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ld.lld SHF_MERGE|SHF_STRINGS duplicate elimination is computation heavy and utilitizes llvm::xxHash64, a simplified version of XXH64. Externally many sources confirm that a new variant XXH3 is much faster. I have picked a few hash implementations and computed the proportion of time spent on hashing in the overall link time (a debug build of clang 16 on a machine using AMD Zen 2 architecture): * llvm::xxHash64: 3.63% * official XXH64 (`#define XXH_VECTOR XXH_SCALAR`): 3.53% * official XXH3_64bits (`#define XXH_VECTOR XXH_SCALAR`): 1.21% * official XXH3_64bits (default, essentially `XXH_SSE2`): 1.22% * this patch llvm::xxh3_64bits: 1.19% The remaining part of lld remains unchanged. Consequently, a lower ratio indicates that hashing is faster. Therefore, it is evident that XXH3 from xxhash is significantly faster than both the official version and our llvm::xxHash64. ( string length: count 1-3: 393434 4-8: 2084056 9-16: 2846249 17-128: 5598928 129-240: 1317989 241-: 328058 ) This patch adds heavily simplified https://github.com/Cyan4973/xxHash, taking account of many simplification ideas from Devin Hussey's xxhash-clean. Important x86-64 optimization ideas: * Make XXH3_len_129to240_64b and XXH3_hashLong_64b noinline * Unroll XXH3_len_17to128_64b * __restrict does not affect Clang code generation Beside SHF_MERGE|SHF_STRINGS duplicate elimination, llvm/ADT/StringMap.h StringMapImpl::LookupBucketFor and a few places in lld can potentially be accelerated by switching to llvm::xxh3_64bits. Link: https://github.com/llvm/llvm-project/issues/63750 Reviewed By: serge-sans-paille Differential Revision: https://reviews.llvm.org/D154812
64 lines
1.9 KiB
C++
64 lines
1.9 KiB
C++
//===- llvm/unittest/Support/xxhashTest.cpp -------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Support/xxhash.h"
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#include "gtest/gtest.h"
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using namespace llvm;
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TEST(xxhashTest, Basic) {
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EXPECT_EQ(0xef46db3751d8e999U, xxHash64(StringRef()));
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EXPECT_EQ(0x33bf00a859c4ba3fU, xxHash64("foo"));
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EXPECT_EQ(0x48a37c90ad27a659U, xxHash64("bar"));
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EXPECT_EQ(0x69196c1b3af0bff9U,
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xxHash64("0123456789abcdefghijklmnopqrstuvwxyz"));
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}
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TEST(xxhashTest, xxh3) {
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constexpr size_t size = 2243;
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uint8_t a[size];
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uint64_t x = 1;
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for (size_t i = 0; i < size; ++i) {
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x ^= x << 13;
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x ^= x >> 7;
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x ^= x << 17;
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a[i] = uint8_t(x);
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}
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#define F(len, expected) \
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EXPECT_EQ(uint64_t(expected), xxh3_64bits(ArrayRef(a, size_t(len))))
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F(0, 0x2d06800538d394c2);
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F(1, 0xd0d496e05c553485);
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F(2, 0x84d625edb7055eac);
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F(3, 0x6ea2d59aca5c3778);
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F(4, 0xbf65290914e80242);
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F(5, 0xc01fd099ad4fc8e4);
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F(6, 0x9e3ea8187399caa5);
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F(7, 0x9da8b60540644f5a);
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F(8, 0xabc1413da6cd0209);
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F(9, 0x8bc89400bfed51f6);
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F(16, 0x7e46916754d7c9b8);
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F(17, 0xed4be912ba5f836d);
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F(32, 0xf59b59b58c304fd1);
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F(33, 0x9013fb74ca603e0c);
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F(64, 0xfa5271fcce0db1c3);
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F(65, 0x79c42431727f1012);
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F(96, 0x591ee0ddf9c9ccd1);
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F(97, 0x8ffc6a3111fe19da);
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F(128, 0x06a146ee9a2da378);
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F(129, 0xbc7138129bf065da);
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F(403, 0xcefeb3ffa532ad8c);
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F(512, 0xcdfa6b6268e3650f);
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F(513, 0x4bb5d42742f9765f);
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F(2048, 0x330ce110cbb79eae);
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F(2049, 0x3ba6afa0249fef9a);
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F(2240, 0xd61d4d2a94e926a8);
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F(2243, 0x0979f786a24edde7);
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#undef F
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}
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