Description of compiler flags for Intel C Compiler 5.0
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/O1 optimize for speed, but disable some optimizations which increase
code size for a small speed benefit. Includes inline expansion
except for intrinsic functions, global optimizations, string
pooling optimizations.
/O2 Optimizes for speed. The -O2 option includes O1 optimizations and
in addition enables inlining of intrinsics and more speed
optimizations. This is the default.
/O3: Builds on -01 and -02 optimizations by enabling high-level
optimization. This level does not guarantee higher performance
unless loop and memory access transformation take place. In
conjunction with -QaxK/-QxK and QaxW/QxW, this switch causes the
compiler to perform more aggressive data dependency analysis than
for -O2. This may result in longer compilation times.
/Oa[-] assume [do not assume] no aliasing in program
/Qax<codes> generate code specialized for processor extensions
specified by <codes> while also generating generic IA-32 code.
<codes> includes one or more of the following characters:
i Pentium Pro and Pentium II processor instructions
M MMX(TM) instructions
K streaming SIMD extensions (implies i and M above)
W Pentium 4 processor with Streaming SIMD Extensions 2
(implies i, M and K)
/Qx<codes> generate specialized code to run exclusively on processors
supporting the extensions indicated by <codes> as
described above.
/Ob{1|2|3} Controls the compiler's inline expansion.
0: disable inlining.
1: disables inlining unless /Qip or /Ob2 are specified.
2: enables inlining of any function. However, the
compiler decides which functions are inlined. This
option enables interprocedural optimizations and has
the same effect as specifying the /Qip option.
/Qip enable single-file IP optimizations
(within files, same as /Ob2)
/Qipo multi-file ip optimizations that includes:
- inline function expansion
- interprocedural constant propogation
- dead code elimination
- propagation of function characteristics
- passing arguments in registers
- loop-invariant code motion
/Qprof_gen instrument program for profiling for the first phase of
two-phase profile guided otimization
/Qprof_use 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
/Qrcd The Intel compiler uses the -Qrcd option to improve the performance of code that requires
floating-point-to-integer conversions.
The system default floating point rounding mode is round-to-nearest. This means that
values are rounded during floating point calculations. However, the C language requires
floating point values to be truncated when a conversion to an integer is involved. To do
this, the compiler must change the rounding mode to truncation before each floating
point-to-integer conversion and change it back afterwards.
The -Qrcd option disables the change to truncation of the rounding mode for all
floating point calculations, including floating point-to-integer conversions.
Turning on this option can improve performance, but floating point conversions to
integer will not conform to C semantics.
/GX Enables the full C++ Exception Handling unwind semantics.
/GR Enables C++ Runtime Type Information (RTTI).
Other Notes:
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"/" and "-" are both allowable starting tokens for flags passed to the
compiler i.e. -QxK and /QxK are identical switches.
Portability options for CPU2000:
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176.gcc:
-Dalloca=_alloca : so as to use the built-in optimized alloca
/Fn : 176.gcc uses alloca and this options tells
the linker to pre-allocate n bytes of stack.
The default amount of stack allocated is not
enough and 176.gcc crashes with a run-time
error
186.crafty:
-DNT_i386 : Specifies that it is a Windows NT Intel
processor-based system which makes the compiler
use "long long" as the 64-bit variable that
186.crafty needs.
253.perlbmk:
-DSPEC_CPU2000_NTOS : This enables the code changes for porting to
Windows get included
-DPERLDLL : On Windows, we need a perl.exe instead of a
perl.exe and perl.dll. This pre-define ensures
that the changes necessary to get a single,
UNIX-style executible without getting the
indirect calls that can cause a 10% performance
degradation. This allows the Windows-based
executible to be as close as possible to
the Unix-based one.
/MT : Use the static multi-threaded library else
it will not compile.
254.gap:
-DSYS_HAS_CALLOC_PROTO :
-DSYS_HAS_MALLOC_PROTO : These two pre-defines tell of the existence
of malloc and calloc prototypes.