To elaborate on what knz42 said, C expects addressable memory but doesn't say anything about registers at all. In fact, the existence of registers is sort of vaguely awkward from the perspective of C's model of computing.
That "register" nowadays is just a sequence of characters that, to those familiar with CPU architecture, rings a bell. Modern C standards do not convey any links between the keyword and hardware registers. http://www.open-std.org/JTC1/SC22/wg14/www/docs/n1124.pdf, section 6.7.1:
"A declaration of an identifier for an object with 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."
And 'non-addressable' only applies to the C 'runtime'. The standard does not say anything about the hardware.
For example, a C compiler for the 6502 could attempt to store variables of storage class 'register' in the zero page. Such storage locations have an address, but you are not allowed to take it from standard C.
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To elaborate on what knz42 said, C expects addressable memory but doesn't say anything about registers at all. In fact, the existence of registers is sort of vaguely awkward from the perspective of C's model of computing.
Considering that C has a "register" storage-class specifier keyword, I don't see how you can make that claim. Granted, modern compilers ignore it.
Certainly, the C specification states that "register" storage is non-addressable, so it does say something.
That "register" nowadays is just a sequence of characters that, to those familiar with CPU architecture, rings a bell. Modern C standards do not convey any links between the keyword and hardware registers. http://www.open-std.org/JTC1/SC22/wg14/www/docs/n1124.pdf, section 6.7.1:
"A declaration of an identifier for an object with 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."
And 'non-addressable' only applies to the C 'runtime'. The standard does not say anything about the hardware.
For example, a C compiler for the 6502 could attempt to store variables of storage class 'register' in the zero page. Such storage locations have an address, but you are not allowed to take it from standard C.
For an even better example, look at http://en.wikipedia.org/wiki/TMS9900. That CPU stored all its general purpose registers in RAM.