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Diffstat (limited to 'gcc/doc/tm.texi')
| -rw-r--r-- | gcc/doc/tm.texi | 23 |
1 files changed, 11 insertions, 12 deletions
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi index c29d249..eb8a618 100644 --- a/gcc/doc/tm.texi +++ b/gcc/doc/tm.texi @@ -6386,23 +6386,22 @@ may eliminate subsequent memory access if subsequent accesses occur to other fields in the same word of the structure, but to different bytes. @end defmac -@defmac SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment}) -Define this macro to be the value 1 if memory accesses described by the +@deftypefn {Target Hook} bool TARGET_SLOW_UNALIGNED_ACCESS (machine_mode @var{mode}, unsigned int @var{align}) +This hook returns true if memory accesses described by the @var{mode} and @var{alignment} parameters have a cost many times greater -than aligned accesses, for example if they are emulated in a trap -handler. This macro is invoked only for unaligned accesses, i.e. when +than aligned accesses, for example if they are emulated in a trap handler. +This hook is invoked only for unaligned accesses, i.e. when @code{@var{alignment} < GET_MODE_ALIGNMENT (@var{mode})}. -When this macro is nonzero, the compiler will act as if -@code{STRICT_ALIGNMENT} were nonzero when generating code for block +When this hook returns true, the compiler will act as if +@code{STRICT_ALIGNMENT} were true when generating code for block moves. This can cause significantly more instructions to be produced. -Therefore, do not set this macro nonzero if unaligned accesses only add a -cycle or two to the time for a memory access. +Therefore, do not make this hook return true if unaligned accesses only +add a cycle or two to the time for a memory access. -If the value of this macro is always zero, it need not be defined. If -this macro is defined, it should produce a nonzero value when -@code{STRICT_ALIGNMENT} is nonzero. -@end defmac +The hook must return true whenever @code{STRICT_ALIGNMENT} is true. +The default implementation returns @code{STRICT_ALIGNMENT}. +@end deftypefn @defmac MOVE_RATIO (@var{speed}) The threshold of number of scalar memory-to-memory move insns, @emph{below} |