Optimize to reduce image size at the expense of increased execution time. For example, large structure copies are done by out-of-line function calls instead of inline code.

Optimize to reduce execution time at the expense of a larger image. For example, compile:

while (expression) body…;

as:

if (expression) {
	do body…;
	while (expression);
}

If neither -Otime or -Ospace is specified, the compiler uses a balance between the two. You can compile time-critical parts of your code with -Otime, and the rest with -Ospace. You should not specify both -Otime and -Ospace at the same time.

Specifies the level of optimization to be used. The optimization levels are:

The compiler selects a value for the maximum number of instructions allowed to generate an integer literal inline before using LDR rx,=value on the basis of the -Otime, -Ospace, and -processor options.

You can alter this behavior by setting Number to an integer between 1 and 4. Lower numbers generate less code at the possible expense of speed, depending on your memory system. The effect of altering this value is small, and is usually not significant.

Allows string literals to be writable, as expected by some UNIX code, by allocating them in the program data area rather than the notionally read-only code area. This also stops the compiler reusing a multiply occurring string literal.

Treats enumerations as signed integers. This option is off by default (no forced integers).

Make char signed. It is normally unsigned in C++ and ANSI C modes, and signed in PCC mode. The sign of char is set by the last option specified that would normally affect it. For example, if you specify both the -ansic and -zc options and you want to make char signed in ANSI C mode, you must specify the -zc option after the -ansic option.

Generates one AOF area for each function. This can result in increased code size.

Normally the compiler generates one AOF function for each C compilation unit, and at least one AOF function for each C++ compilation unit.

This option enables the linker to remove unused functions when the -remove linker option is specified.

Disallows tentative declarations. If this option is specified, the compiler assumes that any occurrence of a top level construct such as int i; is a definition without initializer, rather than a tentative definition. Any subsequent definition with initializer in the same scope will generate an error. This may fault code that conforms to the ANSI specification.

This option has effect only for C, not for C++. Tentative declarations are not permitted in C++. This option is useful in combination with the -zz and -zas options.

Sets the value of the zero-initialized data threshold size. The compiler will place uninitialized global variables in the Zero Initialized (ZI) data area if their size is greater than ZI_Threshold_Size bytes.

For example, you can force uninitialized global variables of any size to be placed in the ZI data area by specifying -zz0, though this may increase your code size.

Use this option in combination with -zt to avoid increased code size. Option -zzt provides a convenient shorthand. The default threshold size is 8 bytes.

Combines the -zt and -zz options. For example, specify -zzt0 to force the compiler to disallow tentative declarations and place all uninitialized global variables in the ZI data area.

Compiles code for an ARM operating with big-endian memory. The most significant byte has lowest address.

Compiles code for an ARM operating with little-endian memory. The least significant byte has lowest address. This is the default.

Instructs the compiler that an inline SWI may overwrite the contents of the link register. This option is usually used for modules that run in Supervisor mode, and that contain inline SWIs. You must use this option when compiling code that contains inline SWIs.

Specifies whether LDR may only access word-aligned addresses. Valid values are:

Limits the number of register values transferred by load multiple and store multiple instructions generated by the compiler to Number. Valid values for Number are 3 to 16 inclusively. The default value is 16.

You can use this option to reduce interrupt latency. Note that the inline assembler is not subject to the limit imposed by the -zr option.

The Thumb compiler does not support this option.

Specifies the minimum byte alignment for structures. Valid values for Number are:

The default is 4 for both ARM and Thumb compilers. This allows structure copying to be implemented more efficiently by copying in units of words, rather than bytes. Setting a lower value reduces the amount of padding required, at the expense of the speed of structure copying.

Specifies whether pointers to structures are assumed to be aligned on at least the minimum byte alignment boundaries, as set by the -zas option. Valid values are:

Specifies the minimum byte alignment for top-level static objects, such as global variables. Valid values for Number are:

The default is 4 for the ARM compilers and 1 for the Thumb compilers.