SPEC CPU2006 Flags Disclosure for the Intel Compilers (v9.1) on Mac OSX

Enables optimizations for speed and disables some optimizations that increase code size and affect speed. To limit code size, this option:

• Enables global optimization; this includes data-flow analysis, code motion, strength reduction and test replacement, split-lifetime analysis, and instruction scheduling.
• Disables intrinsic recognition and intrinsics inlining.
• Disables loop unrolling.

The O1 option may improve performance for applications with very large code size, many branches, and execution time not dominated by code within loops.

On IA-32 Mac OSX platforms, -O1 sets the following:

• -unroll0,
• -fno-builtin,
• -mno-ieee-fp,
• -fomit-frame-pointer (same as -fp),
• -ffunction-sections

Enables optimizations for speed. This is the generally recommended optimization level. This option also enables:

• Inlining of intrinsics
• Intra-file interprocedural optimizations, which include:
  • inlining
  • constant propagation
  • forward substitution
  • routine attribute propagation
  • variable address-taken analysis
  • dead static function elimination
  • removal of unreferenced variables
• The following capabilities for performance gain:
  • constant propagation
  • copy propagation
  • dead-code elimination
  • global register allocation
  • global instruction scheduling and control speculation
  • loop unrolling
  • optimized code selection
  • partial redundancy elimination
  • strength reduction/induction variable simplification
  • variable renaming
  • exception handling optimizations
  • tail recursions
  • peephole optimizations
  • structure assignment lowering and optimizations
  • dead store elimination

Enables O2 optimizations plus more aggressive optimizations, such as prefetching, scalar replacement, and loop and memory access transformations.

Enables optimizations for maximum speed, such as:

• Loop unrolling, including instruction scheduling
• Code replication to eliminate branches
• Padding the size of certain power-of-two arrays to allow more efficient cache use

On IA-32 and Intel EM64T processors, when O3 is used with options -ax or -x (Linux/Mac OSX), the compiler performs more aggressive data dependency analysis than for O2, which may result in longer compilation times.

The O3 optimizations may not cause higher performance unless loop and memory access transformations take place. The optimizations may slow down code in some cases compared to O2 optimizations.

The O3 option is recommended for applications that have loops that heavily use floating-point calculations and process large data sets.

This option enables additional interprocedural optimizations for single file compilation. These optimizations are a subset of full intra-file interprocedural optimizations. One of these optimizations enables the compiler to perform inline function expansion for calls to functions defined within the current source file.

This option enables multi-file interprocedural optimizations that includes:

• inline function expansion
• interprocedural constant propogation
• dead code elimination
• propagation of function characteristics
• passing arguments in registers
• loop-invariant code motion

When you specify this option, the compiler performs inline function expansion for calls to functions defined in separate files.

The -fast option enhances execution speed across the entire program by including the following options that can improve run-time performance:

• -O3 (maximum speed and high-level optimizations)
• -ipo (enables interprocedural optimizations across files)
• -no-prec-div (disable -prec-div), where -prec-div improves precision of FP divides (some speed impact)
• -mdynamic-no-pic, where -mydynamic-no-pic indicates that code is not relocatable

To override one of the options set by -fast, specify that option after the -fast option on the command line. The options set by -fast may change from release to release.

Code is not relocatable, but external references are relocatable.

This option improves precision of floating-point divides. It has a slight impact on speed.

With some optimizations, such as -xN and -xB (Linux) or /QxN and /QxB (Windows), the compiler may change floating-point division computations into multiplication by the reciprocal of the denominator. For example, A/B is computed as A * (1/B) to improve the speed of the computation.

However, sometimes the value produced by this transformation is not as accurate as full IEEE division. When it is important to have fully precise IEEE division, use this option to disable the floating-point division-to-multiplication optimization. The result is more accurate, with some loss of performance.

If you specify -no-prec-div (Linux and Mac OSX), it enables optimizations that give slightly less precise results than full IEEE division. The default is -prec-div.

Instrument program for profiling for the first phase of two-phase profile guided optimization. This instrumentation gathers information about a program's execution paths and data values but does not gather information from hardware performance counters. The profile instrumentation also gathers data for optimizations which are unique to profile-feedback optimization.

Instructs the compiler to produce a profile-optimized executable and merges available dynamic information (.dyn) files into a pgopti.dpi file. If you perform multiple executions of the instrumented program, -Qprof_use merges the dynamic information files again and overwrites the previous pgopti.dpi file.

Without any other options, the current directory is searched for .dyn files

Tells the compiler the maximum number of times (n) to unroll loops.

Disables inline expansion of all intrinsic functions.

Disables conformance to the ANSI C and IEEE 754 standards for floating-point arithmetic.

Allows use of EBP as a general-purpose register in optimizations.

Places each function in its own COMDAT section.

For mixed-language benchmarks, tell the compiler that the main program is not written in Fortran

icc invokes the Intel C++ compiler. It is invoked as:

icc [ options ] file1 [ file2 ... ]

where,

• options: represent zero or more compile options
• fileN: is a C/C++ source (.C .c .cc .cp .cpp .cxx .c++ .i), assembly (.s), object (.o), static library (.a), or other linkable file.

Invoking the compiler using icc compiles .c and .i files as C. Using icc only links in C++ libraries if C++ source is provided on the command line.

The icpc command uses the same compiler options as the icc command. Invoking the compiler using icpc compiles .c, and .i files as C++. Using icpc always links in C++ libraries.

ifort invokes the Intel Fortran compiler. It is invoked as:

ifort [ options ] file1 [ file2 ... ]

where,

• options: represent zero or more compile options
• fileN: is a Fortran source file, assembly file, object file, object library, or other linkable file.

Invoke the Intel C++ compiler in C99 mode for Mac OSX.

Pass options o1, o2, etc. to the linker for processing.

Specifies the initial address of the stack pointer value, where value is a hexadecimal number rounded to the segment alignment. The default segment alignment is the target pagesize (currently, 1000 hexadecimal for the PowerPC and for i386). If -stack_size is specified and -stack_addr is not, a default stack address specific for the architecture being linked will be used and its value printed as a warning message. This creates a segment named __UNIXSTACK. Note that the initial stack address will be either at the high address of the segment or the low address of the segment depending on which direction the stack grows for the architecture being linked.

Specifies the size of the stack segment value, where value is a hexadecimal number rounded to the segment alignment. The default segment alignment is the target pagesize (currently, 1000 hexadecimal for the PowerPC and for i386). If -stack_addr is specified and -stack_size is not, a default stack size specific for the architecture being linked will be used and its value printed as a warning message. This creates a segment named __UNIXSTACK .