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From: cik@l.cc.purdue.edu (Herman Rubin)
Newsgroups: comp.compilers
Subject: Re: Register Allocation
Summary: It is not possible on most computers without excessive cost
Keywords: Pointers
Message-ID: <1990Feb24.210757.4202@esegue.segue.boston.ma.us>
Date: 24 Feb 90 21:07:57 GMT
References: <1990Feb20.155619.3121@esegue.segue.boston.ma.us>
Sender: compilers-sender@esegue.segue.boston.ma.us
Reply-To: cik@l.cc.purdue.edu (Herman Rubin)
Organization: Compilers Central
Lines: 24
Approved: compilers@esegue.segue.boston.ma.us

In article <1990Feb20.155619.3121@esegue.segue.boston.ma.us>, napi@rangkom.MY (Mohd Hanafiah b. Abdullah) writes:
> How does one perform register allocation on scalar variables that may
> be pointed to by others?
> 
> I am curious because, a pointer assumes that the variable it points to
> resides in memory, but in actuality the variable resides in a register.
> 
> I am sure there is a solution to this problem and has been asked before
> in the newsgroup, but could you please e-mail the answer to me anyway?

Unfortunately, this is not the case.  I have frequently wanted to do this,
and I have no difficulty using machine language.  The only mainframes whose
instruction set I have known which are appropriately set up in hardware for
this are the long obsolete UNIVAC 1108 and 1110.  There are some I have seen
for which this can be done with difficulty, but it would not be faster than
keeping the items in memory.
[The PDP-10/DEC-20 has addressable registers as well, but as pointed out
elsewhere that's only a small part of the problem.  As soon as you call
another routine, it's liable to save the register and put something else
there, and you lose.  -John]
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