SLAU132Y September   2004  – June 2021

 

  1.   Read This First
    1.     About This Manual
    2.     Notational Conventions
    3.     Related Documentation
    4.     Related Documentation From Texas Instruments
    5.     Trademarks
  2. 1Introduction to the Software Development Tools
    1. 1.1 Software Development Tools Overview
    2. 1.2 Compiler Interface
    3. 1.3 ANSI/ISO Standard
    4. 1.4 Output Files
    5. 1.5 Utilities
  3. 2Using the C/C++ Compiler
    1. 2.1  About the Compiler
    2. 2.2  Invoking the C/C++ Compiler
    3. 2.3  Changing the Compiler's Behavior with Options
      1. 2.3.1  Linker Options
      2. 2.3.2  Frequently Used Options
      3. 2.3.3  Miscellaneous Useful Options
      4. 2.3.4  Run-Time Model Options
      5. 2.3.5  Symbolic Debugging Options
      6. 2.3.6  Specifying Filenames
      7. 2.3.7  Changing How the Compiler Interprets Filenames
      8. 2.3.8  Changing How the Compiler Processes C Files
      9. 2.3.9  Changing How the Compiler Interprets and Names Extensions
      10. 2.3.10 Specifying Directories
      11. 2.3.11 Assembler Options
      12. 2.3.12 Deprecated Options
    4. 2.4  Controlling the Compiler Through Environment Variables
      1. 2.4.1 Setting Default Compiler Options (MSP430_C_OPTION)
      2. 2.4.2 Naming One or More Alternate Directories (MSP430_C_DIR)
    5. 2.5  Controlling the Preprocessor
      1. 2.5.1  Predefined Macro Names
      2. 2.5.2  The Search Path for #include Files
        1. 2.5.2.1 Adding a Directory to the #include File Search Path (--include_path Option)
      3. 2.5.3  Support for the #warning and #warn Directives
      4. 2.5.4  Generating a Preprocessed Listing File (--preproc_only Option)
      5. 2.5.5  Continuing Compilation After Preprocessing (--preproc_with_compile Option)
      6. 2.5.6  Generating a Preprocessed Listing File with Comments (--preproc_with_comment Option)
      7. 2.5.7  Generating Preprocessed Listing with Line-Control Details (--preproc_with_line Option)
      8. 2.5.8  Generating Preprocessed Output for a Make Utility (--preproc_dependency Option)
      9. 2.5.9  Generating a List of Files Included with #include (--preproc_includes Option)
      10. 2.5.10 Generating a List of Macros in a File (--preproc_macros Option)
    6. 2.6  Passing Arguments to main()
    7. 2.7  Understanding Diagnostic Messages
      1. 2.7.1 Controlling Diagnostic Messages
      2. 2.7.2 How You Can Use Diagnostic Suppression Options
    8. 2.8  Other Messages
    9. 2.9  Generating Cross-Reference Listing Information (--gen_cross_reference Option)
    10. 2.10 Generating a Raw Listing File (--gen_preprocessor_listing Option)
    11. 2.11 Using Inline Function Expansion
      1. 2.11.1 Inlining Intrinsic Operators
      2. 2.11.2 Inlining Restrictions
    12. 2.12 Using Interlist
    13. 2.13 Controlling Application Binary Interface
    14. 2.14 Enabling Entry Hook and Exit Hook Functions
  4. 3Optimizing Your Code
    1. 3.1  Invoking Optimization
    2. 3.2  Controlling Code Size Versus Speed
    3. 3.3  Performing File-Level Optimization (--opt_level=3 option)
      1. 3.3.1 Creating an Optimization Information File (--gen_opt_info Option)
    4. 3.4  Program-Level Optimization (--program_level_compile and --opt_level=3 options)
      1. 3.4.1 Controlling Program-Level Optimization (--call_assumptions Option)
      2. 3.4.2 Optimization Considerations When Mixing C/C++ and Assembly
    5. 3.5  Automatic Inline Expansion (--auto_inline Option)
    6. 3.6  Link-Time Optimization (--opt_level=4 Option)
      1. 3.6.1 Option Handling
      2. 3.6.2 Incompatible Types
    7. 3.7  Using Feedback Directed Optimization
      1. 3.7.1 Feedback Directed Optimization
        1. 3.7.1.1 Phase 1 -- Collect Program Profile Information
        2. 3.7.1.2 Phase 2 -- Use Application Profile Information for Optimization
        3. 3.7.1.3 Generating and Using Profile Information
        4. 3.7.1.4 Example Use of Feedback Directed Optimization
        5. 3.7.1.5 The .ppdata Section
        6. 3.7.1.6 Feedback Directed Optimization and Code Size Tune
        7. 3.7.1.7 Instrumented Program Execution Overhead
        8. 3.7.1.8 Invalid Profile Data
      2. 3.7.2 Profile Data Decoder
      3. 3.7.3 Feedback Directed Optimization API
      4. 3.7.4 Feedback Directed Optimization Summary
    8. 3.8  Using Profile Information to Analyze Code Coverage
      1. 3.8.1 Code Coverage
        1. 3.8.1.1 Phase1 -- Collect Program Profile Information
        2. 3.8.1.2 Phase 2 -- Generate Code Coverage Reports
      2. 3.8.2 Related Features and Capabilities
        1. 3.8.2.1 Path Profiler
        2. 3.8.2.2 Analysis Options
        3. 3.8.2.3 Environment Variables
    9. 3.9  Accessing Aliased Variables in Optimized Code
    10. 3.10 Use Caution With asm Statements in Optimized Code
    11. 3.11 Using the Interlist Feature With Optimization
    12. 3.12 Debugging Optimized Code
    13. 3.13 What Kind of Optimization Is Being Performed?
      1. 3.13.1  Cost-Based Register Allocation
      2. 3.13.2  Alias Disambiguation
      3. 3.13.3  Branch Optimizations and Control-Flow Simplification
      4. 3.13.4  Data Flow Optimizations
      5. 3.13.5  Expression Simplification
      6. 3.13.6  Inline Expansion of Functions
      7. 3.13.7  Function Symbol Aliasing
      8. 3.13.8  Induction Variables and Strength Reduction
      9. 3.13.9  Loop-Invariant Code Motion
      10. 3.13.10 Loop Rotation
      11. 3.13.11 Instruction Scheduling
      12. 3.13.12 Tail Merging
      13. 3.13.13 Integer Division With Constant Divisor
  5. 4Linking C/C++ Code
    1. 4.1 Invoking the Linker Through the Compiler (-z Option)
      1. 4.1.1 Invoking the Linker Separately
      2. 4.1.2 Invoking the Linker as Part of the Compile Step
      3. 4.1.3 Disabling the Linker (--compile_only Compiler Option)
    2. 4.2 Linker Code Optimizations
      1. 4.2.1 Conditional Linking
      2. 4.2.2 Generating Aggregate Data Subsections (--gen_data_subsections Compiler Option)
    3. 4.3 Controlling the Linking Process
      1. 4.3.1 Including the Run-Time-Support Library
        1. 4.3.1.1 Automatic Run-Time-Support Library Selection
          1. 4.3.1.1.1 Using the --issue_remarks Option
        2. 4.3.1.2 Manual Run-Time-Support Library Selection
        3. 4.3.1.3 Library Order for Searching for Symbols
      2. 4.3.2 Run-Time Initialization
      3. 4.3.3 Initialization by the Interrupt Vector
      4. 4.3.4 Initialization of the FRAM Memory Protection Unit
      5. 4.3.5 Initialization of Cinit and Watchdog Timer Hold
      6. 4.3.6 Global Object Constructors
      7. 4.3.7 Specifying the Type of Global Variable Initialization
      8. 4.3.8 Specifying Where to Allocate Sections in Memory
      9. 4.3.9 A Sample Linker Command File
  6. 5C/C++ Language Implementation
    1. 5.1  Characteristics of MSP430 C
      1. 5.1.1 Implementation-Defined Behavior
    2. 5.2  Characteristics of MSP430 C++
    3. 5.3  Using the ULP Advisor
    4. 5.4  Advice on Hardware Configuration
    5. 5.5  Data Types
      1. 5.5.1 Size of Enum Types
    6. 5.6  File Encodings and Character Sets
    7. 5.7  Keywords
      1. 5.7.1 The const Keyword
      2. 5.7.2 The __interrupt Keyword
      3. 5.7.3 The restrict Keyword
      4. 5.7.4 The volatile Keyword
    8. 5.8  C++ Exception Handling
    9. 5.9  Register Variables and Parameters
    10. 5.10 The __asm Statement
    11. 5.11 Pragma Directives
      1. 5.11.1  The BIS_IE1_INTERRUPT
      2. 5.11.2  The CALLS Pragma
      3. 5.11.3  The CHECK_ULP Pragma
      4. 5.11.4  The CODE_ALIGN Pragma
      5. 5.11.5  The CODE_SECTION Pragma
      6. 5.11.6  The DATA_ALIGN Pragma
      7. 5.11.7  The DATA_SECTION Pragma
        1. 5.11.7.1 Using the DATA_SECTION Pragma C Source File
        2. 5.11.7.2 Using the DATA_SECTION Pragma C++ Source File
        3. 5.11.7.3 Using the DATA_SECTION Pragma Assembly Source File
      8. 5.11.8  The Diagnostic Message Pragmas
      9. 5.11.9  The FORCEINLINE Pragma
      10. 5.11.10 The FORCEINLINE_RECURSIVE Pragma
      11. 5.11.11 The FUNC_ALWAYS_INLINE Pragma
      12. 5.11.12 The FUNC_CANNOT_INLINE Pragma
      13. 5.11.13 The FUNC_EXT_CALLED Pragma
      14. 5.11.14 The FUNC_IS_PURE Pragma
      15. 5.11.15 The FUNC_NEVER_RETURNS Pragma
      16. 5.11.16 The FUNC_NO_GLOBAL_ASG Pragma
      17. 5.11.17 The FUNC_NO_IND_ASG Pragma
      18. 5.11.18 The FUNCTION_OPTIONS Pragma
      19. 5.11.19 The INTERRUPT Pragma
      20. 5.11.20 The LOCATION Pragma
      21. 5.11.21 The MUST_ITERATE Pragma
        1. 5.11.21.1 The MUST_ITERATE Pragma Syntax
        2. 5.11.21.2 Using MUST_ITERATE to Expand Compiler Knowledge of Loops
      22. 5.11.22 The NOINIT and PERSISTENT Pragmas
      23. 5.11.23 The NOINLINE Pragma
      24. 5.11.24 The NO_HOOKS Pragma
      25. 5.11.25 The once Pragma
      26. 5.11.26 The pack Pragma
      27. 5.11.27 The PROB_ITERATE Pragma
      28. 5.11.28 The RESET_ULP Pragma
      29. 5.11.29 The RETAIN Pragma
      30. 5.11.30 The SET_CODE_SECTION and SET_DATA_SECTION Pragmas
      31. 5.11.31 The UNROLL Pragma
      32. 5.11.32 The vector Pragma
      33. 5.11.33 The WEAK Pragma
    12. 5.12 The _Pragma Operator
    13. 5.13 Application Binary Interface
    14. 5.14 Object File Symbol Naming Conventions (Linknames)
    15. 5.15 Changing the ANSI/ISO C/C++ Language Mode
      1. 5.15.1 C99 Support (--c99)
      2. 5.15.2 C11 Support (--c11)
      3. 5.15.3 Strict ANSI Mode and Relaxed ANSI Mode (--strict_ansi and --relaxed_ansi)
    16. 5.16 GNU and Clang Language Extensions
      1. 5.16.1 Extensions
      2. 5.16.2 Function Attributes
      3. 5.16.3 For Loop Attributes
      4. 5.16.4 Variable Attributes
      5. 5.16.5 Type Attributes
      6. 5.16.6 Built-In Functions
    17. 5.17 Compiler Limits
  7. 6Run-Time Environment
    1. 6.1  Memory Model
      1. 6.1.1 Code Memory Models
      2. 6.1.2 Data Memory Models
      3. 6.1.3 Support for Near Data
      4. 6.1.4 Sections
      5. 6.1.5 C/C++ Software Stack
      6. 6.1.6 Dynamic Memory Allocation
    2. 6.2  Object Representation
      1. 6.2.1 Data Type Storage
        1. 6.2.1.1 Pointer to Member Function Types
        2. 6.2.1.2 Structure and Array Alignment
        3. 6.2.1.3 Field/Structure Alignment
        4. 6.2.1.4 C Code Definition of var
      2. 6.2.2 Character String Constants
    3. 6.3  Register Conventions
    4. 6.4  Function Structure and Calling Conventions
      1. 6.4.1 How a Function Makes a Call
      2. 6.4.2 How a Called Function Responds
      3. 6.4.3 Accessing Arguments and Local Variables
    5. 6.5  Accessing Linker Symbols in C and C++
    6. 6.6  Interfacing C and C++ With Assembly Language
      1. 6.6.1 Using Assembly Language Modules With C/C++ Code
      2. 6.6.2 Accessing Assembly Language Functions From C/C++
        1. 6.6.2.1 Calling an Assembly Language Function From a C/C++ Program
        2. 6.6.2.2 Assembly Language Program Called by Section 1
        3.       227
      3. 6.6.3 Accessing Assembly Language Variables From C/C++
        1. 6.6.3.1 Accessing Assembly Language Global Variables
          1. 6.6.3.1.1 Assembly Language Variable Program
          2. 6.6.3.1.2 C Program to Access Assembly Language From Section 1
        2.       232
        3. 6.6.3.2 Accessing Assembly Language Constants
          1. 6.6.3.2.1 Accessing an Assembly Language Constant From C
          2. 6.6.3.2.2 Assembly Language Program for Section 1
          3.        236
      4. 6.6.4 Sharing C/C++ Header Files With Assembly Source
      5. 6.6.5 Using Inline Assembly Language
    7. 6.7  Interrupt Handling
      1. 6.7.1 Saving Registers During Interrupts
      2. 6.7.2 Using C/C++ Interrupt Routines
        1.       242
      3. 6.7.3 Using Assembly Language Interrupt Routines
      4. 6.7.4 Interrupt Vectors
      5. 6.7.5 Other Interrupt Information
    8. 6.8  Using Intrinsics to Access Assembly Language Statements
      1. 6.8.1 MSP430 Intrinsics
      2. 6.8.2 Floating Point Conversion Intrinsics
      3. 6.8.3 Deprecated Intrinsics
      4. 6.8.4 The __delay_cycle Intrinsic
      5. 6.8.5 The __never_executed Intrinsic
        1. 6.8.5.1 Using __never_executed With a Vector Generator
          1. 6.8.5.1.1 TBIV Vector Generator
          2.        254
        2. 6.8.5.2 Using __never_executed With General Switch Expressions
          1. 6.8.5.2.1 General Switch Statement
          2.        257
    9. 6.9  System Initialization
      1. 6.9.1 Boot Hook Functions for System Pre-Initialization
      2. 6.9.2 Run-Time Stack
      3. 6.9.3 Automatic Initialization of Variables
        1. 6.9.3.1 Zero Initializing Variables
        2. 6.9.3.2 Direct Initialization
        3. 6.9.3.3 Autoinitialization of Variables at Run Time
        4. 6.9.3.4 Autoinitialization Tables
          1. 6.9.3.4.1 Length Followed by Data Format
          2. 6.9.3.4.2 Zero Initialization Format
          3. 6.9.3.4.3 Run Length Encoded (RLE) Format
          4. 6.9.3.4.4 Lempel-Ziv-Storer-Szymanski Compression (LZSS) Format
        5. 6.9.3.5 Initialization of Variables at Load Time
        6. 6.9.3.6 Global Constructors
      4. 6.9.4 Initialization Tables
    10. 6.10 Compiling for 20-Bit MSP430X Devices
  8. 7Using Run-Time-Support Functions and Building Libraries
    1. 7.1 C and C++ Run-Time Support Libraries
      1. 7.1.1 Linking Code With the Object Library
      2. 7.1.2 Header Files
      3. 7.1.3 Modifying a Library Function
      4. 7.1.4 Support for String Handling
      5. 7.1.5 Minimal Support for Internationalization
      6. 7.1.6 Support for Time and Clock Functions
      7. 7.1.7 Allowable Number of Open Files
      8. 7.1.8 Nonstandard Header Files in the Source Tree
      9. 7.1.9 Library Naming Conventions
    2. 7.2 The C I/O Functions
      1. 7.2.1 High-Level I/O Functions
        1. 7.2.1.1 Formatting and the Format Conversion Buffer
      2. 7.2.2 Overview of Low-Level I/O Implementation
        1.       open
        2.       close
        3.       read
        4.       write
        5.       lseek
        6.       unlink
        7.       rename
      3. 7.2.3 Device-Driver Level I/O Functions
        1.       DEV_open
        2.       DEV_close
        3.       DEV_read
        4.       DEV_write
        5.       DEV_lseek
        6.       DEV_unlink
        7.       DEV_rename
      4. 7.2.4 Adding a User-Defined Device Driver for C I/O
        1. 7.2.4.1 Mapping Default Streams to Device
      5. 7.2.5 The device Prefix
        1.       add_device
        2.       308
        3. 7.2.5.1 Program for C I/O Device
    3. 7.3 Handling Reentrancy (_register_lock() and _register_unlock() Functions)
    4. 7.4 Library-Build Process
      1. 7.4.1 Required Non-Texas Instruments Software
      2. 7.4.2 Using the Library-Build Process
        1. 7.4.2.1 Automatic Standard Library Rebuilding by the Linker
        2. 7.4.2.2 Invoking mklib Manually
          1. 7.4.2.2.1 Building Standard Libraries
          2. 7.4.2.2.2 Shared or Read-Only Library Directory
          3. 7.4.2.2.3 Building Libraries With Custom Options
          4. 7.4.2.2.4 The mklib Program Option Summary
      3. 7.4.3 Extending mklib
        1. 7.4.3.1 Underlying Mechanism
        2. 7.4.3.2 Libraries From Other Vendors
  9. 8C++ Name Demangler
    1. 8.1 Invoking the C++ Name Demangler
    2. 8.2 Sample Usage of the C++ Name Demangler
  10.   A Glossary
    1.     A.1 Terminology
  11.   B Revision History
  12.   329
  13.   330

3.1 Invoking Optimization

The C/C++ compiler is able to perform various optimizations. High-level optimizations are performed in the optimizer and low-level, target-specific optimizations occur in the code generator. Use higher optimization levels, such as --opt_level=2 and --opt_level=3, to achieve optimal code.

The easiest way to invoke optimization is to use the compiler program, specifying the --opt_level=n option on the compiler command line. You can use -On to alias the --opt_level option. The n denotes the level of optimization (0, 1, 2, 3, and 4), which controls the type and degree of optimization.

  • --opt_level=off or -Ooff
    • Performs no optimization
  • --opt_level=0 or -O0
    • Performs control-flow-graph simplification
    • Allocates variables to registers
    • Performs loop rotation
    • Eliminates unused code
    • Simplifies expressions and statements
    • Expands calls to functions declared inline
  • --opt_level=1 or -O1

    Performs all --opt_level=0 (-O0) optimizations, plus:

    • Performs local copy/constant propagation
    • Removes unused assignments
    • Eliminates local common expressions

  • --opt_level=2 or -O2

    Performs all --opt_level=1 (-O1) optimizations, plus:

    • Performs loop optimizations
    • Eliminates global common subexpressions
    • Eliminates global unused assignments
    • Performs loop unrolling

  • --opt_level=3 or -O3

    Performs all --opt_level=2 (-O2) optimizations, plus:

    • Removes all functions that are never called
    • Simplifies functions with return values that are never used
    • Inlines calls to small functions
    • Reorders function declarations; the called functions attributes are known when the caller is optimized
    • Propagates arguments into function bodies when all calls pass the same value in the same argument position
    • Identifies file-level variable characteristics

      If you use --opt_level=3 (-O3), see Section 4.4 and Section 4.5 for more information.

  • --opt_level=4 or -O4

    Performs link-time optimization. See Section 4.7 for details.

For details about how the --opt_level and --opt_for_speed options and various pragmas affect inlining, see Section 3.12.

Debugging is enabled by default, and the optimization level is unaffected by the generation of debug information.

Optimizations are performed by the stand-alone optimization pass. The code generator performs several additional optimizations, particularly processor-specific optimizations. It does so regardless of whether you invoke the optimizer. These optimizations are always enabled, though they are more effective when the optimizer is used.