Generate compact unwind encoding from CFI directives.

We used to generate the compact unwind encoding from the machine
instructions. However, this had the problem that if the user used `-save-temps'
or compiled their hand-written `.s' file (with CFI directives), we wouldn't
generate the compact unwind encoding.

Move the algorithm that generates the compact unwind encoding into the
MCAsmBackend. This way we can generate the encoding whether the code is from a
`.ll' or `.s' file.

<rdar://problem/13623355>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190290 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCAsmBackend.h

@@ -10,7 +10,9 @@
 #ifndef LLVM_MC_MCASMBACKEND_H
 #define LLVM_MC_MCASMBACKEND_H
 
+#include "llvm/ADT/ArrayRef.h"
 #include "llvm/MC/MCDirectives.h"
+#include "llvm/MC/MCDwarf.h"
 #include "llvm/MC/MCFixup.h"
 #include "llvm/Support/DataTypes.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -158,6 +160,12 @@ public:
   /// handleAssemblerFlag - Handle any target-specific assembler flags.
   /// By default, do nothing.
   virtual void handleAssemblerFlag(MCAssemblerFlag Flag) {}
+
+  /// \brief Generate the compact unwind encoding for the CFI instructions.
+  virtual unsigned
+  generateCompactUnwindEncoding(ArrayRef<MCCFIInstruction>) const {
+    return 0;
+  }
 };
 
 } // End llvm namespace

include/llvm/MC/MCStreamer.h

@@ -134,6 +134,8 @@ public:
     return *W64UnwindInfos[i];
   }
 
+  void generateCompactUnwindEncodings(MCAsmBackend &MAB);
+
   /// @name Assembly File Formatting.
   /// @{