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From: brooks@vette.llnl.gov (Eugene Brooks)
Newsgroups: gnu.gcc.bug
Subject: Re: To volatile or not to volatile.
Message-ID: <21856@lll-winken.LLNL.GOV>
Date: 13 Mar 89 23:07:33 GMT
References: <8903130045.AA21334@prep.ai.mit.edu>
Sender: usenet@lll-winken.LLNL.GOV
Reply-To: brooks@maddog.llnl.gov.UUCP (Eugene Brooks)
Distribution: gnu
Organization: Lawrence Livermore National Laboratory
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In article <8903130045.AA21334@prep.ai.mit.edu> cire@CISCO.COM (cire|eric)
writes a description of a problem involving a reference to a volatile int
which is cast to an unsigned char.  I hope that the intent of the ANSI
volatile usage is that the int gets picked up as an int and then is cast
to a unsigned char by truncation.  A volatile int is a volatile int, not
a place to pick up a volatile char!  Does anyone know what the standard
really means in the area?

I would hope, in addition, that the volatile attributes of a reference
are available (in GCC) to the back end at the machine description level.  On
shared memory multiprocessor systems which use explicitly managed caches one
has to use an alternate load instruction to guarrantee a cache miss for
the reference.  Does anyone know if the volatile nature of the reference
is available to the back end pattern matching mechanism for code generation?
If it is not, does anyone know how much trouble it would be to make it
available if one were willing to do the hacking?


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