isolated_call Batch Compiler Option

isolated_call

Option Type	Default Value	#pragma options	C	C++
-qoption	-	ISOLATED_CALL	x	x

Syntax

-qisolated_call=function_name
ISOLATED_CALL=function_name

Purpose
Specifies functions in the source file that have no side effects.

Notes

function_name

Is the name of a function that does not have side effects, except changing the value of a variable pointed to by a pointer or reference parameter, or does not rely on functions or processes that have side effects.
Side effects are any changes in the state of the runtime environment. Examples of such changes are accessing a volatile object, modifying an external object, modifying a file, or calling another function that does any of these things. Functions with no side effects cause no changes to external and static variables.

function_name can be a list of functions separated by colons (:).

Marking a function as isolated can improve the runtime performance of optimized code by indicating the following to the optimizer:

external and static variables are not changed by the called function
calls to the function with loop-invariant parameters may be moved out of loops
multiple calls to the function with the same parameter may be merged into one call
calls to the function may be discarded if the result value is not needed

The #pragma options keyword isolated_call must be specified at the top of the file, before the first C or C++ statement. You can use the #pragma isolated_call directive at any point in your source file.

Example
To compile myprogram.c, specifying that the functions myfunction(int) and classfunction(double) do not have side effects, enter:

xlC myprogram.c -qisolated_call=myfunction:classfunction

List of Batch Compiler Options and Their Defaults
Equivalent Batch Compile-Link and Incremental Build Options