SPEC HPC2021 Flag Description for the Intel(R) oneAPI C++ and Fortran Compiler 2021 for IA32 and Intel 64 applications

Allow aggressive, lossy floating-point optimizations

Sets certain aggressive options to improve the speed of your application. This option improves the speed of your application. On Linux* systems, this option is provided for compatibility with gcc.

Specifies preferred 512b vector width for auto-vectorization. Defaults to 'none' which allows target specific decisions.

The align toggle changes how data elements are aligned. Variables and arrays are analyzed and memory layout can be altered. Specifying array64byte will look for opportunities to transform and reailgn arrays to 64byte boundaries.

Dummy

Option standard-realloc-lhs (the default), tells the compiler that when the left-hand side of an assignment is an allocatable object, it should be reallocated to the shape of the right-hand side of the assignment before the assignment occurs. This is the current Fortran Standard definition. This feature may cause extra overhead at run time. This option has the same effect as option assume realloc_lhs.

If you specify nostandard-realloc-lhs, the compiler uses the old Fortran 2003 rules when interpreting assignment statements. The left-hand side is assumed to be allocated with the correct shape to hold the right-hand side. If it is not, incorrect behavior will occur. This option has the same effect as option assume norealloc_lhs.

The align toggle changes how data elements are aligned. Variables and arrays are analyzed and memory layout can be altered. Specifying array32byte will look for opportunities to transform and reailgn arrays to 32byte boundaries.

Allow optimizations for floating point arithmetic that assume arguments and results are not NaNs or Infinities

Linker options to link a 64-bit application to use large pages for the .bss, .data and .text sections.

Linker options to link a 32-bit application to use large pages for the .bss, .data and .text sections.

Enables optimizations for speed and disables some optimizations that increase code size and affect speed.
To limit code size, this option:

• Enables global optimization; this includes data-flow analysis, code motion, strength reduction and test replacement, split-lifetime analysis, and instruction scheduling.
• Disables intrinsic recognition and intrinsics inlining.

The O1 option may improve performance for applications with very large code size, many branches, and execution time not dominated by code within loops.

Enables optimizations for speed. This is the generally recommended optimization level. This option also enables:
- Inlining of intrinsics
- Intra-file interprocedural optimizations, which include:
- inlining
- constant propagation
- forward substitution
- routine attribute propagation
- variable address-taken analysis
- dead static function elimination
- removal of unreferenced variables
- The following capabilities for performance gain:
- constant propagation
- copy propagation
- dead-code elimination
- global register allocation
- global instruction scheduling and control speculation
- loop unrolling
- optimized code selection
- partial redundancy elimination
- strength reduction/induction variable simplification
- variable renaming
- exception handling optimizations
- tail recursions
- peephole optimizations
- structure assignment lowering and optimizations
- dead store elimination

Enables O2 optimizations plus more aggressive optimizations, such as prefetching, scalar replacement, and loop and memory access transformations. Enables optimizations for maximum speed, such as:

• Loop unrolling, including instruction scheduling
• Code replication to eliminate branches
• Padding the size of certain power-of-two arrays to allow more efficient cache use.

On IA-32 and Intel EM64T processors, when O3 is used with options -ax or -x (Linux) or with options /Qax or /Qx (Windows), the compiler performs more aggressive data dependency analysis than for O2, which may result in longer compilation times. The O3 optimizations may not cause higher performance unless loop and memory access transformations take place. The optimizations may slow down code in some cases compared to O2 optimizations. The O3 option is recommended for applications that have loops that heavily use floating-point calculations and process large data sets.

Tells the compiler the maximum number of times to unroll loops. For example -funroll-loops0 would disable unrolling of loops.

-fno-builtin disables inline expansion for all intrinsic functions.

This option trades off floating-point precision for speed by removing the restriction to conform to the IEEE standard.

EBP is used as a general-purpose register in optimizations.

Places each function in its own COMDAT section.

Flushes denormal results to zero.

Controls the level of memory layout transformations performed by the compiler. This option can improve cache reuse and cache locality.

• 0: Disables memory layout transformations. This is the same as specifying -qno-opt-mem-layout-trans
• 1: Enables basic memory layout transformations like structure splitting, structure peeling, field inlining, field reordering, array field transpose, increase field alignment etc.
• 2: Enables more memory layout transformations like advanced structure splitting. This is the same as specifying -qopt-mem-layout-trans
• 3: Enables more memory layout transformations like copy-in/copy-out of structures for a region of code. You should only use this setting if your system has more than 4GB of physical memory per core.
• 4: Compiler is more aggressive in using memory layout transformations. You should only use this setting if your system has more than 4GB of physical memory per core.

This option sets the maximum number of times a loop can be unrolled, to n. For example, -unroll1 will unroll loops just once. To disable loop unrolling, use -unroll0. .

The -par-schedule option lets you specify a scheduling algorithm or a tuning method for loop iterations.
It specifies how iterations are to be divided among the threads of the team. This option affects performance
tuning and can provide better performance during auto-parallelization.

This option enables additional interprocedural optimizations for single file compilation. These optimizations are a subset of full intra-file interprocedural optimizations. One of these optimizations enables the compiler to perform inline function expansion for calls to functions defined within the current source file.

Multi-file ip optimizations that includes:
- inline function expansion
- interprocedural constant propogation
- dead code elimination
- propagation of function characteristics
- passing arguments in registers
- loop-invariant code motion

This option instructs the compiler to analyze and transform the program so that 64-bit pointers are shrunk to 32-bit pointers, and 64-bit longs (on Linux) are shrunk into 32-bit longs wherever it is legal and safe to do so. In order for this option to be effective the compiler must be able to optimize using the -ipo/-Qipo option and must be able to analyze all library/external calls the program makes.

This option requires that the size of the program executable never exceeds 2^32 bytes and all data values can be represented within 32 bits. If the program can run correctly in a 32-bit system, these requirements are implicitly satisfied. If the program violates these size restrictions, unpredictable behavior might occur.

This option instructs the compiler to analyze and transform the program so that 64-bit pointers are shrunk to 32-bit pointers wherever it is legal and safe to do so. In order for this option to be effective, the compiler must optimize using the -ipo option and must be able to analyze all library/external calls the program makes. This option has no effect unless you specify setting SSE3 or higher for option -x.

This option requires that the application cannot exceed a 32-bit address space, otherwise unpredictable results can occur.

-scalar-rep enables scalar replacement performed during loop transformation. To use this option, you must also specify O3. -scalar-rep- disables this optimization.

This options tells the compiler to assume no aliasing in the program.

The -fast option enhances execution speed across the entire program by including the following options that can improve run-time performance:

-O3   (maximum speed and high-level optimizations)

-ipo (enables interprocedural optimizations across files)

-xT  (generate code specialized for Intel(R) Core(TM)2 Duo processors, Intel(R) Core(TM)2 Quad processors and Intel(R) Xeon(R) processors with SSSE3)

-static  Statically link in libraries at link time

-no-prec-div (disable -prec-div) where -prec-div improves precision of FP divides (some speed impact)

To override one of the options set by /fast, specify that option after the -fast option on the command line. The exception is the xT or QxT option which can't be overridden. The options set by /fast may change from release to release.

Compiler option to statically link in libraries at link time

Code is optimized for Intel(R) Core(TM)2 Duo processors, Intel(R) Core(TM)2 Quad processors and Intel(R) Xeon(R) processors with SSSE3. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.

Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.

Code is optimized for Intel(R) Atom processors with support for MOVBE instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.

Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.

Code is optimized for Intel(R) Atom processors with support for MOVBE instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.

Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.

Code is optimized for Intel(R) processors with support for AVX2 instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.

Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.

Tells the compiler to remove the assumption that source code follows c99 signed overflow rules.

This option tells the compiler to generate instructions for the highest instruction set available on the compilation host processor. The instructions generated by Host differ depending on the compilation host processor.

Code is optimized for Intel(R) Atom(TM) processors that support SSE4.2 and MOVBE instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.

Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.

Code is optimized for Intel(R) Atom(TM) processors that support Intel(R) SSE3 and MOVBE instructions. and MOVBE instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.

Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.

Code is optimized for Intel(R) processors with support for CORE-AVX512 instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.

Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.

Code is optimized for Intel(R) processors with support for COMMON-AVX512 instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.

Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.

Code is optimized for Intel(R) processors with support for MIC-AVX512 instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.

Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.

Code is optimized for Intel(R) processors with support for AVX instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.

Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.

Code is optimized for Intel(R) processors with support for SSE 4.2 instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.

Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.

Code is optimized for Intel(R) processors with support for SSE 4.1 instructions. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.

Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.

This option tells the compiler to generate code specialized for processors that support for SSE3 instructions. Code generated with these options should execute on any compatible, non-Intel processor with support for the SSE3 instruction set.

Code is optimized for Intel Pentium M and compatible Intel processors. The resulting code may contain unconditional use of features that are not supported on other processors. This option also enables new optimizations in addition to Intel processor-specific optimizations including advanced data layout and code restructuring optimizations to improve memory accesses for Intel processors.

Do not use this option if you are executing a program on a processor that is not an Intel processor. If you use this option on a non-compatible processor to compile the main program (in Fortran) or the function main() in C/C++, the program will display a fatal run-time error if they are executed on unsupported processors.

Code is optimized for Intel Pentium 4 and compatible Intel processors; this is the default for Intel?EM64T systems. The resulting code may contain unconditional use of features that are not supported on other processors.

Tells the auto-parallelizer to generate multithreaded code for loops that can be safely executed in parallel. To use this option, you must also specify option O2 or O3. The default numbers of threads spawned is equal to the number of processors detected in the system where the binary is compiled. Can be changed by setting the environment variable OMP_NUM_THREADS

The use of -Qparallel to generate auto-parallelized code requires support libraries that are dynamically linked by default. Specifying libguide40.lib on the link line, statically links in libguide40.lib to allow auto-parallelized binaries to work on systems which do not have the dynamic version of this library installed.

Optimizes for Intel Pentium 4 and compatible processors with Streaming SIMD Extensions 2 (SSE2).

-no-prec-div enables optimizations that give slightly less precise results than full IEEE division.

When you specify -no-prec-div along with some optimizations, such as -xN and -xB (Linux) or /QxN and /QxB (Windows), the compiler may change floating-point division computations into multiplication by the reciprocal of the denominator. For example, A/B is computed as A * (1/B) to improve the speed of the computation.

However, sometimes the value produced by this transformation is not as accurate as full IEEE division. When it is important to have fully precise IEEE division, do not use -no-prec-div. This will enable the default -prec-div and the result will be more accurate, with some loss of performance.

Instrument program for profiling for the first phase of two-phase profile guided otimization. This instrumentation gathers information about a program's execution paths and data values but does not gather information from hardware performance counters. The profile instrumentation also gathers data for optimizations which are unique to profile-feedback optimization.

-profgen:threadsafe option collects profile guided optimization data with guards for threaded applications.

Allows for tuning of application performance by setting the number of threads to use in a parallel region. It has a similar effect as environment variable OMP_NUM_THREADS. This option overrides the environment variable when both are specified. Ex: -par-num-threads=1 specifies one thread to use.

Instructs the compiler to produce a profile-optimized executable and merges available dynamic information (.dyn) files into a pgopti.dpi file. If you perform multiple executions of the instrumented program, -prof-use merges the dynamic information files again and overwrites the previous pgopti.dpi file.
Without any other options, the current directory is searched for .dyn files

Enable SmartHeap and/or other library usage by forcing the linker to ignore multiple definitions if present

MicroQuill SmartHeap Library (64-bit) available from http://www.microquill.com/

MicroQuill SmartHeap Library (32-bit) available from http://www.microquill.com/

Specify build time link path for jemalloc 64bit built to support the CPU2017/2006 build. See jemalloc.net for more information.

Specify build time link path for jemalloc 32bit built to support the CPU2017/CPU2006 build. See jemalloc.net for more information.

Linker toggle to specify jemalloc linker library. See jemalloc.net for more information.

Specify build time link path for qkmalloc library to support the CPU2017/CPU2006 build. See https://software.intel.com/en-us/articles/intel-c-compiler-190-for-linux-release-notes-for-intel-parallel-studio-xe-2019#custalloc for more information.

Linker toggle to specify qkmalloc linker library. See https://software.intel.com/en-us/articles/intel-c-compiler-190-for-linux-release-notes-for-intel-parallel-studio-xe-2019#custalloc for more information.

Enable the use of the 64-bit compiler by passing the directory names for the library and include files

set the stack reserve amount specified to the linker

Enable/disable(DEFAULT) use of ANSI aliasing rules in optimizations; user asserts that the program adheres to these rules.

Enable/disable(DEFAULT) the compiler to generate prefetch instructions to prefetch data.

Directs the compiler to inline calloc() calls as malloc()/memset()

The compiler adds setup code in the C/C++/Fortran main function to enable optimal malloc algorithms:

• n=0: Default, no changes to the malloc options. No call to mallopt() is made.
• n=1: M_MMAP_MAX=2 and M_TRIM_THRESHOLD=0x10000000. Call mallopt with the two settings.
• n=2: M_MMAP_MAX=2 and M_TRIM_THRESHOLD=0x40000000. Call mallopt with these two settings.
• n=3: M_MMAP_MAX=0 and M_TRIM_THRESHOLD=-1. Call mallopt with these two settings. This will cause use of sbrk() calls instead of mmap() calls to get memory from the system.

The two parameters, M_MMAP_MAX and M_TRIM_THRESHOLD, are described below

Function: int mallopt (int param, int value) When calling mallopt, the param argument specifies the parameter to be set, and value the new value to be set. Possible choices for param, as defined in malloc.h, are:

• M_TRIM_THRESHOLD This is the minimum size (in bytes) of the top-most, releasable chunk that will cause sbrk to be called with a negative argument in order to return memory to the system.
• M_TOP_PAD This parameter determines the amount of extra memory to obtain from the system when a call to sbrk is required. It also specifies the number of bytes to retain when shrinking the heap by calling sbrk with a negative argument. This provides the necessary hysteresis in heap size such that excessive amounts of system calls can be avoided.
• M_MMAP_THRESHOLD All chunks larger than this value are allocated outside the normal heap, using the mmap system call. This way it is guaranteed that the memory for these chunks can be returned to the system on free. Note that requests smaller than this threshold might still be allocated via mmap.
• M_MMAP_MAX The maximum number of chunks to allocate with mmap. Setting this to zero disables all use of mmap.

Enables cache/bandwidth optimization for stores under conditionals (within vector loops) This option tells the compiler to perform a conditional check in a vectorized loop. This checking avoids unnecessary stores and may improve performance by conserving bandwidth.

Enable compiler to generate runtime control code for effective automatic parallelization. This option generates code to perform run-time checks for loops that have symbolic loop bounds. If the granularity of a loop is greater than the parallelization threshold, the loop will be executed in parallel. If you do not specify this option, the compiler may not parallelize loops with symbolic loop bounds if the compile-time granularity estimation of a loop can not ensure it is beneficial to parallelize the loop.

Select the method that the register allocator uses to partition each routine into regions

• routine - one region per routine
• block - one region per block
• trace - one region per trace
• loop - one region per loop
• default - compiler selects best option

Multi-versioning is used for generating different versions of the loop based on run time dependence testing, alignment and checking for short/long trip counts. If this option is turned on, it will trigger more versioning at the expense of creating more overhead to check for pointer aliasing and scalar replacement.

Make all local variables AUTOMATIC. Same as -automatic

Enables more aggressive unrolling heuristics

Specifies whether streaming stores are generated:

always - enables generation of streaming stores under the assumption that the application is memory bound

auto - compiler decides when streaming stores are used (DEFAULT)

never - disables generation of streaming stores

Disables inline expansion of all intrinsic functions.

Disables conformance to the ANSI C and IEEE 754 standards for floating-point arithmetic.

Allows use of EBP as a general-purpose register in optimizations.

This option enables most speed optimizations, but disables some that increase code size for a small speed benefit.

This option enables global optimizations.

Specifies the level of inline function expansion.

0 - Disables inlining of user-defined functions. Note that statement functions are always inlined.

1 - Enables inlining when an inline keyword or an inline attribute is specified. Also enables inlining according to the C++ language.

2 - Enables inlining of any function at the compiler's discretion.

Specifies the level of inline function expansion.

Ob0 - Disables inlining of user-defined functions. Note that statement functions are always inlined.

Ob1 - Enables inlining when an inline keyword or an inline attribute is specified. Also enables inlining according to the C++ language.

Ob2 - Enables inlining of any function at the compiler's discretion.

This option tells the compiler to separate functions into COMDATs for the linker.

This option enables read only string-pooling optimization.

This option enables read/write string-pooling optimization.

This option disables stack-checking for routines with 4096 bytes of local variables and compiler temporaries.

USE std C++ libs on Linker

Specifies that the format will be big endian for INTEGER*1, INTEGER*2, INTEGER*4, or INTEGER*8, and big endian IEEE floating-point for REAL*4, REAL*8, REAL*16, COMPLEX*8, COMPLEX*16, or COMPLEX*32.

Specifies that the units for the OPEN statement RECL specifier (record length) value are in bytes for unformatted data files, not longwords (four-byte units). For formatted files, the RECL value is always in bytes.

Change default char type to unsigned.

This macro determines which file system interface will be used. Common file i/o calls like stat() and readdir() return off_t data that may or may not fit within a 32bit data structure if this flag is not used. With _FILE_OFFSET_BITS=64, types like off_t have a size of 64 bits. The truncation that happens without _FILE_OFFSET_BITS=64 has been observed to yield intermittent failures.

Ex: RHEL7 distributions format partitions using xfs. Runtime errors are observed on such systems because sometimes returned values will not fit into 32bit data types that are a mismatch for xfs.

See the gnuc feature test macros article for more information.

For mixed-language benchmarks, tell the compiler to convert routine names to lowercase for compatibility

For mixed-language benchmarks, tell the compiler to assume that routine names end with an underscore

Tell the compiler to treat source files as C++ regardless of the file extension

This option specifies that the main program is not written in Fortran. It is a link-time option that prevents the compiler from linking for_main.o into applications.

For example, if the main program is written in C and calls a Fortran subprogram, specify -nofor-main when compiling the program with the ifort command. If you omit this option, the main program must be a Fortran program.

Invoke the Intel oneAPI C compiler as backend for Intel MPI compiler wrapper.

Invoke the Intel oneAPI Fortran compiler as backend for Intel MPI compiler wrapper.

Invoke the Intel oneAPI C++ compiler as backend for Intel MPI compiler wrapper.

Invoke the Intel C compiler 17.0 for IA32 applications when the environment is set for Intel 64 compilation. Defaults to -std=gnu89. Conforms to ISO C90 plus GNU extensions.

Invoke the Intel C compiler 17.0 for IA32 applications when the environment is set for Intel 64 compilation. Conforms to ISO C11.

Invoke the Intel C++ compiler 17.0 for IA32 applications when the environment is set for Intel 64 compilation.

Invoke the Intel Fortran compiler 17.0 for IA32 applications when the environment is set for Intel 64 compilation.

Invoke the Intel C compiler 17.0 for Intel 64 applications. Conforms to ISO C11.

Invoke the Intel C compiler 17.0 for Intel 64 applications.

Invoke the Intel C++ compiler 17.0 for Intel 64 applications

Invoke the Intel Fortran compiler 17.0 for Intel 64 applications.