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From: "graham.stott at btinternet dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/56932] [regression 4.8]: vrp and/or niter-related wrong-code bug
Date: Fri, 12 Apr 2013 12:22:00 -0000 [thread overview]
Message-ID: <bug-56932-4-WNcnHT9M56@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-56932-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56932
--- Comment #3 from graham.stott at btinternet dot com 2013-04-12 12:21:59 UTC ---
ktietz.
Access to a[250] is undefined as pointed out by andrew.
Increase size of a to 251 to get the test passing.
Graham
>From gcc-bugs-return-419920-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Fri Apr 12 12:40:08 2013
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From: "wschmidt at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/56933] New: [4.9 Regression] Vectorizer missing read-write dependency for interleaved accesses
Date: Fri, 12 Apr 2013 12:40:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: wschmidt at gcc dot gnu.org
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X-Bugzilla-Priority: P3
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Message-ID: <bug-56933-4@http.gcc.gnu.org/bugzilla/>
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http://gcc.gnu.org/bugzilla/show_bug.cgi?idV933
Bug #: 56933
Summary: [4.9 Regression] Vectorizer missing read-write
dependency for interleaved accesses
Classification: Unclassified
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: wschmidt@gcc.gnu.org
CC: bergner@gcc.gnu.org, dje@gcc.gnu.org,
rguenth@gcc.gnu.org
Host: powerpc*-*-*
Target: powerpc*-*-*
Build: powerpc*-*-*
Created attachment 29861
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id)861
Vectorization details dump for the test case
vect_analyze_group_access() in tree-vect-data-refs.c contains a test for
load-store dependencies:
if (GROUP_READ_WRITE_DEPENDENCE (vinfo_for_stmt (next))
|| GROUP_READ_WRITE_DEPENDENCE (vinfo_for_stmt (prev)))
Currently this always returns false because this field has not yet been set in
the vinfo. This began with r196872, where the code to analyze accesses was
moved ahead of the code to analyze dependences.
I put together a test demonstrating that it's possible for us to generate
incorrect code as a result:
subroutine test(a,b,c,d,e,f)
integer k
real*4, intent(out) :: a(1000)
real*4, intent(out) :: b(1000)
real*4, intent(in) :: c(1000)
real*4, intent(inout) :: d(2000)
real*4, intent(out) :: e(1000)
real*4, intent(out) :: f(1000)
do k = 1,1000
a(k) = 3.0 * d(2*k)
e(k) = 3.3 * d(2*k+1)
d(2*k) = 2.0 * c(k)
d(2*k+1) = 2.3 * c(k)
b(k) = d(2*k) - 5.5;
f(k) = d(2*k+1) + 5.5;
enddo
return
end
I'm attaching a detailed dump of the vectorization pass that shows that the
values of d(2*k) and d(2*k+1) used to compute b(k) and f(k) are the ones loaded
prior to the stores to those locations.
To reproduce on powerpc64-unknown-linux-gnu:
$ gfortran -O3 -ffast-math -mcpu=power7 -fno-vect-cost-model interl-lsl-2.f
next prev parent reply other threads:[~2013-04-12 12:22 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-12 10:08 [Bug middle-end/56932] New: " ktietz at gcc dot gnu.org
2013-04-12 11:28 ` [Bug middle-end/56932] " pinskia at gcc dot gnu.org
2013-04-12 11:50 ` glisse at gcc dot gnu.org
2013-04-12 12:22 ` graham.stott at btinternet dot com [this message]
2013-04-12 18:31 ` ktietz at gcc dot gnu.org
2013-04-12 19:00 ` pinskia at gcc dot gnu.org
2013-04-12 20:02 ` glisse at gcc dot gnu.org
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