+@node Scheduling
+@section Adjusting the Instruction Scheduler
+
+The instruction scheduler may need a fair amount of machine-specific
+adjustment in order to produce good code. GCC provides several target
+hooks for this purpose. It is usually enough to define just a few of
+them: try the first ones in this list first.
+
+@deftypefn {Target Hook} int TARGET_SCHED_ISSUE_RATE (void)
+This hook returns the maximum number of instructions that can ever issue
+at the same time on the target machine. The default is one. This value
+must be constant over the entire compilation. If you need it to vary
+depending on what the instructions are, you must use
+@samp{TARGET_SCHED_VARIABLE_ISSUE}.
+@end deftypefn
+
+@deftypefn {Target Hook} int TARGET_SCHED_VARIABLE_ISSUE (FILE *@var{file}, int @var{verbose}, rtx @var{insn}, int @var{more})
+This hook is executed by the scheduler after it has scheduled an insn
+from the ready list. It should return the number of insns which can
+still be issued in the current cycle. Normally this is
+@samp{@w{@var{more} - 1}}. You should define this hook if some insns
+take more machine resources than others, so that fewer insns can follow
+them in the same cycle. @var{file} is either a null pointer, or a stdio
+stream to write any debug output to. @var{verbose} is the verbose level
+provided by @option{-fsched-verbose-@var{n}}. @var{insn} is the
+instruction that was scheduled.
+@end deftypefn
+
+@deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST (rtx @var{insn}, rtx @var{link}, rtx @var{dep_insn}, int @var{cost})
+This function corrects the value of @var{cost} based on the relationship
+between @var{insn} and @var{dep_insn} through the dependence @var{link}.
+It should return the new value. The default is to make no adjustment to
+@var{cost}. This can be used for example to specify to the scheduler
+that an output- or anti-dependence does not incur the same cost as a
+data-dependence.
+@end deftypefn
+
+@deftypefn {Target Hook} int TARGET_SCHED_ADJUST_PRIORITY (rtx @var{insn}, int @var{priority})
+This hook adjusts the integer scheduling priority @var{priority} of
+@var{insn}. It should return the new priority. Reduce the priority to
+execute @var{insn} earlier, increase the priority to execute @var{insn}
+later. Do not define this hook if you do not need to adjust the
+scheduling priorities of insns.
+@end deftypefn
+
+@deftypefn {Target Hook} int TARGET_SCHED_REORDER (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_readyp}, int @var{clock})
+This hook is executed by the scheduler after it has scheduled the ready
+list, to allow the machine description to reorder it (for example to
+combine two small instructions together on @samp{VLIW} machines).
+@var{file} is either a null pointer, or a stdio stream to write any
+debug output to. @var{verbose} is the verbose level provided by
+@option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready
+list of instructions that are ready to be scheduled. @var{n_readyp} is
+a pointer to the number of elements in the ready list. The scheduler
+reads the ready list in reverse order, starting with
+@var{ready}[@var{*n_readyp}-1] and going to @var{ready}[0]. @var{clock}
+is the timer tick of the scheduler. You may modify the ready list and
+the number of ready insns. The return value is the number of insns that
+can issue this cycle; normally this is just @code{issue_rate}. See also
+@samp{TARGET_SCHED_REORDER2}.
+@end deftypefn
+
+@deftypefn {Target Hook} int TARGET_SCHED_REORDER2 (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_ready}, @var{clock})
+Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That
+function is called whenever the scheduler starts a new cycle. This one
+is called once per iteration over a cycle, immediately after
+@samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and
+return the number of insns to be scheduled in the same cycle. Defining
+this hook can be useful if there are frequent situations where
+scheduling one insn causes other insns to become ready in the same
+cycle. These other insns can then be taken into account properly.
+@end deftypefn
+
+@deftypefn {Target Hook} void TARGET_SCHED_INIT (FILE *@var{file}, int @var{verbose}, int @var{max_ready})
+This hook is executed by the scheduler at the beginning of each block of
+instructions that are to be scheduled. @var{file} is either a null
+pointer, or a stdio stream to write any debug output to. @var{verbose}
+is the verbose level provided by @option{-fsched-verbose-@var{n}}.
+@var{max_ready} is the maximum number of insns in the current scheduling
+region that can be live at the same time. This can be used to allocate
+scratch space if it is needed, e.g. by @samp{TARGET_SCHED_REORDER}.
+@end deftypefn
+
+@deftypefn {Target Hook} void TARGET_SCHED_FINISH (FILE *@var{file}, int @var{verbose})
+This hook is executed by the scheduler at the end of each block of
+instructions that are to be scheduled. It can be used to perform
+cleanup of any actions done by the other scheduling hooks. @var{file}
+is either a null pointer, or a stdio stream to write any debug output
+to. @var{verbose} is the verbose level provided by
+@option{-fsched-verbose-@var{n}}.
+@end deftypefn
+
+@deftypefn {Target Hook} rtx TARGET_SCHED_CYCLE_DISPLAY (int @var{clock}, rtx @var{last})
+This hook is called in verbose mode only, at the beginning of each pass
+over a basic block. It should insert an insn into the chain after
+@var{last}, which has no effect, but records the value @var{clock} in
+RTL dumps and assembly output. Define this hook only if you need this
+level of detail about what the scheduler is doing.
+@end deftypefn
+
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