hanchenye-llvm-project/lld/ELF/ICF.h

//===- ICF.h --------------------------------------------------------------===//
//
//                             The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef LLD_ELF_ICF_H
#define LLD_ELF_ICF_H

namespace lld {
namespace elf {
template <class ELFT> void doIcf();
}
}

#endif
ELF: Implement ICF. This patch implements the same algorithm as LLD/COFF's ICF. I'm not going to repeat the same description about how it works, so you want to read the comment in ICF.cpp in this patch if you want to know the details. This algorithm should be more powerful than the ICF algorithm implemented in GNU gold. It can even merge mutually-recursive functions (which is harder than one might think). ICF is a fairly effective size optimization. Here are some examples. LLD: 37.14 MB -> 35.80 MB (-3.6%) Clang: 59.41 MB -> 57.80 MB (-2.7%) The lacking feature is "safe" version of ICF. This merges all identical sections. That is not compatible with a C/C++ language requirement that two distinct functions must have distinct addresses. But as long as your program do not rely on the pointer equality (which is in many cases true), your program should work with the feature. LLD works fine for example. GNU gold implements so-called "safe ICF" that identifies functions that are safe to merge by heuristics -- for example, gold thinks that constructors are safe to merge because there is no way to take an address of a constructor in C++. We have a different idea which David Majnemer suggested that we add NOPs at beginning of merged functions so that two or more pointers can have distinct values. We can do whichever we want, but this patch does not include neither. http://reviews.llvm.org/D17529 llvm-svn: 261912 2016-02-26 02:43:51 +08:00			`//===- ICF.h --------------------------------------------------------------===//`
			`//`
			`// The LLVM Linker`
			`//`
			`// This file is distributed under the University of Illinois Open Source`
			`// License. See LICENSE.TXT for details.`
			`//`
			`//===----------------------------------------------------------------------===//`

			`#ifndef LLD_ELF_ICF_H`
			`#define LLD_ELF_ICF_H`

			`namespace lld {`
Rename elf2 to elf. llvm-svn: 262159 2016-02-28 08:25:54 +08:00			`namespace elf {`
Do not pass Symtab to markLive/doICF since Symtab is globally accessible. llvm-svn: 268286 2016-05-03 03:30:42 +08:00			`template <class ELFT> void doIcf();`
ELF: Implement ICF. This patch implements the same algorithm as LLD/COFF's ICF. I'm not going to repeat the same description about how it works, so you want to read the comment in ICF.cpp in this patch if you want to know the details. This algorithm should be more powerful than the ICF algorithm implemented in GNU gold. It can even merge mutually-recursive functions (which is harder than one might think). ICF is a fairly effective size optimization. Here are some examples. LLD: 37.14 MB -> 35.80 MB (-3.6%) Clang: 59.41 MB -> 57.80 MB (-2.7%) The lacking feature is "safe" version of ICF. This merges all identical sections. That is not compatible with a C/C++ language requirement that two distinct functions must have distinct addresses. But as long as your program do not rely on the pointer equality (which is in many cases true), your program should work with the feature. LLD works fine for example. GNU gold implements so-called "safe ICF" that identifies functions that are safe to merge by heuristics -- for example, gold thinks that constructors are safe to merge because there is no way to take an address of a constructor in C++. We have a different idea which David Majnemer suggested that we add NOPs at beginning of merged functions so that two or more pointers can have distinct values. We can do whichever we want, but this patch does not include neither. http://reviews.llvm.org/D17529 llvm-svn: 261912 2016-02-26 02:43:51 +08:00			`}`
			`}`

			`#endif`