be5a845e4c
This builds on top of commit 9d0754ada5dbbc0c009bcc2f7824488419cc5530
("[MC] Relax fragments eagerly") and relaxes fragments eagerly to
eliminate MCSection::HasLayout and `getFragmentOffset` overhead. The
approach is slightly different from
1a47f3f3db66589c11f8ddacfeaecc03fb80c510 and has less performance
benefit.
The new layout algorithm also addresses the following problems:
* Size change of MCFillFragment/MCOrgFragment did not influence the
fixed-point iteration, which could be problematic for contrived cases.
* The `invalid number of bytes` error was reported too early. Since
`.zero A-B` might have temporary negative values in the first few
iterations.
* X86AsmBackend::finishLayout performed only one iteration, which might
not converge. In addition, the removed `#ifndef NDEBUG` code (disabled
by default) in X86AsmBackend::finishLayout was problematic, as !NDEBUG
and NDEBUG builds evaluated fragment offsets at different times before
this patch.
* The computed layout for relax-recompute-align.s is optimal now.
Builds with many text sections (e.g. full LTO) shall observe a decrease
in compile time while the new algorithm could be slightly slower for
some -O0 -g projects.
Aligned bundling from the deprecated PNaCl placed constraints how we can
perform iteration.
88 lines
2.6 KiB
C++
88 lines
2.6 KiB
C++
//===- lib/MC/MCSection.cpp - Machine Code Section Representation ---------===//
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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 "llvm/MC/MCSection.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/Config/llvm-config.h"
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#include "llvm/MC/MCContext.h"
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#include "llvm/MC/MCFragment.h"
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#include "llvm/MC/MCSymbol.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/raw_ostream.h"
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#include <utility>
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using namespace llvm;
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MCSection::MCSection(SectionVariant V, StringRef Name, bool IsText,
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bool IsVirtual, MCSymbol *Begin)
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: Begin(Begin), BundleGroupBeforeFirstInst(false), HasInstructions(false),
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IsRegistered(false), IsText(IsText), IsVirtual(IsVirtual), Name(Name),
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Variant(V) {
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DummyFragment.setParent(this);
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// The initial subsection number is 0. Create a fragment list.
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CurFragList = &Subsections.emplace_back(0u, FragList{}).second;
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}
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MCSymbol *MCSection::getEndSymbol(MCContext &Ctx) {
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if (!End)
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End = Ctx.createTempSymbol("sec_end");
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return End;
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}
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bool MCSection::hasEnded() const { return End && End->isInSection(); }
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MCSection::~MCSection() {
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for (auto &[_, Chain] : Subsections) {
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for (MCFragment *X = Chain.Head, *Y; X; X = Y) {
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Y = X->Next;
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X->destroy();
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}
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}
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}
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void MCSection::setBundleLockState(BundleLockStateType NewState) {
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if (NewState == NotBundleLocked) {
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if (BundleLockNestingDepth == 0) {
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report_fatal_error("Mismatched bundle_lock/unlock directives");
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}
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if (--BundleLockNestingDepth == 0) {
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BundleLockState = NotBundleLocked;
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}
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return;
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}
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// If any of the directives is an align_to_end directive, the whole nested
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// group is align_to_end. So don't downgrade from align_to_end to just locked.
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if (BundleLockState != BundleLockedAlignToEnd) {
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BundleLockState = NewState;
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}
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++BundleLockNestingDepth;
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}
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StringRef MCSection::getVirtualSectionKind() const { return "virtual"; }
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#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
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LLVM_DUMP_METHOD void MCSection::dump() const {
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raw_ostream &OS = errs();
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OS << "<MCSection Name:" << getName();
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OS << " Fragments:[\n ";
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bool First = true;
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for (auto &F : *this) {
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if (First)
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First = false;
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else
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OS << ",\n ";
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F.dump();
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}
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OS << "]>";
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}
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#endif
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