diff options
Diffstat (limited to 'gcc/doc/tm.texi')
| -rw-r--r-- | gcc/doc/tm.texi | 30 |
1 files changed, 27 insertions, 3 deletions
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi index c001c8b..637dd50 100644 --- a/gcc/doc/tm.texi +++ b/gcc/doc/tm.texi @@ -6116,8 +6116,32 @@ classes returns a value of 2, reload does not check to ensure that the constraints of the insn are met. Setting a cost of other than 2 will allow reload to verify that the constraints are met. You should do this if the @samp{mov@var{m}} pattern's constraints do not allow such copying. + +These macros are obsolete, new ports should use the target hook +@code{TARGET_REGISTER_MOVE_COST} instead. @end defmac +@deftypefn {Target Hook} int TARGET_REGISTER_MOVE_COST (enum machine_mode @var{mode}, enum reg_class @var{from}, enum reg_class @var{to}) +This target hook should return the cost of moving data of mode @var{mode} +from a register in class @var{from} to one in class @var{to}. The classes +are expressed using the enumeration values such as @code{GENERAL_REGS}. +A value of 2 is the default; other values are interpreted relative to +that. + +It is not required that the cost always equal 2 when @var{from} is the +same as @var{to}; on some machines it is expensive to move between +registers if they are not general registers. + +If reload sees an insn consisting of a single @code{set} between two +hard registers, and if @code{TARGET_REGISTER_MOVE_COST} applied to their +classes returns a value of 2, reload does not check to ensure that the +constraints of the insn are met. Setting a cost of other than 2 will +allow reload to verify that the constraints are met. You should do this +if the @samp{mov@var{m}} pattern's constraints do not allow such copying. + +The default version of this function returns 2. +@end deftypefn + @defmac MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in}) A C expression for the cost of moving data of mode @var{mode} between a register of class @var{class} and memory; @var{in} is zero if the value @@ -6149,9 +6173,9 @@ These macros are obsolete, new ports should use the target hook This target hook should return the cost of moving data of mode @var{mode} between a register of class @var{class} and memory; @var{in} is @code{false} if the value is to be written to memory, @code{true} if it is to be read in. -This cost is relative to those in @code{REGISTER_MOVE_COST}. If moving -between registers and memory is more expensive than between two registers, -you should add this target hook to express the relative cost. +This cost is relative to those in @code{TARGET_REGISTER_MOVE_COST}. +If moving between registers and memory is more expensive than between two +registers, you should add this target hook to express the relative cost. If you do not add this target hook, GCC uses a default cost of 4 plus the cost of copying via a secondary reload register, if one is |