A scalar data type holds a single value, such as the integer value 42 or the real value 112.6. The next table lists scalar data types, their size, format and range. Table 3 shows the range and approximate precision for Fortran real data types. Table 4 shows the alignment for different scalar data types. The alignments apply to all scalars, whether they are independent or contained in an array, a structure or a union.

⁽¹⁾ Approximate value

The logical constants .TRUE. and .FALSE. are all ones and all zeroes, respectively. Internally, the value of a logical variable is true if the least significant bit is one and false otherwise. When the option -⁠Munixlogical is set, a logical variable with a non-zero value is true and with a zero value is false.

The PGFORTRAN compiler supports de facto standard extensions to FORTRAN 77 that allow for aggregate data types. An aggregate data type consists of one or more scalar data type objects. You can declare the following aggregate data types:

• An array consists of one or more elements of a single data type placed in contiguous locations from first to last.
• A structure can contain different data types. The members are allocated in the order they appear in the definition but may not occupy contiguous locations.
• A union is a single location that can contain any of a specified set of scalar or aggregate data types. A union can have only one value at a time. The data type of the union member to which data is assigned determines the data type of the union after that assignment.

The alignment of an array, a structure or union (an aggregate) affects how much space the object occupies and how efficiently the processor can address members. Arrays use the alignment of their members.

Array types

align according to the alignment of the array elements. For example, an array of INTEGER*2 data aligns on a 2-byte boundary.

Structures and Unions

align according to the alignment of the most restricted data type of the structure or union. In the next example, the union aligns on a 4-byte boundary since the alignment of c, the most restrictive element, is four.

STRUCTURE /astr/
UNION
 MAP
 INTEGER*2 a ! 2 bytes
 END MAP
 MAP
 BYTE b ! 1 byte
 END MAP
 MAP
 INTEGER*4 c ! 4 bytes
 END MAP
END UNION
END STRUCTURE

Structure alignment can result in unused space called padding. Padding between members of the structure is called internal padding. Padding between the last member and the end of the space is called tail padding.

The offset of a structure member from the beginning of the structure is a multiple of the member's alignment. For example, since an INTEGER*2 aligns on a 2-byte boundary, the offset of an INTEGER*2 member from the beginning of a structure is a multiple of two bytes.

The Fortran 90 standard added formal support for aggregate data types. The TYPE statement begins a derived type data specification or declares variables of a specified user-defined type. For example, the following would define a derived type ATTENDEE:

TYPE ATTENDEE
 CHARACTER(LEN=30) NAME
 CHARACTER(LEN=30) ORGANIZATION
 CHARACTER (LEN=30) EMAIL
END TYPE ATTENDEE

In order to declare a variable of type ATTENDEE and access the contents of such a variable, code such as the following would be used:

TYPE (ATTENDEE) ATTLIST(100)
. . .
ATTLIST(1)%NAME = ‘JOHN DOE’

Table 5 lists C and C++ scalar data types, providing their size and format. The alignment of a scalar data type is equal to its size. Table 6 shows scalar alignments that apply to individual scalars and to scalars that are elements of an array or members of a structure or union. Wide characters are supported (character constants prefixed with an L). The size of each wide character is 4 bytes.

⁽¹⁾ Approximate value

⁽²⁾ Bit fields occupy as many bits as you assign them, up to 4 bytes, and their length need not be a multiple of 8 bits (1 byte)

An aggregate data type consists of one or more scalar data type objects. You can declare the following aggregate data types:

array

consists of one or more elements of a single data type placed in contiguous locations from first to last.

class

(C++ only) is a class that defines an object and its member functions. The object can contain fundamental data types or other aggregates including other classes. The class members are allocated in the order they appear in the definition but may not occupy contiguous locations.

struct

is a structure that can contain different data types. The members are allocated in the order they appear in the definition but may not occupy contiguous locations. When a struct is defined with member functions, its alignment rules are the same as those for a class.

union

is a single location that can contain any of a specified set of scalar or aggregate data types. A union can have only one value at a time. The data type of the union member to which data is assigned determines the data type of the union after that assignment.

Class and structure objects with no virtual entities and with no base classes, that is just direct data field members, are laid out in the same manner as C structures. The following section describes the alignment and size of these C-like structures. C++ classes (and structures as a special case of a class) are more difficult to describe. Their alignment and size is determined by compiler generated fields in addition to user-specified fields. The following paragraphs describe how storage is laid out for more general classes. The user is warned that the alignment and size of a class (or structure) is dependent on the existence and placement of direct and virtual base classes and of virtual function information. The information that follows is for informational purposes only, reflects the current implementation, and is subject to change. Do not make assumptions about the layout of complex classes or structures.

All classes are laid out in the same general way, using the following pattern (in the sequence indicated):

• First, storage for all of the direct base classes (which implicitly includes storage for non-virtual indirect base classes as well):
  • When the direct base class is also virtual, only enough space is set aside for a pointer to the actual storage, which appears later.
  • In the case of a non-virtual direct base class, enough storage is set aside for its own non-virtual base classes, its virtual base class pointers, its own fields, and its virtual function information, but no space is allocated for its virtual base classes.
• Next, storage for the class’s own fields.
• Next, storage for virtual function information (typically, a pointer to a virtual function table).
• Finally, storage for its virtual base classes, with space enough in each case for its own non-virtual base classes, virtual base class pointers, fields, and virtual function information.

The alignment of an array, a structure or union (an aggregate) affects how much space the object occupies and how efficiently the processor can address members.

Arrays

align according to the alignment of the array elements. For example, an array of short data type aligns on a 2-byte boundary.

Structures and Unions

align according to the most restrictive alignment of the enclosing members. In the following example, the union un1 aligns on a 4-byte boundary since the alignment of c, the most restrictive element, is four:

union un1 {
 short a; /* 2 bytes */
 char b; /* 1 byte */
 int c; /* 4 bytes */
 };

Structure alignment can result in unused space, called padding. Padding between members of a structure is called internal padding. Padding between the last member and the end of the space occupied by the structure is called tail padding. Figure 1 illustrates structure alignment. Consider the following structure:

struct strc1 {
 char a; /* occupies byte 0 */
 short b; /* occupies bytes 2 and 3 */
 char c; /* occupies byte 4 */
 int d; /* occupies bytes 8 through 11 */
 };

Figure 1. Internal Padding in a Structure

Figure 2 shows how tail padding is applied to a structure aligned on a doubleword (8 byte) boundary.

struct strc2{
 int m1[4]; /* occupies bytes
0 through 15 */
 double m2; /* occupies bytes 16 through 23 */
 short m3; /* occupies bytes 24 and 25 */
} st;

Bit-fields have the same size and alignment rules as other aggregates, with several additions to these rules:

• Bit-fields are allocated from right to left.
• A bit-field must entirely reside in a storage unit appropriate for its type. Bit-fields never cross unit boundaries.
• Bit-fields may share a storage unit with other structure/union members, including members that are not bit-fields.
• Unnamed bit-field's types do not affect the alignment of a structure or union.

Figure 2. Tail Padding in a Structure

The void data type is neither a scalar nor an aggregate. You can use void or void* as the return type of a function to indicate the function does not return a value, or as a pointer to an unspecified data type, respectively.

The const and volatile type qualifiers do not in themselves define data types, but associate attributes with other types. Use const to specify that an identifier is a constant and is not to be changed. Use volatile to prevent optimization problems with data that can be changed from outside the program, such as memory-mapped I/O buffers.

The options included in the following table pertain to the initial building of your program or application.

The options included in the following table pertain to debugging your program or application.

The options included in the following table pertain to optimizing your program or application code.

The options included in the following table pertain to defining parameters related to linking and running your program or application.

This section describes the -⁠M<pgflag> options that control code generation.

Default: For arguments that you do not specify, the default code generation controls are these:

Related options:-⁠D, -⁠I, -⁠L, -⁠l, -⁠U.

The following list provides the syntax for each -⁠M<pgflag> option that controls code generation. Each option has a description and, if appropriate, any related options.

-Mdaz

Set IEEE denormalized input values to zero; there is a performance benefit but misleading results can occur, such as when dividing a small normalized number by a denormalized number.
To take effect, this option must be set for the main program.

-Mnodaz

Do not treat denormalized numbers as zero.
To take effect, this option must be set for the main program.

-Mnodwarf

Specifies not to add DWARF debug information.
To take effect, this option must be used in combination with -⁠g.

-Mdwarf1

Generate DWARF1 format debug information.
To take effect, this option must be used in combination with -⁠g.

-Mdwarf2

Generate DWARF2 format debug information.
To take effect, this option must be used in combination with -⁠g.

-Mdwarf3

Generate DWARF3 format debug information.
To take effect, this option must be used in combination with -⁠g.

-Mflushz

Set SSE flush-to-zero mode; if a floating-point underflow occurs, the value is set to zero.
To take effect, this option must be set for the main program.

-Mnoflushz

Do not set SSE flush-to-zero mode; generate underflows.
To take effect, this option must be set for the main program.

-Mfunc32

Align functions on 32-byte boundaries.

-Minstrument[=functions] (linux86-64 only)

Generate additional code to enable instrumentation of functions. The option -⁠Minstrument=functions is the same as -⁠Minstrument.
Implies -⁠Minfo=ccff and -⁠Mframe.

-Mlargeaddressaware=[no]

[Win64 only] Generates code that allows for addresses greater than 2 GB, using RIP-relative addressing.
Use-⁠Mlargeaddressaware=no for a direct addressing mechanism that restricts the total addressable memory.

Note: Do not use -⁠Mlargeaddressaware=no if the object file will be placed in a DLL.

If -⁠Mlargeaddressaware=no is used to compile any object file, it must also be used when linking.

-Mlarge_arrays

Enable support for 64-bit indexing and single static data objects larger than 2 GB in size. This option is the default in the presence of -⁠mcmodel=medium. It can be used separately together with the default small memory model for certain 64-bit applications that manage their own memory space.
For more information, refer to the ‘Programming Considerations for 64-Bit Environments’ section of the PGI Compiler User's Guide .

-Mnolarge_arrays

Disable support for 64-bit indexing and single static data objects larger than 2 GB in size. When this option is placed after -⁠mcmodel=medium on the command line, it disables use of 64-bit indexing for applications that have no single data object larger than 2 GB.
For more information, refer to the ‘Programming Considerations for 64-Bit Environments’ section of the PGI Compiler User's Guide .

-Mnomain

Instructs the compiler not to include the object file that calls the Fortran main program as part of the link step. This option is useful for linking programs in which the main program is written in C/C++ and one or more subroutines are written in Fortran (Fortran only).

-Mmpi=option

-⁠Mmpi adds the include and library options to the compile and link commands necessary to build an MPI application using MPI header files and libraries.
To use -⁠Mmpi, you must have a version of MPI installed on your system.
This option tells the compiler to use the headers and libraries for the specified version of MPI.
The -Mmpi options are as specified:

• -Mmpi=mpich – Selects the default MPICH v3 libraries on Linux and macOS.
• -Mmpi=mpich1 – This option has been deprecated. It continues to direct the compiler to include the appropriate MPICH1 header files and to link against the correct MPICH1 libraries but only if you set the environment variable MPIDIR to the root of an MPICH1 installation.
• -Mmpi=mpich2 – This option has been deprecated. It continues to direct the compiler to include the appropriate MPICH2 header files and to link against the correct MPICH2 libraries but only if you set the environment variable MPIDIR to the root of an MPICH2 installation.
• -Mmpi=mvapich1 – This option has been deprecated. It continues to direct the compiler to include the appropriate MVAPICH1 header files and to link against the correct MVAPICH1 libraries but only if you set the environment variable MPIDIR to the root of an MVAPICH1 installation.

For more information, refer to the ‘Programming Considerations for 64-Bit Environments’ section of the PGI Compiler User's Guide .

Note: On Linux and macOS, you can set the environment variable MPIDIR to override the default locations that the compiler looks to find the MPI directory.

-M[no]movnt

Instructs the compiler to generate nontemporal move and prefetch instructions even in cases where the compiler cannot determine statically at compile-time that these instructions will be beneficial.

-M[no]pre

enables [disables] partial redundancy elimination.

-Mprof[=option[,option,...]]

Set performance profiling options. Use of these options changes which sections are included in the binary. These sections can be read by the PGI profiler.
The option argument can be any of the following:

[no]ccff

Enable [disable] common compiler feedback format, CCFF, information.

dwarf

Add limited DWARF symbol information sufficient for most performance profilers.

-Mrecursive

instructs the compiler to allow Fortran subprograms to be called recursively.

-Mnorecursive

Fortran subprograms may not be called recursively.

-Mref_externals

force references to names appearing in EXTERNAL statements (Fortran only).

-Mnoref_externals

do not force references to names appearing in EXTERNAL statements (Fortran only).

-Mreentrant

instructs the compiler to avoid optimizations that can prevent code from being reentrant.

-Mnoreentrant

instructs the compiler not to avoid optimizations that can prevent code from being reentrant.

-Msecond_underscore

instructs the compiler to add a second underscore to the name of a Fortran global symbol if its name already contains an underscore. This option is useful for maintaining compatibility with object code compiled using g77, which uses this convention by default (Fortran only).

-Mnosecond_underscore

instructs the compiler not to add a second underscore to the name of a Fortran global symbol if its name already contains an underscore (Fortran only).

-Msafe_lastval

When a scalar is used after a loop, but is not defined on every iteration of the loop, the compiler does not by default parallelize the loop. However, this option tells the compiler it’s safe to parallelize the loop. For a given loop, the last value computed for all scalars makes it safe to parallelize the loop.

-Msignextend

instructs the compiler to extend the sign bit that is set as a result of converting an object of one data type to an object of a larger signed data type.

-Mnosignextend

instructs the compiler not to extend the sign bit that is set as the result of converting an object of one data type to an object of a larger data type.

-Mstack_arrays

places automatic arrays on the stack.

-Mnostack_arrays

allocates automatic arrays on the heap. -Mnostack_arrays is the default and what traditionally has been the approach used.

-Mstride0

instructs the compiler to inhibit certain optimizations and to allow for stride 0 array references. This option may degrade performance and should only be used if zero-stride induction variables are possible.

-Mnostride0

instructs the compiler to perform certain optimizations and to disallow for stride 0 array references.

-Mvarargs

force Fortran program units to assume procedure calls are to C functions with a varargs-type interface (pgf77, pgf95, andpgfortran only).

This section describes the -⁠M<pgflag> options that affect C/C++ language interpretations by the PGI C and C++ compilers. These options are only valid to the pgcc and pgc++ compiler drivers.

Default: For arguments that you do not specify, the defaults are as follows:

Usage:

In this example, the compiler allows the asm keyword in the source file.

	$ pgcc -Masmkeyword myprog.c

In the following example, the compiler maps the dollar sign to the dot character.

	$ pgcc -Mdollar,. myprog.c

In the following example, the compiler treats floating-point constants as float values.

	$ pgcc -Mfcon myprog.c

In the following example, the compiler does not convert float parameters to double parameters.

	$ pgcc -Msingle myprog.c

Without -⁠Muchar or with -⁠Mschar, the variable ch is a signed character:

	char ch;
	signed char sch;

If -⁠Muchar is specified on the command line:

	$ pgcc -Muchar myprog.c

char ch in the preceding declaration is equivalent to:

 unsigned char ch;

The following list provides the syntax for each -⁠M<pgflag> option that controls code generation in C/C++. Each option has a description and, if appropriate, any related options.

-Masmkeyword

instructs the compiler to allow the asm keyword in C source files. The syntax of the asm statement is as follows:

asm("statement");

Where statement is a legal assembly-language statement. The quote marks are required.

Note: The current default is to support gcc's extended asm, where the syntax of extended asm includes asm strings. The -⁠M[no]asmkeyword switch is useful only if the target device is a Pentium 3 or older cpu type (-⁠tp piii|p6|k7|athlon|athlonxp|px).

-Mnoasmkeyword

instructs the compiler not to allow the asm keyword in C source files. If you use this option and your program includes the asm keyword, unresolved references are generated

-Mdollar,char

char specifies the character to which the compiler maps the dollar sign ($). The PGCC compiler allows the dollar sign in names; ANSI C does not allow the dollar sign in names.

-M[no]eh_frame

instructs the linker to keep eh_frame call frame sections in the executable.

Note: The eh_frame option is available only on newer Linux systems that supply the system unwind libraries.

-Mfcon

instructs the compiler to treat floating-point constants as float data types, instead of double data types. This option can improve the performance of single-precision code.

-M[no]m128

instructs the compiler to recognize [ignore] __m128, __m128d, and __m128i datatypes. floating-point constants as float data types, instead of double data types. This option can improve the performance of single-precision code.

-Mschar

specifies signed char characters. The compiler treats "plain" char declarations as signed char.

-Msingle

do not to convert float parameters to double parameters in non-prototyped functions. This option can result in faster code if your program uses only float parameters. However, since ANSI C specifies that routines must convert float parameters to double parameters in non-prototyped functions, this option results in non-ANSI conformant code.

-Mnosingle

instructs the compiler to convert float parameters to double parameters in non-prototyped functions.

-Muchar

instructs the compiler to treat "plain" char declarations as unsigned char.

This section describes the -⁠M<pgflag> options that control environments.

Default: For arguments that you do not specify, the default environment option depends on your configuration.

The following list provides the syntax for each -⁠M<pgflag> option that controls environments. Each option has a description and, if appropriate, a list of any related options.

-Mnostartup

instructs the linker not to link in the standard startup routine that contains the entry point (_start) for the program.

Note: If you use the -⁠Mnostartup option and do not supply an entry point, the linker issues the following error message: Warning: cannot find entry symbol _start

-M[no]smartalloc[=huge|huge:<n>|hugebss|nohuge]

adds a call to the routine mallopt in the main routine. This option supports large TLBs on Linux and Windows. This option must be used to compile the main routine to enable optimized malloc routines.
The option arguments can be any of the following:

huge

Link in the huge page runtime library.
Enables large 2-megabyte pages to be allocated. The effect is to reduce the number of TLB entries required to execute a program. This option is most effective on newer architectures; older architectures do not have enough TLB entries for this option to be beneficial. By itself, the huge suboption tries to allocate as many huge pages as required.

huge:<n>

Link the huge page runtime library and allocate n huge pages. Use this suboption to limit the number of huge pages allocated to n.
You can also limit the pages allocated by using the environment variable PGI_HUGE_PAGES.

hugebss

(64-bit only) Puts the BSS section in huge pages; attempts to put a program's uninitialized data section into huge pages.

Note: This flag dynamically links the library libhugetlbfs_pgi even if -⁠Bstatic is used.

nohuge

Overrides a previous -⁠Msmartalloc=huge setting.

Tip: To be effective, this switch must be specified when compiling the file containing the Fortran, C, or C++ main program.

-M[no]hugetlb

links in the huge page runtime library.
Enables large 2-megabyte pages to be allocated. The effect is to reduce the number of TLB entries required to execute a program. This option is most effective on newer architectures; older architectures do not have enough TLB entries for this option to be beneficial. By itself, the huge suboption tries to allocate as many huge pages as required.
You can also limit the pages allocated by using the environment variable PGI_HUGE_PAGES.

-M[no]stddef

instructs the compiler not to predefine any macros to the preprocessor when compiling a C program.

-Mnostdinc

instructs the compiler to not search the standard location for include files.

-Mnostdlib

instructs the linker not to link in the standard librarieslibpgftnrtl.a, libm.a, libc.a, and libpgc.a in the library directory lib within the standard directory. You can link in your own library with the -⁠l option or specify a library directory with the -⁠L option.

This section describes the -⁠M<pgflag> options that affect Fortran language interpretations by the PGI Fortran compilers. These options are valid only for the Fortran compiler drivers.

Default: Before looking at all the options, let's look at the defaults. For arguments that you do not specify, the defaults are as follows:

The following list provides the syntax for each -⁠M<pgflag> option that affect Fortran language interpretations. Each option has a description and, if appropriate, a list of any related options.

-Mallocatable=95|03

controls whether Fortran 95 or Fortran 2003 semantics are used in allocatable array assignments. The default behavior is to use Fortran 95 semantics; the 03 option instructs the compiler to use Fortran 2003 semantics.

-Mbackslash

instructs the compiler to treat the backslash as a normal character, and not as an escape character in quoted strings.

-Mnobackslash

instructs the compiler to recognize a backslash as an escape character in quoted strings (in accordance with standard C usage).

-Mcuda

instructs the compiler to enable CUDA Fortran. If more than one option is on the command line, all the specified options occur.

The following suboptions exist:

cc30

Generate code for compute capability 3.0.

cc35

Generate code for compute capability 3.5.

cc3x

Generate code for the lowest 3.x compute capability possible.

cc3+

Is equivalent to cc3x.

cc50

Generate code for compute capability 5.0.

cc60

Generate code for compute capability 6.0.

cc70

Generate code for compute capability 7.0.

ccall

Generate code for all compute capabilities supported by this platform and by the selected or default CUDA Toolkit.

cudaX.Y

Use CUDA X.Y Toolkit compatibility, where installed.

7.5, 8.0, 9.0, 9.1

Support for the X.Y suboption has been removed. Use the cudaX.Y suboption instead.

fastmath

Use routines from the fast math library.

[no]flushz

Enable[disable] flush-to-zero mode for floating point computations in the GPU code generated for CUDA Fortran kernels.

generate rdc

Generate relocatable device code

keepbin

Keep the generated binary (.bin) file for CUDA Fortran.

keepgpu

Keep the generated GPU code for CUDA Fortran.

keepptx

Keep the portable assembly (.ptx) file for the GPU code.

kepler

is equivalent to -Mcuda,cc3x

llvm

Generate code using the llvm-based back-end.

[no]debug

Enable[disable] GPU debug information generation.

[no]lineinfo

Enable[disable] GPU line information generation.

maxregcount:n

Specify the maximum number of registers to use on the GPU. Leaving this blank indicates no limit.

nofma

Do not generate fused multiply-add instructions.

noL1

Prevent the use of L1 hardware data cache to cache global variables.

ptxinfo

Show PTXAS informational messages during compilation.

rdc

Enable CUDA Fortran separate compilation and linking of device routines, including device routines in Fortran modules.
To enable separate compilation and linking, include the command line option -Mcuda=rdc on both the compile and the link steps.

-Mdclchk

instructs the compiler to require that all program variables be declared.

-Mnodclchk

instructs the compiler not to require that all program variables be declared.

-Mdefaultunit

instructs the compiler to treat "*" as a synonym for standard input for reading and standard output for writing.

-Mnodefaultunit

instructs the compiler to treat "*" as a synonym for unit 5 on input and unit 6 on output.

-Mdlines

instructs the compiler to treat lines containing "D" in column 1 as executable statements (ignoring the "D").

-Mnodlines

instructs the compiler not to treat lines containing "D" in column 1 as executable statements. The compiler does not ignore the "D".

-Mdollar,char

char specifies the character to which the compiler maps the dollar sign. The compiler allows the dollar sign in names.

-Mextend

instructs the compiler to accept 132-column source code; otherwise it accepts 72-column code.

-Mfixed

instructs the compiler to assume input source files are in FORTRAN 77-style fixed form format.

-Mfree

instructs the compiler to assume input source files are in Fortran 90/95 freeform format.

-Miomutex

instructs the compiler to generate critical section calls around Fortran I/O statements.

-Mnoiomutex

instructs the compiler not to generate critical section calls around Fortran I/O statements.

-Monetrip

instructs the compiler to force each DO loop to execute at least once. This option is useful for programs written for earlier versions of Fortran.

-Mnoonetrip

instructs the compiler not to force each DO loop to execute at least once.

-Msave

instructs the compiler to assume that all local variables are subject to the SAVE statement.
This may allow older Fortran programs to run, but it can greatly reduce performance.

-Mnosave

instructs the compiler not to assume that all local variables are subject to the SAVE statement.

-Mstandard

instructs the compiler to flag non-ANSI-conforming source code.

-Munixlogical

directs the compiler to treat logical values as true if the value is non-zero and false if the value is zero (UNIX F77 convention). When -⁠Munixlogical is enabled, a logical value or test that is non-zero is .TRUE., and a value or test that is zero is .FALSE.. In addition, the value of a logical expression is guaranteed to be one (1) when the result is .TRUE..

-Mnounixlogical

directs the compiler to use the VMS convention for logical values for true and false. Even values are true and odd values are false.

-Mupcase

instructs the compiler to preserve uppercase letters in identifiers.
With -⁠Mupcase, the identifiers "X" and "x" are different. Keywords must be in lower case.
This selection affects the linking process. If you compile and link the same source code using -⁠Mupcase on one occasion and -⁠Mnoupcase on another, you may get two different executables – depending on whether the source contains uppercase letters. The standard libraries are compiled using the default -⁠Mnoupcase .

-Mnoupcase

instructs the compiler to convert all identifiers to lower case.
This selection affects the linking process. If you compile and link the same source code using -⁠Mupcase on one occasion and -⁠Mnoupcase on another, you may get two different executables, depending on whether the source contains uppercase letters. The standard libraries are compiled using -⁠Mnoupcase.

This section describes the -⁠M<pgflag> options that control function inlining.

Usage:Before looking at all the options, let’s look at a couple examples. In the following example, the compiler extracts functions that have 500 or fewer statements from the source file myprog.f and saves them in the file extract.il.

$ pgfortran -Mextract=500 -o extract.il myprog.f

In the following example, the compiler inlines functions with fewer than approximately 100 statements in the source file myprog.f.

$ pgfortran -Minline=maxsize:100 myprog.f

Related options: -⁠o, -⁠Mextract

The following list provides the syntax for each -⁠M<pgflag> option that controls function inlining. Each option has a description and, if appropriate, a list of any related options.

- M[no]autoinline[=option[,option,...]]

instructs the compiler to inline [not to inline] a C/C++ function at -⁠O2, where the option can be any of these:

maxsize:n

instructs the compiler not to inline functions of size > n. The default size is 100.

totalsize:n

instructs the compiler to stop inlining when the size equals n. The default size is 800.

-Mextract[=option[,option,...]]

Extracts functions from the file indicated on the command line and creates or appends to the specified extract directory where option can be any of the following:

name:func

instructs the extractor to extract function func from the file.

size:number

instructs the extractor to extract functions with number or fewer statements from the file.

lib:filename.ext

instructs the extractor to use directory filename.ext as the extract directory, which is required to save and re-use inline libraries.

If you specify both name and size, the compiler extracts functions that match func, or that have number or fewer statements. For examples of extracting functions, refer to the ‘Using Function Inlining’ section of the PGI Compiler User's Guide.

-Minline[=option[,option,...]]

instructs the compiler to pass options to the function inliner, where the option can be any of the following:

except:func

Inlines all eligible functions except func, a function in the source text. You can use a comma-separated list to specify multiple functions.

[name:]func

Inlines all functions in the source text whose name matches func. You can use a comma-separated list to specify multiple functions.

The function name should be a non-numeric string that does not contain a period. You can also use a name: prefix followed by the function name. If name: is specified, what follows is always the name of a function.

[maxsize:]number

A numeric option is assumed to be a size. Functions of size number or less are inlined. If both number and function are specified, then functions matching the given name(s) or meeting the size requirements are inlined.

The size number need not exactly equal the number of statements in a selected function; the size parameter is merely a rough guage.

[no]reshape

instructs the inliner to allow [disallow] inlining in Fortran even when array shapes do not match. The default is -⁠Minline=noreshape, except with -⁠Mconcur or -⁠mp, where the default is -⁠Minline=reshape,=reshape.

smallsize:number

Always inline functions of size smaller than number regardless of other size limits.

totalsize:number

Stop inlining in a function when the function's total inlined size reaches the number specified.

[lib:]filename.ext

instructs the inliner to inline the functions within the library file filename.ext. The compiler assumes that a filename.ext option containing a period is a library file.

Tip: Create the library file using the -⁠Mextract option. You can also use a lib: prefix followed by the library name.

• If lib: is specified, no period is necessary in the library name. Functions from the specified library are inlined.
• If no library is specified, functions are extracted from a temporary library created during an extract prepass.

If you specify both func and number, the compiler inlines functions that match the function name or have number or fewer statements.

Inlining can be disabled with -⁠Mnoinline.

For examples of inlining functions, refer to ‘Using Function Inlining’ in the PGI Compiler User’s Guide.

This section describes the -⁠M<pgflag> options that control optimization.

Default: Before looking at all the options, let's look at the defaults. For arguments that you do not specify, the default optimization control options are as follows:

Usage: In this example, the compiler invokes the vectorizer with use of packed SSE instructions enabled.

>$ pgfortran -Mvect=sse -Mcache_align myprog.f

Related options:-⁠g, -⁠O

The following list provides the syntax for each -⁠M<pgflag> option that controls optimization. Each option has a description and, if appropriate, a list of any related options.

-Mcache_align

Align unconstrained objects of length greater than or equal to 16 bytes on cache-line boundaries. An unconstrained object is a data object that is not a member of an aggregate structure or common block. This option does not affect the alignment of allocatable or automatic arrays.
To effect cache-line alignment of stack-based local variables, the main program or function must be compiled with -⁠Mcache_align.

-Mconcur[=option [,option,...]]

Instructs the compiler to enable auto-concurrentization of loops. If -⁠Mconcur is specified, multiple processors will be used to execute loops that the compiler determines to be parallelizable.
option is one of the following:

allcores

Instructs the compiler to use all available cores. Use this option at link time.

[no]altcode:n

Instructs the parallelizer to generate alternate serial code for parallelized loops.

• If altcode is specified without arguments, the parallelizer determines an appropriate cutoff length and generates serial code to be executed whenever the loop count is less than or equal to that length.
• If altcode:n is specified, the serial altcode is executed whenever the loop count is less than or equal to n.
• If noaltcode is specified, the parallelized version of the loop is always executed regardless of the loop count.

cncall

Indicates that calls in parallel loops are safe to parallelize.
Loops containing calls are candidates for parallelization. Also, no minimum loop count threshold must be satisfied before parallelization will occur, and last values of scalars are assumed to be safe.

[no]innermost

Instructs the parallelizer to enable parallelization of innermost loops. The default is to not parallelize innermost loops, since it is usually not profitable on dual-core processors.

noassoc

Instructs the parallelizer to disable parallelization of loops with reductions.

When linking, the -⁠Mconcur switch must be specified or unresolved references result. The NCPUS environment variable controls how many processors or cores are used to execute parallelized loops.

Note: This option applies only on shared-memory multi-processor (SMP) or multicore processor-based systems.

-Mcray[=option[,option,...]]

(Fortran only) Force Cray Fortran (CF77) compatibility with respect to the listed options. Possible values of option include:

pointer

for purposes of optimization, it is assumed that pointer-based variables do not overlay the storage of any other variable.

-Mdepchk

instructs the compiler to assume unresolved data dependencies actually conflict.

-Mnodepchk

Instructs the compiler to assume potential data dependencies do not conflict. However, if data dependencies exist, this option can produce incorrect code.

-Mdse

Enables a dead store elimination phase that is useful for programs that rely on extensive use of inline function calls for performance. This is disabled by default.

-Mnodse

Disables the dead store elimination phase. This is the default.

-M[no]fpapprox[=option]

Perform certain floating point operations using low-precision approximation.
-⁠Mnofpapprox specifies not to use low-precision fp approximation operations.
By default -⁠Mfpapprox is not used.
If -⁠Mfpapprox is used without suboptions, it defaults to use approximate div, sqrt, and rsqrt. The available suboptions are these:

div

Approximate floating point division

sqrt

Approximate floating point square root

rsqrt

Approximate floating point reciprocal square root

-M[no]fpmisalign

Instructs the compiler to allow (not allow) vector arithmetic instructions with memory operands that are not aligned on 16-byte boundaries. The default is -⁠Mnofpmisalign on all processors.

-M[no]fprelaxed[=option]

Instructs the compiler to use [not use] relaxed precision in the calculation of some intrinsic functions. Can result in improved performance at the expense of numerical accuracy.
The possible values for option are:

div

Perform divide using relaxed precision.

intrinsic

Enables use of relaxed precision intrinsics.

noorder

Do not allow expression reordering or factoring.

order

Allow expression reordering, including factoring.

recip

Perform reciprocal using relaxed precision.

rsqrt

Perform reciprocal square root (1/sqrt) using relaxed precision.

sqrt

Perform square root with relaxed precision.

With no options, -⁠Mfprelaxed generates relaxed precision code for those operations that generate a significant performance improvement, depending on the target processor.
The default is -⁠Mnofprelaxed which instructs the compiler to not use relaxed precision in the calculation of intrinsic functions.

-Mi4

(Fortran only) instructs the compiler to treat INTEGER variables as INTEGER*4.

-Mipa=<option>[,<option>[,...]]

Pass options to the interprocedural analyzer. Note:-⁠Mipa is not compatible with parallel make environments (e.g., pmake).
-⁠Mipa implies -⁠O2, and the minimum optimization level that can be specified in combination with -⁠Mipa is -⁠O2.
For example, if you specify -⁠Mipa -⁠O1 on the command line, the optimization level is automatically elevated to -⁠O2 by the compiler driver. Typically, as recommended, you would use -⁠Mipa=fast.

Note: As of the PGI 16.3 release, -⁠Mipa has been disabled on Windows.

Many of the following suboptions can be prefaced with no, which reverses or disables the effect of the suboption if it's included in an aggregate suboption such as -⁠Mipa=fast. The choices of option are:

[no]align

recognize when targets of a pointer dummy are aligned. The default is noalign.

[no]arg

remove arguments replaced by const, ptr. The default is noarg.

[no]cg

generate call graph information for viewing using the pgicg command-line utility. The default is nocg.

[no]const

perform interprocedural constant propagation. The default is const.

except:<func>

used with inline to specify functions which should not be inlined. The default is to inline all eligible functions according to internally defined heuristics. Valid only immediately following the inline suboption.

[no]f90ptr

F90/F95 pointer disambiguation across calls. The default is nof90ptr.

fast

choose IPA options generally optimal for the target. To see settings for -⁠Mipa=fast on a given target, use -⁠help.

force

force all objects to re-compile regardless of whether IPA information has changed.

[no]globals

optimize references to global variables. The default is noglobals.

inline[:n]

perform automatic function inlining. If the optional :n is provided, limit inlining to at most n levels. IPA-based function inlining is performed from leaf routines upward.

ipofile

save IPA information in an .ipo file rather than incorporating it into the object file.

jobs[:n]

recompile n jobs in parallel and print source file names as they are compiled.

[no]keepobj

keep the optimized object files, using file name mangling, to reduce re-compile time in subsequent builds. The default is keepobj.

[no]libc

optimize calls to certain standard C library routines. The default is nolibc.

[no]libinline

allow inlining of routines from libraries; implies -⁠Mipa=inline. The default is nolibinline.

[no]libopt

allow recompiling and optimization of routines from libraries using IPA information. The default is nolibopt.

[no]localarg

equivalent to arg plus externalization of local pointer targets. The default is nolocalarg.

main:<func>

specify a function to appear as a global entry point. May appear multiple times and it disables linking.

reaggregation

Enables IPA-guided structure reaggregation, which automatically attempts to reorder elements in a struct, or to split structs into substructs to improve memory locality and cache utilization.

rsqrt

Perform reciprocal square root (1/sqrt) using relaxed precision.

[no]pfo

enable profile feedback information. The nopfo option is valid only immediately following the inline suboption. -⁠Mipa=inline,nopfo tells IPA to ignore PFO information when deciding what functions to inline, if PFO information is available.

[no]ptr

enable pointer disambiguation across procedure calls. The default is noptr.

[no]pure

pure function detection. The default is nopure.

required

return an error condition if IPA is inhibited for any reason, rather than the default behavior of linking without IPA optimization.

[no]reshape

enable [disable] Fortran inline with mismatched array shapes. Valid only immediately following the inline suboption.

safe:[<function>|<library>]

declares that the named function, or all functions in the named library, are safe. A safe procedure does not call back into the known procedures and does not change any known global variables.
Without -⁠Mipa=safe, any unknown procedures cause IPA to fail.

[no]safeall

declares that all unknown procedures are safe. The default is nosafeall. For more information, refer to -⁠Mipa=safe.

[no]shape

perform Fortran 90 array shape propagation. The default is noshape.

summary

only collect IPA summary information when compiling. This option prevents IPA optimization of this file, but allows optimization for other files linked with this file.

[no]vestigial

remove uncalled (vestigial) functions. The default is novestigial.
If you use -⁠Mipa=vestigial in combination with -⁠Mipa=libopt with PGCC, you may encounter unresolved references at link time. These unresolved references are a result of erroneous removal of functions by the vestigial sub-option to -⁠Mipa. You can work around this problem by listing specific sub-options to -⁠Mipa, not including vestigial.

-Mlre[=array | assoc | noassoc]

Enables loop-carried redundancy elimination, an optimization that can reduce the number of arithmetic operations and memory references in loops. The available suboptions are:

array

treat individual array element references as candidates for possible loop-carried redundancy elimination. The default is to eliminate only redundant expressions involving two or more operands.

assoc

allow expression re-association. Specifying this suboption can increase opportunities for loop-carried redundancy elimination but may alter numerical results.

noassoc

disallow expression re-association.

-Mnolre

Disable loop-carried redundancy elimination.

-Mnoframe

Eliminate operations that set up a true stack frame pointer for every function. With this option enabled, you cannot perform a traceback on the generated code and you cannot access local variables.

-Mnoi4

(Fortran only) instructs the compiler to treat INTEGER variables as INTEGER*2.

-Mpre

Enables partial redundancy elimination.

-Mprefetch[=option [,option...]]

enables generation of prefetch instructions on processors where they are supported. Possible values for option include:

d:m

set the fetch-ahead distance for prefetch instructions to m cache lines.

n:p

set the maximum number of prefetch instructions to generate for a given loop to p.

nta

use the prefetch instruction.

plain

use the prefetch instruction (default).

t0

use the prefetcht0 instruction.

w

use the AMD-specific prefetchw instruction.

-Mnoprefetch

Disables generation of prefetch instructions.

-M[no]propcond

Enables or disables constant propagation from assertions derived from equality conditionals.
The default is enabled.

-Mr8

(Fortran only) The compiler promotes REAL variables and constants to DOUBLE PRECISION variables and constants, respectively. DOUBLE PRECISION elements are 8 bytes in length.

-Mnor8

(Fortran only) The compiler does not promote REAL variables and constants to DOUBLE PRECISION. REAL variables will be single precision (4 bytes in length).

-Mr8intrinsics

(pgf77, pgf95, andpgfortran only) The compiler treats the intrinsics CMPLX and REAL as DCMPLX and DBLE, respectively.

-Mnor8intrinsics

(pgf77, pgf95, andpgfortran only) The compiler does not promote the intrinsics CMPLX and REAL to DCMPLX and DBLE, respectively.

-Msafeptr[=option[,option,...]]

(pgcc and pgc++ only) instructs the C/C++ compiler to override data dependencies between pointers of a given storage class. Possible values of option include:

all

assume all pointers and arrays are independent and safe for aggressive optimizations, and in particular that no pointers or arrays overlap or conflict with each other.

arg

instructs the compiler to treat arrays and pointers with the same copyin and copyout semantics as Fortran dummy arguments.

global

instructs the compiler that global or external pointers and arrays do not overlap or conflict with each other and are independent.

local/auto

instructs the compiler that local pointers and arrays do not overlap or conflict with each other and are independent.

static

instructs the compiler that static pointers and arrays do not overlap or conflict with each other and are independent.

-Mscalarsse

Use SSE/SSE2 instructions to perform scalar floating-point arithmetic.

-Mnoscalarsse

Do not use SSE/SSE2 instructions to perform scalar floating-point arithmetic; use x87 instructions instead (on applicable platforms only).

-Msmart

instructs the compiler driver to invoke a post-pass assembly optimization utility.

-Mnosmart

instructs the compiler not to invoke an AMD64-specific post-pass assembly optimization utility.

-Munroll[=option [,option...]]

invokes the loop unroller to execute multiple instances of the loop during each iteration. This also sets the optimization level to 2 if the level is set to less than 2, or if no -⁠O or -⁠g options are supplied. The option is one of the following:

c:m

instructs the compiler to completely unroll loops with a constant loop count less than or equal to m, a supplied constant. If this value is not supplied, the m count is set to 4.

m:<n>

instructs the compiler to unroll multi-block loops n times. This option is useful for loops that have conditional statements. If n is not supplied, then the default value is 4. The default setting is not to enable -⁠Munroll=m.

n:<n>

instructs the compiler to unroll single-block loops n times, a loop that is not completely unrolled, or has a non-constant loop count. If n is not supplied, the unroller computes the number of times a candidate loop is unrolled.

-Mnounroll

instructs the compiler not to unroll loops.

-M[no]vect[=option [,option,...]]

enable [disable] the code vectorizer, where option is one of the following:

altcode

Instructs the vectorizer to generate alternate code (altcode) for vectorized loops when appropriate. For each vectorized loop the compiler decides whether to generate altcode and what type or types to generate, which may be any or all of: altcode without iteration peeling, altcode with non-temporal stores and other data cache optimizations, and altcode based on array alignments calculated dynamically at runtime. The compiler also determines suitable loop count and array alignment conditionals for executing the altcode. This option is enabled by default.

noaltcode

Instructs the vectorizer to disable alternate code generation for vectorized loops.

assoc

Instructs the vectorizer to enable certain associativity conversions that can change the results of a computation due to roundoff error. A typical optimization is to change an arithmetic operation to an arithmetic operation that is mathematically correct, but can be computationally different, due to round-off error.

noassoc

Instructs the vectorizer to disable associativity conversions.

cachesize:n

Instructs the vectorizer, when performing cache tiling optimizations, to assume a cache size of n. The default is set per processor type, either using the -⁠tp switch or auto-detected from the host computer.

[no]gather

Instructs the vectorizer to vectorize loops containing indirect array references, such as this one:

sum = 0.d0
do k=d(j),d(j+1)-1
     sum = sum + a(k)*b(c(k))
enddo

The default is gather.

partial

Instructs the vectorizer to enable partial loop vectorization through innermost loop distribution.

prefetch

Instructs the vectorizer to search for vectorizable loops and, wherever possible, make use of prefetch instructions.

[no]short

Instructs the vectorizer to enable [disable] short vector operations. -Mvect=short enables generation of packed SIMD instructions for short vector operations that arise from scalar code outside of loops or within the body of a loop iteration.

[no]sizelimit

Instructs the vectorizer to generate vector code for all loops where possible regardless of the number of statements in the loop. This overrides a heuristic in the vectorizer that ordinarily prevents vectorization of loops with a number of statements that exceeds a certain threshold. The default is nosizelimit.

smallvect[:n]

Instructs the vectorizer to assume that the maximum vector length is less than or equal to n. The vectorizer uses this information to eliminate generation of the stripmine loop for vectorized loops wherever possible. If the size n is omitted, the default is 100.

Note: No space is allowed on either side of the colon (:).

[no]sse

Instructs the vectorizer to search for vectorizable loops and, wherever possible, make use of SSE, SSE2, and prefetch instructions. The default is nosse.

[no]uniform

Instructs the vectorizer to perform the same optimizations in the vectorized and residual loops.

Note: This option may affect the performance of the residual loop.

-Mnovect

instructs the compiler not to perform vectorization. You can use this option to override a previous instance of -⁠Mvect on the command-line, in particular for cases in which -⁠Mvect is included in an aggregate option such as -⁠fastsse.

-Mvect=[option]

instructs the compiler to enable loop vectorization, where option is one of the following:

partial

Enable partial loop vectorization through innermost loop distribution.

[no]short

Enable [disable] short vector operations. Enables [disables] generation of packed SIMD instructions for short vector operations that arise from scalar code outside of loops or within the body of a loop iteration.

simd[:{128|256}]

Specifies to vectorize using SIMD instructions and data, either 128 bits or 256 bits wide, on processors where there is a choice.

tile

Enable tiling/blocking over multiple nested loops for more efficient cache utilization.

-Mnovintr

instructs the compiler not to perform idiom recognition or introduce calls to hand-optimized vector functions.

This section describes the -⁠M<pgflag> options that do not easily fit into one of the other categories of -⁠M<pgflag> options.

Default: Before looking at all the options, let’s look at the defaults. For arguments that you do not specify, the default miscellaneous options are as follows:

Related options: -⁠m, -⁠S, -⁠V, -⁠v

Usage: In the following example, the compiler includes Fortran source code with the assembly code.

 $ pgfortran -Manno -S myprog.f

In the following example, the assembler does not delete the assembly file myprog.s after the assembly pass.

 $ pgfortran -Mkeepasm myprog.f

In the following example, the compiler displays information about inlined functions with fewer than approximately 20 source lines in the source file myprog.f.

 $ pgfortran -Minfo=inline -Minline=20 myprog.f

In the following example, the compiler creates the listing file myprog.lst.

 $ pgfortran -Mlist myprog.f

In the following example, array bounds checking is enabled.

 $ pgfortran -Mbounds myprog.f

The following list provides the syntax for each miscellaneous -⁠M<pgflag> option. Each option has a description and, if appropriate, a list of any related options.

-Manno

annotate the generated assembly code with source code. Implies -⁠Mkeepasm.

-Mbounds

enables array bounds checking.

• If an array is an assumed size array, the bounds checking only applies to the lower bound.
• If an array bounds violation occurs during execution, an error message describing the error is printed and the program terminates. The text of the error message includes the name of the array, the location where the error occurred (the source file and the line number in the source), and information about the out of bounds subscript (its value, its lower and upper bounds, and its dimension).

The following is a sample error message:

PGFTN-F-Subscript out of range for array a (a.f: 2) 
subscript=3, lower bound=1, upper bound=2, dimension=2

-Mnobounds

disables array bounds checking.

-Mbyteswapio

swap byte-order from big-endian to little-endian or vice versa upon input/output of Fortran unformatted data files.

-Mchkptr

instructs the compiler to check for pointers that are dereferenced while initialized to NULL (Fortran only).

-Mchkstk

instructs the compiler to check the stack for available space in the prologue of a function and before the start of a parallel region. Prints a warning message and aborts the program gracefully if stack space is insufficient.
This option is useful when many local and private variables are declared in an OpenMP program.
If the user also sets the PGI_STACK_USAGE environment variable to any value, then the program displays the stack space allocated and used after the program exits. For example, you might see something similar to the following message:

thread 0 stack: max 8180KB, used 48KB

This message indicates that the program used 48KB of a 8180KB allocated stack. This information is useful when you want to explicitly set a reserved and committed stack size for your programs, such as using the -⁠stack option on Windows.
For more information on the PGI_STACK_USAGE, refer to ‘PGI_STACK_USAGE’ in the PGI Compiler User’s Guide.

-Mcpp[=option [,option,...]]

run the PGI cpp-like preprocessor without execution of any subsequent compilation steps. This option is useful for generating dependence information to be included in makefiles.

Note: Only one of the m, md, mm or mmd options can be present; if multiple of these options are listed, the last one listed is accepted and the others are ignored.

The option is one or more of the following:

m

print makefile dependencies to stdout.

md

print makefile dependencies to filename.d, where filename is the root name of the input file being processed, ignoring system include files.

mm

print makefile dependencies to stdout, ignoring system include files.

mmd

print makefile dependencies to filename.d, where filename is the root name of the input file being processed, ignoring system include files.

[no]comment

do [do not] retain comments in output.

[suffix:]<suff>

use <suff> as the suffix of the output file containing makefile dependencies.

-Mdll

This Windows-only flag has been deprecated. Refer to -⁠Bdynamic. This flag was used to link with the DLL versions of the runtime libraries, and it was required when linking with any DLL built by any PGI compilers. This option implied -⁠D_DLL, which defines the preprocessor symbol _DLL.

-Mgccbug[s]

instructs the compiler to match the behavior of certain gcc bugs.

-Miface[=option]

adjusts the calling conventions for Fortran, where option is one of the following:

cref

uses CREF calling conventions, no trailing underscores.

mixed_str_len_arg

places the lengths of character arguments immediately after their corresponding argument. Has affect only with the CREF calling convention.

nomixed_str_len_arg

places the lengths of character arguments at the end of the argument list. Has affect only with the CREF calling convention.

-Minfo[=option [,option,...]]

instructs the compiler to produce information on standard error, where option is one of the following:

all

instructs the compiler to produce all available -⁠Minfo information. Implies a number of suboptions:

-Mneginfo=accel,inline,ipa,loop,lre,mp,opt,par,vect 

accel

instructs the compiler to enable accelerator information.

ccff

instructs the compiler to append common compiler feedback format information, such as optimization information, to the object file.

ftn

instructs the compiler to enable Fortran-specific information.

inline

instructs the compiler to display information about extracted or inlined functions. This option is not useful without either the -⁠Mextract or -⁠Minline option.

intensity

instructs the compiler to provide informational messages about the intensity of the loop. Specify <n> to get messages on nested loops.

• For floating point loops, intensity is defined as the number of floating point operations divided by the number of floating point loads and stores.
• For integer loops, the loop intensity is defined as the total number of integer arithmetic operations, which may include updates of loop counts and addresses, divided by the total number of integer loads and stores.
• By default, the messages just apply to innermost loops.

ipa

instructs the compiler to display information about interprocedural optimizations.

loop

instructs the compiler to display information about loops, such as information on vectorization.

lre

instructs the compiler to enable LRE, loop-carried redundancy elimination, information.

mp

instructs the compiler to display information about parallelization.

opt

instructs the compiler to display information about optimization.

par

instructs the compiler to enable parallelizer information.

pfo

instructs the compiler to enable profile feedback information.

time

instructs the compiler to display compilation statistics.

unroll

instructs the compiler to display information about loop unrolling.

vect

instructs the compiler to enable vectorizer information.

-Minform=level

instructs the compiler to display error messages at the specified and higher levels, where level is one of the following:

fatal

instructs the compiler to display fatal error messages.

[no]file

instructs the compiler to print or not print source file names as they are compiled. The default is to print the names: -⁠Minform=file.

inform

instructs the compiler to display all error messages (inform, warn, severe and fatal).

severe

instructs the compiler to display severe and fatal error messages.

warn

instructs the compiler to display warning, severe and fatal error messages.

-Minstrumentation=option

specifies the level of instrumentation calls generated. This option implies -Minfo=ccff, -Mframe.
option is one of the following:

level

specifies the level of instrumentation calls generated.

function (default)

generates instrumentation calls for entry and exit to functions.
Just after function entry and just before function exit, the following profiling functions are called with the address of the current function and its call site. (linux86-64 only).

void __cyg_profile_func_enter (void *this_fn, void *call_site);
void __cyg_profile_func_exit (void *this_fn, void *call_site);

In these calls, the first argument is the address of the start of the current function.

-Mkeepasm

instructs the compiler to keep the assembly file as compilation continues. Normally, the assembler deletes this file when it is finished. The assembly file has the same filename as the source file, but with a .s extension.

-M list

instructs the compiler to create a listing file. The listing file is filename.lst, where the name of the source file is filename.f.

-Mmakedll

(Windows only) generate a dynamic link library (DLL).

-Mmakeimplib

(Windows only) generate an import library for a DLL without creating the DLL. When used without -def:deffile, passes the switch -def to the librarian without a deffile.

-Mnames=lowercase|uppercase

specifies the case for the names of Fortran externals.

• lowercase - Use lowercase for Fortran externals.
• uppercase - Use uppercase for Fortran externals.

-Mneginfo[=option [,option,...]]

instructs the compiler to produce information on standard error, where option is one of the following:

all

instructs the compiler to produce all available information on why various optimizations are not performed.

accel

instructs the compiler to enable accelerator information.

ccff

instructs the compiler to append information, such as optimization information, to the object file.

concur

instructs the compiler to produce all available information on why loops are not automatically parallelized. In particular, if a loop is not parallelized due to potential data dependence, the variable(s) that cause the potential dependence are listed in the messages that you see when using the option -⁠Mneginfo.

ftn

instructs the compiler to enable Fortran-specific information.

inline

instructs the compiler to display information about extracted or inlined functions. This option is not useful without either the -⁠Mextract or -⁠Minline option.

ipa

instructs the compiler to display information about interprocedural optimizations.

loop

instructs the compiler to display information about loops, such as information on vectorization.

lre

instructs the compiler to enable LRE, loop-carried redundancy elimination, information.

mp

instructs the compiler to display information about parallelization.

opt

instructs the compiler to display information about optimization.

par

instructs the compiler to enable parallelizer information.

pfo

instructs the compiler to enable profile feedback information.

vect

instructs the compiler to enable vectorizer information.

-Mnolist

the compiler does not create a listing file. This is the default.

-Mnoopenmp

when used in combination with the -⁠mp option, the compiler ignores OpenMP parallelization directives or pragmas, but still processes SGI-style parallelization directives or pragmas.

-Mnosgimp

when used in combination with the -⁠mp option, the compiler ignores SGI-style parallelization directives or pragmas, but still processes OpenMP parallelization directives or pragmas.

-Mnopgdllmain

(Windows only) do not link the module containing the default DllMain() into the DLL. This flag applies to building DLLs with the PGFORTRAN compilers. If you want to replace the default DllMain() routine with a custom DllMain(), use this flag and add the object containing the custom DllMain() to the link line. The latest version of the default DllMain() used by PGFORTRAN is included in the Release Notes for each release. The PGFORTRAN-specific code in this routine must be incorporated into the custom version of DllMain() to ensure the appropriate function of your DLL.

-Mnorpath

(Linux only) Do not add -⁠rpath to the link line.

-Mpreprocess

instruct the compiler to perform cpp-like preprocessing on assembly and Fortran input source files.

-Mwritable_strings

stores string constants in the writable data segment.

Note: Options -⁠Xs and -⁠Xst include -⁠Mwritable_strings.

This directive or pragma has no corresponding command-line option. The compiler determines whether the last values for loop iteration control variables and promoted scalars need to be computed. In certain cases, the compiler must assume that the last values of these variables are needed and therefore computes their last values. The directive nolstval directs the compiler not to compute the last values for those cases.

The syntax for the IGNORE_TKR directive is this:

!DIR$ IGNORE_TKR [ [(<letter>) <dummy_arg>] ... ]

<letter>

is one or any combination of the following:

T – type

K – kind

R – rank

For example, KR indicates to ignore both kind and rank rules and TKR indicates to ignore the type, kind, and rank arguments.

<dummy_arg>

if specified, indicates the dummy argument for which TKR rules should be ignored. If not specified, TKR rules are ignored for all dummy arguments in the procedure that contains the directive.

The following rules apply to this directive:

• IGNORE_TKR must not specify dummy arguments that are allocatable, Fortran 90 pointers, or assumed-shape arrays.
• IGNORE_TKR may appear in the body of an interface block or in the body of a module procedure, and may specify dummy argument names only.
• IGNORE_TKR may appear before or after the declarations of the dummy arguments it specifies.
• If dummy argument names are specified, IGNORE_TKR applies only to those particular dummy arguments.
• If no dummy argument names are specified, IGNORE_TKR applies to all dummy arguments except those that are allocatable objects, Fortran 90 pointers, or assumed-shape arrays.

Consider this subroutine fragment:

subroutine example(A,B,C,D)
!DIR$ IGNORE_TKR A, (R) B, (TK) C, (K) D

Table 15 indicates which rules are ignored for which dummy arguments in the preceding sample subroutine fragment:

Notice that no letters were specified for A, so all type, kind, and rank rules are ignored.

This directive specifies an alternative name with which to resolve a routine.

The syntax for the ALIAS directive is either of the following:

!DEC$ ALIAS routine_name , external_name
!DEC$ ALIAS routine_name : external_name

In this syntax, external_name is used as the external name for the specified routine_name.

If external_name is an identifier name, the name (in uppercase) is used as the external name for the specified routine_name. If external_name is a character constant, it is used as-is; the string is not changed to uppercase, nor are blanks removed.

You can also supply an alias for a routine using the ATTRIBUTES directive, described in the next section:

!DEC$ ATTIRIBUTES ALIAS : 'alias_name' :: routine_name

This directive specifies an alternative name with which to resolve a routine, as illustrated in the following code fragment that provides external names for three routines. In this fragment, the external name for sub1 is name1, for sub2 is name2, and for sub3 is name3.

subroutine sub
!DEC$ alias sub1 , 'name1'
!DEC$ alias sub2 : 'name2'
!DEC$ attributes alias : 'name3' :: sub3 

This directive lets you specify properties for data objects and procedures.

The syntax for the ATTRIBUTES directive is this:

!DEC$ ATTRIBUTES <list>

where <list> is one of the following:

ALIAS : 'alias_name' :: routine_name

Specifies an alternative name with which to resolve routine_name.

C :: routine_name

Specifies that the routine routine_name will have its arguments passed by value. When a routine marked C is called, arguments, except arrays, are sent by value. For characters, only the first character is passed. The standard Fortran calling convention is pass by reference.

DLLEXPORT :: name

Specifies that name is being exported from a DLL.

DLLIMPORT :: name

Specifies that name is being imported from a DLL.

NOMIXED_STR_LEN_ARG

Specifies that hidden lengths are placed in sequential order at the end of the list.

Note: This attribute only applies to routines that are compiled with -Miface=cref or that use the default Windows calling conventions.

REFERENCE :: name

Specifies that the argument name is being passed by reference. Often this attribute is used in conjunction with STDCALL, where STDCALL refers to an entire routine; then individual arguments are modified with REFERENCE.

STDCALL :: routine_name

Specifies that routine routine_name will have its arguments passed by value. When a routine marked STDCALL is called, arguments (except arrays and characters) will be sent by value. The standard Fortran calling convention is pass by reference.

VALUE :: name

Specifies that the argument 'name' is being passed by value.

The DECORATE directive specifies that the name specified in the ALIAS directive should have the prefix and postfix decorations performed on it that are associated with the calling conventions that are in effect. These declarations are the same ones performed on the name when ALIAS is not specified.

The syntax for the DECORATE directive is this:

!DEC$ DECORATE

This directive is front-end based, and tells the compiler at what point within a loop to split into two loops.

The syntax for the DISTRIBUTE directive is either of the following:

!DEC$ DISTRIBUTE POINT
!DEC$ DISTRIBUTEPOINT

subroutine dist(a,b,n)
    integer i
    integer n
    integer a(*)
    integer b(*)
    do i = 1,n
        a(i) = a(i)+2
!DEC$ DISTRIBUTE POINT
        b(i) = b(i)*4
    enddo
end subroutine 

This section describes the standard function calling sequence, including the stack frame, register usage, and parameter passing.

Sections A2.4.1 through A2.4.4 of the ABI for x64 Linux and macOS define the Fortran supplement. The register usage conventions set forth in that document remain the same for Fortran.