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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
Fix potential test failures. Windows does not allow opened files to be removed. This patch fixes two types of errors. - Output file being the same as input file. Because LLD itself holds a file descriptor of the input file, it cannot create an output file with the same name as a new file. - Removing files before releasing MemoryBuffer objects. These tests are not failing no because MemoryBuffer happens to decide not to use mmap on these files. But we shouldn't rely on that behavior. llvm-svn: 280507
2016-09-03 01:19:28 +08:00
# RUN: ld.lld %t -o %t2 --icf=all --verbose | 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
# CHECK-NOT: Selected .text.f1
# CHECK-NOT: Selected .text.f2
.globl _start, f1, f2
_start:
ret
.section .text.f1, "ax"
f1:
mov $1, %rax
.section .text.f2, "ax"
f2:
mov $0, %rax