Intel® Fortran Compiler Classic and Intel® Fortran Compiler Developer Guide and Reference

ID 767251
Date 3/22/2024
Public

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Document Table of Contents

fimf-arch-consistency, Qimf-arch-consistency

Ensures that the math library functions produce consistent results across different microarchitectural implementations of the same architecture.

Syntax

Linux:

-fimf-arch-consistency=value[:funclist]

Windows:

/Qimf-arch-consistency:value[:funclist]

Optional argument funclist is not supported for ifx.

Arguments

value

Is one of the logical values "true" or "false".

funclist

Is an optional list of one or more math library functions to which the attribute should be applied. Do not specify the standard Fortran name of the math function; you must specify the actual math library name. If you specify more than one function, they must be separated with commas.

Precision-specific variants like sin and sinf are considered different functions, so you would need to use -fimf-arch-consistency=true:sin,sinf (or /Qimf-arch-consistency:true:sin,sinf) to specify consistent results for both the single-precision and double-precision sine functions.

You also can specify the symbol /f to denote single-precision divides, symbol / to denote double-precision divides, symbol /l to denote extended-precision divides, and symbol /q to denote quad-precision divides. For example you can specify -fimf-arch-consistency=true:/ or /Qimf-arch-consistency:true:/.

Default

false

Implementations of some math library functions may produce slightly different results on implementations of the same architecture.

Description

This option ensures that the math library functions produce consistent results across different microarchitectural implementations of the same architecture (for example, across different microarchitectural implementations of Intel® 64 architecture). Consistency is only guaranteed for a single binary. Consistency is not guaranteed across different architectures.

If you need to define the accuracy for a math function of a certain precision, specify the function name of the precision that you need. For example:

Linux

If you want double precision, you can specify :sin; if you want single precision, you can specify :sinf, as in -fimf-arch-consistency=true:sin or -fimf-arch-consistency=false:sqrtf.

Windows

If you want double precision, you can specify :sin; if you want single precision, you can specify :sinf, as in /Qimf-arch-consistency:true:sin or /Qimf-arch-consistency:false:sqrtf.

If you do not specify any function names, then the setting applies to all functions (and to all precisions). However, as soon as you specify an individual function name, the setting applies only to the function of corresponding precision. So, for example, sinf applies only to the single-precision sine function, sin applies only to the double-precision sine function, sinl applies only to the extended-precision sine function, etc.

The -fimf-arch-consistency (Linux*) and /Qimf-arch-consistency (Windows*) option may decrease runtime performance, but the option will provide bit-wise consistent results on all Intel® processors and compatible, non-Intel processors, regardless of micro-architecture. This option may not provide bit-wise consistent results between different architectures.

NOTE:

Many routines in libraries LIBM (Math Library) and SVML (Short Vector Math Library) are more highly optimized for Intel® microprocessors than for non-Intel microprocessors.

NOTE:

The standard Fortran names for the various math intrinsic functions do not match the math library names of the math intrinsic functions. You must find the actual math library name that is generated for the relevant Fortran math intrinsic.

One way to do this is to generate assembly code by using one of the following options:

Linux

-S

Windows

/Fa or /S

The assembly code will show the actual math library name.

For example, if you create a program that contains a call to SIN(x) where x is declared as REAL(KIND=4) and then use option S to produce assembly code for the program, the assembly code will show a call to sinf.

To ensure consistent results for the single-precision sine function, you should specify:

Linux

-fimf-arch-consistency=sinf

Windows

/Qimf-arch-consistency:sinf

NOTE:

This option only applies to host compilation. When offloading is enabled, it does not impact device-specific compilation. Offloading can only be enabled when using ifx.

Product and Performance Information

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.

Notice revision #20201201

IDE Equivalent

None

Alternate Options

None