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authorDimitry Andric <dim@FreeBSD.org>2019-12-20 19:53:05 +0000
committerDimitry Andric <dim@FreeBSD.org>2019-12-20 19:53:05 +0000
commit0b57cec536236d46e3dba9bd041533462f33dbb7 (patch)
tree56229dbdbbf76d18580f72f789003db17246c8d9 /contrib/llvm-project/llvm/lib/Target/TargetMachine.cpp
parent718ef55ec7785aae63f98f8ca05dc07ed399c16d (diff)
Notes
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+//===-- TargetMachine.cpp - General Target Information ---------------------==//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file describes the general parts of a Target machine.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/GlobalAlias.h"
+#include "llvm/IR/GlobalValue.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/LegacyPassManager.h"
+#include "llvm/IR/Mangler.h"
+#include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCInstrInfo.h"
+#include "llvm/MC/MCSectionMachO.h"
+#include "llvm/MC/MCTargetOptions.h"
+#include "llvm/MC/SectionKind.h"
+#include "llvm/Target/TargetLoweringObjectFile.h"
+using namespace llvm;
+
+//---------------------------------------------------------------------------
+// TargetMachine Class
+//
+
+TargetMachine::TargetMachine(const Target &T, StringRef DataLayoutString,
+ const Triple &TT, StringRef CPU, StringRef FS,
+ const TargetOptions &Options)
+ : TheTarget(T), DL(DataLayoutString), TargetTriple(TT), TargetCPU(CPU),
+ TargetFS(FS), AsmInfo(nullptr), MRI(nullptr), MII(nullptr), STI(nullptr),
+ RequireStructuredCFG(false), DefaultOptions(Options), Options(Options) {
+}
+
+TargetMachine::~TargetMachine() = default;
+
+bool TargetMachine::isPositionIndependent() const {
+ return getRelocationModel() == Reloc::PIC_;
+}
+
+/// Reset the target options based on the function's attributes.
+// FIXME: This function needs to go away for a number of reasons:
+// a) global state on the TargetMachine is terrible in general,
+// b) these target options should be passed only on the function
+// and not on the TargetMachine (via TargetOptions) at all.
+void TargetMachine::resetTargetOptions(const Function &F) const {
+#define RESET_OPTION(X, Y) \
+ do { \
+ if (F.hasFnAttribute(Y)) \
+ Options.X = (F.getFnAttribute(Y).getValueAsString() == "true"); \
+ else \
+ Options.X = DefaultOptions.X; \
+ } while (0)
+
+ RESET_OPTION(UnsafeFPMath, "unsafe-fp-math");
+ RESET_OPTION(NoInfsFPMath, "no-infs-fp-math");
+ RESET_OPTION(NoNaNsFPMath, "no-nans-fp-math");
+ RESET_OPTION(NoSignedZerosFPMath, "no-signed-zeros-fp-math");
+ RESET_OPTION(NoTrappingFPMath, "no-trapping-math");
+
+ StringRef Denormal =
+ F.getFnAttribute("denormal-fp-math").getValueAsString();
+ if (Denormal == "ieee")
+ Options.FPDenormalMode = FPDenormal::IEEE;
+ else if (Denormal == "preserve-sign")
+ Options.FPDenormalMode = FPDenormal::PreserveSign;
+ else if (Denormal == "positive-zero")
+ Options.FPDenormalMode = FPDenormal::PositiveZero;
+ else
+ Options.FPDenormalMode = DefaultOptions.FPDenormalMode;
+}
+
+/// Returns the code generation relocation model. The choices are static, PIC,
+/// and dynamic-no-pic.
+Reloc::Model TargetMachine::getRelocationModel() const { return RM; }
+
+/// Returns the code model. The choices are small, kernel, medium, large, and
+/// target default.
+CodeModel::Model TargetMachine::getCodeModel() const { return CMModel; }
+
+/// Get the IR-specified TLS model for Var.
+static TLSModel::Model getSelectedTLSModel(const GlobalValue *GV) {
+ switch (GV->getThreadLocalMode()) {
+ case GlobalVariable::NotThreadLocal:
+ llvm_unreachable("getSelectedTLSModel for non-TLS variable");
+ break;
+ case GlobalVariable::GeneralDynamicTLSModel:
+ return TLSModel::GeneralDynamic;
+ case GlobalVariable::LocalDynamicTLSModel:
+ return TLSModel::LocalDynamic;
+ case GlobalVariable::InitialExecTLSModel:
+ return TLSModel::InitialExec;
+ case GlobalVariable::LocalExecTLSModel:
+ return TLSModel::LocalExec;
+ }
+ llvm_unreachable("invalid TLS model");
+}
+
+bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
+ const GlobalValue *GV) const {
+ // If the IR producer requested that this GV be treated as dso local, obey.
+ if (GV && GV->isDSOLocal())
+ return true;
+
+ // If we are not supossed to use a PLT, we cannot assume that intrinsics are
+ // local since the linker can convert some direct access to access via plt.
+ if (M.getRtLibUseGOT() && !GV)
+ return false;
+
+ // According to the llvm language reference, we should be able to
+ // just return false in here if we have a GV, as we know it is
+ // dso_preemptable. At this point in time, the various IR producers
+ // have not been transitioned to always produce a dso_local when it
+ // is possible to do so.
+ // In the case of intrinsics, GV is null and there is nowhere to put
+ // dso_local. Returning false for those will produce worse code in some
+ // architectures. For example, on x86 the caller has to set ebx before calling
+ // a plt.
+ // As a result we still have some logic in here to improve the quality of the
+ // generated code.
+ // FIXME: Add a module level metadata for whether intrinsics should be assumed
+ // local.
+
+ Reloc::Model RM = getRelocationModel();
+ const Triple &TT = getTargetTriple();
+
+ // DLLImport explicitly marks the GV as external.
+ if (GV && GV->hasDLLImportStorageClass())
+ return false;
+
+ // On MinGW, variables that haven't been declared with DLLImport may still
+ // end up automatically imported by the linker. To make this feasible,
+ // don't assume the variables to be DSO local unless we actually know
+ // that for sure. This only has to be done for variables; for functions
+ // the linker can insert thunks for calling functions from another DLL.
+ if (TT.isWindowsGNUEnvironment() && TT.isOSBinFormatCOFF() && GV &&
+ GV->isDeclarationForLinker() && isa<GlobalVariable>(GV))
+ return false;
+
+ // On COFF, don't mark 'extern_weak' symbols as DSO local. If these symbols
+ // remain unresolved in the link, they can be resolved to zero, which is
+ // outside the current DSO.
+ if (TT.isOSBinFormatCOFF() && GV && GV->hasExternalWeakLinkage())
+ return false;
+
+ // Every other GV is local on COFF.
+ // Make an exception for windows OS in the triple: Some firmware builds use
+ // *-win32-macho triples. This (accidentally?) produced windows relocations
+ // without GOT tables in older clang versions; Keep this behaviour.
+ // Some JIT users use *-win32-elf triples; these shouldn't use GOT tables
+ // either.
+ if (TT.isOSBinFormatCOFF() || TT.isOSWindows())
+ return true;
+
+ // Most PIC code sequences that assume that a symbol is local cannot
+ // produce a 0 if it turns out the symbol is undefined. While this
+ // is ABI and relocation depended, it seems worth it to handle it
+ // here.
+ if (GV && isPositionIndependent() && GV->hasExternalWeakLinkage())
+ return false;
+
+ if (GV && !GV->hasDefaultVisibility())
+ return true;
+
+ if (TT.isOSBinFormatMachO()) {
+ if (RM == Reloc::Static)
+ return true;
+ return GV && GV->isStrongDefinitionForLinker();
+ }
+
+ // Due to the AIX linkage model, any global with default visibility is
+ // considered non-local.
+ if (TT.isOSBinFormatXCOFF())
+ return false;
+
+ assert(TT.isOSBinFormatELF() || TT.isOSBinFormatWasm());
+ assert(RM != Reloc::DynamicNoPIC);
+
+ bool IsExecutable =
+ RM == Reloc::Static || M.getPIELevel() != PIELevel::Default;
+ if (IsExecutable) {
+ // If the symbol is defined, it cannot be preempted.
+ if (GV && !GV->isDeclarationForLinker())
+ return true;
+
+ // A symbol marked nonlazybind should not be accessed with a plt. If the
+ // symbol turns out to be external, the linker will convert a direct
+ // access to an access via the plt, so don't assume it is local.
+ const Function *F = dyn_cast_or_null<Function>(GV);
+ if (F && F->hasFnAttribute(Attribute::NonLazyBind))
+ return false;
+
+ bool IsTLS = GV && GV->isThreadLocal();
+ bool IsAccessViaCopyRelocs =
+ GV && Options.MCOptions.MCPIECopyRelocations && isa<GlobalVariable>(GV);
+ Triple::ArchType Arch = TT.getArch();
+ bool IsPPC =
+ Arch == Triple::ppc || Arch == Triple::ppc64 || Arch == Triple::ppc64le;
+ // Check if we can use copy relocations. PowerPC has no copy relocations.
+ if (!IsTLS && !IsPPC && (RM == Reloc::Static || IsAccessViaCopyRelocs))
+ return true;
+ }
+
+ // ELF & wasm support preemption of other symbols.
+ return false;
+}
+
+bool TargetMachine::useEmulatedTLS() const {
+ // Returns Options.EmulatedTLS if the -emulated-tls or -no-emulated-tls
+ // was specified explicitly; otherwise uses target triple to decide default.
+ if (Options.ExplicitEmulatedTLS)
+ return Options.EmulatedTLS;
+ return getTargetTriple().hasDefaultEmulatedTLS();
+}
+
+TLSModel::Model TargetMachine::getTLSModel(const GlobalValue *GV) const {
+ bool IsPIE = GV->getParent()->getPIELevel() != PIELevel::Default;
+ Reloc::Model RM = getRelocationModel();
+ bool IsSharedLibrary = RM == Reloc::PIC_ && !IsPIE;
+ bool IsLocal = shouldAssumeDSOLocal(*GV->getParent(), GV);
+
+ TLSModel::Model Model;
+ if (IsSharedLibrary) {
+ if (IsLocal)
+ Model = TLSModel::LocalDynamic;
+ else
+ Model = TLSModel::GeneralDynamic;
+ } else {
+ if (IsLocal)
+ Model = TLSModel::LocalExec;
+ else
+ Model = TLSModel::InitialExec;
+ }
+
+ // If the user specified a more specific model, use that.
+ TLSModel::Model SelectedModel = getSelectedTLSModel(GV);
+ if (SelectedModel > Model)
+ return SelectedModel;
+
+ return Model;
+}
+
+/// Returns the optimization level: None, Less, Default, or Aggressive.
+CodeGenOpt::Level TargetMachine::getOptLevel() const { return OptLevel; }
+
+void TargetMachine::setOptLevel(CodeGenOpt::Level Level) { OptLevel = Level; }
+
+TargetTransformInfo TargetMachine::getTargetTransformInfo(const Function &F) {
+ return TargetTransformInfo(F.getParent()->getDataLayout());
+}
+
+void TargetMachine::getNameWithPrefix(SmallVectorImpl<char> &Name,
+ const GlobalValue *GV, Mangler &Mang,
+ bool MayAlwaysUsePrivate) const {
+ if (MayAlwaysUsePrivate || !GV->hasPrivateLinkage()) {
+ // Simple case: If GV is not private, it is not important to find out if
+ // private labels are legal in this case or not.
+ Mang.getNameWithPrefix(Name, GV, false);
+ return;
+ }
+ const TargetLoweringObjectFile *TLOF = getObjFileLowering();
+ TLOF->getNameWithPrefix(Name, GV, *this);
+}
+
+MCSymbol *TargetMachine::getSymbol(const GlobalValue *GV) const {
+ const TargetLoweringObjectFile *TLOF = getObjFileLowering();
+ SmallString<128> NameStr;
+ getNameWithPrefix(NameStr, GV, TLOF->getMangler());
+ return TLOF->getContext().getOrCreateSymbol(NameStr);
+}
+
+TargetIRAnalysis TargetMachine::getTargetIRAnalysis() {
+ // Since Analysis can't depend on Target, use a std::function to invert the
+ // dependency.
+ return TargetIRAnalysis(
+ [this](const Function &F) { return this->getTargetTransformInfo(F); });
+}