diff --git a/compiler/utils/assembler_test.h b/compiler/utils/assembler_test.h
index 9c65280..b34e125 100644
--- a/compiler/utils/assembler_test.h
+++ b/compiler/utils/assembler_test.h
@@ -51,30 +51,30 @@
 
   typedef std::string (*TestFn)(AssemblerTest* assembler_test, Ass* assembler);
 
-  void DriverFn(TestFn f, std::string test_name) {
+  void DriverFn(TestFn f, const std::string& test_name) {
     DriverWrapper(f(this, assembler_.get()), test_name);
   }
 
   // This driver assumes the assembler has already been called.
-  void DriverStr(std::string assembly_string, std::string test_name) {
+  void DriverStr(const std::string& assembly_string, const std::string& test_name) {
     DriverWrapper(assembly_string, test_name);
   }
 
-  std::string RepeatR(void (Ass::*f)(Reg), std::string fmt) {
+  std::string RepeatR(void (Ass::*f)(Reg), const std::string& fmt) {
     return RepeatTemplatedRegister<Reg>(f,
         GetRegisters(),
         &AssemblerTest::GetRegName<RegisterView::kUsePrimaryName>,
         fmt);
   }
 
-  std::string Repeatr(void (Ass::*f)(Reg), std::string fmt) {
+  std::string Repeatr(void (Ass::*f)(Reg), const std::string& fmt) {
     return RepeatTemplatedRegister<Reg>(f,
         GetRegisters(),
         &AssemblerTest::GetRegName<RegisterView::kUseSecondaryName>,
         fmt);
   }
 
-  std::string RepeatRR(void (Ass::*f)(Reg, Reg), std::string fmt) {
+  std::string RepeatRR(void (Ass::*f)(Reg, Reg), const std::string& fmt) {
     return RepeatTemplatedRegisters<Reg, Reg>(f,
         GetRegisters(),
         GetRegisters(),
@@ -83,7 +83,7 @@
         fmt);
   }
 
-  std::string RepeatRRNoDupes(void (Ass::*f)(Reg, Reg), std::string fmt) {
+  std::string RepeatRRNoDupes(void (Ass::*f)(Reg, Reg), const std::string& fmt) {
     return RepeatTemplatedRegistersNoDupes<Reg, Reg>(f,
         GetRegisters(),
         GetRegisters(),
@@ -92,7 +92,7 @@
         fmt);
   }
 
-  std::string Repeatrr(void (Ass::*f)(Reg, Reg), std::string fmt) {
+  std::string Repeatrr(void (Ass::*f)(Reg, Reg), const std::string& fmt) {
     return RepeatTemplatedRegisters<Reg, Reg>(f,
         GetRegisters(),
         GetRegisters(),
@@ -101,7 +101,7 @@
         fmt);
   }
 
-  std::string RepeatRRR(void (Ass::*f)(Reg, Reg, Reg), std::string fmt) {
+  std::string RepeatRRR(void (Ass::*f)(Reg, Reg, Reg), const std::string& fmt) {
     return RepeatTemplatedRegisters<Reg, Reg, Reg>(f,
         GetRegisters(),
         GetRegisters(),
@@ -112,7 +112,7 @@
         fmt);
   }
 
-  std::string Repeatrb(void (Ass::*f)(Reg, Reg), std::string fmt) {
+  std::string Repeatrb(void (Ass::*f)(Reg, Reg), const std::string& fmt) {
     return RepeatTemplatedRegisters<Reg, Reg>(f,
         GetRegisters(),
         GetRegisters(),
@@ -121,7 +121,7 @@
         fmt);
   }
 
-  std::string RepeatRr(void (Ass::*f)(Reg, Reg), std::string fmt) {
+  std::string RepeatRr(void (Ass::*f)(Reg, Reg), const std::string& fmt) {
     return RepeatTemplatedRegisters<Reg, Reg>(f,
         GetRegisters(),
         GetRegisters(),
@@ -130,11 +130,11 @@
         fmt);
   }
 
-  std::string RepeatRI(void (Ass::*f)(Reg, const Imm&), size_t imm_bytes, std::string fmt) {
+  std::string RepeatRI(void (Ass::*f)(Reg, const Imm&), size_t imm_bytes, const std::string& fmt) {
     return RepeatRegisterImm<RegisterView::kUsePrimaryName>(f, imm_bytes, fmt);
   }
 
-  std::string Repeatri(void (Ass::*f)(Reg, const Imm&), size_t imm_bytes, std::string fmt) {
+  std::string Repeatri(void (Ass::*f)(Reg, const Imm&), size_t imm_bytes, const std::string& fmt) {
     return RepeatRegisterImm<RegisterView::kUseSecondaryName>(f, imm_bytes, fmt);
   }
 
@@ -145,7 +145,7 @@
                                               const std::vector<Reg2*> reg2_registers,
                                               std::string (AssemblerTest::*GetName1)(const Reg1&),
                                               std::string (AssemblerTest::*GetName2)(const Reg2&),
-                                              std::string fmt) {
+                                              const std::string& fmt) {
     std::string str;
     std::vector<int64_t> imms = CreateImmediateValuesBits(abs(imm_bits), (imm_bits > 0));
 
@@ -195,7 +195,7 @@
                                               std::string (AssemblerTest::*GetName1)(const Reg1&),
                                               std::string (AssemblerTest::*GetName2)(const Reg2&),
                                               int imm_bits,
-                                              std::string fmt) {
+                                              const std::string& fmt) {
     std::vector<int64_t> imms = CreateImmediateValuesBits(abs(imm_bits), (imm_bits > 0));
 
     WarnOnCombinations(reg1_registers.size() * reg2_registers.size() * imms.size());
@@ -245,7 +245,7 @@
                                              int imm_bits,
                                              const std::vector<Reg*> registers,
                                              std::string (AssemblerTest::*GetName)(const RegType&),
-                                             std::string fmt) {
+                                             const std::string& fmt) {
     std::string str;
     std::vector<int64_t> imms = CreateImmediateValuesBits(abs(imm_bits), (imm_bits > 0));
 
@@ -281,7 +281,7 @@
   }
 
   template <typename ImmType>
-  std::string RepeatRRIb(void (Ass::*f)(Reg, Reg, ImmType), int imm_bits, std::string fmt) {
+  std::string RepeatRRIb(void (Ass::*f)(Reg, Reg, ImmType), int imm_bits, const std::string& fmt) {
     return RepeatTemplatedRegistersImmBits<Reg, Reg, ImmType>(f,
         imm_bits,
         GetRegisters(),
@@ -292,7 +292,7 @@
   }
 
   template <typename ImmType>
-  std::string RepeatRIb(void (Ass::*f)(Reg, ImmType), int imm_bits, std::string fmt) {
+  std::string RepeatRIb(void (Ass::*f)(Reg, ImmType), int imm_bits, const std::string& fmt) {
     return RepeatTemplatedRegisterImmBits<Reg, ImmType>(f,
         imm_bits,
         GetRegisters(),
@@ -301,7 +301,9 @@
   }
 
   template <typename ImmType>
-  std::string RepeatFRIb(void (Ass::*f)(FPReg, Reg, ImmType), int imm_bits, std::string fmt) {
+  std::string RepeatFRIb(void (Ass::*f)(FPReg, Reg, ImmType),
+                         int imm_bits,
+                         const std::string& fmt) {
     return RepeatTemplatedRegistersImmBits<FPReg, Reg, ImmType>(f,
         imm_bits,
         GetFPRegisters(),
@@ -311,7 +313,7 @@
         fmt);
   }
 
-  std::string RepeatFF(void (Ass::*f)(FPReg, FPReg), std::string fmt) {
+  std::string RepeatFF(void (Ass::*f)(FPReg, FPReg), const std::string& fmt) {
     return RepeatTemplatedRegisters<FPReg, FPReg>(f,
                                                   GetFPRegisters(),
                                                   GetFPRegisters(),
@@ -320,7 +322,7 @@
                                                   fmt);
   }
 
-  std::string RepeatFFF(void (Ass::*f)(FPReg, FPReg, FPReg), std::string fmt) {
+  std::string RepeatFFF(void (Ass::*f)(FPReg, FPReg, FPReg), const std::string& fmt) {
     return RepeatTemplatedRegisters<FPReg, FPReg, FPReg>(f,
                                                          GetFPRegisters(),
                                                          GetFPRegisters(),
@@ -331,7 +333,7 @@
                                                          fmt);
   }
 
-  std::string RepeatFFR(void (Ass::*f)(FPReg, FPReg, Reg), std::string fmt) {
+  std::string RepeatFFR(void (Ass::*f)(FPReg, FPReg, Reg), const std::string& fmt) {
     return RepeatTemplatedRegisters<FPReg, FPReg, Reg>(
         f,
         GetFPRegisters(),
@@ -345,7 +347,7 @@
 
   std::string RepeatFFI(void (Ass::*f)(FPReg, FPReg, const Imm&),
                         size_t imm_bytes,
-                        std::string fmt) {
+                        const std::string& fmt) {
     return RepeatTemplatedRegistersImm<FPReg, FPReg>(f,
                                                      GetFPRegisters(),
                                                      GetFPRegisters(),
@@ -356,7 +358,9 @@
   }
 
   template <typename ImmType>
-  std::string RepeatFFIb(void (Ass::*f)(FPReg, FPReg, ImmType), int imm_bits, std::string fmt) {
+  std::string RepeatFFIb(void (Ass::*f)(FPReg, FPReg, ImmType),
+                         int imm_bits,
+                         const std::string& fmt) {
     return RepeatTemplatedRegistersImmBits<FPReg, FPReg, ImmType>(f,
                                                                   imm_bits,
                                                                   GetFPRegisters(),
@@ -367,7 +371,9 @@
   }
 
   template <typename ImmType>
-  std::string RepeatIbFF(void (Ass::*f)(ImmType, FPReg, FPReg), int imm_bits, std::string fmt) {
+  std::string RepeatIbFF(void (Ass::*f)(ImmType, FPReg, FPReg),
+                         int imm_bits,
+                         const std::string& fmt) {
     return RepeatTemplatedImmBitsRegisters<ImmType, FPReg, FPReg>(f,
                                                                   GetFPRegisters(),
                                                                   GetFPRegisters(),
@@ -377,7 +383,7 @@
                                                                   fmt);
   }
 
-  std::string RepeatFR(void (Ass::*f)(FPReg, Reg), std::string fmt) {
+  std::string RepeatFR(void (Ass::*f)(FPReg, Reg), const std::string& fmt) {
     return RepeatTemplatedRegisters<FPReg, Reg>(f,
         GetFPRegisters(),
         GetRegisters(),
@@ -386,7 +392,7 @@
         fmt);
   }
 
-  std::string RepeatFr(void (Ass::*f)(FPReg, Reg), std::string fmt) {
+  std::string RepeatFr(void (Ass::*f)(FPReg, Reg), const std::string& fmt) {
     return RepeatTemplatedRegisters<FPReg, Reg>(f,
         GetFPRegisters(),
         GetRegisters(),
@@ -395,7 +401,7 @@
         fmt);
   }
 
-  std::string RepeatRF(void (Ass::*f)(Reg, FPReg), std::string fmt) {
+  std::string RepeatRF(void (Ass::*f)(Reg, FPReg), const std::string& fmt) {
     return RepeatTemplatedRegisters<Reg, FPReg>(f,
         GetRegisters(),
         GetFPRegisters(),
@@ -404,7 +410,7 @@
         fmt);
   }
 
-  std::string RepeatrF(void (Ass::*f)(Reg, FPReg), std::string fmt) {
+  std::string RepeatrF(void (Ass::*f)(Reg, FPReg), const std::string& fmt) {
     return RepeatTemplatedRegisters<Reg, FPReg>(f,
         GetRegisters(),
         GetFPRegisters(),
@@ -413,7 +419,9 @@
         fmt);
   }
 
-  std::string RepeatI(void (Ass::*f)(const Imm&), size_t imm_bytes, std::string fmt,
+  std::string RepeatI(void (Ass::*f)(const Imm&),
+                      size_t imm_bytes,
+                      const std::string& fmt,
                       bool as_uint = false) {
     std::string str;
     std::vector<int64_t> imms = CreateImmediateValues(imm_bytes, as_uint);
@@ -651,7 +659,7 @@
   std::string RepeatTemplatedRegister(void (Ass::*f)(RegType),
                                       const std::vector<RegType*> registers,
                                       std::string (AssemblerTest::*GetName)(const RegType&),
-                                      std::string fmt) {
+                                      const std::string& fmt) {
     std::string str;
     for (auto reg : registers) {
       (assembler_.get()->*f)(*reg);
@@ -679,7 +687,7 @@
                                        const std::vector<Reg2*> reg2_registers,
                                        std::string (AssemblerTest::*GetName1)(const Reg1&),
                                        std::string (AssemblerTest::*GetName2)(const Reg2&),
-                                       std::string fmt) {
+                                       const std::string& fmt) {
     WarnOnCombinations(reg1_registers.size() * reg2_registers.size());
 
     std::string str;
@@ -717,7 +725,7 @@
                                               const std::vector<Reg2*> reg2_registers,
                                               std::string (AssemblerTest::*GetName1)(const Reg1&),
                                               std::string (AssemblerTest::*GetName2)(const Reg2&),
-                                              std::string fmt) {
+                                              const std::string& fmt) {
     WarnOnCombinations(reg1_registers.size() * reg2_registers.size());
 
     std::string str;
@@ -758,7 +766,7 @@
                                        std::string (AssemblerTest::*GetName1)(const Reg1&),
                                        std::string (AssemblerTest::*GetName2)(const Reg2&),
                                        std::string (AssemblerTest::*GetName3)(const Reg3&),
-                                       std::string fmt) {
+                                       const std::string& fmt) {
     std::string str;
     for (auto reg1 : reg1_registers) {
       for (auto reg2 : reg2_registers) {
@@ -803,7 +811,7 @@
                                           std::string (AssemblerTest::*GetName1)(const Reg1&),
                                           std::string (AssemblerTest::*GetName2)(const Reg2&),
                                           size_t imm_bytes,
-                                          std::string fmt) {
+                                          const std::string& fmt) {
     std::vector<int64_t> imms = CreateImmediateValues(imm_bytes);
     WarnOnCombinations(reg1_registers.size() * reg2_registers.size() * imms.size());
 
@@ -895,8 +903,9 @@
 
  private:
   template <RegisterView kRegView>
-  std::string RepeatRegisterImm(void (Ass::*f)(Reg, const Imm&), size_t imm_bytes,
-                                  std::string fmt) {
+  std::string RepeatRegisterImm(void (Ass::*f)(Reg, const Imm&),
+                                size_t imm_bytes,
+                                const std::string& fmt) {
     const std::vector<Reg*> registers = GetRegisters();
     std::string str;
     std::vector<int64_t> imms = CreateImmediateValues(imm_bytes);
@@ -938,7 +947,7 @@
   virtual void Pad(std::vector<uint8_t>& data ATTRIBUTE_UNUSED) {
   }
 
-  void DriverWrapper(std::string assembly_text, std::string test_name) {
+  void DriverWrapper(const std::string& assembly_text, const std::string& test_name) {
     assembler_->FinalizeCode();
     size_t cs = assembler_->CodeSize();
     std::unique_ptr<std::vector<uint8_t>> data(new std::vector<uint8_t>(cs));
diff --git a/compiler/utils/assembler_test_base.h b/compiler/utils/assembler_test_base.h
index 8c71292..ac24ee9 100644
--- a/compiler/utils/assembler_test_base.h
+++ b/compiler/utils/assembler_test_base.h
@@ -106,7 +106,9 @@
   // Driver() assembles and compares the results. If the results are not equal and we have a
   // disassembler, disassemble both and check whether they have the same mnemonics (in which case
   // we just warn).
-  void Driver(const std::vector<uint8_t>& data, std::string assembly_text, std::string test_name) {
+  void Driver(const std::vector<uint8_t>& data,
+              const std::string& assembly_text,
+              const std::string& test_name) {
     EXPECT_NE(assembly_text.length(), 0U) << "Empty assembly";
 
     NativeAssemblerResult res;
@@ -229,7 +231,7 @@
     bool success = Exec(args, error_msg);
     if (!success) {
       LOG(ERROR) << "Assembler command line:";
-      for (std::string arg : args) {
+      for (const std::string& arg : args) {
         LOG(ERROR) << arg;
       }
     }
@@ -238,7 +240,7 @@
 
   // Runs objdump -h on the binary file and extracts the first line with .text.
   // Returns "" on failure.
-  std::string Objdump(std::string file) {
+  std::string Objdump(const std::string& file) {
     bool have_objdump = FileExists(FindTool(objdump_cmd_name_));
     EXPECT_TRUE(have_objdump) << "Cannot find objdump: " << GetObjdumpCommand();
     if (!have_objdump) {
@@ -287,8 +289,9 @@
   }
 
   // Disassemble both binaries and compare the text.
-  bool DisassembleBinaries(const std::vector<uint8_t>& data, const std::vector<uint8_t>& as,
-                           std::string test_name) {
+  bool DisassembleBinaries(const std::vector<uint8_t>& data,
+                           const std::vector<uint8_t>& as,
+                           const std::string& test_name) {
     std::string disassembler = GetDisassembleCommand();
     if (disassembler.length() == 0) {
       LOG(WARNING) << "No dissassembler command.";
@@ -324,7 +327,7 @@
     return result;
   }
 
-  bool DisassembleBinary(std::string file, std::string* error_msg) {
+  bool DisassembleBinary(const std::string& file, std::string* error_msg) {
     std::vector<std::string> args;
 
     // Encaspulate the whole command line in a single string passed to
@@ -345,7 +348,7 @@
     return Exec(args, error_msg);
   }
 
-  std::string WriteToFile(const std::vector<uint8_t>& buffer, std::string test_name) {
+  std::string WriteToFile(const std::vector<uint8_t>& buffer, const std::string& test_name) {
     std::string file_name = GetTmpnam() + std::string("---") + test_name;
     const char* data = reinterpret_cast<const char*>(buffer.data());
     std::ofstream s_out(file_name + ".o");
@@ -354,7 +357,7 @@
     return file_name + ".o";
   }
 
-  bool CompareFiles(std::string f1, std::string f2) {
+  bool CompareFiles(const std::string& f1, const std::string& f2) {
     std::ifstream f1_in(f1);
     std::ifstream f2_in(f2);
 
@@ -369,7 +372,9 @@
   }
 
   // Compile the given assembly code and extract the binary, if possible. Put result into res.
-  bool Compile(std::string assembly_code, NativeAssemblerResult* res, std::string test_name) {
+  bool Compile(const std::string& assembly_code,
+               NativeAssemblerResult* res,
+               const std::string& test_name) {
     res->ok = false;
     res->code.reset(nullptr);
 
@@ -438,7 +443,7 @@
   // Check whether file exists. Is used for commands, so strips off any parameters: anything after
   // the first space. We skip to the last slash for this, so it should work with directories with
   // spaces.
-  static bool FileExists(std::string file) {
+  static bool FileExists(const std::string& file) {
     if (file.length() == 0) {
       return false;
     }
@@ -478,7 +483,7 @@
     return getcwd(temp, 1024) ? std::string(temp) + "/" : std::string("");
   }
 
-  std::string FindTool(std::string tool_name) {
+  std::string FindTool(const std::string& tool_name) {
     // Find the current tool. Wild-card pattern is "arch-string*tool-name".
     std::string gcc_path = GetRootPath() + GetGCCRootPath();
     std::vector<std::string> args;
@@ -522,7 +527,8 @@
 
   // Helper for below. If name_predicate is empty, search for all files, otherwise use it for the
   // "-name" option.
-  static void FindToolDumpPrintout(std::string name_predicate, std::string tmp_file) {
+  static void FindToolDumpPrintout(const std::string& name_predicate,
+                                   const std::string& tmp_file) {
     std::string gcc_path = GetRootPath() + GetGCCRootPath();
     std::vector<std::string> args;
     args.push_back("find");
@@ -562,7 +568,7 @@
   }
 
   // For debug purposes.
-  void FindToolDump(std::string tool_name) {
+  void FindToolDump(const std::string& tool_name) {
     // Check with the tool name.
     FindToolDumpPrintout(architecture_string_ + "*" + tool_name, GetTmpnam());
     FindToolDumpPrintout("", GetTmpnam());
diff --git a/compiler/utils/jni_macro_assembler_test.h b/compiler/utils/jni_macro_assembler_test.h
index 829f34b..293f4cd 100644
--- a/compiler/utils/jni_macro_assembler_test.h
+++ b/compiler/utils/jni_macro_assembler_test.h
@@ -39,12 +39,12 @@
 
   typedef std::string (*TestFn)(JNIMacroAssemblerTest* assembler_test, Ass* assembler);
 
-  void DriverFn(TestFn f, std::string test_name) {
+  void DriverFn(TestFn f, const std::string& test_name) {
     DriverWrapper(f(this, assembler_.get()), test_name);
   }
 
   // This driver assumes the assembler has already been called.
-  void DriverStr(std::string assembly_string, std::string test_name) {
+  void DriverStr(const std::string& assembly_string, const std::string& test_name) {
     DriverWrapper(assembly_string, test_name);
   }
 
@@ -128,7 +128,7 @@
   virtual void Pad(std::vector<uint8_t>& data ATTRIBUTE_UNUSED) {
   }
 
-  void DriverWrapper(std::string assembly_text, std::string test_name) {
+  void DriverWrapper(const std::string& assembly_text, const std::string& test_name) {
     assembler_->FinalizeCode();
     size_t cs = assembler_->CodeSize();
     std::unique_ptr<std::vector<uint8_t>> data(new std::vector<uint8_t>(cs));
diff --git a/compiler/utils/mips/assembler_mips32r6_test.cc b/compiler/utils/mips/assembler_mips32r6_test.cc
index 3ef2f94..a52f519 100644
--- a/compiler/utils/mips/assembler_mips32r6_test.cc
+++ b/compiler/utils/mips/assembler_mips32r6_test.cc
@@ -219,7 +219,7 @@
   void BranchCondTwoRegsHelper(void (mips::MipsAssembler::*f)(mips::Register,
                                                               mips::Register,
                                                               mips::MipsLabel*),
-                               std::string instr_name) {
+                               const std::string& instr_name) {
     mips::MipsLabel label;
     (Base::GetAssembler()->*f)(mips::A0, mips::A1, &label);
     constexpr size_t kAdduCount1 = 63;
diff --git a/compiler/utils/mips/assembler_mips_test.cc b/compiler/utils/mips/assembler_mips_test.cc
index 75149cf..c24e1b1 100644
--- a/compiler/utils/mips/assembler_mips_test.cc
+++ b/compiler/utils/mips/assembler_mips_test.cc
@@ -188,7 +188,7 @@
 
   void BranchCondOneRegHelper(void (mips::MipsAssembler::*f)(mips::Register,
                                                              mips::MipsLabel*),
-                              std::string instr_name) {
+                              const std::string& instr_name) {
     mips::MipsLabel label;
     (Base::GetAssembler()->*f)(mips::A0, &label);
     constexpr size_t kAdduCount1 = 63;
@@ -217,7 +217,7 @@
   void BranchCondTwoRegsHelper(void (mips::MipsAssembler::*f)(mips::Register,
                                                               mips::Register,
                                                               mips::MipsLabel*),
-                               std::string instr_name) {
+                               const std::string& instr_name) {
     mips::MipsLabel label;
     (Base::GetAssembler()->*f)(mips::A0, mips::A1, &label);
     constexpr size_t kAdduCount1 = 63;
diff --git a/compiler/utils/mips64/assembler_mips64_test.cc b/compiler/utils/mips64/assembler_mips64_test.cc
index 1fdef96..ba8f25e 100644
--- a/compiler/utils/mips64/assembler_mips64_test.cc
+++ b/compiler/utils/mips64/assembler_mips64_test.cc
@@ -212,7 +212,7 @@
 
   void BranchCondOneRegHelper(void (mips64::Mips64Assembler::*f)(mips64::GpuRegister,
                                                                  mips64::Mips64Label*),
-                              std::string instr_name) {
+                              const std::string& instr_name) {
     mips64::Mips64Label label;
     (Base::GetAssembler()->*f)(mips64::A0, &label);
     constexpr size_t kAdduCount1 = 63;
@@ -241,7 +241,7 @@
   void BranchCondTwoRegsHelper(void (mips64::Mips64Assembler::*f)(mips64::GpuRegister,
                                                                   mips64::GpuRegister,
                                                                   mips64::Mips64Label*),
-                               std::string instr_name) {
+                               const std::string& instr_name) {
     mips64::Mips64Label label;
     (Base::GetAssembler()->*f)(mips64::A0, mips64::A1, &label);
     constexpr size_t kAdduCount1 = 63;