ARM® Compiler toolchain Version 4.1 Using the Compiler Copyright © 2010-2011 ARM. All rights reserved. ARM DUI 0472C (ID080411) ARM Compiler toolchain Using the Compiler Copyright © 2010-2011 ARM. All rights reserved. Release Information The following changes have been made to this book. Change History Date Issue Confidentiality Change 28 May 2010 A Non-Confidential ARM Compiler toolchain v4.1 Release 30 September 2010 B Non-Confidential Update 1 for ARM Compiler toolchain v4.1 28 January 2011 C Non-Confidential Update 2 for ARM Compiler toolchain v4.1 Patch 3 30 April 2011 C Non-Confidential Update 3 for ARM Compiler toolchain v4.1 Patch 4 30 September 2011 C Non-Confidential Update 4 for ARM Compiler toolchain v4.1 Patch 5 Proprietary Notice Words and logos marked with ™ or ® are registered trademarks or trademarks of ARM in the EU and other countries, except as otherwise stated below in this proprietary notice. 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All rights reserved. ii ID080411 Non-Confidential Contents ARM Compiler toolchain Using the Compiler Chapter 1 Conventions and Feedback Chapter 2 Overview of the compiler 2.1 The compiler ................................................................................................................. 2-2 2.2 Source language modes of the compiler ...................................................................... 2-3 2.3 The C and C++ libraries ................................................................................................ 2-4 Chapter 3 Getting started with the Compiler 3.1 Compiler command-line syntax .................................................................................... 3-3 3.2 Compiler command-line options listed by group ........................................................... 3-4 3.3 Default compiler behavior ............................................................................................. 3-9 3.4 Order of compiler command-line options .................................................................... 3-11 3.5 Using stdin to input source code to the compiler ........................................................ 3-12 3.6 Directing output to stdout ............................................................................................ 3-14 3.7 Filename suffixes recognized by the compiler ............................................................ 3-15 3.8 Compiler output files ................................................................................................... 3-17 3.9 Factors influencing how the compiler searches for header files ................................. 3-18 3.10 Compiler command-line options and search paths ..................................................... 3-19 3.11 Compiler search rules and the current place .............................................................. 3-20 3.12 The ARMCC41INC environment variable ................................................................... 3-21 3.13 Code compatibility between separately compiled and assembled modules ............... 3-22 3.14 Linker feedback during compilation ............................................................................ 3-23 3.15 Unused function code ................................................................................................. 3-24 3.16 Minimizing code size by eliminating unused functions during compilation ................. 3-25 3.17 Minimizing code size by reducing compilation required for interworking .................... 3-26 3.18 Compilation build time ................................................................................................ 3-27 3.19 How to minimize compilation build time ...................................................................... 3-29 3.20 Minimizing compilation build time with a single armcc invocation .............................. 3-31 3.21 Effect of --multifile on compilation build time .............................................................. 3-32 ARM DUI 0472C Copyright © 2010-2011 ARM. All rights reserved. iii ID080411 Non-Confidential Contents 3.22 Minimizing compilation build time with parallel make ................................................. 3-33 3.23 Compilation build time and operating system choice .................................................. 3-34 Chapter 4 Using the NEON Vectorizing Compiler 4.1 NEON technology ......................................................................................................... 4-3 4.2 The NEON unit ............................................................................................................. 4-4 4.3 Methods of writing code for NEON ............................................................................... 4-6 4.4 Generating NEON instructions from C or C++ code ..................................................... 4-7 4.5 NEON C extensions ...................................................................................................... 4-8 4.6 Automatic vectorization ................................................................................................. 4-9 4.7 Data references within a vectorizable loop ................................................................. 4-10 4.8 Stride patterns and data accesses ............................................................................. 4-11 4.9 Factors affecting NEON vectorization performance ................................................... 4-12 4.10 NEON vectorization performance goals ..................................................................... 4-13 4.11 Recommended loop structure for vectorization .......................................................... 4-14 4.12 Data dependency conflicts when vectorizing code ..................................................... 4-15 4.13 Carry-around scalar variables and vectorization ........................................................ 4-17 4.14 Reduction of a vector to a scalar ................................................................................ 4-18 4.15 Vectorization on loops containing pointers ................................................................. 4-19 4.16 Nonvectorization on loops containing pointers and indirect addressing ..................... 4-21 4.17 Nonvectorization on conditional loop exits .................................................................. 4-22 4.18 Vectorizable loop iteration counts ............................................................................... 4-23 4.19 Indicating loop iteration counts to the compiler with __promise(expr) ........................ 4-25 4.20 Vectorizable and nonvectorizable use of structures ................................................... 4-27 4.21 Grouping use of structures for vectorization ............................................................... 4-28 4.22 struct member lengths and vectorization .................................................................... 4-29 4.23 Nonvectorization of function calls to non-inline functions from within loops ............... 4-30 4.24 Conditional statements and efficient vectorization ...................................................... 4-31 4.25 Vectorization diagnostics to tune code for improved performance ............................. 4-32 4.26 Vectorizable code example ......................................................................................... 4-34 4.27 DSP vectorizable code example ................................................................................. 4-37 4.28 What can limit or prevent automatic vectorization ...................................................... 4-40 Chapter 5 Compiler Features 5.1 About Profiler-guided optimization ................................................................................ 5-3 5.2 Profiler-guided optimizations with link-time code generation ........................................ 5-4 5.3 Compiler intrinsics .......................................................................................................