switch to using a smallvector to avoid allocations for most normal size instructions.

llvm-svn: 131837
diff --git a/llvm/lib/MC/MCDisassembler/Disassembler.cpp b/llvm/lib/MC/MCDisassembler/Disassembler.cpp
index 29fc192..6e636f0 100644
--- a/llvm/lib/MC/MCDisassembler/Disassembler.cpp
+++ b/llvm/lib/MC/MCDisassembler/Disassembler.cpp
@@ -147,8 +147,8 @@
   if (!DisAsm->getInstruction(Inst, Size, MemoryObject, PC, /*REMOVE*/ nulls()))
     return 0;
 
-  std::string InsnStr;
-  raw_string_ostream OS(InsnStr);
+  SmallVector<char, 64> InsnStr;
+  raw_svector_ostream OS(InsnStr);
   IP->printInst(&Inst, OS);
   OS.flush();