Implement integer sign-extension.

Change-Id: I0c256131a8a631ba13fac0e2714e7637d058fd3e
diff --git a/src/compiler_llvm/method_compiler.cc b/src/compiler_llvm/method_compiler.cc
index 3612d24..56d9166 100644
--- a/src/compiler_llvm/method_compiler.cc
+++ b/src/compiler_llvm/method_compiler.cc
@@ -1692,7 +1692,13 @@
 
 void MethodCompiler::EmitInsn_SExt(uint32_t dex_pc,
                                    Instruction const* insn) {
-  // UNIMPLEMENTED(WARNING);
+
+  Instruction::DecodedInstruction dec_insn(insn);
+
+  llvm::Value* src_value = EmitLoadDalvikReg(dec_insn.vB_, kInt, kAccurate);
+  llvm::Value* result_value = irb_.CreateSExt(src_value, irb_.getJLongTy());
+  EmitStoreDalvikReg(dec_insn.vA_, kLong, kAccurate, result_value);
+
   irb_.CreateBr(GetNextBasicBlock(dex_pc));
 }