IBM-XL IBM XL Compiler Flags and Common Unix Commands and Environment Settings
Compilers: IBM XL C/C++ Enterprise Edition Version 8.0 for AIX

Compilers: IBM XL Fortran Enterprise Edition Version 10.1 for AIX

Compilers: IBM XL C/C++ Enterprise Edition Version 9.0 for AIX

Compilers: IBM XL Fortran Enterprise Edition Version 11.1 for AIX

Compilers: IBM XL C/C++ Version 10.1 for AIX

Compilers: IBM XL Fortran Version 12.1 for AIX

Compilers: IBM XL C/C++ Version 11.1 for AIX

Compilers: IBM XL Fortran Version 13.1 for AIX

Last updated: 20-Apr-2011

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xlc, xlc_r Invoke the IBM XL C compiler. 32-bit binaries are produced by default.

]]> xlC, xlC_r Invoke the IBM XL C++ compiler. 32-bit binaries are produced by default.

]]> xlf95, xlf95_r Invoke the IBM XL Fortran compiler. 32-bit binaries are produced by default.

]]> -O5 Perform optimizations for maximum performance. This includes maximum interprocedural analysis on all of the objects presented on the "link" step. This level of optimization will increase the compiler's memory usage and compile time requirements. -O5 Provides all of the functionality of the -O4 option, but also provides the functionality of the -qipa=level=2 option.

-O5 is equivalent to the following flags ]]> -O4 Perform optimizations for maximum performance. This includes interprocedural analysis on all of the objects presented on the "link" step.

-O4 is equivalent to the following flags ]]> -O3
  • In-depth memory access analysis
  • Better loop scheduling
  • High-order loop analysis and transformations (-qhot=level=0)
  • Inlining of small procedures within a compilation unit by default
  • Eliminating implicit compile-time memory usage limits
  • Widening, which merges adjacent load/stores and other operations
  • Pointer aliasing improvements to enhance other optimizations
    • -O3 is equivalent to the following flags ]]>     -O2
  • Eliminates redundant code
  • Basic loop optimization
  • Can structure code to take advantage of -qarch and -qtune settings
    • ]]>     -O -qarch Produces object code containing instructions that will run on the specified processors. "auto" selects the processor the compile is being done on. "pwr5x" is the POWER5+ processor.

    Supported values for this flag are

    ]]>     -qtune Specifies the system architecture for which the executable program is optimized. This includes instruction scheduling and cache setting.

    The supported values for suboption are

    ]]>     This option specifies that no functions are to be inlined. This option inlines glue code that optimizes external function calls when compiling. -qhot, -qhot=level=1, -qhot=simd Performs high-order transformations on loops during optimization. The supported values for suboption are:

    Specifying -qhot without suboptions implies -qhot=nosimd, -qhot=noarraypad, -qhot=vector and -qhot=level=1. The -qhot option is also implied by -O4, and -O5.

    ]]>     -qipa=level Enhances optimization by doing detailed analysis across procedures (interprocedural analysis or IPA). The level determines the amount of interprocedural analysis and optimization that is performed.

    level=0 Does only minimal interprocedural analysis and optimization

    level=1 turns on inlining , limited alias analysis, and limited call-site tailoring

    level=2 turns on full interprocedural data flow and alias analysis

    ]]>     Suppresses interprocedural analysis (IPA), which is enabled by default at optimization levels -O4 and -O5.

    ]]>     The option used in the first pass of a profile directed feedback compile that causes pdf information to be generated. The profile directed feedback optimization gathers data on both execution path and data values. It does not use hardware counters, nor gather any data other than path and data values for PDF specific optimizations. The option used in the second pass of a profile directed feedback compile that causes PDF information to be utilized during optimization. The compiler generates additional symbol information for use by the AIX "fdpr" binary optimization tool. -qxlf90=nosignedzero -qxlf90=<suboption> Determines whether the compiler provides the Fortran 90 or the Fortran 95 level of support for certain aspects of the language. <suboption> can be one of the following: signedzero | nosignedzero Determines how the SIGN(A,B) function handles signed real 0.0. In addition, determines whether negative internal values will be prefixed with a minus when formatted output would produce a negative sign zero. autodealloc | noautodealloc Determines whether the compiler deallocates allocatable arrays that are declared locally without either the SAVE or the STATIC attribute and have a status of currently allocated when the subprogram terminates. oldpad | nooldpad When the PAD=specifier is present in the INQUIRE statement, specifying -qxlf90=nooldpad returns UNDEFINED when there is no connection, or when the connection is for unformatted I/O. This behavior conforms with the Fortran 95 standard and above. Specifying -qxlf90=oldpad preserves the Fortran 90 behavior. Default: o signedzero, autodealloc and nooldpad for the xlf95, xlf95_r, xlf95_r7 and f95 invocation commands. o nosignedzero, noautodealloc and oldpad for all other invocation commands. ]]> -q64 Generates 64 bit ABI binaries. The default is to generate 32 bit ABI binaries. Indicates that a program, designed to execute in a large page memory environment, can take advantage of large 16 MB pages provided on POWER4 and higher based systems. Indicates that the compiler understands how to do alloca(). Causes the Fortran compiler to allocate dynamic arrays on the heap instead of the stack Specifies that all local variables be treated as STATIC. -qsimd -qnosimd Enables the generation of vector instructions for processors that support them. -qenablevmx -qnoenablevmx Enables the generation of vector instructions for processors that support them. Specifies whether to use volatile or non-volatile vector registers. Volatile vector registers are registers whose value is not preserved across function calls so the compiler will not depend on values in them across function calls. Link the mathematical acceleration subsystem libraries (MASS), which contain libraries of tuned mathematical intrinsic functions. Link the Engineering and Scientific Subroutine Library (ESSL). Specifies that, if either -lessl or -lesslsmp are also specified, then Engineering and Scientific Subroutine Library (ESSL) routines should be used in place of some Fortran 90 intrinsic procedures when there is a safe opportunity to do so. Cause the C++ compiler to generate Run Time Type Identification code Causes the compiler to treat "char" variables as signed instead of the default of unsigned. Indicates that the input fortran source program is in fixed form. Adds an underscore to global entities to match the C compiler ABI -qcpluscmt Permits the usage of "//" to introduce a comment that lasts until the end of the current source line, as in C++.

    ]]>     -qalias=noansi, -qalias=nostd qalias=ansi | noansi If ansi is specified, type-based aliasing is used during optimization, which restricts the lvalues that can be safely used to access a data object. The default is ansi for the xlc, xlC, and c89 commands. This option has no effect unless you also specify the -O option. qalias=std |nostd Indicates whether the compilation units contain any non-standard aliasing (see Compiler Reference for more information). If so, specify nostd. ]]> -qalign=natural Specifies what aggregate alignment rules the compiler uses for file compilation, where the alignment options are: bit_packed The compiler uses the bit_packed alignment rules. full The compiler uses the RISC System/6000 alignment rules. This is the same as power. mac68k The compiler uses the Macintosh alignment rules. This suboption is valid only for 32- bit compilations. natural The compiler maps structure members to their natural boundaries. packed The compiler uses the packed alignment rules. power The compiler uses the RISC System/6000 alignment rules. twobyte The compiler uses the Macintosh alignment rules. This suboption is valid only for 32- bit compilations. The mac68k option is the same as twobyte. The default is -qalign=full. ]]> -qassert=refalign qassert=refalign | norefalign Specifies that all pointers inside the compilation unit only point to data that is naturally aligned according to the length of the pointer types. ]]> -qprefetch=aggressive qprefetch=aggressive Aggressively prefetch data ]]> -qxflag=DSCRVAL=31 The xflag=DSCRVAL option in conjunction with the -qprefetch=aggressive option, causes the Data Streams Control Register to be set to the value specified when executing this program.

    ]]>     -qrestrict qrestrict TBD ]]> Causes the compiler to automatically generate parallel code using OMP controls when possible. Tell the compiler that OMP controls are used to identify parallel code. -qstrict, -qnostrict Ensures that optimizations done by default at optimization levels -O3 and higher, and, optionally at -O2, do not alter the semantics of a program. The -qstrict=all, -qstrict=precision, -qstrict=exceptions, -qstrict=ieeefp, and -qstrict=order suboptions and their negative forms are group suboptions that affect multiple, individual suboptions. Group suboptions act as if either the positive or the no form of every suboption of the group is specified. Default: o Always -qstrict or -qstrict=all when the -qnoopt or -O0 optimization level is in effect o -qstrict or -qstrict=all is the default when the -O2 or -O optimization level is in effect o -qnostrict or -qstrict=none is the default when -O3 or a higher optimization level is in effect <suboptions_list> is a colon-separated list of one or more of the following: all | none all disables all semantics-changing transformations, including those controlled by the ieeefp, order, library, precision, and exceptions suboptions. none enables these transformations. precision | noprecision precision disables all transformations that are likely to affect floating-point precision, including those controlled by the subnormals, operationprecision, association, reductionorder, and library suboptions. noprecision enables these transformations. exceptions | noexceptions exceptions disables all transformations likely to affect exceptions or be affected by them, including those controlled by the nans, infinities, subnormals, guards, and library suboptions. noexceptions enables these transformations. ieeefp | noieeefp ieeefp disables transformations that affect IEEE floating-point compliance, including those controlled by the nans, infinities, subnormals, zerosigns, and operationprecision suboptions. noieeefp enables these transformations. nans | nonans nans disables transformations that may produce incorrect results in the presence of, or that may incorrectly produce IEEE floating-point signaling NaN (not-a-number) values. nonans enables these transformations. infinities | noinfinities infinities disables transformations that may produce incorrect results in the presence of, or that may incorrectly produce floating-point infinities. noinfinities enables these transformations. subnormals | nosubnormals subnormals disables transformations that may produce incorrect results in the presence of, or that may incorrectly produce IEEE floating-point subnormals (formerly known as denorms). nosubnormals enables these transformations. zerosigns | nozerosigns zerosigns disables transformations that may affect or be affected by whether the sign of a floating-point zero is correct. nozerosigns enables these transformations. operationprecision | nooperationprecision operationprecision disables transformations that produce approximate results for individual floating-point operations. nooperationprecision enables these transformations. order | noorder order disables all code reordering between multiple operations that may affect results or exceptions, including those controlled by the association, reductionorder, and guards suboptions. noorder enables code reordering. association | noassociation association disables reordering operations within an expression. noassociation enables reordering operations. reductionorder | noreductionorder reductionorder disables parallelizing floating-point reductions. noreductionorder enables these reductions. guards | noguards guards disables moving operations past guards or calls which control whether the operation should be executed or not. enables these moving operations. library | nolibrary library disables transformations that affect floating-point library functions. nolibrary enables these transformations. ]]> Allows most any c dialect. -qipa=inline=limit=1000 -qipa=inline=threshold=100 The inline suboption specifies the threshold and limit of inlined functions

    ]]>     -qipa=noobject Specifies whether to include standard object code in the object files. The noobject suboption can substantially reduce overall compilation time, by not generating object code during the first IPA phase. This option does not affect the code in the final binary created.

    ]]>     -qipa=partition=large The partition suboption specifies the size of the program sections that are analysed together. Larger partitons may produce better analysis but require more storage. Default is medium.

    ]]>     -qipa=threads The threads suboption allows the IPA optimizer to run portions of the optimization process in parallel threads, which can speed up the compilation process on multi-processor systems. All the available threads, or the number specified by N, may be used. N must be a positive integer. Specifying nothreads does not run any parallel threads; this is equivalent to running one serial thread. This option does not affect the code in the final binary created.

    ]]>     -qspillsize=512, -qspillsize=32648 Specifies the size of the compiler's internal program storage areas, in bytes.

    ]]>     Causes the compiler to output a traceback if it abends. -qsuppress=msg1:msg2 -qsuppress=1500-036, -qsuppress=cmpmsg Suppresses the message with the message number specified. Suppresses informational, language-level, and warning messages. This option sets -qflag=e:e.