Compilers: IBM XL C/C++ Enterprise Edition Version 8.0
Compilers: IBM XL Fortran Enterprise Edition Version 10.1
Compilers: IBM XL C/C++ Enterprise Edition Version 9.0
Compilers: IBM XL Fortran Enterprise Edition Version 11.1
Compilers: IBM XL C/C++ Enterprise Edition Version 10.1
Compilers: IBM XL Fortran Enterprise Edition Version 12.1
Last updated: 04-Aug-2008
Selecting one of the following will take you directly to that section:
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
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 Performs additional optimizations that are memory intensive, compile-time intensive, and may change the semantics of the program slightly, unless -qstrict is specified. We recommend these optimizations when the desire for run-time speed improvements outweighs the concern for limiting compile-time resources. The optimizations provided include:
-O3 is equivalent to the following flags
-O2 Performs a set of optimizations that are intended to offer improved performance without an unreasonable increase in time or storage that is required for compilation including:
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
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 inlines glue code that optimizes external function calls when compiling.
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.
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=
Determines whether the compiler provides the
Fortran 90 or the Fortran 95 level of support for
certain aspects of the language. 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.
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.
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
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.
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.
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.
Turns off aggressive optimizations which have the
potential to alter the semantics of your program.
-qstrict sets -qfloat=nofltint:norsqrt. -qnostrict
sets -qfloat=rsqrt. This option is only valid with
-O2 or higher optimization levels.
Default:
o -qnostrict at -O3 or higher.
o -qstrict otherwise.
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
Permits the usage of "//" to introduce a comment that lasts until the end of the current source line, as in C++.
Invoke the IBM XL C compiler. 32-bit binaries are produced by default.
Invoke the IBM XL C++ compiler. 32-bit binaries are produced by default.
Invoke the IBM XL Fortran compiler. 32-bit binaries are produced by default.
Allows most any c dialect.
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.
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.
Specifies the size of the compiler's internal program storage areas, in bytes.
Causes the compiler to output a traceback if it abends.
Suppresses the message with the message number specified.
Suppresses informational, language-level, and warning messages. This option sets -qflag=e:e.
The fdpr command (Feedback Directed Program Restructuring) is a performance-tuning utility that may help
improve the execution time and the real memory utilization of user-level application programs. The fdpr program
optimizes the executable image of a program by collecting information on the behavior of the program while the
program is used for some typical workload, and then creating a new version of the program that is optimized for
that workload. The new program generated by fdpr typically runs faster and uses less real memory.
Usage:
fdpr [options] -p program [-x invocation]
where -p specifies the input program, in a form of executable, shared object
or archive file
-x specifies how to invoke the program
[options] can be one or more of the following:
Action Options:
-123 Specifies which actions/phases to run, where:
-1 generates instrumented program for profile gathering
-2 runs the instrumented program and updates profile data (requires -x <invocation>)
-3 generates optimized program
Default is set to run all three phases (-123)
-a/--action [action] Specifies customized actions
where [action] can be one of the following:
anl analyze program
instr generate instrumented program for profile gathering (same as -1)
opt generate optimized program (same as -3)
check_sign check fdpr signature in the input program
Analysis Options:
-esa, --extra-safe-analysis
Do not attempt to analyze unconventional CSects
containing hand-written assembly code (when used, must
be specified at both instrumentation and optimization
phases)
-aawc/-noaawc, --analyze-assembly-written-csects/--noanalyze-assembly-written-csects
Analyze/Do not analyze objects written in assembly (when
used/not used, must be specified at both
instrumentation and optimization phases). The default
is set to analyze assembly written modules
-iinf, --ignore-info Ignore .info sections produced with the -qfdpr option
during compile time
-fca, --funcsect-analysis
Apply special analysis for an input executable that was
compiled with the -qfuncsect compiler option
-ff <string>, --file-format <string>
Input file format: can be LM (load module) or PO
(program object)
Instrumentation Options:
-ei, --embedded-instrumentation
Perform embedded instrumentation. Profile will be
collected into global variables
-infp, --ignore-not-found-procedures
Ignore not found procedures
-fd <Fdesc>, --file-descriptor <Fdesc>
Set file descriptor number to be used when opening the
profile file that is mapped to the shared memory area
during profiling. The default of <Fdesc> is set to the
maximum-allowed open files
-M <addr>, --profile-map <addr>
Set shared memory segment address for profiling.
Alternate shared memory addresses are needed when the
instrumented program application creates a conflict
with the shared-memory addresses preserved for the
profiling. Typical alternative values are 0x40000000,
0x50000000, ... up to 0xC0000000. Default is set to
0x3000000
-ri/-nori, --register-instrumentation/--noregister-instrumentation
Instrument/Do not instrument the input program file to
collect profile information about indirect branches via
registers (applicable only with the -a instr option).
The default is set to collect the profile information
-sfp/-nosfp, --save-floating-point-registers/--nosave-floating-point-registers
Save/Do not save floating point registers in
instrumented code (the default is set to save floating
point registers)
-ipnvr, --instrumentation-preserve-non-volatile-registers
Preserve non volatile registers while calling stubs
-iplr/-noiplr, --instrumentation-preserve-link-register/--noinstrumentation-preserve-link-register
Preserve/Do not preserve link register while calling
stubs
-ipcr/-noipcr, --instrumentation-preserve-condition-register/--noinstrumentation-preserve-condition-register
Preserve/Do not preserve Condition Register while
calling stubs
-ipctr/-noipctr, --instrumentation-preserve-count-register/--noinstrumentation-preserve-count-register
Preserve/Do not preserve Count Register while calling
stubs
-ipxer/-noipxer, --instrumentation-preserve-fixed-point-exception-register/--noinstrumentation-preserve-fixed-point-exception-register
Preserve/Do not preserve Fixed-Point Exception Register
while calling stubs
-ipspr/-noipspr, --instrumentation-preserve-special-registers/--noinstrumentation-preserve-special-registers
Preserve/Do not preserve special purpose registers while
calling stubs
-ipvr/-noipvr, --instrumentation-preserve-volatile-registers/--noinstrumentation-preserve-volatile-registers
Preserve/Do not preserve volatile registers while
calling stubs. -noipvr implies -noipnvr and -nosfp
-ipe/-noipe, --instrumentation-preserve-environment/--noinstrumentation-preserve-environment
Do not preserve registers that are not overwritten while
calling stubs. -noipe implies -noipvr -noipspr
-spescr <0-127>, --spe-scratch-register <0-127>
Specify a global SPE scratch register, decreasing
instrumenation overhead, in order to minimize
possibility of local store overflow
Profile Files Options:
-af <prof_file>, --ascii-profile-file <prof_file>
Set the name of an ASCII profile file containing profile
information given by three different XML entry options:
<Simple .. >, <Cond .. > and <Reg .. > for profiling
data on regular, conditional or branch via registers
instructions accordingly
-aop, --accept-old-profile
Accept old profile file collected on previous versions
of the input program file (requires the -f flag)
-f <prof_file>, --profile-file <prof_file>
Set the profile file name. The profile file is created
during the instrumentation phase when issued with -a
instr option. The file is read by fdpr when issued with
the -a opt or -a anl options. Note, the profile file is
updated automatically when running the instrumented
program
-spefdir <directory>, --spe-profile-directory <directory>
Set the directory where SPE profiles are located in
integrated mode (see -cell). Default is where <program>
is located
Optimization Options:
-A <num_of_bytes>, --align-code <num_of_bytes>
Align program code according to given <num_of_bytes>
-bldcg, --build-dcg Build a DCG (data connectivity graph) for enhanced data
reordering (applicable only with the -RD flag)
-btcar, --branch-table-csect-anchor-removal
Eliminate load instructions related to the usage of
branch tables in the code
-cRD, --conservativeRD
Perform conservative static data reordering by packing
all frequently referenced static variables together
-cbtd, --convert-bss-to-data
Convert bss section into a data section (useful for more
aggressive tocload and RD optimizations)
-dce, --dead-code-elimination
Eliminate instructions related to unused local variables
within frequently executed functions (useful mainly
after applying function inlining optimization)
-dp, --data-prefetch Insert dcbt instructions to improve data-cache
performance
-dpht <threshold>, --data-placement-hotness-threshold <threshold>
Set data placement algorithm hotness threshold between
(0,1), where 0 will reorder the static variables in
large groups based on the control flow, and 1 reorders
the variables in very small groups based on their
access frequency. (applicable only with the -RD flag)
-dpnf <factor>, --data-placement-normalization-factor <factor>
Set data placement algorithm normalization factor
between (0,1), where 0 causes static variables to be
reordered regardless of their size, and 1 locates only
small sized variables first. (applicable only with the
-RD flag)
-ece, --epilog-code-eliminate
Reduce code size by grouping common instructions in
functions' epilogs, into a single unified code
-fc, --function-cloning
Enable only function cloning phase during function
inlining optimizations (applicable only with function
inlining flags: -i, -si, -ihf, -isf, -shci)
-hr, --hco-reschedule Relocate instructions from frequently executed code to
rarely executed code areas, when possible
-hrf <factor>, --hco-resched-factor <factor>
Set the aggressiveness of the -hr optimization option
according to a factor value between (0,1), where 0 is
the least aggressive factor (applicable only with the
-hr option)
-i, --inline Same as --selective-inline with --inline-small-funcs 12
-ihf <pct>, --inline-hot-functions <pct>
Inline all function call sites to functions that have a
frequency count greater than the given <pct> frequency
percentage
-isf <size>, --inline-small-funcs <size>
Inline all functions that are smaller or equal to the
given <size> in bytes
-kr, --killed-registers
Eliminate stores and restores of registers that are
killed (overwritten) after frequently executed function
calls
-lap, --load-address-propagation
Eliminate load instructions of variables' addresses by
re-using pre-loaded addresses of adjacent variables
-las, --load-after-store
Add NOP instructions to place each load instruction
further apart following a store instruction that
reference the same memory address
-lro, --link-register-optimization
Eliminate saves and restores of the link register in
frequently-executed functions
-lu <aggressiveness_factor>, --loop-unroll <aggressiveness_factor>
Unroll short loops containing of one to several basic
blocks according to an aggressiveness factor between
(1,9), where 1 is the least aggressive unrolling option
for very hot and short loops
-lun <unrolling_number>, --loop-unrolling-number <unrolling_number>
Set the number of unrolled iterations in each unrolled
loop. The allowed range is between (2,50). Default is
set to 2. (applicable only with the -lu flag)
-O Switch on basic optimizations only. Same as -RC -nop -bp
-bf
-O2 Switch on less aggressive optimization flags. Same as -O
-hr -pto -isf 8 -tlo -kr
-O3 Switch on aggressive optimization flags. Same as -O2 -RD
-isf 12 -si -dp -lro -las -vro -btcar -lu 9 -rt 0
-O4 Switch on aggressive optimization flags together with
aggressive function inlining. Same as -O3 -sidf 50 -ihf
20
-pc, --preserve-csects
Preserve CSects' boundaries in reordered code
-pca, --propagate-constant-area
Relocate the constant variables area to the top of the
code section when possible
-pfb, --preserve-first-bb
Preserve original location of the entry point basic
block in program
-pp, --preserve-functions
Preserve functions' boundaries in reordered code
-pr/-nopr, --ptrgl-r11/--noptrgl-r11
Perform/Do not perform removal of R11 load instruction
in _ptrgl csect (the default is to perform the
optimization)
-pto, --ptrgl-optimization
Perform optimization of indirect call instructions via
registers by replacing them with conditional direct
jumps
-ptosl <limit_size>, --ptrgl-optimization-size-limit <limit_size>
Set the limit of the number of conditional statements
generated by -pto optimization. Allowed values are
between 1..100. Default value set to 3. (applicable
only with the -pto flag)
-ptoht <heatness_threshold>, --ptrgl-optimization-heatness-threshold <heatness_threshold>
Set the frequency threshold for indirect calls that are
to be optimized by -pto optimization. Allowed range
between 0..1. Default is set to 0.8. (applicable only
with -pto flag)
-rcaf <aggressiveness_factor>, --reorder-code-aggressivenes-factor <aggressiveness_factor>
Set the aggressiveness of code reordering optimization.
Allowed values are 1 and 2, where 1 is less aggressive.
Default is set to 1. (applicable only with the -RC
flag)
-rcctf <termination_factor>, --reorder-code-chain-termination-factor <termination_factor>
Set the threshold fraction which determines when to
terminate each chain of basic blocks during code
reordering. Allowed input range is between 0.0 to 1.0
where 0.0 generates long chains and 1.0 creates single
basic block chains. Default is set to 0.05. (applicable
only with the -RC flag)
-rccrf <reversal_factor>, --reorder-code-condition-reversal-factor <reversal_factor>
Set the threshold fraction which determines when to
enable condition reversal for each conditional branch
during code reordering. Allowed input range is between
0.0 to 1.0 when 0.0 tries to preserve original
condition direction and 1.0 ignores it. Default is set
to 0.8 (applicable only with the -RC flag)
-RD, --reorder-data Perform static data reordering
-rmte, --remove-multiple-toc-entries
Remove multiple TOC entries pointing to the same
location in the input program file
-rt <removal_factor>, --reduce-toc <removal_factor>
Perform removal of TOC entries according to a removal
factor between (0,1), where 0 removes non-accessed TOC
entries only, and 1 removes all possible TOC entries
-sdp <aggressiveness_factor>, --stride-data-prefetch <aggressiveness_factor>
Perform data prefetching within frequently executed
loops based on stride analysis, according to an
aggressiveness factor between (1,9), where 1 is least
aggressive
-sdpla <iterations_number>, --stride-data-prefetch-look-ahead <iterations_number>
Set the number of iterations for which data is
prefetched into the cache ahead of time. Default value
is set to 4 iterations. (applicable only with the -sdp
flag)
-sdpms <stride_min_size>, --stride-data-prefetch-min-size <stride_min_size>
Set the minimal stride size in bytes, for which data
will be considered as a candidate for prefetching.
Default value is set to 128 bytes. (applicable only
with the -sdp flag)
-shci <pct>, --selective-hot-code-inline <pct>
Perform selective inlining of functions in order to
decrease the total execution counts
-si, --selective-inline
Perform selective inlining of dominant hot function
calls
-sll <Lib1:Prof1,...,LibN:ProfN>, --static-link-libraries <Lib1:Prof1,...,LibN:ProfN>
Statically link hot code from specified dynamically
linked libraries to the input program. The parameter
consists of comma-separated list of libraries and their
profiles. IMPORTANT: licensing rights of specified
libraries should be observed when applying this copying
optimization
-sllht <hotness_threshold>, --static-link-libraries-hotness-threshold <hotness_threshold>
Set hotness threshold for the --static-link-libraries
optimization. The allowed input range is between 0
(least aggressive) to 1, or -1, which does not require
profile and selects all code that might be called by
the input program from the given libraries. Default is
0.5
-sidf <percentage_factor>, --selective-inline-dominant-factor <percentage_factor>
Set a dominant factor percentage for selective inline
optimization. The allowed range is between (0,100).
Default is set to 80 (applicable only with the -si and
-pbsi flags)
-siht <frequency_factor>, --selective-inline-hotness-threshold <frequency_factor>
Set a hotness threshold factor percentage for selective
inline optimization to inline all dominant function
calls that have a frequency count greater than the
given frequency percentage. Default is set to 100
(applicable only with the -si -pbsi flags)
-so, --stack-optimization
Reduce the stack frame size of functions which are
called with a small number of arguments
-stf, --stack-flattening
Merge the stack frames of inlined functions with the
frames of the calling functions
-tb, --preserve-traceback-tables
Force the restructuring of traceback tables in reordered
code. If -tb option is omitted, traceback tables are
automatically included only for C++ applications which
use the Try & Catch mechanism
-rtb, --remove-traceback-tables
Remove traceback tables in reordered code
-tlo, --tocload-optimization
Replace each load instruction that references the TOC
with a corresponding add-immediate instruction via the
TOC anchor register, when possible
-ucde, --unreachable-code-data-elimination
Remove unreachable code and non-accessed static data
-vro, --volatile-registers-optimization
Eliminate stores and restores of non-volatile registers
in frequently executed functions by using available
volatile registers
Output Options:
-d, --disassemble-text
Print the disassembled text section of the output
program into <output_file>.dis_text file
-dap, --dump-ascii-profile
Dump profile information in ASCII format into
<program>.aprof (requires the -f flag)
-db, --disassemble-bss
Print the disassembled bss section of the output program
into <output_file>.dis_bss file
-dd, --disassemble-data
Print the disassembled data section of the output
program into <output_file>.dis_data file
-diap, --dump-initial-ascii-profile
Dump initial profile information in ASCII format into
<program>.aprof.init (requires the -f flag)
-dim, --dump-instruction-mix
Dump instruction mix statistics based on gathered
profile information
-dm, --dump-mapper Print a map of basic blocks and static variables with
their respective new -> old addresses into a
<program>.mapper file
-o <output_file>, --output-file <output_file>
Set the name of the output file. The default
instrumented file is <program>.instr. The default
optimized file is <program>.fdpr
-pif, --print-inlined-funcs
Print the list of inlined functions along with their
corresponding calling functions, in ASCII format into a
<program>.inlined file (requires the -si or -i or -isf
flags)
-ppcf, --print-prof-counts-file
Print the profiling counters in ASCII format into a
<program>.counts file (requires the -f flag)
-simo, --single-input-multiple-outputs
Optimize in parallel into multiple outputs as specified
by option sets read from stdin
-sf, --strip-file Strip the optimized output file
-spe, --speculative-profile-enhancement
Complements given partial profile information of basic
blocks' frequencies, i.e., transforms basic block
profile to a complete edge profile
-spedir <directory>, --spe-directory <directory>
Set the directory into which SPE executables will be
extracted and from which they will be encapsulated
-enc, --encapsulate Encapsulate SPE executables present in the PPE input
(see --spe-directory)
General Options:
-gro, --generate-relinkable-output
Generate relinkable output
-h, --help Print online usage help
-m <machine-model>, --machine <machine-model>
Generate code for the specified machine model. Target
machine can be one of the following models: power2,
power3, ppc405, ppc440, power4, ppc970, power5, power6,
spe, spe_edp. Default is set to no machine
-q, --quiet Set quiet output mode, suppressing informational
messages
-st <stat_file>, --statistics <stat_file>
Output statistics information to <stat_file>. If
<stat_file> is '-', output goes to standard output. See
--verbose for the default
-V, --version Print version
-v <level>, --verbose <level>
Set verbose output mode level. When set, various
statistics about the target optimized program are
printed into file <program>.stat. Allowed level range
is between (0,3). Default is set to 0
-cell, --cell-supervisor
Integrated PPE/SPE processing. Perform SPE extraction,
processing, and encapsulation automatically prior to
PPE processing
-armember For archive files - list of archive members to be
optimized, if -armember is not specified, all members
will be optimized