f27e4548fc
ICF = Identical C(ode|OMDAT) Folding
This is the LLD ELF/COFF algorithm, adapted for MachO. So far, only `-icf all` is supported. In order to support `-icf safe`, we will need to port address-significance tables (`.addrsig` directives) to MachO, which will come in later diffs.
`check-{llvm,clang,lld}` have 0 regressions for `lld -icf all` vs. baseline ld64.
We only run ICF on `__TEXT,__text` for reasons explained in the block comment in `ConcatOutputSection.cpp`.
Here is the perf impact for linking `chromium_framekwork` on a Mac Pro (16-core Xeon W) for the non-ICF case vs. pre-ICF:
```
N Min Max Median Avg Stddev
x 20 4.27 4.44 4.34 4.349 0.043029977
+ 20 4.37 4.46 4.405 4.4115 0.025188761
Difference at 95.0% confidence
0.0625 +/- 0.0225658
1.43711% +/- 0.518873%
(Student's t, pooled s = 0.0352566)
```
Reviewed By: #lld-macho, int3
Differential Revision: https://reviews.llvm.org/D103292
81 lines
2.7 KiB
C++
81 lines
2.7 KiB
C++
//===- Symbols.cpp --------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "Symbols.h"
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#include "InputFiles.h"
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#include "SyntheticSections.h"
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using namespace llvm;
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using namespace lld;
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using namespace lld::macho;
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// Returns a symbol for an error message.
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static std::string demangle(StringRef symName) {
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if (config->demangle)
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return demangleItanium(symName);
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return std::string(symName);
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}
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std::string lld::toString(const Symbol &sym) { return demangle(sym.getName()); }
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std::string lld::toMachOString(const object::Archive::Symbol &b) {
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return demangle(b.getName());
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}
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uint64_t Symbol::getStubVA() const { return in.stubs->getVA(stubsIndex); }
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uint64_t Symbol::getGotVA() const { return in.got->getVA(gotIndex); }
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uint64_t Symbol::getTlvVA() const { return in.tlvPointers->getVA(gotIndex); }
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bool Symbol::isLive() const {
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if (isa<DylibSymbol>(this) || isa<Undefined>(this))
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return used;
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if (auto *d = dyn_cast<Defined>(this)) {
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// Non-absolute symbols might be alive because their section is
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// no_dead_strip or live_support. In that case, the section will know
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// that it's live but `used` might be false. Non-absolute symbols always
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// have to use the section's `live` bit as source of truth.
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if (d->isAbsolute())
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return used;
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return d->isec->canonical()->isLive(d->value);
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}
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assert(!isa<CommonSymbol>(this) &&
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"replaceCommonSymbols() runs before dead code stripping, and isLive() "
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"should only be called after dead code stripping");
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// Assume any other kind of symbol is live.
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return true;
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}
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uint64_t Defined::getVA() const {
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assert(isLive() && "this should only be called for live symbols");
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if (isAbsolute())
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return value;
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if (!isec->canonical()->isFinal) {
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// A target arch that does not use thunks ought never ask for
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// the address of a function that has not yet been finalized.
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assert(target->usesThunks());
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// ConcatOutputSection::finalize() can seek the address of a
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// function before its address is assigned. The thunking algorithm
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// knows that unfinalized functions will be out of range, so it is
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// expedient to return a contrived out-of-range address.
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return TargetInfo::outOfRangeVA;
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}
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return isec->canonical()->getVA(value);
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}
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uint64_t DylibSymbol::getVA() const {
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return isInStubs() ? getStubVA() : Symbol::getVA();
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}
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void LazySymbol::fetchArchiveMember() { getFile()->fetch(sym); }
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