Default Compiler Optimizations

If you invoke the Intel® Fortran Compiler without specifying any compiler options, the default state of each option takes effect. The following tables summarize the options whose default status is ON as they are required for Intel Fortran Compiler default operation. The tables group the options by their functionality.

For the default states and values of all options, see the Alphabetical Quick Reference Guide in the Intel® Fortran Compiler Options Quick Reference. The table provides links to the sections describing the functionality of the options. If an option has a default value, such value is indicated.

Depending on your application requirements, you can disable one or more options. For general methods of disabling optimizations, see Volume I.

The following tables list all options that compiler uses for its default optimizations.

Data Setting and Fortran Language Conformance

Default Option	Description
-align records	Analyzes and reorders memory layout for variables and arrays.
-align rec8byte	Specifies 8-byte boundary for alignment constraint.
-altparam	Specifies that the alternate form of parameter constant declarations is recognized.
-ansi_alias	Enables assumption of the program's ANSI conformance.
-assume cc_omp	Enables OpenMP conditional compilation directives.
-ccdefault default	Specifies default carriage control for units 6 and *.
-double_size 64	Defines DOUBLE PRECISION declarations, constants, functions, and intrinsics as REAL*8.
-dps	Enables DEC* parameter statement recognition.
-error_limit 30	Specifies the maximum number of error-level or fatal-level compiler errors permissible.
-fpe3	Specifies floating-point exception handling at run time for the main program.
-integer_size 32	Makes default integer and logical variables 4 bytes long. INTEGER and LOGICAL declarations are treated as (KIND=4).
-pad	Enables changing variable and array memory layout.
-pc80 IA-32 only	-pc{32\|64\|80} enables floating-point significand precision control as follows: -pc32 to 24-bit significand, -pc64 to 53-bit significand, and -pc80 to 64-bit significand.
-real_size 64	Specifies the size of REAL and COMPLEX declarations, constants, functions, and intrinsics.
-save	Saves all variables in static allocation. Disables -auto, that is, disables setting all variables AUTOMATIC.
-Zp8	-Zpn specifies alignment constraint for structures on 1-, 2-, 4-, 8-, or 16-byte boundary. To disable, use -noalign or -Zp1.

Optimizations

Default Option	Description
-assume cc_omp	Enables OpenMP conditional compilation directives.
-fp IA-32 only	Disables the use of the ebp register in optimizations. Directs to use the ebp-based stack frame for all functions.
-fpe3	Specifies floating-point exception handling at run time for the main program. -fpe0 disables the option.
-IPF_fltacc- Itanium® compiler	Enables the compiler to apply optimizations that affect floating-point accuracy.
-IPF_fma Itanium compiler	Enables the contraction of floating-point multiply and add/subtract operations into a single operation.
-IPF_fp_speculation fast Itanium compiler	Sets the compiler to speculate on floating-point operations. -IPF_fp_speculationoff disables this optimization.
-O, -O2	Optimizes for maximum speed.
-openmp_report1	Indicates loops, regions, and sections parallelized.
-opt_report_levelmin	Specifies the minimal level of the optimizations report.
-par_report1	Indicates loops successfully auto-parallelized.
-tpp2 Itanium compiler	Optimizes code for the Intel® Itanium® 2 processor for Itanium-based applications. Generated code is compatible with the Itanium processor.
-tpp7 IA-32 only	Optimizes code for the Intel® Pentium® 4 and Intel® Xeon(TM) processor for IA-32 applications.
-unroll	-unroll[n]: omit n to let the compiler decide whether to perform unrolling or not (default). Specify n to set maximum number of times to unroll a loop. The Itanium compiler currently uses only n = 0, -unroll0 (disabled option) for compatibility.
-vec_report1	Indicates loops successfully vectorized.

Disabling Default Options

To disable an option, you can generally use one of the following:

To disable one or a group of optimization options, use -O0 option. For example:

ifort -O2 -O0 input_file(s)

Note
The -O0 option is part of a mutually-exclusive group of options that includes -O0, -O, -O1, -O2, and -O3. The last of any of these options specified on the command line will override the previous options from this group.

To disable options that include optional "-" shown as [-], use that version of the option in the command line, for example: -ftz-.
To disable options that have an {n} parameter, use n=0 version, for example: -unroll0.

Note
If there are enabling and disabling versions of options on the line, the last one takes precedence.