Adding the MicroBlaze backend.

The MicroBlaze is a highly configurable 32-bit soft-microprocessor for
use on Xilinx FPGAs. For more information see:
http://www.xilinx.com/tools/microblaze.htm
http://en.wikipedia.org/wiki/MicroBlaze

The current LLVM MicroBlaze backend generates assembly which can be
compiled using the an appropriate binutils assembler.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96969 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/MBlaze/MBlazeTargetObjectFile.cpp

@@ -0,0 +1,88 @@
+//===-- MBlazeTargetObjectFile.cpp - MBlaze object files ------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "MBlazeTargetObjectFile.h"
+#include "MBlazeSubtarget.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/GlobalVariable.h"
+#include "llvm/MC/MCSectionELF.h"
+#include "llvm/Target/TargetData.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Support/CommandLine.h"
+using namespace llvm;
+
+void MBlazeTargetObjectFile::
+Initialize(MCContext &Ctx, const TargetMachine &TM) {
+  TargetLoweringObjectFileELF::Initialize(Ctx, TM);
+
+  SmallDataSection =
+    getELFSection(".sdata", MCSectionELF::SHT_PROGBITS,
+                  MCSectionELF::SHF_WRITE | MCSectionELF::SHF_ALLOC,
+                  SectionKind::getDataRel());
+
+  SmallBSSSection =
+    getELFSection(".sbss", MCSectionELF::SHT_NOBITS,
+                  MCSectionELF::SHF_WRITE | MCSectionELF::SHF_ALLOC,
+                  SectionKind::getBSS());
+
+}
+
+// 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) {
+  return Size > 0 && Size <= 8;
+}
+
+bool MBlazeTargetObjectFile::
+IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM) const {
+  if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
+    return false;
+
+  return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
+}
+
+/// IsGlobalInSmallSection - Return true if this global address should be
+/// placed into small data/bss section.
+bool MBlazeTargetObjectFile::
+IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
+                       SectionKind Kind) const {
+  // Only global variables, not functions.
+  const GlobalVariable *GVA = dyn_cast<GlobalVariable>(GV);
+  if (!GVA)
+    return false;
+
+  // We can only do this for datarel or BSS objects for now.
+  if (!Kind.isBSS() && !Kind.isDataRel())
+    return false;
+
+  // If this is a internal constant string, there is a special
+  // section for it, but not in small data/bss.
+  if (Kind.isMergeable1ByteCString())
+    return false;
+
+  const Type *Ty = GV->getType()->getElementType();
+  return IsInSmallSection(TM.getTargetData()->getTypeAllocSize(Ty));
+}
+
+const MCSection *MBlazeTargetObjectFile::
+SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
+                       Mangler *Mang, const TargetMachine &TM) const {
+  // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
+  // sections?
+
+  // Handle Small Section classification here.
+  if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
+    return SmallBSSSection;
+  if (Kind.isDataNoRel() && IsGlobalInSmallSection(GV, TM, Kind))
+    return SmallDataSection;
+
+  // Otherwise, we work the same as ELF.
+  return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
+}