Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ukma!tut.cis.ohio-state.edu!ATHENA.MIT.EDU!raeburn
From: raeburn@ATHENA.MIT.EDU (Ken Raeburn)
Newsgroups: gnu.gcc.bug
Subject: trouble with -fvolatile and -traditional
Message-ID: <8902090147.AA00600@MULTICS.MIT.EDU>
Date: 9 Feb 89 01:47:32 GMT
Sender: daemon@tut.cis.ohio-state.edu
Distribution: gnu
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Lines: 42


(Using gcc 1.33, configured for vax.  Optimization by default turns on
combine-regs and strength-reduce options in our config file.)

The following source file, when compiled (optimized) with -traditional
or with -Dvolatile=, generates no assembler code for the references to
the "foo" element, as would be expected, since the value read is not
really used.

#ifndef __STDC__
#define volatile
#endif

struct fooreg {
    short csr;
    short foo;
};

extern volatile struct fooreg *x;

void foo () {
    register volatile struct fooreg *y = x;
    short z;
    y->csr = 0;
    z = y->foo;
    z = y->foo;
    y->csr = 0x100;
}

However, according to the documentation, using "-fvolatile" should
cause the compiler to "consider all memory references through pointers
to be volatile," so they should not be removed.  This does not appear
to be the case, neither with "-traditional -fvolatile" nor with
"-Dvolatile= -fvolatile"; neither of the references is generated.

-- Ken

P.S.  Would it be reasonable to consider adding keywords "__inline"
and "__typeof" that work in the obvious way, but are not disabled when
the traditional or strict-ANSI modes are selected?  I think it would
be useful to be able to do function inlining in "traditional GNU C,"
which I'm going to wind up using a lot this spring.