ansialias

Syntax

    -qansialias | -qnoansialias 
    ANSIALIAS | NOANSIALIAS 

Purpose
Specifies whether type-based aliasing is to be used during optimization. Type-based aliasing restricts the lvalues that can be used to access a data object safely.

Default Values
The default with xlc, xlC and c89 is ansialias. The optimizer assumes that pointers can only point to an object of the same type.

The default with cc is noansialias.

Notes
This option is obsolete. Use -qalias= in your new applications.

This option has no effect unless you also specify the -O option.

If you select noansialias, the optimizer makes worst-case aliasing assumptions. It assumes that a pointer of a given type can point to an external object or any object whose address is already taken, regardless of type.

The following are not subject to type-based aliasing:

• Signed and unsigned types; for example, a pointer to a signed int can point to an unsigned int.
• Character pointer types can point to any type.
• Types qualified as volatile or const; for example, a pointer to a const int can point to an int.

Example
To specify worst-case aliasing assumptions when compiling myprogram.c, enter:

xlC myprogram.c -O -qnoansialias

List of Batch Compiler Options and Their Defaults
Options that Define the Compiler Object Code Produced
Equivalent Batch Compile-Link and Incremental Build Options