Add decoder ctor and dtor

There is one usage of Capstone per decoder. This should be threadsafe
as it doesn't make sense to use a decoder with multiple threads
simultaneously. See comments in ctor for why there are two Capstone
handles per decoder.

instructionAPI/src/x86/decoder.C

@@ -7,11 +7,41 @@
 
 namespace Dyninst { namespace InstructionAPI {
 
-  x86_decoder::x86_decoder(Dyninst::Architecture a): InstructionDecoderImpl(a),
-      mode{a == Dyninst::Arch_x86_64 ? CS_MODE_64 : CS_MODE_32} {}
+  x86_decoder::x86_decoder(Dyninst::Architecture a): InstructionDecoderImpl(a) {
 
-  x86_decoder::~x86_decoder() {}
+    mode = (a == Dyninst::Arch_x86_64) ? CS_MODE_64 : CS_MODE_32;
 
+    auto create = [this](disassem &d, cs_opt_value v) {
+      cs_open(CS_ARCH_X86, this->mode, &d.handle);
+      cs_option(d.handle, CS_OPT_DETAIL, v);
+      d.insn = cs_malloc(d.handle);
+    };
+
+    /*
+     *  With details enabled, a Capstone instruction object has complete information.
+     *
+     *  This is used in 'decodeOperands' because all of the details are needed.
+    */
+    create(dis_with_detail, CS_OPT_ON);
+
+    /*
+     *  Without details, a Capstone instruction object has fewer populated fields
+     *  (e.g., no operand details) so takes up less space and time. Capstone instruction
+     *  objects _always_ populate the mnemonic and a string representation of the operands.
+     *
+     *  This is used in 'decodeOpcode' to quickly create an Instruction object.
+    */
+    create(dis_without_detail, CS_OPT_OFF);
+  }
+
+  x86_decoder::~x86_decoder() {
+    cs_free(dis_with_detail.insn, 1);
+    cs_close(&dis_with_detail.handle);
+
+    cs_free(dis_without_detail.insn, 1);
+    cs_close(&dis_without_detail.handle);
+  }
+
   void x86_decoder::doDelayedDecode(Instruction const*) {}
   void x86_decoder::decodeOpcode(InstructionDecoder::buffer&) {}
   bool x86_decoder::decodeOperands(Instruction const*) { return true; }

instructionAPI/src/x86/decoder.h

@@ -40,7 +40,13 @@ namespace Dyninst { namespace InstructionAPI {
 
   class x86_decoder final : public InstructionDecoderImpl {
     cs_mode mode{};
-    csh handle{};
+
+    struct disassem final {
+      csh handle{};
+      cs_insn *insn{};
+    };
+    disassem dis_with_detail{};
+    disassem dis_without_detail{};
 
   public: