bb03cdcb44
Follow-up to #140494 `shouldForceRelocation` is conservative and produces redundant relocations. For example, RISCVAsmBackend::ForceRelocs (introduced to support mixed relax/norelax code) leads to redundant relocations in the following example adapted from #77436 ``` .option norelax j label // For assembly input, RISCVAsmParser::ParseInstruction sets ForceRelocs (https://reviews.llvm.org/D46423). // For direct object emission, RISCVELFStreamer sets ForceRelocs (#77436) .option relax call foo // linker-relaxable .option norelax j label // redundant relocation due to ForceRelocs .option relax label: ``` Root problem: The `isSymbolRefDifferenceFullyResolvedImpl` condition in MCAssembler::evaluateFixup does not check whether two locations are separated by a fragment whose size can be indeterminate due to linker instruction (e.g. MCDataFragment with relaxation, or MCAlignFragment due to indeterminate start offst). This patch * Updates the fragment walk code in `attemptToFoldSymbolOffsetDifference` to treat MCRelaxableFragment (for --riscv-asm-relax-branches) as fixed size after finishLayout. * Adds a condition in `addReloc` to complement `isSymbolRefDifferenceFullyResolvedImpl`. * Removes the no longer needed `shouldForceRelocation`. This fragment walk code path handles nicely handles mixed relax/norelax case from https://discourse.llvm.org/t/possible-problem-related-to-subtarget-usage/75283 and allows us to remove `MCSubtargetInfo` argument (#73721) as a follow-up. This fragment walk code should be avoided in the absence of linker-relaxable fragments within the current section. Adjust two bolt/test/RISCV tests (#141310) Pull Request: https://github.com/llvm/llvm-project/pull/140692
87 lines
2.6 KiB
C++
87 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/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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HasLayout(false), IsRegistered(false), IsText(IsText),
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IsVirtual(IsVirtual), LinkerRelaxable(false), Name(Name), 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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