CPU2006 Flag Description
IBM Corporation IBM Power 780 (3.7 GHz, 128 core, RHEL, GCC)

Compilers: GNU GCC 4.1, 4.3, 4.4, 4.7

Compilers: IBM Advance Toolchain 5.0

Compilers: IBM Advance Toolchain 6.0

Operating systems: SUSE Linux Enterprise 10, SUSE Linux Enterprise 11, and Red Hat Enterprise Linux Advanced Platform 5 and 6

Last updated: October 2012

Implicitly Included Flags

This section contains descriptions of flags that were included implicitly by other flags, but which do not have a permanent home at SPEC.

• • -finline-functions
  • 

  • Integrate all simple functions into their callers. The compiler heuristically decides which functions are simple enough to be worth integrating in this way.

    If all calls to a given function are integrated, and the function is declared "static", then the function is normally not output as assembler code in its own right.

• • -funswitch-loops
  • 

  • Move branches with loop invariant conditions out of the loop, with duplicates of the loop on both branches (modified according to result of the condition).

• • -fgcse-after-reload
  • 

  • When -fgcse-after-reload is enabled, a redundant load elimination pass is performed after reload. The purpose of this pass is to cleanup redundant spilling.

• • -O2
  • 

  • -O2 Optimize even more. GCC performs nearly all supported optimizations that do not involve a space-speed tradeoff. The compiler does not perform loop unrolling or function inlining when you specify -O2. As compared to -O, this option increases both compilation time and the performance of the generated code. -O2 turns on all optimization flags specified by -O. It also turns on the following optimization flags: -fthread-jumps -fcrossjumping -foptimize-sibling-calls -fcse-follow-jumps -fcse-skip-blocks -fgcse -fgcse-lm -fexpensive-optimizations -fstrength-reduce -frerun-cse-after-loop -frerun-loop-opt -fcaller-saves -fpeephole2 -fschedule-insns -fschedule-insns2 -fsched-interblock -fsched-spec -fregmove -fstrict-aliasing -fdelete-null-pointer-checks -freorder-blocks -freorder-functions -funit-at-a-time -falign-functions -falign-jumps -falign-loops -falign-labels -ftree-vrp -ftree-pre

  • Includes:
    • -fthread-jumps
    • -fcrossjumping
    • -foptimize-sibling-calls
    • -fcse-follow-jumps
    • -fcse-skip-blocks
    • -fgcse
    • -fgcse-lm
    • -fexpensive-optimizations
    • -fstrength-reduce
    • -frerun-cse-after-loop
    • -frerun-loop-opt
    • -fcaller-saves
    • -fpeephole2
    • -fschedule-insns
    • -fschedule-insns2
    • -fsched-interblock
    • -fsched-spec
    • -fregmove
    • -fstrict-aliasing
    • -fdelete-null-pointer-checks
    • -freorder-blocks
    • -freorder-functions
    • -funit-at-a-time
    • -falign-functions, -falign-functions=n
    • -falign-jumps, -falign-jumps=n
    • -falign-loops, -falign-loops=n
    • -falign-labels
    • -ftree-vrp
    • -O1
      • -fdefer-pop
      • -fdelayed-branch
      • -fguess-branch-probability
      • -fcprop-registers
      • -floop-optimize
      • -fif-conversion
      • -fif-conversion2
      • -ftree-ccp
      • -ftree-dce
      • -ftree-dominator-opts
      • -ftree-dse
      • -ftree-ter
      • -ftree-lrs
      • -ftree-sra
      • -ftree-copyrename
      • -ftree-fre
      • -ftree-ch
      • -fmerge-constants
• • -fthread-jumps
  • 

  • Perform optimizations where we check to see if a jump branches to a location where another comparison subsumed by the first is found. If so, the first branch is redirected to either the destination of the second branch or a point immediately following it, depending on whether the condition is known to be true or false. Enabled at levels -O2, -O3, -Os.

• • -fcrossjumping
  • 

  • Perform cross-jumping transformation. This transformation unifies equivalent code and save code size. The resulting code may or may not perform better than without cross-jumping. Enabled at levels -O2, -O3, -Os.

• • -foptimize-sibling-calls
  • 

  • Optimize sibling and tail recursive calls. Enabled at levels -O2, -O3, -Os.

• • -fcse-follow-jumps
  • 

  • In common subexpression elimination, scan through jump instructions when the target of the jump is not reached by any other path. For example, when CSE encounters an if statement with an else clause, CSE will follow the jump when the condition tested is false. Enabled at levels -O2, -O3, -Os.

• • -fcse-skip-blocks
  • 

  • This is similar to -fcse-follow-jumps, but causes CSE to follow jumps which conditionally skip over blocks. When CSE encounters a simple if statement with no else clause, -fcse-skip-blocks causes CSE to follow the jump around the body of the if. Enabled at levels -O2, -O3, -Os.

• • -fgcse
  • 

  • Perform a global common subexpression elimination pass. This pass also performs global constant and copy propagation. Note: When compiling a program using computed gotos, a GCC extension, you may get better runtime performance if you disable the global common subexpression elimination pass by adding -fno-gcse to the command line. Enabled at levels -O2, -O3, -Os.

• • -fgcse-lm
  • 

  • When -fgcse-lm is enabled, global common subexpression elimination will attempt to move loads which are only killed by stores into themselves. This allows a loop containing a load/store sequence to be changed to a load outside the loop, and a copy/store within the loop. Enabled by default when gcse is enabled.

• • -fexpensive-optimizations
  • 

  • Perform a number of minor optimizations that are relatively expensive. Enabled at levels -O2, -O3, -Os.

• • -fstrength-reduce
  • 

  • Perform the optimizations of loop strength reduction and elimination of iteration variables. Enabled at levels -O2, -O3, -Os.

• • -frerun-cse-after-loop
  • 

  • Re-run common subexpression elimination after loop optimizations have been performed.

• • -frerun-loop-opt
  • 

  • Run the loop optimizer twice. Enabled at levels -O2, -O3, -Os.

• • -fcaller-saves
  • 

  • Enable values to be allocated in registers that will be clobbered by function calls, by emitting extra instructions to save and restore the registers around such calls. Such allocation is done only when it seems to result in better code than would otherwise be produced. This option is always enabled by default on certain machines, usually those which have no call-preserved registers to use instead. Enabled at levels -O2, -O3, -Os.

• • -fpeephole2
  • 

  • Disable any machine-specific peephole optimizations. The difference between -fno-peephole and -fno-peephole2 is in how they are implemented in the compiler; some targets use one, some use the other, a few use both. -fpeephole is enabled by default. -fpeephole2 enabled at levels -O2, -O3, -Os.

• • -fschedule-insns
  • 

  • If supported for the target machine, attempt to reorder instructions to eliminate execution stalls due to required data being unavailable. This helps machines that have slow floating point or memory load instructions by allowing other instructions to be issued until the result of the load or floating point instruction is required. Enabled at levels -O2, -O3, -Os

• • -fschedule-insns2
  • 

  • Similar to -fschedule-insns, but requests an additional pass of instruction scheduling after register allocation has been done. This is especially useful on machines with a relatively small number of registers and where memory load instructions take more than one cycle. Enabled at levels -O2, -O3, -Os.

• • -fsched-interblock
  • 

  • Schedule instructions across basic blocks. This is enabled by default when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher.

• • -fsched-spec
  • 

  • Don't allow speculative motion of non-load instructions. This is normally enabled by default when scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher.

• • -fregmove
  • 
  • Attempt to reassign register numbers in move instructions and as operands of other simple instructions in order to maximize the amount of register tying. This is especially helpful on machines with two-operand instructions. Note -fregmove and -foptimize-register-move are the same optimization. Enabled at levels -O2, -O3, -Os.

• • -fstrict-aliasing
  • 

  • Allows the compiler to assume the strictest aliasing rules applicable to the language being compiled. For C (and C++), this activates optimizations based on the type of expressions. In particular, an object of one type is assumed never to reside at the same address as an object of a different type, unless the types are almost the same. For example, an "unsigned int" can alias an "int", but not a "void*" or a "double". A character type may alias any other type.

    Pay special attention to code like this:

    
       union a_union {
    
         int i;
    
         double d;
    
       };
    
    
    
       int f() {
    
         a_union t;
    
         t.d = 3.0;
    
         return t.i;
    
       }
    
    

    The practice of reading from a different union member than the one most recently written to (called ``type-punning'') is common. Even with -fstrict-aliasing, type-punning is allowed, provided the memory is accessed through the union type. So, the code above will work as expected. However, this code might not:

    
       int f() {
    
         a_union t;
    
         int* ip;
    
         t.d = 3.0;
    
         ip = &t.i;
    
         return *ip;
    
       }
    
    

• • -fdelete-null-pointer-checks
  • 

  • Use global dataflow analysis to identify and eliminate useless checks for null pointers. The compiler assumes that dereferencing a null pointer would have halted the program. If a pointer is checked after it has already been dereferenced, it cannot be null. In some environments, this assumption is not true, and programs can safely dereference null pointers. Use -fno-delete-null-pointer-checks to disable this optimization for programs which depend on that behavior. Enabled at levels -O2, -O3, -Os.

• • -freorder-blocks
  • 

  • Reorder basic blocks in the compiled function in order to reduce number of taken branches and improve code locality. Enabled at levels -O2, -O3.

• • -freorder-functions
  • 

  • Reorder functions in the object file in order to improve code locality. This is implemented by using special subsections .text.hot for most frequently executed functions and .text.unlikely for unlikely executed functions. Reordering is done by the linker so object file format must support named sections and linker must place them in a reasonable way. Also profile feedback must be available in to make this option effective. See -fprofile-arcs for details. Enabled at levels -O2, -O3, -Os.

• • -funit-at-a-time
  • 

  • Parse the whole compilation unit before starting to produce code. This allows some extra optimizations to take place but consumes more memory (in general). There are some compatibility issues with unit-at-at-time mode: * enabling unit-at-a-time mode may change the order in which functions, variables, and top-level asm statements are emitted, and will likely break code relying on some particular ordering. The majority of such top-level asm statements, though, can be replaced by section attributes. * unit-at-a-time mode removes unreferenced static variables and functions. This may result in undefined references when an asm statement refers directly to variables or functions that are otherwise unused. In that case either the variable/function shall be listed as an operand of the asm statement operand or, in the case of top-level asm statements the attribute used shall be used on the declaration. * Static functions now can use non-standard passing conventions that may break asm statements calling functions directly. Again, attribute used will prevent this behavior. As a temporary workaround, -fno-unit-at-a-time can be used, but this scheme may not be supported by future releases of GCC. Enabled at levels -O2, -O3.

• • -falign-functions, -falign-functions=n
  • 

  • Align the start of functions to the next power-of-two greater than n, skipping up to n bytes. For instance, -falign-functions=32 aligns functions to the next 32-byte boundary, but -falign-functions=24 would align to the next 32-byte boundary only if this can be done by skipping 23 bytes or less.

    -fno-align-functions and -falign-functions=1 are equivalent and mean that functions will not be aligned.

    Some assemblers only support this flag when n is a power of two; in that case, it is rounded up.

    If n is not specified, use a machine-dependent default.

• • -falign-jumps, -falign-jumps=n
  • 

  • Align branch targets to a power-of-two boundary, for branch targets where the targets can only be reached by jumping, skipping up to n bytes like -falign-functions. In this case, no dummy operations need be executed.

• • -falign-loops, -falign-loops=n
  • 

  • Align loops to a power-of-two boundary, skipping up to n bytes like -falign-functions. The hope is that the loop will be executed many times, which will make up for any execution of the dummy operations.

• • -falign-labels
  • 

  • -falign-labels=n Align all branch targets to a power-of-two boundary, skipping up to n bytes like -falign-functions. This option can easily make code slower, because it must insert dummy operations for when the branch target is reached in the usual flow of the code. -fno-align-labels and -falign-labels=1 are equivalent and mean that labels will not be aligned. If -falign-loops or -falign-jumps are applicable and are greater than this value, then their values are used instead. If n is not specified or is zero, use a machine-dependent default which is very likely to be `1', meaning no alignment. Enabled at levels -O2, -O3.

• • -ftree-vrp
  • 

  • Perform Value Range Propagation on trees. This is similar to the constant propagation pass, but instead of values, ranges of values are propagated. This allows the optimizers to remove unnecessary range checks like array bound checks and null pointer checks. This is enabled by default at -O2 and higher. Null pointer check elimination is only done if -fdelete-null-pointer-checks is enabled.

• • -O1
  • 

  • Optimize. Optimizing compilation takes somewhat more time, and a lot more memory for a large function. With -O, the compiler tries to reduce code size and execution time, without performing any optimizations that take a great deal of compilation time. -O turns on the following optimization flags: -fdefer-pop -fdelayed-branch -fguess-branch-probability -fcprop-registers -floop-optimize -fif-conversion -fif-conversion2 -ftree-ccp -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-ter -ftree-lrs -ftree-sra -ftree-copyrename -ftree-fre -ftree-ch -fmerge-constants -O also turns on -fomit-frame-pointer on machines where doing so does not interfere with debugging.

  • Includes:
    • -fdefer-pop
    • -fdelayed-branch
    • -fguess-branch-probability
    • -fcprop-registers
    • -floop-optimize
    • -fif-conversion
    • -fif-conversion2
    • -ftree-ccp
    • -ftree-dce
    • -ftree-dominator-opts
    • -ftree-dse
    • -ftree-ter
    • -ftree-lrs
    • -ftree-sra
    • -ftree-copyrename
    • -ftree-fre
    • -ftree-ch
    • -fmerge-constants
• • -fdefer-pop
  • 

  • Always pop the arguments to each function call as soon as that function returns. For machines which must pop arguments after a function call, the compiler normally lets arguments accumulate on the stack for several function calls and pops them all at once. -fnodefer-pop is disabled at levels -O, -O2, -O3, -Os.

• • -fdelayed-branch
  • 

  • If supported for the target machine, attempt to reorder instructions to exploit instruction slots available after delayed branch instructions. Enabled at levels -O, -O2, -O3, -Os.

• • -fguess-branch-probability
  • 

  • If supported for the target machine, attempt to reorder instructions to exploit instruction slots available after delayed branch instructions. -fnoguess-branch-probability is enabled at levels -O, -O2, -O3, -Os.

• • -fcprop-registers
  • 

  • After register allocation and post-register allocation instruction splitting, we perform a copy-propagation pass to try to reduce scheduling dependencies and occasionally eliminate the copy. -fno-cprop-registers is disabled at levels -O, -O2, -O3, -Os.

• • -floop-optimize
  • 

  • Perform loop optimizations: move constant expressions out of loops, simplify exit test conditions and optionally do strength-reduction as well. Enabled at levels -O, -O2, -O3, -Os.

• • -fif-conversion
  • 

  • Attempt to transform conditional jumps into branch-less equivalents. This include use of conditional moves, min, max, set flags and abs instructions, and some tricks doable by standard arithmetics. The use of conditional execution on chips where it is available is controlled by if-conversion2. Enabled at levels -O, -O2, -O3, -Os.

• • -fif-conversion2
  • 

  • Use conditional execution (where available) to transform conditional jumps into branch-less equivalents. Enabled at levels -O, -O2, -O3, -Os.

• • -ftree-ccp
  • 

  • Perform sparse conditional constant propagation (CCP) on trees. This pass only operates on local scalar variables and is enabled by default at -O and higher.

• • -ftree-dce
  • 

  • Perform dead code elimination (DCE) on trees. This flag is enabled by default at -O and higher.

• • -ftree-dominator-opts
  • 

  • Perform a variety of simple scalar cleanups (constant/copy propagation, redundancy elimination, range propagation and expression simplification) based on a dominator tree traversal. This also performs jump threading (to reduce jumps to jumps). This flag is enabled by default at -O and higher.

• • -ftree-dse
  • 

  • Not described in Manual for gcc 4.1

• • -ftree-ter
  • 

  • Perform temporary expression replacement during the SSA->normal phase. Single use/single def temporaries are replaced at their use location with their defining expression. This results in non-GIMPLE code, but gives the expanders much more complex trees to work on resulting in better RTL generation. This is enabled by default at -O and higher.

• • -ftree-lrs
  • 

  • Perform live range splitting during the SSA->normal phase. Distinct live ranges of a variable are split into unique variables, allowing for better optimization later. This is enabled by default at -O and higher.

• • -ftree-sra
  • 

  • Perform scalar replacement of aggregates. This pass replaces structure references with scalars to prevent committing structures to memory too early. This flag is enabled by default at -O and higher.

• • -ftree-copyrename
  • 

  • Perform copy renaming on trees. This pass attempts to rename compiler temporaries to other variables at copy locations, usually resulting in variable names which more closely resemble the original variables. This flag is enabled by default at -O and higher.

• • -ftree-fre
  • 

  • Perform Full Redundancy Elimination (FRE) on trees. The difference between FRE and PRE is that FRE only considers expressions that are computed on all paths leading to the redundant computation. This analysis faster than PRE, though it exposes fewer redundancies. This flag is enabled by default at -O and higher.

• • -ftree-ch
  • 

  • Perform loop header copying on trees. This is beneficial since it increases effectiveness of code motion optimizations. It also saves one jump. This flag is enabled by default at -O and higher. It is not enabled for -Os, since it usually increases code size.

• • -fmerge-constants
  • 

  • Attempt to merge identical constants (string constants and floating point constants) across compilation units. This option is the default for optimized compilation if the assembler and linker support it. Use -fno-merge-constants to inhibit this behavior. Enabled at levels -O, -O2, -O3, -Os.

• • -fno-math-errno
  • 

  • 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.

    Use of this option may result in incorrect output for programs which depend on an exact implementation of IEEE or ISO rules/specifications for math functions.

• • -funsafe-math-optimizations
  • 

  • Allow optimizations for floating-point arithmetic that (a) assume that arguments and results are valid and (b) may violate IEEE or ANSI standards. When used at link-time, it may include libraries or startup files that change the default FPU control word or other similar optimizations.

    Use of this option may result in incorrect output for programs which depend on an exact implementation of IEEE or ISO rules/specifications for math functions.

• • -fno-trapping-math
  • 

  • Compile code assuming that floating-point operations cannot generate user-visible traps. These traps include division by zero, overflow, underflow, inexact result and invalid operation. This option implies -fno-signaling-nans. Setting this option may allow faster code if one relies on `non-stop' IEEE arithmetic, for example.

    Use of this option can result in incorrect output for programs which depend on an exact implementation of IEEE or ISO rules/specifications for math functions.

  • Includes:
    • -fno-signaling-nans
• • -fno-signaling-nans
  • 

  • Compile code assuming that IEEE signaling NaNs may not generate user-visible traps during floating-point operations. Setting this option enabled optimizations that may change the number of exceptions visible with signaling NaNs.

• • -ffinite-math-only
  • 

  • Allow optimizations for floating-point arithmetic that assume that arguments and results are not NaNs or +-Infs.

    Use of this option may result in incorrect output for programs which depend on an exact implementation of IEEE or ISO rules/specifications for math functions.

Virtualization Settings

• ulimit -s 1048576
  Sets the maximum stack size to "1048576 KB".
• To reserve 200 huge pages out of the physical memory pool, issue the following command,

  echo 200 > /proc/sys/vm/nr_hugepages
  

  or

  echo 200 > /proc/sys/vm/nr_overcommit_hugepages
  

  to allocate from the dynamic hugepage pool.
• chsyscfg -m system -r prof -i name=profile,lpar_name=partition,lpar_proc_compat_mode=POWER6_enhanced
  This command enables the POWERPC architecture optional instructions supported on POWER6.
  

  Usage: chsyscfg -r lpar | prof | sys | sysprof | frame
                  -m <managed system> | -e <managed frame>
                  -f <configuration file> | -i "<configuration data>"
                  [--help]
  
  Changes partitions, partition profiles, system profiles, or the attributes of a
  managed system or a managed frame.
  
      -r                        - the type of resource(s) to be changed:
                                    lpar    - partition
                                    prof    - partition profile
                                    sys     - managed system
                                    sysprof - system profile
                                    frame   - managed frame
      -m <managed system>       - the managed system's name
      -e <managed frame>        - the managed frame's name
      -f <configuration file>   - the name of the file containing the
                                  configuration data for this command.
                                  The format is:
                                    attr_name1=value,attr_name2=value,...
                                  or
                                    "attr_name1=value1,value2,...",...
      -i "<configuration data>" - the configuration data for this command.
                                  The format is:
                                    "attr_name1=value,attr_name2=value,..."
                                  or
                                    ""attr_name1=value1,value2,...",..."
      --help                    - prints this help
  
  The valid attribute names for this command are:
      -r prof     required: name, lpar_id | lpar_name
                  optional: ...
                            lpar_proc_compat_mode (default | POWER6_enhanced)
  

• Each process was bound to a cpu using submit= with the numactl command

   
  submit = numactl --membind=\$SPECCOPYNUM --physcpubind=\$SPECCOPYNUM $command
  

• numactl : Control NUMA policy for processes or shared memory

       --membind=nodes
         Only  allocate  memory  from  nodes.   Allocation will fail when
         there is not enough memory available on these nodes.
  
      --physcpubind=cpus
         Only execute process on cpus.  This accepts physical cpu numbers
         as shown in the processor fields of /proc/cpuinfo.
  

• Environment variables that can be set before the run:

  HUGETLB_VERBOSE=0 : Turn off any debugging message from libhugetlbfs
  HUGETLB_MORECORE=yes:  Instructs libhugetlbfs to override libc's normal morecore() function with a hugepage version and use it for malloc(). 
  HUGETLB_MORECORE_HEAPBASE=0x50000000: Specifies that the hugepage heap address to start at 0x50000000. 
  HUGETLB_ELFMAP=R ; Instructs libhugetlbfs to place text segment in hugepages.
  HUGETLB_ELFMAP=W ; Instructs libhugetlbfs to place data and BSS segments in hugepages.
  HUGETLB_ELFMAP=RW ; Instructs libhugetlbfs to place all segments in hugepages.
  HUGETLB_ELFMAP=no ; Instructs libhugetlbfs not to place any segment in hugepages.
  XLFRTEOPTS=intrinthrds=1 : Causes the Fortran runtime to only use a single thread.
  

• IBM Post-Link Optimization (fdprpro):

      - First we copied the original executable (baseexe) to baseexe.orig. 

      - Then, the executable is instrumented and its initial profile generated, as follows: 
        $ fdprpro -a instr baseexe 
        The output will be generated (by default) in baseexe.instr and its profile in baseexe.nprof. 

      - Next, run baseexe.instr using the training data. This will fill the profile file with information that characterizes the training workload.

      - Finally, re-run FDPR-Pro with the profile file provided, as follows: 
        $ fdprpro -a opt -f baseexe.nprof [optimization options] baseexe 

      Instrumentation Options Descriptions:
       -ei, --embedded-instrumentation
            Perform embedded instrumentation. The profile will be collected
            into global variables.

       -fd Fdesc, --file-descriptor Fdesc
            Set the file descriptor number to be used when opening the profile
            file. The default of Fdesc is set to the maximum-allowed number of
            open files.

       -imullX, --mullX-instrumentation
            perform value profiling of RA and RB operands in mullX instruc-
            tions.

       -issu, --instrumentation-safe-stack-usage
            Ensure additional stack space is properly allocated for the
            instrumented run. Use this option if your application uses stack
            extensively (e.g., when the program uses alloca()). Note that this
            option adds extra overhead on instrumentation code.

       -iso offset, --instrumentation-stack-offset offset
            Set the offset from the stack, a negative number, where the
            instrumentation's area for saving registers is kept at runtime.
            Use with care.

       -M addr, --profile-map addr
            Set shared memory segment address for profiling. Alternative
            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. The default is set
            to 0x3000000.

       -[no]ri, --[no]register-instrumentation
            Instrument the input program file to collect profile information
            about indirect branches via registers. The default is set to col-
            lect the profile information.

       -[no]sfp, --[no]save-floating-point-registers
            Save floating point registers in instrumented code. The default is
            set to save floating point registers.

       Optimization Options Descriptions:

       -A alignment, --align-code alignment
            Align program so that hot code will be aligned on alignment-byte
            addresses.

       -abb factor, --align-basic-blocks factor
            Align basic blocks that are hotter than the average by a given
            (float) factor. This is a lower-level machine-specific alignment
            compared to --align-code. Value of -1 (the default) disables this
            option.

       -bf, --branch-folding
            Eliminate branch to branch instructions.

       -bldcg, --build-dcg
            Build a Data Connectivity Graph (DCG) for enhanced data reordering
            (applicable only with the -RD flag).

       -bp, --branch-prediction
            Set branch prediction bit for conditional branches according to
            the collected profile.

       -btcar, --branch-table-csect-anchor-removal
            Eliminate load instructions used when accessing branch tables.

       -cbtd, --convert-bss-to-data
            Convert BSS section into a data section. This is useful for more
            aggressive tocload and RD optimizations.

       -cRD, --conservativeRD
            Perform conservative static data reordering by packing together
            all frequently referenced static variables.

       -dce, --dead-code-elimination
            Eliminate instructions related to unused local variables within
            frequently executed functions. This is useful mainly after apply-
            ing function inlining optimization.

       -dp, --data-prefetch
            Insert data-cache prefetch instructions to improve data-cache per-
            formance.

       -dpht threshold, --data-placement-hotness-threshold threshold
            Set data placement algorithm hotness threshold between (0,1),
            where 0 reorders 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. (This is 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 function epi-
            logs, into a single unified code.

       -fc, --function-cloning
            Enable function cloning phase only during function inlining opti-
            mizations (applicable only with function inlining flags: -i, -si,
            -ihf, -isf, -shci).

       -hr, --hco-reschedule
            Relocate instructions from frequently executed code to rarely exe-
            cuted 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 fac-
            tor (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 than or equal to the given
            size in bytes.

       -kr, --killed-registers
            Eliminate stores and restores of registers that are killed (over-
            written) after frequently executed function calls.

       -lap, --load-address-propagation
            Eliminate load instructions of variable 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 references 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 one to several basic blocks accord-
            ing 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).

       -nop, --nop-removal
            Remove NOP instructions from reordered code.

       -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 -so.

       -O4  Switch on aggressive optimization flags together with aggressive
            function inlining. Same as -O3 -sidf 50 -ihf 20 -sdp 9 -shci 90
            and -bldcg (for XCOFF files).

       -O5  Switch on aggressive optimization flags together with HLR opti-
            mization. Same as -O4 -sa -gcpyp -gcnstp -dce -vrox.

       -omullX, --mullX-optimization
            Optimize mullX instructions by adding a run-time check on RA and
            RB and performing equivalent operations with lower penalty. The
            optimization requires the use of -imullX in the instrumentation
            phase.

       -pbsi, --path-based-selective-inline
            Perform selective inlining of dominant hot function calls based on
            the control flow paths leading to hot functions.

       -pc, --preserve-csects
            Preserve CSects' boundaries in reordered code.

       -pca, --propagate-constant-area
            Relocate the constant variables area to the top of the code sec-
            tion when possible.

       -pfb, --preserve-first-bb
            Preserve original location of the entry point basic block in pro-
            gram.

       -pp, --preserve-functions
            Preserve functions' boundaries in reordered code.

       -[no]pr, --[no]ptrgl-r11
            Perform removal of R11 load instruction in _ptrgl csect.

       -pto, --ptrgl-optimization
            Perform optimization of indirect call instructions via registers
            by replacing them with conditional direct jumps.

       -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 and 1.
            Default is set to 0.8. (Applicable only with -pto flag).

       -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 and 100. Default
            value is set to 3. (Applicable only with the -pto flag).

       -RC, --reorder-code
            Perform code reordering.

       -rcaf aggressiveness_factor, --reorder-code-aggressivenes-factor
       aggressiveness_factor
            Set the aggressiveness of code reordering optimization. Allowed
            values are [0 1 2], where 0 preserves then original code order
            and 2 is the most aggressive. Default is set to 1. (Applicable
            only with the -RC flag).

       -rccrf reversal_factor, --reorder-code-condition-reversal-factor rever-
       sal_factor
            Set the threshold fraction that determines when to enable condi-
            tion reversal for each conditional branch during code reordering.
            Allowed input range is between 0.0 and 1.0 where 0.0 tries to pre-
            serve original condition direction and 1.0 ignores it. Default is
            set to 0.8 (Applicable only with the -RC flag).

       -rcctf termination_factor, --reorder-code-chain-termination-factor ter-
       mination_factor
            Set the threshold fraction that determines when to terminate each
            chain of basic blocks during code reordering. Allowed input range
            is between 0.0 and 1.0 where 0.0 generates long chains and 1.0
            creates single basic block chains. Default is set to 0.05. (Appli-
            cable 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.

       -rtb, --remove-traceback-tables
            Remove traceback tables in reordered code.

       -sdp aggressiveness_factor, --stride-data-prefetch aggressiveness_fac-
       tor
            Perform data prefetching within frequently executed loops based on
            stride analysis, according to an aggressiveness factor between
            (1,9), where 1 is the least aggressive.

       -sdpla iterations_number, --stride-data-prefetch-look-ahead itera-
       tions_number
            Set the number of iterations for which data is prefetched into the
            cache ahead of time. Default value is set to 4 iterations. (Appli-
            cable 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 con-
            sidered a candidate for prefetching. Default value is set to 128
            bytes. (Applicable only with the -sdp flag).

       -see level
            Use simplified prolog/epilog for functions that perform condi-
            tional early-exit. Use basic optimization with level=0 and maximal
            with level=1.

       -shci pct, --selective-hot-code-inline pct
            Perform selective inlining of functions in order to decrease the
            total number of execution counts, so that only functions with hot-
            ness above the given percentage are inlined.

       -si, --selective-inline
            Perform selective inlining of dominant hot function calls.

       -sidf percentage_factor, --selective-inline-dominant-factor percent-
       age_factor
            Set a dominant factor percentage for selective inline optimiza-
            tion. The allowed range is between 0 and 100. Default is set to
            80. (Applicable only with the -si and -pbsi flags).

       -siht frequency_factor, --selective-inline-hotness-threshold fre-
       quency_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).

       -slbp, --spinlock-branch-prediction
            Perform branch prediction bit setting for conditional branches in
            spinlock code containing l*arx and st*cx instructions. (Applicable
            after -bp flag).

       -sldp, --spinlock-data-prefetch
            Perform data prefetching for memory access instructions preceding
            spinlock code containing l*arx and st*cx instructions.

       -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 a comma-
            separated list of libraries and their profiles. IMPORTANT: Licens-
            ing 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 optimiza-
            tion. The allowed input range is between 0 (least aggressive) and
            1, or -1, which does not require a profile and selects all code
            that might be called by the input program from the given
            libraries. Default is set at 0.5.

       -so, --stack-optimization
            Reduce the stack frame size of functions that are called with a
            small number of arguments.

       -spc, --shortcut-plt-calls
            Shortcut PLT calls in shared libraries to local functions if they
            exist. Note: Resolving to external symbols is disabled for such
            calls.

       -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 that use the Try & Catch mechanism.

       -tlo, --tocload-optimization
            Replace each load instruction that references the TOC with a cor-
            responding add-immediate instruction via the TOC anchor register,
            where 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 fre-
            quently executed functions by using available volatile registers.

       -vrox, --volatile-registers-extended-optimization
            Eliminate stores and restores of non-volatile registers in fre-
            quently executed functions by using available volatile registers,
            the extended version supports FP registers and transparency.

       General Options:

       -h, --help
            Print online 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, ppe, spe, spe_edp, z10, z9. 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 '-', the output goes to standard output. See --verbose for the default.

       -v level, --verbose level
            Set verbose output mode level. When set, various statistics about the target optimized program are printed into the file pro-
            gram.stat. Allowed level range is between 0 and 3. Default is set to 0.

       -V, --version
            Print version.

Flag description origin markings:

	Indicates that the flag description came from the user flags file.
	Indicates that the flag description came from the suite-wide flags file.
	Indicates that the flag description came from a per-benchmark flags file.

For questions about the meanings of these flags, please contact the tester.
For other inquiries, please contact webmaster@spec.org
Copyright 2006-2014 Standard Performance Evaluation Corporation
Tested with SPEC CPU2006 v1.2.
Report generated on Thu Jul 24 13:38:03 2014 by SPEC CPU2006 flags formatter v6906.