giguere@aries5.uucp (Eric Giguere) (07/18/89)
I for one am quite surprised that the various tests for register allocation
posted over the last few days can be compiled by any compiler. In the case
of ANSI compilers the following section applies:
"... storage-class specifier register suggests that access to the
object be as fast as possible. The extent to which such suggestions
are effective is implementation-defined." (3.5.1)
to which the following (important!) footnote is added:
"The implementation may treat any register declaration simply as an
auto declaration. However, whether or not addressable storage is
actually used, the address of any part of an object declared with
storage-class specifier register may not be computed, either explicitly
(by use of the unary & operator as discussed in 3.3.3.2) or implicitly
(by converting an array name to a pointer as discussed in 3.2.2.1).
Thus the only operator that can be applied to an array declared with
storage-class specifier register is sizeof."
So if I write
main()
{
register int a, b, c, d, e, /* etc. */ x, y, z;
int *ptr;
ptr = &z;
}
the compiler should flag this as an error, whether or not the underlying
architecture has 1, 2, 7, 15 or 26 registers available to be allocated.
Probably the only way to determine the number of registers a compiler
allocates is by disassembling the final object code. This method is
quite portable :-)
Eric Giguere 268 Phillip St #CL-46
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