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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/101179] y % (x ? 16 : 4) and y % (4 << (2 * (bool)x)) produce different code
Date: Thu, 24 Jun 2021 06:40:24 +0000 [thread overview]
Message-ID: <bug-101179-4-4uIxqea6Hp@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-101179-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101179
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Blocks| |85316
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #1)
> On IRC Richi said: "VRP has code to do that but maybe for some reason shifts
> are not handled"
Specifically simplify_using_ranges::simplify has
/* Convert:
LHS = CST BINOP VAR
Where VAR is two-valued and LHS is used in GIMPLE_COND only
To:
LHS = VAR == VAL1 ? (CST BINOP VAL1) : (CST BINOP VAL2)
Also handles:
LHS = VAR BINOP CST
Where VAR is two-valued and LHS is used in GIMPLE_COND only
To:
LHS = VAR == VAL1 ? (VAL1 BINOP CST) : (VAL2 BINOP CST) */
restrictions that stand in the way:
if (TREE_CODE_CLASS (rhs_code) == tcc_binary
...
&& single_imm_use (lhs, &use_p, &use_stmt)
&& gimple_code (use_stmt) == GIMPLE_COND)
VRP1 sees
<bb 2> [local count: 1073741824]:
_1 = y_7(D) % 100;
x_8 = _1 == 0;
_2 = (int) x_8;
_3 = _2 * 2;
_4 = 4 << _3;
_5 = y_7(D) % _4;
_6 = _5 == 0;
_9 = (int) _6;
return _9;
so it would consider _2 * 2 but its single use is in a shift, the
condition is after another op, the modulo, and there the condition
is in an assignment, not in a GIMPLE_COND.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85316
[Bug 85316] [meta-bug] VRP range propagation missed cases
next prev parent reply other threads:[~2021-06-24 6:40 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-23 11:05 [Bug tree-optimization/101179] New: " redi at gcc dot gnu.org
2021-06-23 13:58 ` [Bug tree-optimization/101179] " redi at gcc dot gnu.org
2021-06-23 17:51 ` pinskia at gcc dot gnu.org
2021-06-23 17:55 ` redi at gcc dot gnu.org
2021-06-23 18:05 ` pinskia at gcc dot gnu.org
2021-06-23 20:10 ` pinskia at gcc dot gnu.org
2021-06-24 6:40 ` rguenth at gcc dot gnu.org [this message]
2021-07-01 20:43 ` pinskia at gcc dot gnu.org
2021-07-01 20:43 ` pinskia at gcc dot gnu.org
2021-07-01 20:49 ` pinskia at gcc dot gnu.org
2023-01-18 16:51 ` pinskia at gcc dot gnu.org
2023-05-06 21:52 ` pinskia at gcc dot gnu.org
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