161 lines
6.5 KiB
C++
161 lines
6.5 KiB
C++
/*
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* Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*
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*/
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#include "precompiled.hpp"
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#include "gc/shared/memset_with_concurrent_readers.hpp"
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#include "runtime/prefetch.inline.hpp"
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#include "utilities/align.hpp"
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#include "utilities/debug.hpp"
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#include "utilities/globalDefinitions.hpp"
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#include "utilities/macros.hpp"
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#if INCLUDE_ALL_GCS
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// An implementation of memset, for use when there may be concurrent
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// readers of the region being stored into.
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//
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// We can't use the standard library memset if it is implemented using
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// block initializing stores. Doing so can result in concurrent readers
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// seeing spurious zeros.
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//
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// We can't use the obvious C/C++ for-loop, because the compiler may
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// recognize the idiomatic loop and optimize it into a call to the
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// standard library memset; we've seen exactly this happen with, for
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// example, Solaris Studio 12.3. Hence the use of inline assembly
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// code, hiding loops from the compiler's optimizer.
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//
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// We don't attempt to use the standard library memset when it is safe
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// to do so. We could conservatively do so by detecting the presence
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// of block initializing stores (VM_Version::has_blk_init()), but the
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// implementation provided here should be sufficient.
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inline void fill_subword(void* start, void* end, int value) {
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STATIC_ASSERT(BytesPerWord == 8);
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assert(pointer_delta(end, start, 1) < (size_t)BytesPerWord, "precondition");
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// Dispatch on (end - start).
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void* pc;
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__asm__ volatile(
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// offset := (7 - (end - start)) + 3
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// 3 instructions from rdpc to DISPATCH
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" sub %[offset], %[end], %[offset]\n\t" // offset := start - end
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" sllx %[offset], 2, %[offset]\n\t" // scale offset for instruction size of 4
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" add %[offset], 40, %[offset]\n\t" // offset += 10 * instruction size
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" rd %%pc, %[pc]\n\t" // dispatch on scaled offset
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" jmpl %[pc]+%[offset], %%g0\n\t"
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" nop\n\t"
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// DISPATCH: no direct reference, but without it the store block may be elided.
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"1:\n\t"
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" stb %[value], [%[end]-7]\n\t" // end[-7] = value
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" stb %[value], [%[end]-6]\n\t"
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" stb %[value], [%[end]-5]\n\t"
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" stb %[value], [%[end]-4]\n\t"
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" stb %[value], [%[end]-3]\n\t"
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" stb %[value], [%[end]-2]\n\t"
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" stb %[value], [%[end]-1]\n\t" // end[-1] = value
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: /* only temporaries/overwritten outputs */
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[pc] "=&r" (pc), // temp
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[offset] "+&r" (start)
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: [end] "r" (end),
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[value] "r" (value)
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: "memory");
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}
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void memset_with_concurrent_readers(void* to, int value, size_t size) {
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Prefetch::write(to, 0);
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void* end = static_cast<char*>(to) + size;
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if (size >= (size_t)BytesPerWord) {
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// Fill any partial word prefix.
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uintx* aligned_to = static_cast<uintx*>(align_up(to, BytesPerWord));
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fill_subword(to, aligned_to, value);
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// Compute fill word.
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STATIC_ASSERT(BitsPerByte == 8);
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STATIC_ASSERT(BitsPerWord == 64);
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uintx xvalue = value & 0xff;
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xvalue |= (xvalue << 8);
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xvalue |= (xvalue << 16);
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xvalue |= (xvalue << 32);
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uintx* aligned_end = static_cast<uintx*>(align_down(end, BytesPerWord));
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assert(aligned_to <= aligned_end, "invariant");
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// for ( ; aligned_to < aligned_end; ++aligned_to) {
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// *aligned_to = xvalue;
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// }
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uintptr_t temp;
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__asm__ volatile(
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// Unroll loop x8.
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" sub %[aend], %[ato], %[temp]\n\t"
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" cmp %[temp], 56\n\t" // cc := (aligned_end - aligned_to) > 7 words
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" ba %%xcc, 2f\n\t" // goto TEST always
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" sub %[aend], 56, %[temp]\n\t" // limit := aligned_end - 7 words
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// LOOP:
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"1:\n\t" // unrolled x8 store loop top
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" cmp %[temp], %[ato]\n\t" // cc := limit > (next) aligned_to
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" stx %[xvalue], [%[ato]-64]\n\t" // store 8 words, aligned_to pre-incremented
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" stx %[xvalue], [%[ato]-56]\n\t"
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" stx %[xvalue], [%[ato]-48]\n\t"
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" stx %[xvalue], [%[ato]-40]\n\t"
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" stx %[xvalue], [%[ato]-32]\n\t"
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" stx %[xvalue], [%[ato]-24]\n\t"
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" stx %[xvalue], [%[ato]-16]\n\t"
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" stx %[xvalue], [%[ato]-8]\n\t"
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// TEST:
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"2:\n\t"
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" bgu,a %%xcc, 1b\n\t" // goto LOOP if more than 7 words remaining
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" add %[ato], 64, %[ato]\n\t" // aligned_to += 8, for next iteration
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// Fill remaining < 8 full words.
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// Dispatch on (aligned_end - aligned_to).
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// offset := (7 - (aligned_end - aligned_to)) + 3
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// 3 instructions from rdpc to DISPATCH
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" sub %[ato], %[aend], %[ato]\n\t" // offset := aligned_to - aligned_end
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" srax %[ato], 1, %[ato]\n\t" // scale offset for instruction size of 4
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" add %[ato], 40, %[ato]\n\t" // offset += 10 * instruction size
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" rd %%pc, %[temp]\n\t" // dispatch on scaled offset
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" jmpl %[temp]+%[ato], %%g0\n\t"
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" nop\n\t"
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// DISPATCH: no direct reference, but without it the store block may be elided.
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"3:\n\t"
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" stx %[xvalue], [%[aend]-56]\n\t" // aligned_end[-7] = xvalue
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" stx %[xvalue], [%[aend]-48]\n\t"
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" stx %[xvalue], [%[aend]-40]\n\t"
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" stx %[xvalue], [%[aend]-32]\n\t"
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" stx %[xvalue], [%[aend]-24]\n\t"
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" stx %[xvalue], [%[aend]-16]\n\t"
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" stx %[xvalue], [%[aend]-8]\n\t" // aligned_end[-1] = xvalue
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: /* only temporaries/overwritten outputs */
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[temp] "=&r" (temp),
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[ato] "+&r" (aligned_to)
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: [aend] "r" (aligned_end),
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[xvalue] "r" (xvalue)
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: "cc", "memory");
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to = aligned_end; // setup for suffix
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}
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// Fill any partial word suffix. Also the prefix if size < BytesPerWord.
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fill_subword(to, end, value);
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}
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#endif // INCLUDE_ALL_GCS
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