Portable C Improvements

[WILCOX%NOSC-TECR at tgr.UUCP]

Some thoughts for improving the portable C compiler:

(1) Don't force all FCONs to become NAMEs.  Some folks may have machines
    that permit an FCON, or its ICON binary representation, to be coded as
    a field of a machine instruction.

(2) Don't force all FCONs to be double.  Often the least-significant
    fraction bits permit type float to be used which saves space.

(3) Provide not only for "A" and "B" registers, but also for registers
    that are adjacent to particular registers.  This comes up on machines
    where an ASG MUL operator must use a hardware multiply instruction
    that produces a 32-bit product from two 16-bit multiplicands, or a
    64-bit product from two 32-bit multiplicands, and the registers are
    smaller than 64 bits wide.

(4) Provide a compile #ifdef to select/deselect register-pairing (even
    boundary addressing) on registers since not all machines require
    registers pairing.

(5) Provide a routine to avoid placing computations into a temporary
    register that ultimately are ASSIGNed to a non-temporary register
    if they can be done in place within the destination register.
    The Sethi-Ullman numbers can help here.

				Dwight R. Wilcox
				wilcox at nosc-tecr.arpa

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