Red Hat ENTERPRISE LINUX 4 Manual page 68

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-foptimize-register-move
-fregmove
Attempt to reassign register numbers in move instructions and as operands of other simple
instructions in order to maximize the amount of register tying. This is especially helpful on
machines with two-operand instructions.
Note
-fregmove
Enabled at levels
-fdelayed-branch
If supported for the target machine, attempt to reorder instructions to exploit instruction slots
available after delayed branch instructions.
Enabled at levels
-fschedule-insns
If supported for the target machine, attempt to reorder instructions to eliminate execution stalls
due to required data being unavailable. This helps machines that have slow floating point or
memory load instructions by allowing other instructions to be issued until the result of the load
or floating point instruction is required.
Enabled at levels
-fschedule-insns2
Similar to
-fschedule-insns
register allocation has been done. This is especially useful on machines with a relatively small
number of registers and where memory load instructions take more than one cycle.
Enabled at levels
-fno-sched-interblock
Don't schedule instructions across basic blocks. This is normally enabled by default when
scheduling before register allocation, i.e. with
-fno-sched-spec
Don't allow speculative motion of non-load instructions. This is normally enabled by default
when scheduling before register allocation, i.e. with
-fsched-spec-load
Allow speculative motion of some load instructions. This only makes sense when scheduling
before register allocation, i.e. with
-fsched-spec-load-dangerous
Allow speculative motion of more load instructions. This only makes sense when scheduling
before register allocation, i.e. with
-fsched-stalled-insns=
Define how many insns (if any) can be moved prematurely from the queue of stalled insns into
the ready list, during the second scheduling pass.
-fsched-stalled-insns-dep=
Define how many insn groups (cycles) will be examined for a dependency on a stalled insn that
is candidate for premature removal from the queue of stalled insns. Has an effect only during the
second scheduling pass, and only if
and
-foptimize-register-move
, , .
-O2 -O3 -Os
, , , .
-O -O2 -O3 -Os
, , .
-O2 -O3 -Os
, but requests an additional pass of instruction scheduling after
, , .
-O2 -O3 -Os
-fschedule-insns
-fschedule-insns
n
n
-fsched-stalled-insns
Chapter 4. GCC Command Options
are the same optimization.
-fschedule-insns
-fschedule-insns
or at or higher.
-O2
or at or higher.
-O2
is used and its value is not zero.
or at or higher.
-O2
or at or higher.
-O2