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llvm-project/lld/test/ELF/icf4.s

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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
# REQUIRES: x86
# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
Use ErrorOS for log messages as well as error log are also diagnostics so it seems like they should to the same place as errors and debug messages. Without this change when I enable --verbose those messages go to stdout, but when I enable "-mllvm -debug" those messages go to stderr (because dbgs() goes to stderr by default). So I end up having to do this a lot: lld <args> > output_message 2>&1 Differential Revision: https://reviews.llvm.org/D41033 llvm-svn: 320427
2017-12-12 05:57:31 +08:00
# RUN: ld.lld %t -o %t2 --icf=all --verbose 2>&1 | FileCheck %s
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
[ELF] Add --print-icf-sections flag Currently ICF information is output through stderr if the "--verbose" flag is used. This differs to Gold for example, which uses an explicit flag to output this to stdout. This commit adds the "--print-icf-sections" and "--no-print-icf-sections" flags and changes the output message format for clarity and consistency with "--print-gc-sections". These messages are still output to stderr if using the verbose flag. However to avoid intermingled message output to console, this will not occur when the "--print-icf-sections" flag is used. Existing tests have been modified to expect the new message format from stderr. Patch by Owen Reynolds. Differential Revision: https://reviews.llvm.org/D42375 Reviewers: ruiu, rafael Reviewed by: llvm-svn: 323976
2018-02-02 00:00:46 +08:00
# CHECK-NOT: selected section '.text.f1'
# CHECK-NOT: selected section '.text.f2'
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
.globl _start, f1, f2
_start:
ret
.section .text.f1, "ax"
f1:
mov $1, %rax
.section .text.f2, "ax"
f2:
mov $0, %rax