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Compiler User Guide

Preface Overview of the Compiler Getting Started with the Compiler Compiler Features Compiler intrinsics Performance benefits of compiler intrinsics ARM assembler instruction intrinsics Generic intrinsics Compiler intrinsics for controlling IRQ and FIQ in Compiler intrinsics for inserting optimization bar Compiler intrinsics for inserting native instructi Compiler intrinsics for Digital Signal Processing Compiler support for European Telecommunications S Overflow and carry status flags for C and C++ code Texas Instruments (TI) C55x intrinsics for optimiz Compiler support for accessing registers using nam Pragmas recognized by the compiler Compiler and processor support for bit-banding Compiler type attribute, __attribute__((bitband)) --bitband compiler command-line option How the compiler handles bit-band objects placed o Compiler support for thread-local storage Compiler support for literal pools Compiler eight-byte alignment features Precompiled Header (PCH) files Automatic Precompiled Header (PCH) file processing Precompiled Header (PCH) file processing and the h Precompiled Header (PCH) file creation requirement Compilation with multiple Precompiled Header (PCH) Obsolete Precompiled Header (PCH) files Manually specifying the filename and location of a Selectively applying Precompiled Header (PCH) file Suppressing Precompiled Header (PCH) file processi Message output during Precompiled Header (PCH) pro Performance issues with Precompiled Header (PCH) f Default compiler options that are affected by opti Compiler Coding Practices 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

Performance issues with Precompiled Header (PCH) files

3.31 Performance issues with Precompiled Header (PCH) files

Typically, the overhead of creating and reading a PCH file is small, even for reasonably large header files. If the PCH file is used, there is typically a significant decrease in compilation time. However, PCH files can range in size from about 250KB to several megabytes or more, so you might not want to create many PCH files.


Support for Precompiled Header (PCH) files is deprecated from ARM Compiler 5.05 onwards on all platforms. Note that ARM Compiler on Windows 8 never supported PCH files.
PCH processing might not always be appropriate, for example, where you have an arbitrary set of files with non-uniform initial sequences of preprocessing directives.
The benefits of PCH processing occur when several source files can share the same PCH file. The more sharing, the less disk space is consumed. Sharing minimizes the disadvantage of large PCH files, without giving up the advantage of a significant decrease in compilation times.
Therefore, to take full advantage of header file precompilation, you might have to re-order the #include sections of your source files, or group #include directives within a commonly used header file.
Different environments and different projects might have differing requirements. Be aware, however, that making the best use of PCH support might require some experimentation and probably some minor changes to source code.
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