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[ELF] Remove .strtab deduplication 

D118577: the 0.1~1.1% .strtab size reduction does not justify the 3~6%
link time increase. Just remove it even for -O2. release/14.x
has D118577 and the release note mentioned that this may be removed.

Fix https://github.com/ClangBuiltLinux/linux/issues/1578
caused by D118577 (empty string not in stringMap).
This commit is contained in:
Fangrui Song 2022-02-18 14:54:10 -08:00
parent e3b9bb5a18
commit c12d49c4e2
3 changed files with 38 additions and 36 deletions
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5
lld/ELF/SyntheticSections.cpp
View File

@ -1230,6 +1230,7 @@ StringTableSection::StringTableSection(StringRef name, bool dynamic)
dynamic(dynamic) {
// ELF string tables start with a NUL byte.
strings.push_back("");
stringMap.try_emplace(CachedHashStringRef(""), 0);
size = 1;
}
@ -2156,9 +2157,7 @@ void SymbolTableBaseSection::sortSymTabSymbols() {
void SymbolTableBaseSection::addSymbol(Symbol *b) {
// Adding a local symbol to a .dynsym is a bug.
assert(this->type != SHT_DYNSYM || !b->isLocal());
bool hashIt = b->isLocal() && config->optimize >= 2;
symbols.push_back({b, strTabSec.addString(b->getName(), hashIt)});
symbols.push_back({b, strTabSec.addString(b->getName(), false)});
}
size_t SymbolTableBaseSection::getSymbolIndex(Symbol *sym) {

33
lld/test/ELF/strtab-dedup.s
View File

@ -1,33 +0,0 @@
# REQUIRES: x86
# RUN: split-file %s %t
# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/a.s -o %t/a.o
# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/b.s -o %t/b.o
## By default local symbol names are not deduplicated.
# RUN: ld.lld %t/a.o %t/b.o -o %t/a
# RUN: llvm-readelf -p .strtab %t/a | FileCheck %s --check-prefix=NODEDUP
# NODEDUP: [ 1] local
# NODEDUP-NEXT: [ 7] local
# NODEDUP-NEXT: [ d] foo
# NODEDUP-EMPTY:
## -O2 deduplicates local symbol names.
# RUN: ld.lld -O2 %t/a.o %t/b.o -o %t/a
# RUN: llvm-readelf -p .strtab %t/a | FileCheck %s --check-prefix=DEDUP
# DEDUP: [ 1] local
# DEDUP-NEXT: [ 7] foo
# DEDUP-EMPTY:
#--- a.s
.global foo
foo:
local:
ret
#--- b.s
.weak foo
foo:
local:
ret

36
lld/test/ELF/strtab-nodedup.s Normal file
View File

@ -0,0 +1,36 @@
# REQUIRES: x86
# RUN: split-file %s %t
# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/a.s -o %t/a.o
# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/b.s -o %t/b.o
## Non-empty local symbol names are not deduplicated. This helps parallel
## .symtab write. We used to perform deduplication at -O2.
# RUN: ld.lld %t/a.o %t/b.o -o %t/a
# RUN: llvm-readelf -p .strtab %t/a | FileCheck %s --check-prefix=NODEDUP
# RUN: ld.lld -r -O2 %t/a.o %t/b.o -o %t/a.ro
# RUN: llvm-readelf -p .strtab %t/a.ro | FileCheck %s --check-prefix=NODEDUP
# NODEDUP: [ 1] local
# NODEDUP-NEXT: [ 7] local
# NODEDUP-NEXT: [ d] foo
# NODEDUP-EMPTY:
# RUN: llvm-readelf -s %t/a.ro | FileCheck %s --check-prefix=SYMTAB
# SYMTAB: 0: {{0+}} 0 NOTYPE LOCAL DEFAULT UND
# SYMTAB-NEXT: NOTYPE LOCAL DEFAULT [[#]] local
# SYMTAB-NEXT: SECTION LOCAL DEFAULT [[#]] .text
# SYMTAB-NEXT: NOTYPE LOCAL DEFAULT [[#]] local
# SYMTAB-NEXT: NOTYPE GLOBAL DEFAULT [[#]] foo
#--- a.s
.global foo
foo:
local:
ret
#--- b.s
.weak foo
foo:
local:
ret