[lanai] Add Lanai backend.

Add the Lanai backend to lib/Target.

General Lanai backend discussion on llvm-dev thread "[RFC] Lanai backend" (http://lists.llvm.org/pipermail/llvm-dev/2016-February/095118.html).

Differential Revision: http://reviews.llvm.org/D17011

llvm-svn: 264578

1 files changed, 123 insertions, 0 deletions

diff --git a/llvm/lib/Target/Lanai/LanaiTargetObjectFile.cpp b/llvm/lib/Target/Lanai/LanaiTargetObjectFile.cpp
new file mode 100644
index 00000000000..a4a6de859cb
--- /dev/null
+++ b/llvm/lib/Target/Lanai/LanaiTargetObjectFile.cpp
@@ -0,0 +1,123 @@
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "LanaiTargetObjectFile.h"
+
+#include "LanaiSubtarget.h"
+#include "LanaiTargetMachine.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCSectionELF.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/ELF.h"
+#include "llvm/Target/TargetMachine.h"
+
+using namespace llvm;
+
+static cl::opt<unsigned> SSThreshold(
+    "lanai-ssection-threshold", cl::Hidden,
+    cl::desc("Small data and bss section threshold size (default=0)"),
+    cl::init(0));
+
+void LanaiTargetObjectFile::Initialize(MCContext &Ctx,
+                                       const TargetMachine &TM) {
+  TargetLoweringObjectFileELF::Initialize(Ctx, TM);
+  InitializeELF(TM.Options.UseInitArray);
+
+  SmallDataSection = getContext().getELFSection(
+      ".sdata", ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
+  SmallBSSSection = getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
+                                               ELF::SHF_WRITE | ELF::SHF_ALLOC);
+}
+
+// A address must be loaded from a small section if its size is less than the
+// small section size threshold. Data in this section must be addressed using
+// gp_rel operator.
+static bool isInSmallSection(uint64_t Size) {
+  // gcc has traditionally not treated zero-sized objects as small data, so this
+  // is effectively part of the ABI.
+  return Size > 0 && Size <= SSThreshold;
+}
+
+// Return true if this global address should be placed into small data/bss
+// section.
+bool LanaiTargetObjectFile::isGlobalInSmallSection(
+    const GlobalValue *GV, const TargetMachine &TM) const {
+  // We first check the case where global is a declaration, because finding
+  // section kind using getKindForGlobal() is only allowed for global
+  // definitions.
+  if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
+    return isGlobalInSmallSectionImpl(GV, TM);
+
+  return isGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
+}
+
+// Return true if this global address should be placed into small data/bss
+// section.
+bool LanaiTargetObjectFile::isGlobalInSmallSection(const GlobalValue *GV,
+                                                   const TargetMachine &TM,
+                                                   SectionKind Kind) const {
+  return (isGlobalInSmallSectionImpl(GV, TM) &&
+          (Kind.isData() || Kind.isBSS() || Kind.isCommon()));
+}
+
+// Return true if this global address should be placed into small data/bss
+// section. This method does all the work, except for checking the section
+// kind.
+bool LanaiTargetObjectFile::isGlobalInSmallSectionImpl(
+    const GlobalValue *GV, const TargetMachine &TM) const {
+  // Only global variables, not functions.
+  const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
+  if (!GVA)
+    return false;
+
+  if (GV->hasLocalLinkage())
+    return false;
+
+  if (((GV->hasExternalLinkage() && GV->isDeclaration()) ||
+       GV->hasCommonLinkage()))
+    return false;
+
+  Type *Ty = GV->getType()->getElementType();
+  return isInSmallSection(
+      GV->getParent()->getDataLayout().getTypeAllocSize(Ty));
+}
+
+MCSection *
+LanaiTargetObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
+                                              SectionKind Kind, Mangler &Mang,
+                                              const TargetMachine &TM) const {
+  // Handle Small Section classification here.
+  if (Kind.isBSS() && isGlobalInSmallSection(GV, TM, Kind))
+    return SmallBSSSection;
+  if (Kind.isData() && isGlobalInSmallSection(GV, TM, Kind))
+    return SmallDataSection;
+
+  // Otherwise, we work the same as ELF.
+  return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,
+                                                             TM);
+}
+
+/// Return true if this constant should be placed into small data section.
+bool LanaiTargetObjectFile::isConstantInSmallSection(
+    const DataLayout &DL, const Constant *CN) const {
+  return isInSmallSection(DL.getTypeAllocSize(CN->getType()));
+}
+
+MCSection *LanaiTargetObjectFile::getSectionForConstant(const DataLayout &DL,
+                                                        SectionKind Kind,
+                                                        const Constant *C,
+                                                        unsigned &Align) const {
+  if (isConstantInSmallSection(DL, C))
+    return SmallDataSection;
+
+  // Otherwise, we work the same as ELF.
+  return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C, Align);
+}