[Bug inline-asm/41294] New: "=&rm" constraints give overlapping memory addresses

[Bug inline-asm/41294] New: "=&rm" constraints give overlapping memory addresses

[jdemeyer at cage dot ugent dot be]

In some cases in inline asm, an output parameter with no-clobber "=&rm"
constraint gets the same address as an input parameter, even when they refer to
two different C variables.  This seems to happen when the following conditions
are satisfied:

* The variables involved appear only in inline asm (as the output of one asm
statement and the input of a second).
* The output constraint is "=&rm" ("=m" works correctly).
* There are too many clobbered variables forcing some of the output parameters
into memory.

The attached testcase works for i386, x86_64, powerpc and powerpc64.  For other
targets, change the clobber list to include as much registers as possible.
Compile with gcc -O1 -save-temps -c -o bug.o bug.c

Tested with gcc -v:
Using built-in specs.
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc/configure CC=/usr/bin/gcc-4.3.4
--prefix=/home/jdemeyer/local --enable-checking=release
Thread model: posix
gcc version 4.5.0 20090904 (experimental) (GCC)


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           Summary: "=&rm" constraints give overlapping memory addresses
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: inline-asm
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jdemeyer at cage dot ugent dot be


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41294

[Bug inline-asm/41294] "=&rm" constraints give overlapping memory addresses

[jdemeyer at cage dot ugent dot be]

------- Comment #1 from jdemeyer at cage dot ugent dot be  2009-09-07 10:49 -------
Created an attachment (id=18528)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=18528&action=view)
Testcase


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41294

[Bug inline-asm/41294] "=&rm" constraints give overlapping memory addresses

[rguenth at gcc dot gnu dot org]

------- Comment #2 from rguenth at gcc dot gnu dot org  2009-09-07 15:45 -------
I think you need to mark both alternatives early-clobber, not only the register
one.  Thus "=&r&m" at least according to the manual.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41294

[Bug inline-asm/41294] "=&rm" constraints give overlapping memory addresses

[jdemeyer at cage dot ugent dot be]

------- Comment #3 from jdemeyer at cage dot ugent dot be  2009-09-07 19:30 -------
(In reply to comment #2)
> I think you need to mark both alternatives early-clobber, not only the register
> one.  Thus "=&r&m" at least according to the manual.

That doesn't seem to change anything.  It looks to me like the parser only
checks for the presence of at least one "&", since it even accepts "=&&r&&m&&"
(maybe that's another bug?).  On the other hand, using "=&m" as constraint
gives an error
bug.c:141:2: error: '&' constraint used with no register class

According to http://gcc.gnu.org/onlinedocs/gcc/Multi_002dAlternative.html,
the constraint "=&rm" counts as ONE alternative, since alternatives are
seperated by commas.  This is one alternative, allowing both a register or
memory location.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41294

[Bug inline-asm/41294] "=&rm" constraints give overlapping memory addresses

[pinskia at gcc dot gnu dot org]

------- Comment #4 from pinskia at gcc dot gnu dot org  2009-11-21 09:15 -------


*** This bug has been marked as a duplicate of 37195 ***


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pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |DUPLICATE


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41294