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Chapter 42. Xtensa Dependent Features

All the Xtensa specific directives that apply to a region of code use this syntax.

The directive applies to code between the

.begin

and the

.end

. The state of the option after the

.end

reverts to what it was before the

.begin

. A nested

.begin

/

.end

region can further change the state

of the directive without having to be aware of its outer state. For example, consider:

.begin no density

L:

add a0, a1, a2

.begin density

M:

add a0, a1, a2

.end density

N:

add a0, a1, a2

.end no density

The generic

ADD

opcodes at

L

and

N

in the outer

no density

region both result in

ADD

machine

instructions, but the assembler selects an

ADD.N

instruction for the generic

ADD

at

M

in the inner

density

region.

The advantage of this style is that it works well inside macros which can preserve the context of their

callers.

When command line options and assembler directives are used at the same time and conflict, the

one that overrides a default behavior takes precedence over one that is the same as the default. For

example, if the code density option is available, the default is to select density instructions whenever

possible. So, if the above is assembled with the

 no density

flag, which overrides the default, all

the generic

ADD

instructions result in

ADD

machine instructions. If assembled with the

 density

flag,

which is already the default, the

no density

directive takes precedence and only one of the generic

ADD

instructions is optimized to be a

ADD.N

machine instruction. An underscore prefix identifying a

specific opcode always takes precedence over directives and command line flags.

The following directives are available:

42.5.1. density

The

density

and

no density

directives enable or disable optimization of generic instructions into

density instructions within the region. Section 42.3.1 Using Density Instructions.

.begin [no ]density

.end [no ]density

This optimization is enabled by default unless the Xtensa configuration does not support the code

density option or the

 no density

command line option was specified.

42.5.2. relax

The

relax

directive enables or disables relaxation within the region. Section 42.4 Xtensa Relaxation.

Note: In the current implementation, these directives also control whether assembler optimizations

are performed, making them equivalent to the

generics

and

no generics

directives.

.begin [no ]relax

.end [no ]relax