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Make __start_sec __end_sec handling more precise.

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With this we only ask LTO to keep a C named section if there is a
__start_ or __end symbol.

This is not as strict as lld's --gc-sections, but is as good as we can
get without having a far more detailed ir summary.

llvm-svn: 309232
This commit is contained in:
Rafael Espindola 2017-07-26 23:39:10 +00:00
parent 268f89d540
commit 4b075bb218
3 changed files with 29 additions and 3 deletions
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12
lld/ELF/LTO.cpp
View File

@ -11,6 +11,7 @@
#include "Config.h"
#include "Error.h"
#include "InputFiles.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "lld/Core/TargetOptionsCommandFlags.h"
#include "llvm/ADT/STLExtras.h"
@ -107,7 +108,14 @@ static std::unique_ptr<lto::LTO> createLTO() {
Config->LTOPartitions);
}
BitcodeCompiler::BitcodeCompiler() : LTOObj(createLTO()) {}
BitcodeCompiler::BitcodeCompiler() : LTOObj(createLTO()) {
for (Symbol *Sym : Symtab->getSymbols()) {
StringRef Name = Sym->body()->getName();
for (StringRef Prefix : {"__start_", "__stop_"})
if (Name.startswith(Prefix))
UsedStartStop.insert(Name.substr(Prefix.size()));
}
}
BitcodeCompiler::~BitcodeCompiler() = default;
@ -138,7 +146,7 @@ void BitcodeCompiler::add(BitcodeFile &F) {
R.VisibleToRegularObj = Sym->IsUsedInRegularObj ||
(R.Prevailing && Sym->includeInDynsym()) ||
isValidCIdentifier(ObjSym.getSectionName());
UsedStartStop.count(ObjSym.getSectionName());
if (R.Prevailing)
undefine(Sym);
R.LinkerRedefined = Config->RenamedSymbols.count(Sym);

2
lld/ELF/LTO.h
View File

@ -22,6 +22,7 @@
#define LLD_ELF_LTO_H
#include "lld/Core/LLVM.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/SmallString.h"
#include <memory>
#include <vector>
@ -50,6 +51,7 @@ private:
std::unique_ptr<llvm::lto::LTO> LTOObj;
std::vector<SmallString<0>> Buff;
std::vector<std::unique_ptr<MemoryBuffer>> Files;
llvm::DenseSet<StringRef> UsedStartStop;
};
} // namespace elf
} // namespace lld

18
lld/test/ELF/lto/section-name.ll
View File

@ -7,5 +7,21 @@ target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@foo = hidden global i32 42, section "foo_section"
@bar = hidden global i32 42, section "bar_section"
@zed = hidden global i32 42, section "zed_section"
; CHECK: foo_section PROGBITS
@__start_foo_section = external global i32
@__stop_bar_section = external global i32
define i32* @use1() {
ret i32* @__start_foo_section
}
define i32* @use2() {
ret i32* @__stop_bar_section
}
; CHECK-NOT: zed_section
; CHECK: foo_section PROGBITS
; CHECK-NEXT: bar_section PROGBITS
; CHECK-NOT: zed_section