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8299179: ArrayFill with store on backedge needs to reduce length by 1
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Backport-of: d716ec5d3034240b7dd0aed86d9bb371bc3e5f5a
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TobiHartmann committed Apr 4, 2023
1 parent 71deb0b commit 760ff6e
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20 changes: 20 additions & 0 deletions src/hotspot/share/opto/loopTransform.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -4242,6 +4242,19 @@ bool PhaseIdealLoop::intrinsify_fill(IdealLoopTree* lpt) {
Node* len = new SubINode(head->limit(), head->init_trip());
_igvn.register_new_node_with_optimizer(len);

// If the store is on the backedge, it is not executed in the last
// iteration, and we must subtract 1 from the len.
Node* backedge = head->loopexit()->proj_out(1);
if (store->in(0) == backedge) {
len = new SubINode(len, _igvn.intcon(1));
_igvn.register_new_node_with_optimizer(len);
#ifndef PRODUCT
if (TraceOptimizeFill) {
tty->print_cr("ArrayFill store on backedge, subtract 1 from len.");
}
#endif
}

BasicType t = store->as_Mem()->memory_type();
bool aligned = false;
if (offset != NULL && head->init_trip()->is_Con()) {
Expand Down Expand Up @@ -4344,5 +4357,12 @@ bool PhaseIdealLoop::intrinsify_fill(IdealLoopTree* lpt) {
_igvn.replace_node(n, C->top());
}

#ifndef PRODUCT
if (TraceOptimizeFill) {
tty->print("ArrayFill call ");
call->dump();
}
#endif

return true;
}
178 changes: 178 additions & 0 deletions test/hotspot/jtreg/compiler/loopopts/TestBackedgeLoadArrayFill.jasm
Original file line number Diff line number Diff line change
@@ -0,0 +1,178 @@
/*
* Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/

super public class TestBackedgeLoadArrayFill
{
public Method "<init>":"()V"
stack 2 locals 1
{
aload_0;
invokespecial Method java/lang/Object."<init>":"()V";
return;
}

static Method test_101:"()V"
stack 20 locals 20
{
// test_002 in jasm: using try-catch
ldc 6;
istore_0; // i = 6
ldc 25;
newarray int;
astore_1; // arr = new int[25]
HEAD:
aload_1;
iload_0;
iconst_1;
iastore; // arr[i] = 1
// second block - the only one -> head block can be copied: one before, one on backedge
try t0;
aload_1;
iload_0;
aload_1;
iload_0;
iaload;
iastore; // arr[i] = arr[i]
goto FINALLY;
endtry t0;
catch t0 java/lang/Exception;
pop; // exception
FINALLY:
iinc 0, 1; // i++
iload_0;
ldc 21;
if_icmplt HEAD; // if i < 21
// write array
aload_1;
putstatic Field TestBackedgeLoadArrayFillMain.intA:"[I";
return;
}

static Method test_102:"()V"
stack 20 locals 20
{
// test_002 in jasm: without try-catch
ldc 5;
istore_0; // i = 5
ldc 25;
newarray int;
astore_1; // arr = new int[25]
HEAD:
aload_1;
iload_0;
iconst_1;
iastore; // arr[i] = 1
goto SECOND;
// second block - the only one -> head block can be copied: one before, one on backedge
// must have some material before inc, else it is partial peeled away
// And if we set -XX:-PartialPeelLoop, then the counted loop is never detected
SECOND:
aload_1;
iload_0;
aload_1;
iload_0;
iaload;
iastore; // arr[i] = arr[i]
iinc 0, 1; // i++
iload_0;
ldc 21;
if_icmplt HEAD; // if i < 21
// write array
aload_1;
putstatic Field TestBackedgeLoadArrayFillMain.intA:"[I";
return;
}

static Method test_103:"()V"
stack 20 locals 20
{
// test_002 in jasm: without try-catch, and second array
ldc 7;
istore_0; // i = 7
ldc 25;
newarray int;
astore_1; // arr = new int[25]
ldc 25;
newarray int;
astore_2; // arr2 = new int[25]
HEAD:
aload_1;
iload_0;
iconst_1;
iastore; // arr[i] = 1
goto SECOND;
// second block - the only one -> head block can be copied: one before, one on backedge
SECOND:
// we can also do the identity read-write on another array - it just has to eventually disappear
aload_2;
iload_0;
aload_2;
iload_0;
iaload;
iastore; // arr2[i] = arr2[i]

iinc 0, 1; // i++
iload_0;
ldc 21;
if_icmplt HEAD; // if i < 21
// write array
aload_1;
putstatic Field TestBackedgeLoadArrayFillMain.intA:"[I";
return;
}

static Method test_104:"()V"
stack 20 locals 20
{
ldc 9;
istore_0; // i = 9
ldc 25;
newarray int;
astore_1; // arr = new int[25]
HEAD:
aload_1;
iload_0;
iconst_1;
iastore; // arr[i] = 1
goto SECOND;
// second block - the only one -> head block can be copied: one before, one on backedge
SECOND:
// CFG leads to partial peel -> load moved into loop body, then intrinsified
iload_0;
ldc 2;
irem;
ifeq SKIP;

SKIP:

iinc 0, 1; // i++
iload_0;
ldc 21;
if_icmplt HEAD; // if i < 21
// write array
aload_1;
putstatic Field TestBackedgeLoadArrayFillMain.intA:"[I";
return;
}
}

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