals 0 tho?  Thats t=
he
only other case that might need consideration.

The attached patch implements the above and appears to fix the test. I just
want to be sure I have it right.=