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Diffstat (limited to 'gcc/doc/tm.texi')
| -rw-r--r-- | gcc/doc/tm.texi | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi index d13b53e..064120d 100644 --- a/gcc/doc/tm.texi +++ b/gcc/doc/tm.texi @@ -2614,6 +2614,44 @@ letter @samp{Q} is defined as representing a memory address that does a @samp{Q} constraint on the input and @samp{r} on the output. The next alternative specifies @samp{m} on the input and a register class that does not include r0 on the output. + +@findex EXTRA_MEMORY_CONSTRAINT +@item EXTRA_MEMORY_CONSTRAINT (@var{c}) +A C expression that defines the optional machine-dependent constraint +letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should +be treated like memory constraints by the reload pass. + +It should return 1 if the operand type represented by the constraint +letter @var{c} comprises a subset of all memory references including +all those whose address is simply a base register. This allows the reload +pass to reload an operand, if it does not directly correspond to the operand +type of @var{c}, by copying its address into a base register. + +For example, on the S/390, some instructions do not accept arbitrary +memory references, but only those that do not make use of an index +register. The constraint letter @samp{Q} is defined via +@code{EXTRA_CONSTRAINT} as representing a memory address of this type. +If the letter @samp{Q} is marked as @code{EXTRA_MEMORY_CONSTRAINT}, +a @samp{Q} constraint can handle any memory operand, because the +reload pass knows it can be reloaded by copying the memory address +into a base register if required. This is analogous to the way +a @samp{o} constraint can handle any memory operand. + +@findex EXTRA_ADDRESS_CONSTRAINT +@item EXTRA_ADDRESS_CONSTRAINT (@var{c}) +A C expression that defines the optional machine-dependent constraint +letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should +be treated like address constraints by the reload pass. + +It should return 1 if the operand type represented by the constraint +letter @var{c} comprises a subset of all memory addresses including +all those that consist of just a base register. This allows the reload +pass to reload an operand, if it does not directly correspond to the operand +type of @var{c}, by copying it into a base register. + +Any constraint marked as @code{EXTRA_ADDRESS_CONSTRAINT} can only +be used with the @code{address_operand} predicate. It is treated +analogously to the @samp{p} constraint. @end table @node Stack and Calling |