i960 Command-line Options
-------------------------
`-ACA | -ACA_A | -ACB | -ACC | -AKA | -AKB | -AKC | -AMC'
Select the 80960 architecture. Instructions or features not
supported by the selected architecture cause fatal errors.
`-ACA' is equivalent to `-ACA_A'; `-AKC' is equivalent to `-AMC'.
Synonyms are provided for compatibility with other tools.
If you do not specify any of these options, `as' generates code
for any instruction or feature that is supported by _some_ version
of the 960 (even if this means mixing architectures!). In
principle, `as' attempts to deduce the minimal sufficient
processor type if none is specified; depending on the object code
format, the processor type may be recorded in the object file. If
it is critical that the `as' output match a specific architecture,
specify that architecture explicitly.
`-b'
Add code to collect information about conditional branches taken,
for later optimization using branch prediction bits. (The
conditional branch instructions have branch prediction bits in the
CA, CB, and CC architectures.) If BR represents a conditional
branch instruction, the following represents the code generated by
the assembler when `-b' is specified:
call INCREMENT ROUTINE
.word 0 # pre-counter
Label: BR
call INCREMENT ROUTINE
.word 0 # post-counter
The counter following a branch records the number of times that
branch was _not_ taken; the differenc between the two counters is
the number of times the branch _was_ taken.
A table of every such `Label' is also generated, so that the
external postprocessor `gbr960' (supplied by Intel) can locate all
the counters. This table is always labelled `__BRANCH_TABLE__';
this is a local symbol to permit collecting statistics for many
separate object files. The table is word aligned, and begins with
a two-word header. The first word, initialized to 0, is used in
maintaining linked lists of branch tables. The second word is a
count of the number of entries in the table, which follow
immediately: each is a word, pointing to one of the labels
illustrated above.
+------------+------------+------------+ ... +------------+
| | | | | |
| *NEXT | COUNT: N | *BRLAB 1 | | *BRLAB N |
| | | | | |
+------------+------------+------------+ ... +------------+
__BRANCH_TABLE__ layout
The first word of the header is used to locate multiple branch
tables, since each object file may contain one. Normally the links
are maintained with a call to an initialization routine, placed at
the beginning of each function in the file. The GNU C compiler
generates these calls automatically when you give it a `-b' option.
For further details, see the documentation of `gbr960'.
`-no-relax'
Normally, Compare-and-Branch instructions with targets that require
displacements greater than 13 bits (or that have external targets)
are replaced with the corresponding compare (or `chkbit') and
branch instructions. You can use the `-no-relax' option to
specify that `as' should generate errors instead, if the target
displacement is larger than 13 bits.
This option does not affect the Compare-and-Jump instructions; the
code emitted for them is _always_ adjusted when necessary
(depending on displacement size), regardless of whether you use
`-no-relax'.