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

1 files changed, 27 insertions, 2 deletions

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.