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Compiler User Guide

Preface Overview of the Compiler Getting Started with the Compiler Compiler Features Compiler Coding Practices The compiler as an optimizing compiler Compiler optimization for code size versus speed Compiler optimization levels and the debug view Selecting the target processor at compile time Enabling FPU for bare-metal Optimization of loop termination in C code Loop unrolling in C code Compiler optimization and the volatile keyword Code metrics Code metrics for measurement of code size and data Stack use in C and C++ Benefits of reducing debug information in objects Methods of reducing debug information in objects a Guarding against multiple inclusion of header file Methods of minimizing function parameter passing o Returning structures from functions through regist Functions that return the same result when called Comparison of pure and impure functions Recommendation of postfix syntax when qualifying f Inline functions Compiler decisions on function inlining Automatic function inlining and static functions Inline functions and removal of unused out-of-line Automatic function inlining and multifile compilat Restriction on overriding compiler decisions about Compiler modes and inline functions Inline functions in C++ and C90 mode Inline functions in C99 mode Inline functions and debugging Types of data alignment Advantages of natural data alignment Compiler storage of data objects by natural byte a Relevance of natural data alignment at compile tim Unaligned data access in C and C++ code The __packed qualifier and unaligned data access i Unaligned fields in structures Performance penalty associated with marking whole Unaligned pointers in C and C++ code Unaligned Load Register (LDR) instructions generat Comparisons of an unpacked struct, a __packed stru Compiler support for floating-point arithmetic Default selection of hardware or software floating Example of hardware and software support differenc Vector Floating-Point (VFP) architectures Limitations on hardware handling of floating-point Implementation of Vector Floating-Point (VFP) supp Compiler and library support for half-precision fl Half-precision floating-point number format Compiler support for floating-point computations a Types of floating-point linkage Compiler options for floating-point linkage and co Floating-point linkage and computational requireme Processors and their implicit Floating-Point Units Integer division-by-zero errors in C code Software floating-point division-by-zero errors in About trapping software floating-point division-by Identification of software floating-point division Software floating-point division-by-zero debugging New language features of C99 New library features of C99 // comments in C99 and C90 Compound literals in C99 Designated initializers in C99 Hexadecimal floating-point numbers in C99 Flexible array members in C99 __func__ predefined identifier in C99 inline functions in C99 long long data type in C99 and C90 Macros with a variable number of arguments in C99 Mixed declarations and statements in C99 New block scopes for selection and iteration state _Pragma preprocessing operator in C99 Restricted pointers in C99 Additional library functions in C99 Complex numbers in C99 Boolean type and in C99 Extended integer types and functions in floating-point environment access in C99 snprintf family of functions in C99 type-generic math macros in C99 wide character I/O functions in C99 How to prevent uninitialized data from being initi Compiler Diagnostic Messages Using the Inline and Embedded Assemblers of the AR Compiler Command-line Options Language Extensions Compiler-specific Features C and C++ Implementation Details What is Semihosting? Via File Syntax Summary Table of GNU Language Extensions Standard C Implementation Definition Standard C++ Implementation Definition C and C++ Compiler Implementation Limits

Inline functions in C++ and C90 mode

4.27 Inline functions in C++ and C90 mode

The inline keyword is not available in C90. The effect of __inline in C90, and __inline and inline in C++, is identical.

When declaring an extern function to be inline, you must define it in every translation unit that it is used in. You must ensure that you use the same definition in each translation unit.
The requirement of defining the function in every translation unit applies even though it has external linkage.
If an inline function is used by more than one translation unit, its definition is typically placed in a header file.
ARM does not recommend placing definitions of non-inline functions in header files, because this can result in the creation of a separate function in each translation unit. If the non-inline function is an extern function, this leads to duplicate symbols at link time. If the non-inline function is static, this can lead to unwanted code duplication.
Member functions defined within a C++ structure, class, or union declaration, are implicitly inline. They are treated as if they are declared with the inline or __inline keyword.
Inline functions have extern linkage unless they are explicitly declared static. If an inline function is declared to be static, any out-of-line copies of the function must be unique to their translation unit, so declaring an inline function to be static could lead to unwanted code duplication.
The compiler generates a regular call to an out-of-line copy of a function when it cannot inline the function, and when it decides not to inline it.
The requirement of defining a function in every translation unit it is used in means that the compiler is not required to emit out-of-line copies of all extern inline functions. When the compiler does emit out-of-line copies of an extern inline function, it uses Common Groups, so that the linker eliminates duplicates, keeping at most one copy in the same out-of-line function from different object files.
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