.bundle_align_mode abs-expr.bundle_align_mode enables or disables aligned instruction
bundle mode. In this mode, sequences of adjacent instructions are grouped
into fixed-sized bundles. If the argument is zero, this mode is
disabled (which is the default state). If the argument it not zero, it
gives the size of an instruction bundle as a power of two (as for the
.p2align directive, see P2align).
For some targets, it's an ABI requirement that no instruction may span a
certain aligned boundary. A bundle is simply a sequence of
instructions that starts on an aligned boundary. For example, if
abs-expr is 5 then the bundle size is 32, so each aligned
chunk of 32 bytes is a bundle. When aligned instruction bundle mode is in
effect, no single instruction may span a boundary between bundles. If an
instruction would start too close to the end of a bundle for the length of
that particular instruction to fit within the bundle, then the space at the
end of that bundle is filled with no-op instructions so the instruction
starts in the next bundle. As a corollary, it's an error if any single
instruction's encoding is longer than the bundle size.
.bundle_lock and .bundle_unlockThe .bundle_lock and directive .bundle_unlock directives
allow explicit control over instruction bundle padding. These directives
are only valid when .bundle_align_mode has been used to enable
aligned instruction bundle mode. It's an error if they appear when
.bundle_align_mode has not been used at all, or when the last
directive was .bundle_align_mode 0.
For some targets, it's an ABI requirement that certain instructions may
appear only as part of specified permissible sequences of multiple
instructions, all within the same bundle. A pair of .bundle_lock
and .bundle_unlock directives define a bundle-locked
instruction sequence. For purposes of aligned instruction bundle mode, a
sequence starting with .bundle_lock and ending with
.bundle_unlock is treated as a single instruction. That is, the
entire sequence must fit into a single bundle and may not span a bundle
boundary. If necessary, no-op instructions will be inserted before the
first instruction of the sequence so that the whole sequence starts on an
aligned bundle boundary. It's an error if the sequence is longer than the
bundle size.
For convenience when using .bundle_lock and .bundle_unlock
inside assembler macros (see Macro), bundle-locked sequences may be
nested. That is, a second .bundle_lock directive before the next
.bundle_unlock directive has no effect except that it must be
matched by another closing .bundle_unlock so that there is the
same number of .bundle_lock and .bundle_unlock directives.