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Diffstat (limited to 'gcc/tm.texi')
| -rw-r--r-- | gcc/tm.texi | 45 |
1 files changed, 45 insertions, 0 deletions
diff --git a/gcc/tm.texi b/gcc/tm.texi index ad578386be6..9a8887fdaf9 100644 --- a/gcc/tm.texi +++ b/gcc/tm.texi @@ -4223,6 +4223,51 @@ address. The compiler has standard ways of doing so in all cases. In fact, it is safe for this macro to do nothing. But often a machine-dependent strategy can generate better code. +@findex LEGITIMIZE_RELOAD_ADDRESS +@item LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win}) +A C compound statement that attempts to replace @var{x}, which is an address +that needs reloading, with a valid memory address for an operand of mode +@var{mode}. @var{win} will be a C statement label elsewhere in the code. +It is not necessary to define this macro, but it might be useful for +performance reasons. + +For example, on the i386, it is sometimes possible to use a single +reload register instead of two by reloading a sum of two pseudo +registers into a register. On the other hand, for number of RISC +processors offsets are limited so that often an intermediate address +needs to be generated in order to address a stack slot. By defining +LEGITIMIZE_RELOAD_ADDRESS appropriately, the intermediate addresses +generated for adjacent some stack slots can be made identical, and thus +be shared. + +@findex strict_memory_address_p +The macro definition may use @code{strict_memory_address_p} to test if +the address has become legitimate. + +@findex push_reload +It may use @code{push_reload} to indicate parts that need reloading. +@var{opnum}, @var{type} and @var{ind_levels} are usually suitable to be +passed unaltered to push_reload. + +The code generated by this macro should not alter the substructure of +@var{x}. If it transforms @var{x} into a more legitimate form, it +should assign @var{x} (which will always be a C variable) a new value. +This also applies to parts that you change indirectly by calling +@code{push_reload}. + +@findex copy_rtx +If you want to change only a part of @var{x}, one standard way of doing +this is to use @code{copy_rtx}. Note, however, that is unshares only a +single level of rtl. Thus, if the part to be changed is not at the +top level, you'll need to replace first the top leve +It is not necessary for this macro to come up with a legitimate +address; but often a machine-dependent strategy can generate better code. + +@emph{Note}: This macro should be used with caution. It is necessary +to know something of how reload works in order to effectively use this, +and it is quite easy to produce macros that build in too much knowledge +of reload internals. + @findex GO_IF_MODE_DEPENDENT_ADDRESS @item GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label}) A C statement or compound statement with a conditional @code{goto |