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Diffstat (limited to 'gcc/tm.texi')
| -rw-r--r-- | gcc/tm.texi | 20 |
1 files changed, 11 insertions, 9 deletions
diff --git a/gcc/tm.texi b/gcc/tm.texi index 6f66c09a866..838fd7d349e 100644 --- a/gcc/tm.texi +++ b/gcc/tm.texi @@ -2180,17 +2180,19 @@ between these kinds. @findex EXTRA_CONSTRAINT @item EXTRA_CONSTRAINT (@var{value}, @var{c}) A C expression that defines the optional machine-dependent constraint -letters (@samp{Q}, @samp{R}, @samp{S}, @samp{T}, @samp{U}) that can -be used to segregate specific types of operands, usually memory -references, for the target machine. Normally this macro will not be -defined. If it is required for a particular target machine, it should -return 1 if @var{value} corresponds to the operand type represented by -the constraint letter @var{c}. If @var{c} is not defined as an extra +letters that can be used to segregate specific types of operands, usually +memory references, for the target machine. Any letter that is not +elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} +may be used. Normally this macro will not be defined. + +If it is required for a particular target machine, it should return 1 +if @var{value} corresponds to the operand type represented by the +constraint letter @var{c}. If @var{c} is not defined as an extra constraint, the value returned should be 0 regardless of @var{value}. -For example, on the ROMP, load instructions cannot have their output in r0 if -the memory reference contains a symbolic address. Constraint letter -@samp{Q} is defined as representing a memory address that does +For example, on the ROMP, load instructions cannot have their output +in r0 if the memory reference contains a symbolic address. Constraint +letter @samp{Q} is defined as representing a memory address that does @emph{not} contain a symbolic address. An alternative is specified with 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 |