MachO: Add linker-optimisation hint framework to MC.

Another part of the ARM64 backend (so tests will be following soon).
This is currently used by the linker to relax adrp/ldr pairs into nops
where possible, though could well be more broadly applicable.

llvm-svn: 205084

6 files changed, 86 insertions, 2 deletions

diff --git a/llvm/lib/MC/CMakeLists.txt b/llvm/lib/MC/CMakeLists.txt
index eb3f9e52d73..ab7dabc9c74 100644
--- a/llvm/lib/MC/CMakeLists.txt
+++ b/llvm/lib/MC/CMakeLists.txt
@@ -24,6 +24,7 @@ add_llvm_library(LLVMMC
   MCInstPrinter.cpp
   MCInstrAnalysis.cpp
   MCLabel.cpp
+  MCLinkerOptimizationHint.cpp
   MCMachOStreamer.cpp
   MCMachObjectTargetWriter.cpp
   MCModule.cpp
diff --git a/llvm/lib/MC/MCAsmStreamer.cpp b/llvm/lib/MC/MCAsmStreamer.cpp
index 59af4101afa..cc30d056a21 100644
--- a/llvm/lib/MC/MCAsmStreamer.cpp
+++ b/llvm/lib/MC/MCAsmStreamer.cpp
@@ -126,6 +126,7 @@ public:
   void ChangeSection(const MCSection *Section,
                      const MCExpr *Subsection) override;
 
+  void EmitLOHDirective(MCLOHType Kind, const MCLOHArgs &Args) override;
   void EmitLabel(MCSymbol *Symbol) override;
   void EmitDebugLabel(MCSymbol *Symbol) override;
 
@@ -342,6 +343,27 @@ void MCAsmStreamer::EmitLabel(MCSymbol *Symbol) {
   EmitEOL();
 }
 
+void MCAsmStreamer::EmitLOHDirective(MCLOHType Kind, const MCLOHArgs &Args) {
+  StringRef str = MCLOHIdToName(Kind);
+
+#ifndef NDEBUG
+  int NbArgs = MCLOHIdToNbArgs(Kind);
+  assert(NbArgs != -1 && ((size_t)NbArgs) == Args.size() && "Malformed LOH!");
+  assert(str != "" && "Invalid LOH name");
+#endif
+
+  OS << "\t" << MCLOHDirectiveName() << " " << str << "\t";
+  bool IsFirst = true;
+  for (MCLOHArgs::const_iterator It = Args.begin(), EndIt = Args.end();
+       It != EndIt; ++It) {
+    if (!IsFirst)
+      OS << ", ";
+    IsFirst = false;
+    OS << **It;
+  }
+  EmitEOL();
+}
+
 void MCAsmStreamer::EmitDebugLabel(MCSymbol *Symbol) {
   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
   MCStreamer::EmitDebugLabel(Symbol);
diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 5536087bd0c..724ca292bef 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -355,6 +355,7 @@ void MCAssembler::reset() {
   getBackend().reset();
   getEmitter().reset();
   getWriter().reset();
+  getLOHContainer().reset();
 }
 
 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
diff --git a/llvm/lib/MC/MCLinkerOptimizationHint.cpp b/llvm/lib/MC/MCLinkerOptimizationHint.cpp
new file mode 100644
index 00000000000..628a6156fd8
--- /dev/null
+++ b/llvm/lib/MC/MCLinkerOptimizationHint.cpp
@@ -0,0 +1,30 @@
+//===-- llvm/MC/MCLinkerOptimizationHint.cpp ----- LOH handling -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/MC/MCLinkerOptimizationHint.h"
+#include "llvm/MC/MCAsmLayout.h"
+#include "llvm/Support/LEB128.h"
+#include "llvm/MC/MCStreamer.h"
+
+using namespace llvm;
+
+namespace llvm {
+template<>
+void MCLOHDirective::Emit_impl(raw_ostream &OutStream,
+                               const MachObjectWriter &ObjWriter,
+                               const MCAsmLayout &Layout) const {
+  const MCAssembler &Asm = Layout.getAssembler();
+  encodeULEB128(Kind, OutStream);
+  encodeULEB128(Args.size(), OutStream);
+  for (LOHArgs::const_iterator It = Args.begin(), EndIt = Args.end();
+       It != EndIt; ++It)
+    encodeULEB128(ObjWriter.getSymbolAddress(&Asm.getSymbolData(**It), Layout),
+                  OutStream);
+}
+} // end namespace llvm
diff --git a/llvm/lib/MC/MCMachOStreamer.cpp b/llvm/lib/MC/MCMachOStreamer.cpp
index 742f7846496..7e437f4bcb8 100644
--- a/llvm/lib/MC/MCMachOStreamer.cpp
+++ b/llvm/lib/MC/MCMachOStreamer.cpp
@@ -17,6 +17,7 @@
 #include "llvm/MC/MCDwarf.h"
 #include "llvm/MC/MCExpr.h"
 #include "llvm/MC/MCInst.h"
+#include "llvm/MC/MCLinkerOptimizationHint.h"
 #include "llvm/MC/MCMachOSymbolFlags.h"
 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCObjectStreamer.h"
@@ -104,6 +105,10 @@ public:
     llvm_unreachable("macho doesn't support this directive");
   }
 
+  void EmitLOHDirective(MCLOHType Kind, const MCLOHArgs &Args) override {
+    getAssembler().getLOHContainer().addDirective(Kind, Args);
+  }
+
   void FinishImpl() override;
 };
 
diff --git a/llvm/lib/MC/MachObjectWriter.cpp b/llvm/lib/MC/MachObjectWriter.cpp
index bbe589f3385..5fcea5f06c1 100644
--- a/llvm/lib/MC/MachObjectWriter.cpp
+++ b/llvm/lib/MC/MachObjectWriter.cpp
@@ -761,6 +761,14 @@ void MachObjectWriter::WriteObject(MCAssembler &Asm,
     LoadCommandsSize += sizeof(MachO::linkedit_data_command);
   }
 
+  // Add the loh load command size, if used.
+  uint64_t LOHRawSize = Asm.getLOHContainer().getEmitSize(*this, Layout);
+  uint64_t LOHSize = RoundUpToAlignment(LOHRawSize, is64Bit() ? 8 : 4);
+  if (LOHSize) {
+    ++NumLoadCommands;
+    LoadCommandsSize += sizeof(MachO::linkedit_data_command);
+  }
+
   // Add the symbol table load command sizes, if used.
   unsigned NumSymbols = LocalSymbolData.size() + ExternalSymbolData.size() +
     UndefinedSymbolData.size();
@@ -849,6 +857,12 @@ void MachObjectWriter::WriteObject(MCAssembler &Asm,
                              DataRegionsSize);
   }
 
+  // Write the loh load command, if used.
+  uint64_t LOHTableEnd = DataInCodeTableEnd + LOHSize;
+  if (LOHSize)
+    WriteLinkeditLoadCommand(MachO::LC_LINKER_OPTIMIZATION_HINT,
+                             DataInCodeTableEnd, LOHSize);
+
   // Write the symbol table load command, if used.
   if (NumSymbols) {
     unsigned FirstLocalSymbol = 0;
@@ -865,10 +879,10 @@ void MachObjectWriter::WriteObject(MCAssembler &Asm,
 
     // If used, the indirect symbols are written after the section data.
     if (NumIndirectSymbols)
-      IndirectSymbolOffset = DataInCodeTableEnd;
+      IndirectSymbolOffset = LOHTableEnd;
 
     // The symbol table is written after the indirect symbol data.
-    uint64_t SymbolTableOffset = DataInCodeTableEnd + IndirectSymbolSize;
+    uint64_t SymbolTableOffset = LOHTableEnd + IndirectSymbolSize;
 
     // The string table is written after symbol table.
     uint64_t StringTableOffset =
@@ -935,6 +949,17 @@ void MachObjectWriter::WriteObject(MCAssembler &Asm,
     Write16(Data->Kind);
   }
 
+  // Write out the loh commands, if there is one.
+  if (LOHSize) {
+#ifndef NDEBUG
+    unsigned Start = OS.tell();
+#endif
+    Asm.getLOHContainer().Emit(*this, Layout);
+    // Pad to a multiple of the pointer size.
+    WriteBytes("", OffsetToAlignment(LOHRawSize, is64Bit() ? 8 : 4));
+    assert(OS.tell() - Start == LOHSize);
+  }
+
   // Write the symbol table data, if used.
   if (NumSymbols) {
     // Write the indirect symbol entries.