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defaults.h (TARGET_PTRMEMFUNC_VBIT_LOCATION): Define. 

* defaults.h (TARGET_PTRMEMFUNC_VBIT_LOCATION): Define.
* tm.texi (TARGET_PRTMEMFUNC_VBIT_LOCATION): Document.

From-SVN: r41989
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Alexandre Oliva 2001-05-12 10:41:21 +00:00 committed by Alexandre Oliva
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2001-05-12 Alexandre Oliva <aoliva@redhat.com>
* defaults.h (TARGET_PTRMEMFUNC_VBIT_LOCATION): Define.
* tm.texi (TARGET_PRTMEMFUNC_VBIT_LOCATION): Document.
2001-05-11 Richard Henderson <rth@redhat.com>
* defaults.h (ASM_PREFERRED_EH_DATA_FORMAT): New.

11
gcc/defaults.h
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@ -325,5 +325,16 @@ do { \
#define ASM_PREFERRED_EH_DATA_FORMAT(CODE,GLOBAL) DW_EH_PE_absptr
#endif
/* By default, the C++ compiler will use the lowest bit of the pointer
to function to indicate a pointer-to-member-function points to a
virtual member function. However, if FUNCTION_BOUNDARY indicates
function addresses aren't always even, the lowest bit of the delta
field will be used. */
#ifndef TARGET_PTRMEMFUNC_VBIT_LOCATION
#define TARGET_PTRMEMFUNC_VBIT_LOCATION \
(FUNCTION_BOUNDARY >= 2 * BITS_PER_UNIT \
? ptrmemfunc_vbit_in_pfn : ptrmemfunc_vbit_in_delta)
#endif
#endif /* GCC_DEFAULTS_H */

39
gcc/tm.texi
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@ -1451,6 +1451,45 @@ label.
On certain machines, it is important to have a separate label for each
selector because this enables the linker to eliminate duplicate selectors.
@findex TARGET_PTRMEMFUNC_VBIT_LOCATION
@item TARGET_PTRMEMFUNC_VBIT_LOCATION
The C++ compiler represents a pointer-to-member-function with a struct
that looks like:
@example
struct @{
union @{
void (*fn)();
ptrdiff_t vtable_index;
@};
ptrdiff_t delta;
@};
@end example
@noindent
The C++ compiler must use one bit to indicate whether the function that
will be called through a pointer-to-member-function is virtual.
Normally, we assume that the low-order bit of a function pointer must
always be zero. Then, by ensuring that the vtable_index is odd, we can
distinguish which variant of the union is in use. But, on some
platforms function pointers can be odd, and so this doesn't work. In
that case, we use the low-order bit of the @code{delta} field, and shift
the remainder of the @code{delta} field to the left.
GCC will automatically make the right selection about where to store
this bit using the @code{FUNCTION_BOUNDARY} setting for your platform.
However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY}
set such that functions always start at even addresses, but the lowest
bit of pointers to functions indicate whether the function at that
address is in ARM or Thumb mode. If this is the case of your
architecture, you should define this macro to
@code{ptrmemfunc_vbit_in_delta}.
In general, you should not have to define this macro. On architectures
in which function addresses are always even, according to
@code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to
@code{ptrmemfunc_vbit_in_pfn}.
@findex TARGET_BELL
@item TARGET_BELL
A C constant expression for the integer value for escape sequence