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Be less conservative wrt. linker dead code elimination

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This commit is contained in:
Martin Kinkelin 2023-02-10 21:39:10 +01:00
parent 95ac5cadb8
commit aa9eb33cb1
3 changed files with 22 additions and 21 deletions
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1
CHANGELOG.md
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@ -1,6 +1,7 @@
# LDC master
#### Big news
- Linker-level dead code elimination is enabled by default for Apple, wasm and *all* ELF targets too now. (#4320)
#### Platform support

16
driver/linker-gcc.cpp
View file

@ -479,6 +479,8 @@ void ArgsBuilder::addSanitizers(const llvm::Triple &triple) {
void ArgsBuilder::build(llvm::StringRef outputPath,
const std::vector<std::string> &defaultLibNames) {
const auto &triple = *global.params.targetTriple;
// object files
for (auto objfile : global.params.objfiles) {
args.push_back(objfile);
@ -494,7 +496,7 @@ void ArgsBuilder::build(llvm::StringRef outputPath,
// Link with profile-rt library when generating an instrumented binary.
if (opts::isInstrumentingForPGO()) {
addProfileRuntimeLinkFlags(*global.params.targetTriple);
addProfileRuntimeLinkFlags(triple);
}
if (opts::enableDynamicCompile) {
@ -521,10 +523,10 @@ void ArgsBuilder::build(llvm::StringRef outputPath,
args.push_back("-o");
args.push_back(std::string(outputPath));
addSanitizers(*global.params.targetTriple);
addSanitizers(triple);
if (opts::fXRayInstrument) {
addXRayLinkFlags(*global.params.targetTriple);
addXRayLinkFlags(triple);
}
// Add LTO link flags before adding the user link switches, such that the user
@ -559,16 +561,14 @@ void ArgsBuilder::build(llvm::StringRef outputPath,
addLdFlag("-rpath", rpath);
}
if (global.params.targetTriple->getOS() == llvm::Triple::Linux ||
(global.params.targetTriple->getOS() == llvm::Triple::FreeBSD &&
(useInternalLLDForLinking() ||
(!opts::linker.empty() && opts::linker != "bfd") ||
(opts::linker.empty() && isLldDefaultLinker())))) {
// Make sure we don't do --gc-sections when generating a profile-
// instrumented binary. The runtime relies on magic sections, which
// would be stripped by gc-section on older version of ld, see bug:
// https://sourceware.org/bugzilla/show_bug.cgi?id=19161
if (!opts::disableLinkerStripDead && !opts::isInstrumentingForPGO()) {
if (triple.isOSBinFormatMachO()) {
addLdFlag("-dead_strip");
} else {
addLdFlag("--gc-sections");
}
}

16
driver/targetmachine.cpp
View file

@ -492,14 +492,14 @@ createTargetMachine(const std::string targetTriple, const std::string arch,
break;
}
// Right now, we only support linker-level dead code elimination on Linux
// and FreeBSD using GNU or LLD linkers (based on the --gc-sections flag).
// The Apple ld on OS X supports a similar flag (-dead_strip) that doesn't
// require emitting the symbols into different sections. The MinGW ld doesn't
// seem to support --gc-sections at all.
if (!noLinkerStripDead && (triple.getOS() == llvm::Triple::Linux ||
triple.getOS() == llvm::Triple::FreeBSD ||
triple.getOS() == llvm::Triple::Win32)) {
// Linker-level dead code elimination for ELF/wasm binaries using GNU or LLD
// linkers (based on the --gc-sections flag) requires a separate section per
// symbol.
// The Apple ld64 on macOS supports a similar flag (-dead_strip) that doesn't
// require emitting the symbols into different sections.
// On Windows, the MSVC link.exe / lld-link.exe has `/REF`; LLD enforces
// separate sections with LTO, so do the same here.
if (!noLinkerStripDead && !triple.isOSBinFormatMachO()) {
targetOptions.FunctionSections = true;
targetOptions.DataSections = true;
}