PGI 7.1-0 and PathScale 3.0 Compilers for Linux. Optimization, Compiler, and Other flags for use by SPEC CPU2006

Use C99 language features.

Chooses generally optimal flags for the target platform. As of the PGI 7.0 release, the flags "-fast" and "-fastsse" are equivlent for 64-bit compilations. For 32-bit compilations "-fast" does not include "-Mscalasse", "-Mcache_align", or "-Mvect=sse".

Specify the basic level of optimization desired.
The options can be one of the following:

0    Turn off all optimizations.

1    Turn on local optimizations that can be done quickly. Do peephole optimizations and instruction scheduling.

2    Turn on extensive optimization. This is the default.
The optimizations at this level are generally conservative, in the sense that they are virtually always beneficial and avoid changes which affect such things as floating point accuracy. In addition to the level 1 optimizations, do inner loop unrolling, if-conversion, two passes of instruction scheduling, global register allocation, dead store elimination, instruction scheduling across basic blocks, and partial redundancy elimination.

3    Turn on aggressive optimization.
The optimizations at this level are distinguished from -O2 by their aggressiveness, generally seeking highest-quality generated code even if it requires extensive compile time. They may include optimizations that are generally beneficial but may hurt performance.
This includes but is not limited to turning on the Loop Nest Optimizer, -LNO:opt=1, and setting -OPT:roundoff=1:IEEE_arithmetic=2:Olimit=9000:reorg_common=ON.

s    Specify that code size is to be given priority in tradeoffs with execution time.

Do not set ERRNO after calling math functions that are executed with a single instruction, e.g. sqrt. A program that relies on IEEE exceptions for math error handling may want to use this flag for speed while maintaining IEEE arithmetic compatibility. This is implied by -Ofast. The default is -fmath-errno.

(For C++ only) -fexceptions enables exception handling. This is the default. -fno-exceptions disables exception handling.

-ffast-math improves FP speed by relaxing ANSI & IEEE rules. -fno-fast-math tells the compiler to conform to ANSI and IEEE math rules at the expense of speed. -ffast- math implies -OPT:IEEE_arithmetic=2 -fno-math-errno. -fno-fast-math implies -OPT:IEEE_arithmetic=1 -fmath-errno.

-OPT:div_split=(ON|OFF)
Enable or disable changing x/y into x*(recip(y)). This is OFF by default, but enabled by -OPT:Ofast or -OPT:IEEE_arithmetic=3. This transformation generates fairly accurate code.

-OPT:Olimit=N
Disable optimization when size of program unit is > N. When N is 0, program unit size is ignored and optimization process will not be disabled due to compile time limit. The default is 0 when -OPT:Ofast is specified, 9000 when -O3 is specified; otherwise the default is 6000.

Equivalent to -O3 -ipa -OPT:Ofast -fno-math-errno -ffast-math.
Use optimizations selected to maximize performance. Although the optimizations are generally safe, they may affect floating point accuracy due to rearrangement of computations.

NOTE: -Ofast enables -ipa (inter-procedural analysis), which places limitations on how libraries and .o files are built.

-fb_create <path>
Used to specify that an instrumented executable program is to be generated. Such an executable is suitable for producing feedback data files with the specified prefix for use in feedback-directed optimization (FDO). The commonly used prefix is "fbdata".
This is OFF by default.

During the training run, the instrumented executable produces information regarding execution paths and data values, but does not generate information by using hardware performance counters.

-fb_opt <prefix for feedback data files>
Used to specify feedback-directed optimization (FDO) by extracting feedback data from files with the specified prefix, which were previously generated using -fb-create. The commonly used prefix is "fbdata". The same optimization flags should be used for both the -fb-create and fb_opt compile steps. Feedback data files created from executables compiled with different optimization flags may give checksum errors.
FDO is OFF by default.

During the -fb_opt compilation phase, information regarding execution paths and data values are used to improve the information available to the optimizer. FDO enables some optimizations which are only performed when the feedback data file is available. The safety of optimizations performed under FDO is consistent with the level of safety implied by the other optimization flags (outside of fb_create and fb_opt) specified on the compile and link lines.

Invoke inter-procedural analysis (IPA). Specifying this option is identical to specifying -IPA or -IPA:. Default settings for the individual IPA suboptions are used.

-CG:load_exe=N : Specify the threshold for subsuming a memory load operation into the operand of an arithmetic instruction. The value of 0 turns off this subsumption optimization. If N is 1, this subsumption is performed only when the result of the load has only one use. This subsumption is not performed if the number of times the result of the load is used exceeds the value N, a non-negative integer.
If the ABI is 64-bit and the language is Fortran, the default for N is 2, otherwise the default is 1.

-CG:movnti=N : Convert ordinary stores to non-temporal stores when writing memory blocks of size larger than N KB. When N is set to 0, this transformation is avoided. The default value is 120 (KB).

-INLINE:aggressive : Tell the compiler to be more aggressive about inlining. The default is -INLINE:aggressive=OFF.

-IPA:plimit=N : This option stops inlining into a specific subprogram once it reaches size N in the intermediate representation. Default is 2500.

Specify options and transformations performed on loop nests by the Loop Nest Optimizer (LNO). The -LNO options are enabled only if -O3 is also specified on the pathf95 command line.

-LNO:blocking : Enable or disable the cache blocking transformation. The default is ON.

-LNO:full_unroll,fu=N : Fully unroll loops with trip_count <= N inside LNO. N can be any integer between 0 and 100. The default value for N is 5. Setting this flag to 0 disables full unrolling of small trip count loops inside LNO.

-LNO:fission=N : Perform loop fission. N can be one of the following:
0 = Disable loop fission (default)
1 = Perform normal loop fission as necessary
2 = Specify that fission be tried before fusion

Because -LNO:fusion is on by default, turning on fission without turning off fusion may result in their effects being nullified. Ordinarily, fusion is applied before fission. Specifying -LNO:fission=2 will turn on fission and cause it to be applied before fusion.

-LNO:ignore_feedback=(on|off|0|1) : If the flag is ON then feedback information from the loop annotations will be ignored in LNO transformations. The default is OFF.

Enable or disable moving loop-invariant expressions out of loops. The default is ON.

This option controls the LNO optimization level. The options can be one of the following:
0 = Disable nearly all loop nest optimizations.
1 = Perform full loop nest transformations. This is the default.

-LNO:ou_prod_max=N : This option indicates that the product of unrolling of the various outer loops in a given loop nest is not to exceed N, where N is a positive integer. The default is 16.

-LNO:prefetch_ahead=N : Prefetch N cache line(s) ahead. The default is 2.

-LNO:prefetch=(0|1|2|3) : This option specifies the level of prefetching.

0 = Prefetch disabled.

1 = Prefetch is done only for arrays that are always referenced in each iteration of a loop.

2 = Prefetch is done without the above restriction. This is the default.

3 = Most aggressive.

-LNO:simd=(0|1|2) : This option enables or disables inner loop vectorization.

0 = Turn off the vectorizer.

1 = (Default) Vectorize only if the compiler can determine that there is no undesirable performance impact due to sub-optimal alignment. Vectorize only if vectorization does not introduce accuracy problems with floating-point operations.

2 = Vectorize without any constraints (most aggressive).

Compile for 32-bit ABI, also known as x86 or IA32.

The -OPT: option group controls miscellaneous optimizations. These options override defaults based on the main optimization level.

-OPT:alias=<name>
Specify the pointer aliasing model to be used. By specifying one or more of the following for <name>, the compiler is able to make assumptions throughout the compilation:

typed
Assume that the code adheres to the ANSI/ISO C standard which states that two pointers of different types cannot point to the same location in memory. This is ON by default when -OPT:Ofast is specified.

restrict
Specify that distinct pointers are assumed to point to distinct, non-overlapping objects. This is OFF by default.

disjoint
Specify that any two pointer expressions are assumed to point to distinct, non-overlapping objects. This is OFF by default.

-OPT:IEEE_arithmetic,IEEE_arith,IEEE_a=(1|2|3)
Specify the level of conformance to IEEE 754 floating pointing roundoff/overflow behavior. The options can be one of the following:

1 Adhere to IEEE accuracy. This is the default when optimization levels -O0, -O1 and -O2 are in effect.

2 May produce inexact result not conforming to IEEE 754. This is the default when -O3 is in effect.

3 All mathematically valid transformations are allowed.

-OPT:malloc_alg=(0|1)
Select an alternate malloc algorithm which may improve speed. The compiler adds setup code in the C/C++/Fortran "main" function to enable the chosen algorithm. The default is 0.

-OPT:Ofast
Use optimizations selected to maximize performance. Although the optimizations are generally safe, they may affect floating point accuracy due to rearrangement of computations. This effectively turns on the following optimizations: -OPT:ro=2:Olimit=0:div_split=ON:alias=typed.

-OPT:roundoff,ro=(0|1|2|3)
Specify the level of acceptable departure from source language floating-point, round-off, and overflow semantics. The options can be one of the following:

0 = Inhibit optimizations that might affect the floating-point behavior. This is the default when optimization levels -O0, -O1, and -O2 are in effect.

1 = Allow simple transformations that might cause limited round-off or overflow differences. Compounding such transformations could have more extensive effects. This is the default when -O3 is in effect.

2 = Allow more extensive transformations, such as the reordering of reduction loops. This is the default level when -OPT:Ofast is specified.

3 = Enable any mathematically valid transformation.

-OPT:unroll_size=N
Set the ceiling of maximum number of instructions for an unrolled inner loop. If N=0, the ceiling is disregarded. The default is 40.

-OPT:unroll_times_max=N
Unroll inner loops by a maximum of N. The default is 4.

-L/cpu2006/work/cpu2006/SmartHeap -lsmartheap
when used as an EXTRA_CLIB or EXTRA_CXXLIB variable, results in linking with MicroQuill's SmartHeap 8 (32-bit) library for Linux. This is a library that optimizes calls to new, delete, malloc and free.

The -WOPT: Specifies options that affect the global optimizer. The options are enabled at -O2 or above.

-WOPT:aggstr=N
This controls the aggressiveness of the strength reduction optimization performed by the scalar optimizer, in which induction expressions within a loop are replaced by temporaries that are incremented together with the loop variable. When strength reduction is overdone, the additional temporaries increase register pressure, resulting in excessive register spills that decrease performance. The value specified must be a positive integer value, which specifies the maximum number of induction expressions that will be strength-reduced across an index variable increment. When set at 0, strength reduction is only performed for non-trivial induction expressions. The default is 11.

-WOPT:retype_expr=(ON|OFF)
Enables the optimization in the compiler that converts 64-bit address computation to use 32-bit arithmetic as much as possible. Default is OFF.

Disable C++ exception handling support.

Disable C++ run time type information support.

Generate zero-overhead C++ exception handlers.

Inline functions declared with the inline keyword.

Disable inlining of functions declared with the inline keyword.

Align "unconstrained" data objects of size greater than or equal to 16 bytes on cache-line boundaries. An "unconstrained" object is a variable or array that is not a member of an aggregate structure or common block, is not allocatable, and is not an automatic array. On by default on 64-bit Linux systems.

Set SSE to flush-to-zero mode; if a floating-point underflow occurs, the value is set to zero.

Treat denormalized numbers as zero. Included with "-fast" on Intel based systems. For AMD based systems, "-Mdaz" is not included by default with "-fast".

Generate code to set up a stack frame.

Eliminates 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.

Instructs the compiler to use relaxed precision in the calculation of floating-point reciprocal square root (1/sqrt). Can result in improved performance at the expense of numerical accuracy.

Instructs the compiler to use relaxed precision in the calculation of floating-point square root. Can result in improved performance at the expense of numerical accuracy.

Instructs the compiler to use relaxed precision in the calculation of floating-point division. Can result in improved performance at the expense of numerical accuracy.

Instructs the compiler to allow floating-point expression reordering, including factoring. Can result in improved performance at the expense of numerical accuracy.

Instructs the compiler to use relaxed precision in the calculation of some intrinsic functions. Can result in improved performance at the expense of numerical accuracy. The default on an AMD system is "-Mfprelaxed=rsqrt,order". The default on an Intel system is "-Mfprelaxed=rsqrt,sqrt,div,order"

Instructs the compiler to use low-precision approximation in the calculation of reciprocal square root (1/sqrt). Can result in improved performance at the expense of numerical accuracy.

Instructs the compiler to use low-precision approximation in the calculation of square root. Can result in improved performance at the expense of numerical accuracy.

Instructs the compiler to use low-precision approximation in the calculation of divides. Can result in improved performance at the expense of numerical accuracy.

Instructs the compiler to perform low-precision approximation in the calculation of floating-point division, square-root, and reciprocal square root. Can result in improved performance at the expense of numerical accuracy.

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

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

Use the prefetchnta instruction.

Use the prefetch instruction.

Use the prefetcht0 instruction.

Use the AMD-specific prefetchw instruction.

Enable generation of prefetch instructions on processors where they are supported.

Disable generation of prefetch instructions.

Use SSE/SSE2 instructions to perform scalar floating-point arithmetic on targets where these instructions are supported.

Do not use SSE/SSE2 instructions to perform scalar floating-point arithmetic; use x87 operations instead.

Instructs the compiler to extend the sign bit that is set as a result of an object's conversion from one data type to an object of a larger signed data type.

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.

Allow expression re-association; specifying this sub-option can increase opportunities for loop-carried redundancy elimination.

Disable expression re-association.

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

Disable loop-carried redundancy elimination.

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

Generate profile-feedback instrumentation (PFI); this includes extra code to collect run-time statistics and dump them to a trace file for use in a subsequent compilation. PFI gathers information about a program's execution and data values but does not gather information from hardware performance counters. PFI does gather data for optimizations which are unique to profile-feedback optimization.

Enable profile-feedback optimizations.

Interprocedural Analysis option: Recognize when targets of pointer dummy are aligned.

Interprocedural Analysis option: Disable recognizition when targets of pointer dummy are aligned.

Interprocedural Analysis option: Remove arguments replaced by -Mipa=ptr,const

Interprocedural Analysis option: Do not remove arguments replaced by -Mipa=ptr,const

Interprocedural Analysis option: Generate call graph information for pgicg tool.

Interprocedural Analysis option: Do not generate call graph information for pgicg tool.

Interprocedural Analysis option: Enable interprocedural constant propagation.

Interprocedural Analysis option: Disable interprocedural constant propagation.

Interprocedural Analysis option: Used with -Mipa=inline to specify functions which should not be inlined.

Instructs the compiler to perform interprocedural analysis. Equivalant to -Mipa=align,arg,const,f90ptr,shape,globals,libc,localarg,ptr,pure.

Interprocedural Analysis option: Force all objects to recompile regardless whether IPA information has changed.

Interprocedural Analysis option: Optimize references to global values.

Interprocedural Analysis option: Do not optimize references to global values.

Interprocedural Analysis option: Automatically determine which functions to inline, limit to n levels. IPA-based function inlining is performed from leaf routines upward.

Interprocedural Analysis option: Automatically determine which functions to inline. IPA-based function inlining is performed from leaf routines upward.

Interprocedural Analysis option: Allow inlining of routines from libraries.

Interprocedural Analysis option: Do not inline routines from libraries.

Interprocedural Analysis option: Used to optimize calls to certain functions in the system standard C library, libc.

Interprocedural Analysis option: Allow recompiling and optimization of routines from libraries using IPA information.

Interprocedural Analysis option: Don't optimize routines in libraries.

Interprocedural Analysis option: -Mipa=arg plus externalizes local pointer targets.

Interprocedural Analysis option: -Mipa=arg plus externalizes local pointer targets.

Interprocedural Analysis option: Do not externalize local pointer targets.

Interprocedural Analysis option: Enable pointer disambiguation across procedure calls.

Interprocedural Analysis option: Disable pointer disambiguation.

Interprocedural Analysis option: Fortran 90/95 Pointer disambiguation across calls.

Interprocedural Analysis option: Disable Fortran 90/95 pointer disambiguation

Interprocedural Analysis option: Pure function detection.

Interprocedural Analysis option: Disable pure function detection.

Interprocedural Analysis option: Allows inlining in Fortran even when array shapes do not match.

Interprocedural Analysis option: Perform Fortran 90 array shape propagation.

Interprocedural Analysis option: Disable Fortran 90 array shape propagation.

Interprocedural Analysis option: Remove functions that are never called.

Interprocedural Analysis option: Do not remove functions that are never called.

Enable Interprocedural Analysis.

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

Instructs the parallelizer to generate alternate serial code for parallelized loops. With arguments, the serial altcode is executed whenever the loop count is less than or equal to n.

Always execute the parallelized version of a loop regardless of the loop count.

Disables parallelization of loops with reductions.

Assume loops containing calls are safe to parallelize and allows loops containing calls to be 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.

Do not assume loops containing calls are safe to parallelize.

Parallelize with block distribution. Contiguous blocks of iterations of a parallelizable loop are assigned to the available processors.

Parallelize with cyclic distribution. The outermost parallelizable loop in any loop nest is parallelized. If a parallelized loop is innermost, its iterations are allocated to processors cyclically. For example, if there are 3 processors executing a loop, processor 0 performs iterations 0, 3, 6, etc.; processor 1 performs iterations 1, 4, 7, etc.; and processor 2 performs iterations 2, 5, 8, etc.

Enable parallelization of innermost loops.

Disable parallelization of innermost loops.

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.

Instructs the inliner to inline the functions within the library filename.ext.

Instructs the inliner to inline all eligible functions except func, a function in the source text. Multiple functions can be listed, comma-separated.

Instructs the inliner to inline function func.

Allows inlining in Fortran even when array shapes do not match.

Instructs the inliner to inline functions with n or fewer statements.

Instructs the inliner to perform n levels of inlining.

Instructs the inliner to perform 1 level of inlining.

Disable constant propagation from assertions derived from equality conditionals.

Link with the huge page runtime library and allocate a maximum n huge pages.

Link with the huge page runtime library.

Link with the huge page runtime library. Use huge pages for an executable's .BSS section.

Adds a call to the routine "mallopt" in the main routine. This option can have a dramatic impact on the performance of programs that dynamically allocate memory, especially for those which have a few large mallocs. To be effective, this switch must be specified when compiling the file containing the Fortran, C, or C++ main routine.

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

Instructs the compiler that arrays and pointers are treated with the same copyin and copyout semantics as Fortran dummy arguments.

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

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

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

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

Instructs the C/C++ compiler to override data dependencies between pointers of a given storage class.

"-Munroll=c:n" instructs the compiler to completely unroll loops with a constant loop count of less than or equal to n where n is a supplied constant value. If no constant value is given, then a default of 4 is used.

"-Munroll=n:n" instructs the compiler to unroll loops n times where n is a supplied constant value. If no constant value is given, then a default of 4 is used.

"-Munroll=m:n" instructs the compiler to unroll loops with multiple blocks n times where n is a supplied constant value. If no constant value is given, then a default of 4 is used.

Instructs the compiler to unroll loops with multiple blocks using the default value of 4 times

Invokes the loop unroller.

Disable loop unrolling.

Don't check dependence relations for vector or parallel code.

Allow parallelization of loops with conditional scalar assignments.

Generate code to check for zero loop increments.

Enable an optional post-pass instruction scheduling.

Disable an optional post-pass instruction scheduling.

Disable automatic vector pipelining.

Instructs the vectorizer to generate alternate code 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
• Altcode base on array alignments calculated dynamically at runtime.

The compiler also determines suitable loop count and array alignment conditions for executing the altcode.

Disables alternate code generation for vectorized loops.

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

Instructs the vectorizer to disable associativity conversions.

Instructs the vectorizer, when performing cache tiling optimizations, to assume a cache size of n. The default size is n=262144.

Instructs the vectorizer to enable loop fusion.

Instructs the vectorizer to disable vectorization of indirect array references.

Instructs the vectorizer to enable idiom recognition.

Instructs the vectorizer to disable idiom recognition.

Generate vector loops 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 exceed a certain threshold.

Instructs the vectorizer to generate prefetch instructions.

Instructs the vectorizer to search for vectorizable loops and, where possible, make use of SSE, SSE2, and prefetch instructions.

Enable automatic vector pipelining.

Disables -Ktrap=fp.

-Ktrap is only processed by the compilers when compiling main functions' programs. The options inv, denorm, divz, ovf, unf, and inexact correspond to the processor's exception mask bits invalid operation, denormalized operand, divide-by-zero, overflow, underflow, and precision, respectively. Normally, the processor's exception mask bits are on (floating-point exceptions are masked the processor recovers from the exceptions and continues). If a floating-point exception occurs and its corresponding mask bit is off (or unmasked ), execution terminates with an arithmetic exception (C's SIGFPE signal). -Ktrap=fp is equivalent to -Ktrap=inv,divz,ovf.

Enable long branches.

Link with the AMD Core Math Library. Available from www.amd.com

Use the -mp option to instruct the compiler to interpret user-inserted OpenMP shared-memory parallel programming directives and generate an executable file which will utilize multiple processors in a shared-memory parallel system. When used strictly as a linker flag, the PGI OpenMP runtime will be linked and users can use the environment variables MP_BIND and MP_BLIST to bind a serial program to a CPU.

The align sub-option to -mp forces loop iterations to be allocated to OpenMP processes using an algorithm that maximizes alignment of vector sub-sections in loops that are both parallelized and vectorized for SSE. This can improve performance in program units that include many such loops. It can result in load-balancing problems that significantly decrease performance in program units with relatively short loops that contain a large amount of work in each iteration.

The numa suboption to -mp uses libnuma on systems where it is available.

The nonuma suboption to -mp tells the driver to not link with libnuma.

(For use only on 64-bit Linux targets) Generate code for the medium memory model in the linux86-64 execution environment. The default small memory model of the linux86-64 environment limits the combined area for a user's object or executable to 1GB, with the Linux kernel managing usage of the second 1GB of address for system routines, shared libraries, stacks, etc. Programs are started at a fixed address, and the program can use a single instruction to make most memory references. The medium memory model allows for larger than 2GB data areas, or .bss sections. Program units compiled using either -mcmodel=medium or -fpic require additional instructions to reference memory. The effect on performance is a function of the data-use of the application. The -mcmodel=medium switch must be used at both compile time and link time to create 64-bit executables. Program units compiled for the default small memory model can be linked into medium memory model executables as long as they are compiled -fpic, or position-independent.

Enable support for 64-bit indexing and single static data objects larger than 2GB in size. This option is default in the presence of -mcmodel=medium. Can be used separately together with the default small memory model for certain 64-bit applications that manage their own memory space.

Enable dead store elimination.

Enable optimizations using ANSI C type-based pointer disambiguation.

Staticily link with the PGI runtime libraries. System libraries may still be dynamically linked.

Set the optimization level to -O2

A basic block is generated for each C statement. No scheduling is done between statements. No global optimizations are performed.

Level-one optimization specifies local optimization (-O1). The compiler performs scheduling of basic blocks as well as register allocation. This optimization level is a good choice when the code is very irregular; that is it contains many short statements containing IF statements and the program does not contain loops (DO or DO WHILE statements). For certain types of code, this optimization level may perform better than level-two (-O2) although this case rarely occurs.

The PGI compilers perform many different types of local optimizations, including but not limited to:

• Algebraic identity removal
• Constant folding
• Common subexpression elimination
• Local register optimization
• Peephole optimizations
• Redundant load and store elimination
• Strength reductions

Level-two optimization (-O2 or -O) specifies global optimization. The -fast option generally will specify global optimization; however, the -fast switch will vary from release to release depending on a reasonable selection of switches for any one particular release. The -O or -O2 level performs all level-one local optimizations as well as global optimizations. Control flow analysis is applied and global registers are allocated for all functions and subroutines. Loop regions are given special consideration. This optimization level is a good choice when the program contains loops, the loops are short, and the structure of the code is regular.

The PGI compilers perform many different types of global optimizations, including but not limited to:

• Branch to branch elimination
• Constant propagation
• Copy propagation
• Dead store elimination
• Global register allocation
• Invariant code motion
• Induction variable elimination

All level 1 and 2 optimizations are performed. In addition, this level enables more aggressive code hoisting and scalar replacement optimizations that may or may not be profitable.

Performs all level 1, 2, and 3 optimizations and enables hoisting of guarded invariant floating point expressions.

Create a Unified Binary using multiple targets.

Specify the type of the target processor as AMD64 Processor 32-bit mode.

Specify the type of the target processor as AMD64 Processor 64-bit mode.

Specify the type of the target processor as AMD64 Barcelona Processor 64-bit mode.

Specify the type of the target processor as AMD64 Barcelona Processor 32-bit mode.

Specify the type of the target processor as AMD64 Barcelona Processor 32-bit mode.

Specify the type of the target processor as Intel P7 Architecture with EM64t, 64-bit mode.

Specify the type of the target processor as Intel P7 Architecture (Pentium 4, Xeon, Centrino).

Specify the type of the target processor as Intel Core 2 EM64T or compatible architecture using 64-bit mode.

Specify the type of the target processor as Intel Core 2 or compatible architecture using 32-bit mode.

Use the unified AMD/Intel 64-bit mode.

Link using MicroQuill's SmartHeap 8 (32-bit) library for Linux. Description from Microquill:

SmartHeap is a fast (3X-100X faster than compiler-supplied libraries), portable (Windows, Linux, Solaris, HP-UX, IBM-AIX, Dec OSF Tru64, SGI Irix), reliable, ANSI-compliant malloc/operator new library. SmartHeap supports multiple memory pools, includes a fixed-size allocator, and is thread-safe. SmartHeap also includes comprehensive memory debugging APIs to detect leakage, overwrites, double-frees, wild pointers, out of memory, references to previously freed memory, and other memory errors.

CFP2006:

If -funderscoring is in effect, and the original Fortran external identifier contained an underscore, -fsecond-underscore appends a second underscore to the one added by -funderscoring. -fno-second-underscore does not append a second underscore. The default is both -funderscoring and -fsecond-underscore, the same defaults as g77 uses. -fno-second-underscore corresponds to the default policies of PGI Fortran and Intel Fortran.

Don't include Fortran main program object module.

The PGI C compiler.

The PGI C++ compiler.

The PGI Fortran 95 compiler.

Invoke the PathScale C compiler.
Also used to invoke linker for C programs.

Invoke the PathScale C++ compiler.
Also used to invoke linker for C++ programs.

Invoke the PathScale Fortran 77, 90 and 95 compilers.
Also used to invoke linker for Fortran programs and for mixed C / Fortran. pathf90 and pathf95 are synonymous.

-static: On systems that support dynamic linking, this prevents linking with the shared libraries. On other systems, this option has no effect.

Disable warning messages.

The NCPUS environment variable can be used to set the number of processes or threads used in parallel regions. The default is to use only one process or thread (serial mode). If both OMP_NUM_THREADS and NCPUS are set, the value of OMP_NUM_THREADS takes precedence. Warning: setting NCPUS to a value larger than the number of physical processors or cores in your system can cause parallel programs to run very slowly.

The MP_BIND environment variable can be set to yes or y to bind processes or threads executing in a parallel region to physical processors, or to no or n to disable such binding. The default is to not bind processes to processors. This is an execution time environment variable interpreted by the PGI runtime support libraries. It does not affect the behavior of the PGI compilers in any way. Note: the MP_BIND environment variable is not supported on all platforms.

In addition to the MP_BIND variable, it is possible to define the thread-CPU relationship. For example, setting MP_BLIST=3,2,1,0 maps CPUs 3, 2, 1 and 0 to threads 0, 1, 2 and 3 respectively.

Sets the maxium number of huge pages each process is allowed to used. If not set, then the process may use all available huge pages.

Specifies a directory to search for libraries. Use -L to add directories to the search path for library files. Multiple -L options are valid. However, the position of multiple -L options is important relative to -l options supplied.