rust/src/rustllvm/PassWrapper.cpp
Alex Crichton 58ab4a0064 rustc: Enable -f{function,data}-sections
The compiler has previously been producing binaries on the order of 1.8MB for
hello world programs "fn main() {}". This is largely a result of the compilation
model used by compiling entire libraries into a single object file and because
static linking is favored by default.

When linking, linkers will pull in the entire contents of an object file if any
symbol from the object file is used. This means that if any symbol from a rust
library is used, the entire library is pulled in unconditionally, regardless of
whether the library is used or not.

Traditional C/C++ projects do not normally encounter these large executable
problems because their archives (rust's rlibs) are composed of many objects.
Because of this, linkers can eliminate entire objects from being in the final
executable. With rustc, however, the linker does not have the opportunity to
leave out entire object files.

In order to get similar benefits from dead code stripping at link time, this
commit enables the -ffunction-sections and -fdata-sections flags in LLVM, as
well as passing --gc-sections to the linker *by default*. This means that each
function and each global will be placed into its own section, allowing the
linker to GC all unused functions and data symbols.

By enabling these flags, rust is able to generate much smaller binaries default.
On linux, a hello world binary went from 1.8MB to 597K (a 67% reduction in
size). The output size of dynamic libraries remained constant, but the output
size of rlibs increased, as seen below:

    libarena         -  2.27% bigger (   292872 =>    299508)
    libcollections   -  0.64% bigger (  6765884 =>   6809076)
    libflate         -  0.83% bigger (   186516 =>    188060)
    libfourcc        - 14.71% bigger (   307290 =>    352498)
    libgetopts       -  4.42% bigger (   761468 =>    795102)
    libglob          -  2.73% bigger (   899932 =>    924542)
    libgreen         -  9.63% bigger (  1281718 =>   1405124)
    libhexfloat      - 13.88% bigger (   333738 =>    380060)
    liblibc          - 10.79% bigger (   551280 =>    610736)
    liblog           - 10.93% bigger (   218208 =>    242060)
    libnative        -  8.26% bigger (  1362096 =>   1474658)
    libnum           -  2.34% bigger (  2583400 =>   2643916)
    librand          -  1.72% bigger (  1608684 =>   1636394)
    libregex         -  6.50% bigger (  1747768 =>   1861398)
    librustc         -  4.21% bigger (151820192 => 158218924)
    librustdoc       -  8.96% bigger ( 13142604 =>  14320544)
    librustuv        -  4.13% bigger (  4366896 =>   4547304)
    libsemver        -  2.66% bigger (   396166 =>    406686)
    libserialize     -  1.91% bigger (  6878396 =>   7009822)
    libstd           -  3.59% bigger ( 39485286 =>  40902218)
    libsync          -  3.95% bigger (  1386390 =>   1441204)
    libsyntax        -  4.96% bigger ( 35757202 =>  37530798)
    libterm          - 13.99% bigger (   924580 =>   1053902)
    libtest          -  6.04% bigger (  2455720 =>   2604092)
    libtime          -  2.84% bigger (  1075708 =>   1106242)
    liburl           -  6.53% bigger (   590458 =>    629004)
    libuuid          -  4.63% bigger (   326350 =>    341466)
    libworkcache     -  8.45% bigger (  1230702 =>   1334750)

This increase in size is a result of encoding many more section names into each
object file (rlib). These increases are moderate enough that this change seems
worthwhile to me, due to the drastic improvements seen in the final artifacts.
The overall increase of the stage2 target folder (not the size of an install)
went from 337MB to 348MB (3% increase).

Additionally, linking is generally slower when executed with all these new
sections plus the --gc-sections flag. The stage0 compiler takes 1.4s to link the
`rustc` binary, where the stage1 compiler takes 1.9s to link the binary. Three
megabytes are shaved off the binary. I found this increase in link time to be
acceptable relative to the benefits of code size gained.

This commit only enables --gc-sections for *executables*, not dynamic libraries.
LLVM does all the heavy lifting when producing an object file for a dynamic
library, so there is little else for the linker to do (remember that we only
have one object file).

I conducted similar experiments by putting a *module's* functions and data
symbols into its own section (granularity moved to a module level instead of a
function/static level). The size benefits of a hello world were seen to be on
the order of 400K rather than 1.2MB. It seemed that enough benefit was gained
using ffunction-sections that this route was less desirable, despite the lesser
increases in binary rlib size.
2014-04-29 10:29:00 -07:00

267 lines
8.7 KiB
C++

// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
#include <stdio.h>
#include "rustllvm.h"
#include "llvm/Support/CBindingWrapping.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include "llvm/Transforms/IPO/PassManagerBuilder.h"
#include "llvm-c/Transforms/PassManagerBuilder.h"
using namespace llvm;
extern cl::opt<bool> EnableARMEHABI;
typedef struct LLVMOpaquePass *LLVMPassRef;
typedef struct LLVMOpaqueTargetMachine *LLVMTargetMachineRef;
DEFINE_STDCXX_CONVERSION_FUNCTIONS(Pass, LLVMPassRef)
DEFINE_STDCXX_CONVERSION_FUNCTIONS(TargetMachine, LLVMTargetMachineRef)
DEFINE_STDCXX_CONVERSION_FUNCTIONS(PassManagerBuilder, LLVMPassManagerBuilderRef)
extern "C" void
LLVMInitializePasses() {
PassRegistry &Registry = *PassRegistry::getPassRegistry();
initializeCore(Registry);
initializeCodeGen(Registry);
initializeScalarOpts(Registry);
initializeVectorization(Registry);
initializeIPO(Registry);
initializeAnalysis(Registry);
initializeIPA(Registry);
initializeTransformUtils(Registry);
initializeInstCombine(Registry);
initializeInstrumentation(Registry);
initializeTarget(Registry);
}
extern "C" bool
LLVMRustAddPass(LLVMPassManagerRef PM, const char *PassName) {
PassManagerBase *pm = unwrap(PM);
StringRef SR(PassName);
PassRegistry *PR = PassRegistry::getPassRegistry();
const PassInfo *PI = PR->getPassInfo(SR);
if (PI) {
pm->add(PI->createPass());
return true;
}
return false;
}
extern "C" LLVMTargetMachineRef
LLVMRustCreateTargetMachine(const char *triple,
const char *cpu,
const char *feature,
CodeModel::Model CM,
Reloc::Model RM,
CodeGenOpt::Level OptLevel,
bool EnableSegmentedStacks,
bool UseSoftFloat,
bool NoFramePointerElim,
bool FunctionSections,
bool DataSections) {
std::string Error;
Triple Trip(Triple::normalize(triple));
const llvm::Target *TheTarget = TargetRegistry::lookupTarget(Trip.getTriple(),
Error);
if (TheTarget == NULL) {
LLVMRustSetLastError(Error.c_str());
return NULL;
}
TargetOptions Options;
Options.NoFramePointerElim = NoFramePointerElim;
#if LLVM_VERSION_MINOR < 5
Options.EnableSegmentedStacks = EnableSegmentedStacks;
#endif
Options.FloatABIType = FloatABI::Default;
Options.UseSoftFloat = UseSoftFloat;
if (UseSoftFloat) {
Options.FloatABIType = FloatABI::Soft;
}
TargetMachine *TM = TheTarget->createTargetMachine(Trip.getTriple(),
cpu,
feature,
Options,
RM,
CM,
OptLevel);
TM->setDataSections(DataSections);
TM->setFunctionSections(FunctionSections);
return wrap(TM);
}
extern "C" void
LLVMRustDisposeTargetMachine(LLVMTargetMachineRef TM) {
delete unwrap(TM);
}
// Unfortunately, LLVM doesn't expose a C API to add the corresponding analysis
// passes for a target to a pass manager. We export that functionality through
// this function.
extern "C" void
LLVMRustAddAnalysisPasses(LLVMTargetMachineRef TM,
LLVMPassManagerRef PMR,
LLVMModuleRef M) {
PassManagerBase *PM = unwrap(PMR);
#if LLVM_VERSION_MINOR >= 5
PM->add(new DataLayoutPass(unwrap(M)));
#else
PM->add(new DataLayout(unwrap(M)));
#endif
unwrap(TM)->addAnalysisPasses(*PM);
}
// Unfortunately, the LLVM C API doesn't provide a way to set the `LibraryInfo`
// field of a PassManagerBuilder, we expose our own method of doing so.
extern "C" void
LLVMRustAddBuilderLibraryInfo(LLVMPassManagerBuilderRef PMB, LLVMModuleRef M) {
Triple TargetTriple(unwrap(M)->getTargetTriple());
unwrap(PMB)->LibraryInfo = new TargetLibraryInfo(TargetTriple);
}
// Unfortunately, the LLVM C API doesn't provide a way to create the
// TargetLibraryInfo pass, so we use this method to do so.
extern "C" void
LLVMRustAddLibraryInfo(LLVMPassManagerRef PMB, LLVMModuleRef M) {
Triple TargetTriple(unwrap(M)->getTargetTriple());
unwrap(PMB)->add(new TargetLibraryInfo(TargetTriple));
}
// Unfortunately, the LLVM C API doesn't provide an easy way of iterating over
// all the functions in a module, so we do that manually here. You'll find
// similar code in clang's BackendUtil.cpp file.
extern "C" void
LLVMRustRunFunctionPassManager(LLVMPassManagerRef PM, LLVMModuleRef M) {
FunctionPassManager *P = unwrap<FunctionPassManager>(PM);
P->doInitialization();
for (Module::iterator I = unwrap(M)->begin(),
E = unwrap(M)->end(); I != E; ++I)
if (!I->isDeclaration())
P->run(*I);
P->doFinalization();
}
extern "C" void
LLVMRustSetLLVMOptions(int Argc, char **Argv) {
// Initializing the command-line options more than once is not allowed. So,
// check if they've already been initialized. (This could happen if we're
// being called from rustpkg, for example). If the arguments change, then
// that's just kinda unfortunate.
static bool initialized = false;
if (initialized) return;
initialized = true;
cl::ParseCommandLineOptions(Argc, Argv);
}
extern "C" bool
LLVMRustWriteOutputFile(LLVMTargetMachineRef Target,
LLVMPassManagerRef PMR,
LLVMModuleRef M,
const char *path,
TargetMachine::CodeGenFileType FileType) {
PassManager *PM = unwrap<PassManager>(PMR);
std::string ErrorInfo;
#if LLVM_VERSION_MINOR >= 4
raw_fd_ostream OS(path, ErrorInfo, sys::fs::F_None);
#else
raw_fd_ostream OS(path, ErrorInfo, raw_fd_ostream::F_Binary);
#endif
if (ErrorInfo != "") {
LLVMRustSetLastError(ErrorInfo.c_str());
return false;
}
formatted_raw_ostream FOS(OS);
unwrap(Target)->addPassesToEmitFile(*PM, FOS, FileType, false);
PM->run(*unwrap(M));
return true;
}
extern "C" void
LLVMRustPrintModule(LLVMPassManagerRef PMR,
LLVMModuleRef M,
const char* path) {
PassManager *PM = unwrap<PassManager>(PMR);
std::string ErrorInfo;
#if LLVM_VERSION_MINOR >= 4
raw_fd_ostream OS(path, ErrorInfo, sys::fs::F_None);
#else
raw_fd_ostream OS(path, ErrorInfo, raw_fd_ostream::F_Binary);
#endif
formatted_raw_ostream FOS(OS);
#if LLVM_VERSION_MINOR >= 5
PM->add(createPrintModulePass(FOS));
#else
PM->add(createPrintModulePass(&FOS));
#endif
PM->run(*unwrap(M));
}
extern "C" void
LLVMRustPrintPasses() {
LLVMInitializePasses();
struct MyListener : PassRegistrationListener {
void passEnumerate(const PassInfo *info) {
if (info->getPassArgument() && *info->getPassArgument()) {
printf("%15s - %s\n", info->getPassArgument(),
info->getPassName());
}
}
} listener;
PassRegistry *PR = PassRegistry::getPassRegistry();
PR->enumerateWith(&listener);
}
extern "C" void
LLVMRustAddAlwaysInlinePass(LLVMPassManagerBuilderRef PMB, bool AddLifetimes) {
unwrap(PMB)->Inliner = createAlwaysInlinerPass(AddLifetimes);
}
extern "C" void
LLVMRustRunRestrictionPass(LLVMModuleRef M, char **symbols, size_t len) {
PassManager passes;
ArrayRef<const char*> ref(symbols, len);
passes.add(llvm::createInternalizePass(ref));
passes.run(*unwrap(M));
}
extern "C" void
LLVMRustMarkAllFunctionsNounwind(LLVMModuleRef M) {
for (Module::iterator GV = unwrap(M)->begin(),
E = unwrap(M)->end(); GV != E; ++GV) {
GV->setDoesNotThrow();
Function *F = dyn_cast<Function>(GV);
if (F == NULL)
continue;
for (Function::iterator B = F->begin(), BE = F->end(); B != BE; ++B) {
for (BasicBlock::iterator I = B->begin(), IE = B->end();
I != IE; ++I) {
if (isa<InvokeInst>(I)) {
InvokeInst *CI = cast<InvokeInst>(I);
CI->setDoesNotThrow();
}
}
}
}
}