00647a18ce
If multiple globals are placed in an explicit section, there's a chance that the large data threshold will cause the different globals to be inconsistent in whether they're large or small. Mixing sections with mismatched large section flags can cause undesirable issues like increased relocation pressure because there may be 32-bit references to the section in some TUs, but the section is considered large since input section flags are unioned and other TUs added the large section flag. An explicit code model on the global still overrides the decision. We can do this for globals without any references to them, like what we did with asan_globals in #74514. If we have some precompiled small code model files where asan_globals is not considered large mixed with medium/large code model files, that's ok because the section is considered large and placed farther. However, overriding the code model for globals in some TUs but not others and having references to them from code will still result in the above undesired behavior. This mitigates a whole class of mismatched large section flag issues like what #77986 was trying to fix. This ends up not adding the SHF_X86_64_LARGE section flag on explicit sections in the medium/large code model. This is ok for the large code model since all references from large text must use 64-bit relocations anyway.
293 lines
10 KiB
C++
293 lines
10 KiB
C++
//===-- TargetMachine.cpp - General Target Information ---------------------==//
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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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//
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// This file describes the general parts of a Target machine.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/GlobalValue.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/Mangler.h"
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#include "llvm/MC/MCAsmInfo.h"
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#include "llvm/MC/MCContext.h"
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#include "llvm/MC/MCInstrInfo.h"
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#include "llvm/MC/MCRegisterInfo.h"
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#include "llvm/MC/MCSubtargetInfo.h"
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#include "llvm/Support/CodeGen.h"
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#include "llvm/Target/TargetLoweringObjectFile.h"
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using namespace llvm;
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//---------------------------------------------------------------------------
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// TargetMachine Class
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//
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TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
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const Triple &TT, StringRef CPU, StringRef FS,
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const TargetOptions &Options)
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: TheTarget(T), DL(DataLayoutString), TargetTriple(TT),
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TargetCPU(std::string(CPU)), TargetFS(std::string(FS)), AsmInfo(nullptr),
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MRI(nullptr), MII(nullptr), STI(nullptr), RequireStructuredCFG(false),
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O0WantsFastISel(false), Options(Options) {}
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TargetMachine::~TargetMachine() = default;
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bool TargetMachine::isLargeGlobalValue(const GlobalValue *GVal) const {
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if (getTargetTriple().getArch() != Triple::x86_64)
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return false;
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auto *GO = GVal->getAliaseeObject();
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// Be conservative if we can't find an underlying GlobalObject.
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if (!GO)
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return true;
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auto *GV = dyn_cast<GlobalVariable>(GO);
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// Functions/GlobalIFuncs are only large under the large code model.
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if (!GV)
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return getCodeModel() == CodeModel::Large;
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if (GV->isThreadLocal())
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return false;
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// For x86-64, we treat an explicit GlobalVariable small code model to mean
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// that the global should be placed in a small section, and ditto for large.
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if (auto CM = GV->getCodeModel()) {
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if (*CM == CodeModel::Small)
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return false;
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if (*CM == CodeModel::Large)
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return true;
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}
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// Treat all globals in explicit sections as small, except for the standard
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// large sections of .lbss, .ldata, .lrodata. This reduces the risk of linking
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// together small and large sections, resulting in small references to large
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// data sections. The code model attribute overrides this above.
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if (GV->hasSection()) {
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StringRef Name = GV->getSection();
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auto IsPrefix = [&](StringRef Prefix) {
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StringRef S = Name;
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return S.consume_front(Prefix) && (S.empty() || S[0] == '.');
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};
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return IsPrefix(".lbss") || IsPrefix(".ldata") || IsPrefix(".lrodata");
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}
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// Respect large data threshold for medium and large code models.
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if (getCodeModel() == CodeModel::Medium ||
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getCodeModel() == CodeModel::Large) {
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if (!GV->getValueType()->isSized())
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return true;
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const DataLayout &DL = GV->getParent()->getDataLayout();
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uint64_t Size = DL.getTypeSizeInBits(GV->getValueType()) / 8;
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return Size == 0 || Size > LargeDataThreshold;
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}
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return false;
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}
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bool TargetMachine::isPositionIndependent() const {
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return getRelocationModel() == Reloc::PIC_;
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}
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/// Reset the target options based on the function's attributes.
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/// setFunctionAttributes should have made the raw attribute value consistent
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/// with the command line flag if used.
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//
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// FIXME: This function needs to go away for a number of reasons:
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// a) global state on the TargetMachine is terrible in general,
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// b) these target options should be passed only on the function
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// and not on the TargetMachine (via TargetOptions) at all.
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void TargetMachine::resetTargetOptions(const Function &F) const {
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#define RESET_OPTION(X, Y) \
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do { \
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Options.X = F.getFnAttribute(Y).getValueAsBool(); \
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} while (0)
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RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
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RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
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RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
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RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
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RESET_OPTION(ApproxFuncFPMath, "approx-func-fp-math");
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}
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/// Returns the code generation relocation model. The choices are static, PIC,
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/// and dynamic-no-pic.
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Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
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uint64_t TargetMachine::getMaxCodeSize() const {
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switch (getCodeModel()) {
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case CodeModel::Tiny:
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return llvm::maxUIntN(10);
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case CodeModel::Small:
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case CodeModel::Kernel:
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case CodeModel::Medium:
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return llvm::maxUIntN(31);
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case CodeModel::Large:
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return llvm::maxUIntN(64);
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}
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llvm_unreachable("Unhandled CodeModel enum");
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}
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/// Get the IR-specified TLS model for Var.
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static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
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switch (GV->getThreadLocalMode()) {
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case GlobalVariable::NotThreadLocal:
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llvm_unreachable("getSelectedTLSModel for non-TLS variable");
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break;
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case GlobalVariable::GeneralDynamicTLSModel:
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return TLSModel::GeneralDynamic;
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case GlobalVariable::LocalDynamicTLSModel:
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return TLSModel::LocalDynamic;
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case GlobalVariable::InitialExecTLSModel:
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return TLSModel::InitialExec;
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case GlobalVariable::LocalExecTLSModel:
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return TLSModel::LocalExec;
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}
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llvm_unreachable("invalid TLS model");
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}
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bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
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const GlobalValue *GV) const {
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const Triple &TT = getTargetTriple();
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Reloc::Model RM = getRelocationModel();
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// According to the llvm language reference, we should be able to
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// just return false in here if we have a GV, as we know it is
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// dso_preemptable. At this point in time, the various IR producers
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// have not been transitioned to always produce a dso_local when it
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// is possible to do so.
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//
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// As a result we still have some logic in here to improve the quality of the
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// generated code.
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if (!GV)
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return false;
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// If the IR producer requested that this GV be treated as dso local, obey.
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if (GV->isDSOLocal())
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return true;
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if (TT.isOSBinFormatCOFF()) {
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// DLLImport explicitly marks the GV as external.
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if (GV->hasDLLImportStorageClass())
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return false;
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// On MinGW, variables that haven't been declared with DLLImport may still
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// end up automatically imported by the linker. To make this feasible,
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// don't assume the variables to be DSO local unless we actually know
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// that for sure. This only has to be done for variables; for functions
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// the linker can insert thunks for calling functions from another DLL.
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if (TT.isWindowsGNUEnvironment() && GV->isDeclarationForLinker() &&
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isa<GlobalVariable>(GV))
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return false;
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// Don't mark 'extern_weak' symbols as DSO local. If these symbols remain
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// unresolved in the link, they can be resolved to zero, which is outside
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// the current DSO.
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if (GV->hasExternalWeakLinkage())
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return false;
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// Every other GV is local on COFF.
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return true;
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}
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if (TT.isOSBinFormatGOFF())
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return true;
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if (TT.isOSBinFormatMachO()) {
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if (RM == Reloc::Static)
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return true;
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return GV->isStrongDefinitionForLinker();
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}
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assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm() ||
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TT.isOSBinFormatXCOFF());
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return false;
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}
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bool TargetMachine::useEmulatedTLS() const { return Options.EmulatedTLS; }
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TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
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bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
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Reloc::Model RM = getRelocationModel();
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bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
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bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
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TLSModel::Model Model;
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if (IsSharedLibrary) {
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if (IsLocal)
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Model = TLSModel::LocalDynamic;
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else
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Model = TLSModel::GeneralDynamic;
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} else {
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if (IsLocal)
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Model = TLSModel::LocalExec;
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else
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Model = TLSModel::InitialExec;
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}
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// If the user specified a more specific model, use that.
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TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
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if (SelectedModel > Model)
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return SelectedModel;
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return Model;
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}
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/// Returns the optimization level: None, Less, Default, or Aggressive.
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CodeGenOptLevel TargetMachine::getOptLevel() const { return OptLevel; }
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void TargetMachine::setOptLevel(CodeGenOptLevel Level) { OptLevel = Level; }
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TargetTransformInfo
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TargetMachine::getTargetTransformInfo(const Function &F) const {
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return TargetTransformInfo(F.getParent()->getDataLayout());
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}
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void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
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const GlobalValue *GV, Mangler &Mang,
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bool MayAlwaysUsePrivate) const {
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if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
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// Simple case: If GV is not private, it is not important to find out if
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// private labels are legal in this case or not.
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Mang.getNameWithPrefix(Name, GV, false);
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return;
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}
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const TargetLoweringObjectFile *TLOF = getObjFileLowering();
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TLOF->getNameWithPrefix(Name, GV, *this);
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}
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MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
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const TargetLoweringObjectFile *TLOF = getObjFileLowering();
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// XCOFF symbols could have special naming convention.
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if (MCSymbol *TargetSymbol = TLOF->getTargetSymbol(GV, *this))
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return TargetSymbol;
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SmallString<128> NameStr;
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getNameWithPrefix(NameStr, GV, TLOF->getMangler());
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return TLOF->getContext().getOrCreateSymbol(NameStr);
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}
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TargetIRAnalysis TargetMachine::getTargetIRAnalysis() const {
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// Since Analysis can't depend on Target, use a std::function to invert the
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// dependency.
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return TargetIRAnalysis(
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[this](const Function &F) { return this->getTargetTransformInfo(F); });
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}
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std::pair<int, int> TargetMachine::parseBinutilsVersion(StringRef Version) {
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if (Version == "none")
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return {INT_MAX, INT_MAX}; // Make binutilsIsAtLeast() return true.
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std::pair<int, int> Ret;
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if (!Version.consumeInteger(10, Ret.first) && Version.consume_front("."))
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Version.consumeInteger(10, Ret.second);
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return Ret;
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}
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