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Reland #120514 after 2f6e3df08a8b7cd29273980e47310cf09c6fdbd8 fixed iteration order issue and libstdc++/libc++ differences. --- Both options instruct the linker to optimize section layout with the following goals: * `--bp-compression-sort=[data|function|both]`: Improve Lempel-Ziv compression by grouping similar sections together, resulting in a smaller compressed app size. * `--bp-startup-sort=function --irpgo-profile=<file>`: Utilize a temporal profile file to reduce page faults during program startup. The linker determines the section order by considering three groups: * Function sections ordered according to the temporal profile (`--irpgo-profile=`), prioritizing early-accessed and frequently accessed functions. * Function sections. Sections containing similar functions are placed together, maximizing compression opportunities. * Data sections. Similar data sections are placed together. Within each group, the sections are ordered using the Balanced Partitioning algorithm. The linker constructs a bipartite graph with two sets of vertices: sections and utility vertices. * For profile-guided function sections: + The number of utility vertices is determined by the symbol order within the profile file. + If `--bp-compression-sort-startup-functions` is specified, extra utility vertices are allocated to prioritize nearby function similarity. * For sections ordered for compression: Utility vertices are determined by analyzing k-mers of the section content and relocations. The call graph profile is disabled during this optimization. When `--symbol-ordering-file=` is specified, sections described in that file are placed earlier. Co-authored-by: Pengying Xu <xpy66swsry@gmail.com>
38 lines
1.3 KiB
C++
38 lines
1.3 KiB
C++
//===- BPSectionOrderer.h -------------------------------------------------===//
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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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///
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/// This file uses Balanced Partitioning to order sections to improve startup
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/// time and compressed size.
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///
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//===----------------------------------------------------------------------===//
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#ifndef LLD_ELF_BPSECTION_ORDERER_H
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#define LLD_ELF_BPSECTION_ORDERER_H
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/StringRef.h"
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namespace lld::elf {
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struct Ctx;
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class InputSectionBase;
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/// Run Balanced Partitioning to find the optimal function and data order to
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/// improve startup time and compressed size.
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///
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/// It is important that -ffunction-sections and -fdata-sections compiler flags
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/// are used to ensure functions and data are in their own sections and thus
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/// can be reordered.
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llvm::DenseMap<const InputSectionBase *, int>
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runBalancedPartitioning(Ctx &ctx, llvm::StringRef profilePath,
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bool forFunctionCompression, bool forDataCompression,
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bool compressionSortStartupFunctions, bool verbose);
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} // namespace lld::elf
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#endif
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