Table 4 Options for +FP[flags]

Flag

Description

 

 

V (v)

Trap on invalid floating-point operations.

 

 

Z (z)

Trap on divide by zero.

 

 

O (o)

Trap on floating-point overflow.

 

 

U (u)

Trap on floating-point underflow.

 

 

I (i)

Trap on floating-point operations that produce inexact results.

 

 

D (d)

Enable sudden underflow (flush to zero) of denormalized values.

 

 

To dynamically change these settings at runtime, see fesetenv(3M).

+FPmode

+FPmode specifies how the run-time environment for floating-point operations should be initialized at program start up. By default, modes are as specified in the IEEE floating-point standard: all traps disabled, gradual underflow, and rounding to nearest. See ld(1) for specific values of mode.

To dynamically change these settings at run time, refer to fenv(5), fesettrapenable(3M), and fesetround(3M).

+O[no]libmerrno

+O[no]libmerrno

Description:

The +O[no]libmerrno option enables [disables] support for errno in libm functions. The default is +Onolibmerrno for C++, c99, or –AC99.

In C-mode, the default is +Olibmerrno with -Aaoption.

+Oprefetch_latency

+Oprefetch_latency=cycles

The +Oprefetch_latency option applies to loops for which the compiler generates data prefetch instructions. cycles represents the number of cycles for a data cache miss. For a given loop, the compiler divides cycles by the estimated loop length to arrive at the number of loop iterations for which to generate advanced prefetches.

cycles must be in the range of 0 to 10000. A value of 0 instructs the compiler to use the default value, which is 480 cycles for loops containing floating-point accesses and 150 cycles for loops that do not contain any floating-point accesses.

For tuning purposes, it is recommended that users measure their application’s performance using a few different prefetch latency settings to determine the optimal value. Some floating-point codes may benefit by increasing the distance to 960. Parallel applications frequently benefit from a shorter prefetch distance of 150.

+O[no]preserved_fpregs

+O[no]preserved_fpregs

The +O[no]preserved_fprefs option specifies whether the compiler is allowed [not allowed] to make use of the preserved subset of the floating-point register file as defined by the Itanium runtime architecture.

The default is +Opreserved_fpregs.

44 Command-Line Options