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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/52631] [4.6/4.7/4.8 Regression] VN does not use simplified expression for lookup
Date: Wed, 21 Mar 2012 00:30:00 -0000 [thread overview]
Message-ID: <bug-52631-4-BQR4CedVt9@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-52631-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52631
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-03-21 00:14:37 UTC ---
(In reply to comment #3)
> Hmm, but then you'd pessimize the case where b_2 & 1 were available? Thus,
> don't you need to do the lookup with the original expression anyway if the
> lookup for the simplified expression fails? Oh, and doesn't the testcase
> show a missed canonicalization?
My patch just gets us back to where we were before tuples.
Before tuples we would do:
else if (simplified)
{
if (TREE_CODE (lhs) == SSA_NAME)
{
VN_INFO (lhs)->has_constants = expr_has_constants (simplified);
/* We have to unshare the expression or else
valuizing may change the IL stream. */
VN_INFO (lhs)->expr = unshare_expr (simplified);
}
rhs = simplified;
}
And then use rhs in the switch statement for visit_unary_op/visit_binary_op .
I don't see a missed canonicalization anywhere as we are combing (a>>31)&1 and
then calling fold on it and it returns a>>31 which is the correct thing to do.
The main issue is we never do a lookup on a>>31 after we do the simplification,
we only do it on the b&1.
Let me see if I can understand the question about b&1 being available, a
testcase would be something like:
unsigned f(unsigned a, unsigned b, unsigned c)
{
unsigned d = c&1;
if(b)
c = a>>31;
return (c & 1) + d;
}
--- CUT ---
PRE produces (with both the patch and before):
<bb 2>:
d_3 = c_2(D) & 1;
if (b_4(D) != 0)
goto <bb 3>;
else
goto <bb 5>;
<bb 5>:
goto <bb 4>;
<bb 3>:
c_6 = a_5(D) >> 31;
pretmp.3_11 = c_6 & 1;
<bb 4>:
# c_1 = PHI <c_2(D)(5), c_6(3)>
# prephitmp.4_12 = PHI <d_3(5), pretmp.3_11(3)>
D.1713_7 = prephitmp.4_12;
D.1712_8 = D.1713_7 + d_3;
return D.1712_8;
Which means we don't even do the simplifications while doing a PRE anyways.
next prev parent reply other threads:[~2012-03-21 0:14 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-20 6:09 [Bug tree-optimization/52631] New: " pinskia at gcc dot gnu.org
2012-03-20 6:58 ` [Bug tree-optimization/52631] [4.6/4.7/4.8 Regression] " pinskia at gcc dot gnu.org
2012-03-20 7:34 ` pinskia at gcc dot gnu.org
2012-03-20 11:20 ` rguenth at gcc dot gnu.org
2012-03-21 0:30 ` pinskia at gcc dot gnu.org [this message]
2012-03-24 3:21 ` pinskia at gcc dot gnu.org
2012-03-24 5:06 ` pinskia at gcc dot gnu.org
2012-04-13 13:10 ` rguenth at gcc dot gnu.org
2012-06-14 8:21 ` rguenth at gcc dot gnu.org
2012-09-20 10:18 ` jakub at gcc dot gnu.org
2013-01-20 5:01 ` law at gcc dot gnu.org
2013-01-20 5:02 ` law at redhat dot com
2013-03-04 11:13 ` gjl at gcc dot gnu.org
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