Compiler Porng Guide for ICC NextGen Contents Compiler Por+ng Guide for ICC NextGen ......................................................................................................1 Nomenclature ...........................................................................................................................................2 Guiding Principles for ICC NextGen ..........................................................................................................2 Major Changes in Compiler Defaults ........................................................................................................2 Important New Op+ons ............................................................................................................................3 Op+ons to aid Intel Analyzers and other profiling tools. Use all of these to assist Analyzers. .............3 ICC NextGen OpenMP Op+ons .............................................................................................................3 Compiler Versioning .................................................................................................................................3 Data Parallel C++ Version String ............................................................................................................3 ICC NextGen Version String ..................................................................................................................4 Important Compiler Op+ons Mapping .....................................................................................................4 Pragma Support ........................................................................................................................................5 Predefined Macro Support .......................................................................................................................6 Built-In Func+ons ......................................................................................................................................6 Support for Pre-Compiled Header Files ....................................................................................................7 Changes in Diagnos+cs Op+ons and Diagnos+c Message Numbering .....................................................7 Linking, IPO and PGO changes ..................................................................................................................9 Language Features ....................................................................................................................................9 Intrinsic Usage Model Change ..................................................................................................................9 Example of LLVM Intrinsics Handling Differences ...............................................................................10 Intrinsics Via Func+on Defini+on __a\ribute__((target())) In the above example we used a compiler op+on to target a specific instruc+on set ( -mavx512f ). This can be used if just one instruc+on set exists in the source file. Oaen, source files will contain mul+ple instruc+on sets represented in intrinsic data declara+ons and intrinsic instruc+ons. This is done to call specific func+ons or code sec+ons based on the run+me processor discovery. Typically, these func+ons or code sec+ons are protected by #IFDEFs with specific target architectures and the user code does processor dispatch to these sec+ons or func+ons. ...........................................................................................................13 Intel Proprietary Processsor Targe+ng Pragmas and Func+ons Support ............................................14 Legacy Intrinsics Promo+on with Op+on intrinsic-promote: ..............................................................14 Floa+ng Point Reproducibility Controls ..................................................................................................15 Brutus or Bisec+onal Op+miza+on Support ...........................................................................................15 Appendix I: ICC Classic Compiler Op+ons Status ...................................................................................15 March 6, 2020 1 Nomenclature • For simplicity and clarity, we will informally refer to the Intel® C++ Compiler Next Genera+on framework as “ICC NextGen” and the classic or “tradi+onal ICC” Intel® C++ Compiler as “ICC Classic” throughout this document. Guiding Principles for ICC NextGen • ICC Classic and ICC NextGen use the same name for many of the compiler drivers ( icc, icpc, icl ). In addi+on to providing a core C++ compiler, ICC NextGen is the base compiler for the Intel® Data Parallel C++ compiler and its new driver, ‘dpcpp’. ICC NextGen is our newer “Next Genera+on” compiler. Keep this in mind: ICC NextGen is not a drop-in replacement for ICC Classic. Although considerable effort is being made to make the transi+on from ICC Classic to ICC NextGen as smooth and as effortless as possible, customers can expect that some effort may be required to port and tune exis+ng applica+ons from ICC Classic to ICC NextGen. o For Data Parallel C++ applica0ons: Our underlying compiler is ICC NextGen. The driver is named ‘dpcpp’. o For standard C++ applica0ons: ICC Classic (icc/icpc/icl drivers) will remain Intel’s recommended produc+on compiler AND THE DEFAULT compiler un+l ICC NextGen has performance and features superior to ICC Classic. In the future, when ICC NextGen func+onality and performance equivalence or be\er against ICC Classic is achieved, Intel may change the default for ICC to be ICC NextGen, instead of, ICC Classic. We have no set +meline for this transi+on as it is condi+onal on reaching equivalence or be\er than current ICC Classic technology. Going forward BOTH ICC Classic and ICC NextGen compilers will be provided in Intel Compiler packages. Compiler op+ons will be used to select one or the other compilers. Major Changes in Compiler Defaults 1. C++ Users: The compiler driver name is s+ll icc/icpc (Linux*) or icl (Windows*), but requires the – qnextgen (Linux*) or /Qnextgen (Windows*) op+on to invoke the ICC NextGen compiler. Without the [-q|/Q]nextgen op+on the ICC Classic compiler will be invoked. 2. DPC++ Users: Use the ‘dpcpp’ driver which invokes ICC NextGen with DPC++ extensions. 3. Default floa+ng point model is -fp:precise –no-fma. 4. Macro __INTEL_LLVM_COMPILER is defined for ICC NextGen, instead of, the __INTEL_COMPILER macro used in ICC Classic. To see all defined values for the compiler, use -E -dM opons which will either create a .ii file with this informa+on or write the values to stderr. For example: for Data Parallel C++ dpcpp -E -dM ./hello.cpp more hello.ii for ICC NextGen the output will be sent to stderr icc -qnextgen -E -dM ./hello.cpp 5. No diagnos+cs numbers are listed for remarks/warnings/notes. Every diagnos+c is emi\ed with the corresponding compiler op+on to disable the same. March 6, 2020 2 6. Compiler intrinsics will not be automa+cally recognized without processor targe+ng op+ons, unlike the behavior in ICC Classic. If you use intrinsics, please read more on this intrinsic behavior change later in this document. Important New Op>ons Op>ons to aid Intel Analyzers and other profiling tools. Use all of these to assist Analyzers. • -gline-tables-only This opon is helpful for profiling tools. This opon generates line table debug informa+on only. This allows symbolic back traces with inlining informa+on, but does not include any informa+on about variables, their loca+ons, or types. • -fdebug-info-for-profiling adds extra debug info for more accurate profile ICC NextGen OpenMP Op>ons • -fiopenmp Compile and recognize OpenMP parallel and SIMD pragmas/direc+ves and clauses and use the Intel OpenMP run+me libraries. • -fopenmp-targets=spir64 is needed when OpenMP 4.5/5.0 TARGET pragmas/direc+ves are used. • OpenMP 4.5/5.0 TARGET direc+ves are only recognized by the ICC NextGen compiler that is included in the Intel® oneAPI HPC Toolkit. Use the two compiler op+ons above together: o icc -qnextgen -fiopenmp -fopenmp-targets=spir64 o icpc -qnextgen -fiopenmp -fopenmp-targets=spir64 Compiler Versioning Data Parallel C++ Version String The Data Parallel C++ compiler version string is new. An example: dpcpp --version DPC++ Compiler 2021.1-betaXX (2019.8.x.1010) The format is: VVVV.MINOR -[beta]XX (build string) where • VVVVV is the product VERSION in the format of year. • MINOR is a single-digit minor version number, star+ng at “1” for ini+al release and incremented as needed for minor releases. • [beta] may or may not appear. If the compiler is a Beta compiler you will see the string “beta”, else this will not be present for produc+on compilers. • XX is the beta release • The (build string) can be decoded: (YYYY.<Clang Version>.PULL.UPDATE .<build date> ) March 6, 2020 3 where • YYYY is the year • <Clang Version> is the version of Clang incorporated into ICC NextGen front-end. • PULL is 1- or 2-digit and indicates the month we pulled Clang and merged into our build. • UPDATE is a single-digit minor version number. Typically it is “x” for beta, unless two or more compilers are released in a given month. • <build date> is of the form yyyymmdd. For example, (2019.8.x.1108) This compiler was built in 2019. The Clang front end is version 8. The PULL in this beta is “x”, but in a later compiler this will indicate the pull date or minor version. The exact date of the build is 2019 1108 in YYYY MMDD Another example: If, hypothe+cally, Clang 9 releases and we