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Table Of Contents Optimizing Applications: Overview .....................................................................9 How to Use This Document .............................................................................11 Notation Conventions...................................................................................11 Programming for High Performance.................................................................13 Programming for High Performance: Overview .............................................13 Programming Guidelines..............................................................................13 Setting Data Type and Alignment..............................................................13 Using Arrays Efficiently.............................................................................20 Improving I/O Performance.......................................................................25 Improving Run-time Efficiency ..................................................................30 Using Intrinsics for Itanium®-based Systems ............................................33 Coding Guidelines for Intel® Architectures................................................34 Analyzing and Timing Your Application.........................................................37 Using Intel Performance Analysis Tools ....................................................37 Timing Your Application............................................................................38 Compiler Optimizations ...................................................................................41 Compiler Optimizations Overview.................................................................41 Optimizing the Compilation Process .............................................................41 Optimizing the Compilation Process Overview ..........................................41 Efficient Compilation.................................................................................41 Little-endian-to-Big-endian Conversion .....................................................45 iii Table Of Contents Default Compiler Optimizations.................................................................48 Using Compilation Options .......................................................................51 Optimizing Different Application Types .........................................................61 Optimizing Different Application Types Overview.......................................61 Setting Optimizations with -On Options.....................................................62 Restricting Optimizations..........................................................................65 Floating-point Arithmetic Optimizations.........................................................66 Options Used for Both IA-32 and Itanium® Architectures...........................66 Floating-point Arithmetic Precision for IA-32 Systems................................69 Floating-point Arithmetic Precision for Itanium®-based Systems................70 Improving/Restricting FP Arithmetic Precision ...........................................71 Optimizing for Specific Processors ...............................................................73 Optimizing for Specific Processors Overview.............................................73 Targeting a Processor, -tpp{n} ..................................................................73 Processor-specific Optimization (IA-32 only) .............................................75 Automatic Processor-specific Optimization (IA-32 only).............................76 Processor-specific Run-time Checks, IA-32 Systems.................................77 Interprocedural Optimizations (IPO)..............................................................79 Overview of Interprocedural Optimizations ................................................79 IPO Compilation Model.............................................................................80 Command Line for Creating an IPO Executable ........................................81 Generating Multiple IPO Object Files ........................................................82 Capturing Intermediate Outputs of IPO .....................................................83 iv Table Of Contents Creating an IPO Executable Using xild......................................................83 Code Layout and Multi-Object IPO............................................................85 Compilation with Real Object Files............................................................86 Creating a Library from IPO Objects..........................................................87 Using -ip with -Qoption Specifiers .............................................................88 Inline Expansion of Functions ...................................................................90 Profile-guided Optimizations.........................................................................93 Profile-guided Optimizations Overview......................................................93 Profile-guided Optimizations Methodology and Usage Model.....................94 Basic PGO Options ..................................................................................97 Advanced PGO Options ...........................................................................98 PGO Environment Variables.....................................................................99 Example of Profile-Guided Optimization ..................................................100 Merging the .dyn Files ............................................................................101 Using profmerge to Relocate the Source Files.........................................102 Code-coverage Tool ...............................................................................103 Test Prioritization Tool ............................................................................111 PGO API: Profile Information Generation Support ...................................118 High-level Language Optimizations (HLO)..................................................121 HLO Overview........................................................................................121 Loop Transformations.............................................................................122 Scalar Replacement (IA-32 Only)............................................................123 Loop Unrolling with -unroll[n]...................................................................123 v Table Of Contents Memory Dependency with IVDEP Directive.............................................124 Prefetching.............................................................................................125 Parallel Programming with Intel® Fortran.......................................................127 Parallelism: an Overview............................................................................127 Parallel Program Development ...............................................................128 Auto-vectorization (IA-32 Only)...................................................................130