Monitoring Data Settings

The options described below provide monitoring of Intel compiler-generated code.

Specifying Structure Tag Alignments

You can specify an alignment constraint for structures and unions in two ways:

Place a pack pragma in your source file, or
Enter the alignment option on the command line

Both specifications change structure tag alignment constraints.

Use the -Zp option to determine the alignment constraint for structure declarations. Generally, smaller constraints result in smaller data sections while larger constraints support faster execution.

The form of the -Zp option is -Zpn.

The alignment constraint is indicated by one of the following values:

n=1	1 byte.
n=2	2 bytes.
n=4	4 bytes.
n=8	8 bytes
n=16	16 bytes.

For example, to specify 2 bytes as the alignment constraint for all structures and unions in the file prog.c, use the following command:

IA-32 Systems: prompt>icc -Zp2 prog.c
Itanium®-based Systems: prompt>ecc -Zp2 prog.c

Note
Changing the alignment may cause problems if you are using system libraries compiled with the default alignment.

Flushing Denormal Values to Zero for Itanium-based Systems Only

Option -ftz flushes denormal results to zero when the application is in the gradual underflow mode. Use this option if the denormal values are not critical to application behavior. Flushing the denormal values to zero with -ftz may improve performance of your application. The default status of -ftz is OFF. By default, the compiler lets results gradually underflow.

The -ftz switch only needs to be used on the source containing function main(). The effect of the -ftz switch is to turn on FTZ mode for the process started by main(). The initial thread and any threads subsequently created by that process will operate in FTZ mode.

Note

The -O3 option turns -ftz ON. Use -ftz- to disable flushing denormal results to zero.

Allocation of Zero-initialized Variables

By default, variables explicitly initialized with zeros are placed in the BSS section. But using the -nobss_init option, you can place any variables that are explicitly initialized with zeros in the DATA section if required.

Avoiding Incorrect Decoding of Certain Instructions (IA-32 Only)

Some instructions have 2-byte opcodes in which the first byte contains 0f. In rare cases, the Pentium® processor can decode these instructions incorrectly. Specify the -0f_check option to avoid the incorrect decoding of these instructions.