diff options
Diffstat (limited to 'gcc/doc/tm.texi')
| -rw-r--r-- | gcc/doc/tm.texi | 41 |
1 files changed, 19 insertions, 22 deletions
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi index 0c77b53..35141ac 100644 --- a/gcc/doc/tm.texi +++ b/gcc/doc/tm.texi @@ -2017,8 +2017,9 @@ consecutive registers are needed for a given mode. A C expression for the number of consecutive hard registers, starting at register number @var{regno}, required to hold a value of mode @var{mode}. This macro must never return zero, even if a register -cannot hold the requested mode - indicate that with HARD_REGNO_MODE_OK -and/or CANNOT_CHANGE_MODE_CLASS instead. +cannot hold the requested mode - indicate that with +@code{TARGET_HARD_REGNO_MODE_OK} and/or @code{CANNOT_CHANGE_MODE_CLASS} +instead. On a machine where all registers are exactly one word, a suitable definition of this macro is @@ -2066,22 +2067,18 @@ happens for example on SPARC 64-bit where the natural size of floating-point registers is still 32-bit. @end defmac -@defmac HARD_REGNO_MODE_OK (@var{regno}, @var{mode}) -A C expression that is nonzero if it is permissible to store a value +@deftypefn {Target Hook} bool TARGET_HARD_REGNO_MODE_OK (unsigned int @var{regno}, machine_mode @var{mode}) +This hook returns true if it is permissible to store a value of mode @var{mode} in hard register number @var{regno} (or in several -registers starting with that one). For a machine where all registers -are equivalent, a suitable definition is - -@smallexample -#define HARD_REGNO_MODE_OK(REGNO, MODE) 1 -@end smallexample +registers starting with that one). The default definition returns true +unconditionally. You need not include code to check for the numbers of fixed registers, because the allocation mechanism considers them to be always occupied. @cindex register pairs On some machines, double-precision values must be kept in even/odd -register pairs. You can implement that by defining this macro to reject +register pairs. You can implement that by defining this hook to reject odd register numbers for such modes. The minimum requirement for a mode to be OK in a register is that the @@ -2091,9 +2088,9 @@ value into the register and back out not alter it. Since the same instruction used to move @code{word_mode} will work for all narrower integer modes, it is not necessary on any machine for -@code{HARD_REGNO_MODE_OK} to distinguish between these modes, provided -you define patterns @samp{movhi}, etc., to take advantage of this. This -is useful because of the interaction between @code{HARD_REGNO_MODE_OK} +this hook to distinguish between these modes, provided you define +patterns @samp{movhi}, etc., to take advantage of this. This is +useful because of the interaction between @code{TARGET_HARD_REGNO_MODE_OK} and @code{MODES_TIEABLE_P}; it is very desirable for all integer modes to be tieable. @@ -2108,16 +2105,16 @@ On some machines, though, the converse is true: fixed-point machine modes may not go in floating registers. This is true if the floating registers normalize any value stored in them, because storing a non-floating value there would garble it. In this case, -@code{HARD_REGNO_MODE_OK} should reject fixed-point machine modes in +@code{TARGET_HARD_REGNO_MODE_OK} should reject fixed-point machine modes in floating registers. But if the floating registers do not automatically normalize, if you can store any bit pattern in one and retrieve it unchanged without a trap, then any machine mode may go in a floating -register, so you can define this macro to say so. +register, so you can define this hook to say so. The primary significance of special floating registers is rather that they are the registers acceptable in floating point arithmetic instructions. However, this is of no concern to -@code{HARD_REGNO_MODE_OK}. You handle it by writing the proper +@code{TARGET_HARD_REGNO_MODE_OK}. You handle it by writing the proper constraints for those instructions. On some machines, the floating registers are especially slow to access, @@ -2125,7 +2122,7 @@ so that it is better to store a value in a stack frame than in such a register if floating point arithmetic is not being done. As long as the floating registers are not in class @code{GENERAL_REGS}, they will not be used unless some pattern's constraint asks for one. -@end defmac +@end deftypefn @defmac HARD_REGNO_RENAME_OK (@var{from}, @var{to}) A C expression that is nonzero if it is OK to rename a hard register @@ -2142,9 +2139,9 @@ The default is always nonzero. A C expression that is nonzero if a value of mode @var{mode1} is accessible in mode @var{mode2} without copying. -If @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and -@code{HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same for -any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})} +If @code{TARGET_HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and +@code{TARGET_HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same +for any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})} should be nonzero. If they differ for any @var{r}, you should define this macro to return zero unless some other mechanism ensures the accessibility of the value in a narrower mode. @@ -2331,7 +2328,7 @@ When a value occupying several consecutive registers is expected in a certain class, all the registers used must belong to that class. Therefore, register classes cannot be used to enforce a requirement for a register pair to start with an even-numbered register. The way to -specify this requirement is with @code{HARD_REGNO_MODE_OK}. +specify this requirement is with @code{TARGET_HARD_REGNO_MODE_OK}. Register classes used for input-operands of bitwise-and or shift instructions have a special requirement: each such class must have, for |